EFFECT OF COMMON RAIL PRESSURE ON THE RELATIONSHIP …

The Pennsylvania State University

The Graduate School

Department of Mechanical and Nuclear Engineering

EFFECT OF COMMON RAIL PRESSURE ON THE RELATIONSHIP

BETWEEN BSFC AND BSPM AT NOx PARITY

A Thesis in

Mechanical Engineering

by

Bhaskar Prabhakar

2009 Bhaskar Prabhakar

Submitted in Partial Fulfillment

of the Requirements

for the Degree of

Master of Science

August 2009

ii

The thesis of Bhaskar Prabhakar was reviewed and approved* by the following:

André L. Boehman

Professor of Fuel Science and Material Science and Engineering

Thesis Advisor

Daniel C. Haworth

Professor of Mechanical Engineering

Karen A. Thole

Professor of Mechanical Engineering

Head of the Department of Mechanical and Nuclear Engineering

*Signatures are on file in the Graduate School

iii

ABSTRACT

This study concerns the effect of common rail pressure on the relationship

between brake specific fuel consumption (BSFC) and brake specific particulate matter

(BSPM) at NOx parity using a DDC/VM-Motori 2.5 L, 4 cylinder, turbocharged, direct

injection, light duty diesel engine. The research was divided into two tests. Test 1 was

performed holding the load constant (40% load at the rated speed) while speed was

increased in steps of 300 rpm from 1500 rpm to 2100 rpm. Test 2 was performed holding

the speed constant (1800 rpm) while the load was varied in steps of 7.5% from 40% to

55%. Three rail pressures of 425 bar, 500 bar and 575 bar were selected to be within a

safe operating range for the engine. Injection was limited to single pulse injection for

ease of control. Ultra low sulfur diesel (ULSD) was used as the fuel to perform the

experiments.

An engine map of the exhaust gas composition, mainly NOx, was created at the

given speeds, loads and rail pressures. A sweep of the injection timing was performed

over a given range of operating conditions and points of constant NOx were identified on

a brake specific basis. While conducting these tests, the influence of engine parameters

on performance and emissions were determined. These included the effects of speed and

load on specific fuel consumption and NOx, and the effect of injection timing on BSFC.

Results confirmed the well established trend that retarding the injection timing helped

reduce NOx but at the expense of fuel consumption. Increasing the rail pressure increased

NOx emissions while particulate matter (PM) was reduced. Findings at constant NOx

iv

indicated the dominance of either speed or injection timing which resulted in high PM at

a few conditions of rail pressure and speed. Heat release profiles and bulk temperatures

from Test 2 indicated several trends concerning PM formation and its oxidation. A

reduction in the engine load resulted in less PM exhausted from the engine. A high bulk

temperature from high engine load conditions indicated a preference of PM oxidation to

its formation.

To determine the influence of engine parameters on soot reactivity, particulate

matter was collected at six different conditions at constant NOx for further investigation

using thermogravimetric analysis (TGA). Raman spectroscopy was performed on all of

these samples to determine the degree of disorder in the primary soot particles to support

observations from TGA. Results suggested that increasing the rail pressure made soot

more reactive, while a significant impact of speed and injection timing on reactivity was

observed, whose trends could not be justified on the basis of a single parameter.

v

TABLE OF CONTENTS

LIST OF FIGURES ......................................................................................................... viii

LIST OF TABLES ........................................................................................................... xiii

NOMENCLATURE ........................................................................................................ xiv

ACKNOWLEDGEMENTS ............................................................................................. xvi

Chapter 1 Introduction ............................................................................................1

1.1 General Introduction ................................................................................1

1.2 Pros and cons of a diesel Engine..............................................................1

1.3 Motivation and thesis overview ...............................................................4

1.4 Objectives ................................................................................................6

1.4.1 Tasks ........................................................................................................6

1.4.2 Subtasks ...................................................................................................6

Chapter 2 Literature Review ..................................................................................7

2.1 Diesel engine operating principles ...........................................................7

2.2 Diesel combustion ..................................................................................10

2.3 NOx emissions from internal combustion engines ................................13

2.4 Particulate matter emissions ..................................................................14

2.4.1 Stages of soot formation ...............................................................15

2.4.2 Reducing particulate matter emissions .........................................18

vi

2.5 Injection pressure, timing, and common rail injection system ..............20

2.6 Spray and droplet characteristics ...........................................................21

Chapter 3 Experimental Setup .............................................................................23

3.1 Engine and engine related information ..................................................23

3.2 Load generation and dynamometer ........................................................24

3.3 Engine control and the ECU ..................................................................25

3.4 Data acquisition .....................................................................................25

3.5 Pressure trace and needle lift sensor ......................................................26

3.6 Mass of air flow (MAF) and diesel fuel flow rate .................................26

3.7 Engine emissions measurement .............................................................27

3.8 Particulate matter measurement: BG-3 sampling system ......................28

3.9 Facility for bulk sampling ......................................................................30

3.10 Thermogravimetric analysis (TGA) .......................................................31

3.11 Raman spectroscopy ..............................................................................32

3.12 Test conditions .......................................................................................33

Chapter 4 Results and Discussion Part I .............................................................35

4.1 Engine NOx map at constant load .........................................................35

4.2 Effect of injection timing & rail pressure at constant load on BSFC ....41

4.3 Effect of speed and injection timing at constant load on BSFC ............44

4.4 Effect of rail pressure on BSFC vs. BSPM at NOx parity (Test 1) .......47

4.5 Thermogravimetric analysis...................................................................52

vii

4.6 Raman spectroscopy ..............................................................................55

Chapter 5 Results and Discussion Part II ............................................................60

5.1 Engine NOx map at constant speed .......................................................60

5.2 Effect of load on BSFC at constant speed .............................................63

5.3 Effect of rail pressure on BSFC vs. BSPM at NOx parity (Test 2) .......65

Chapter 6 Conclusions ...........................................................................................70

6.1 Conclusions ............................................................................................70

6.2 Recommendations for future work ........................................................73

References ................................................................................................................74

Appendix A Fuel specifications .................................................................................79

Appendix B Results from Subtasks I and II ...............................................................81

Appendix C Additional results from TGA and Raman spectroscopy ........................86

Appendix D Brake specific emissions calculations ....................................................94

viii

LIST OF FIGURES

Figure 1-1 Comparison of part load specific fuel consumption for spark ignited, direct

and indirect injection diesel engines ............................................................2

Figure 1-2 Variation of NOx and PM for different levels of intake swirl .....................3

Figure 2-1 Diesel engine operating cycle ......................................................................7

Figure 2-2 Four strokes of the diesel cycle ....................................................................9

Figure 2-3 Typical heat release profile of a diesel engine ...........................................11

Figure 2-4 Stages of soot formation within a diesel engine ........................................17

Figure 2-5 Typical diesel soot nanostructure...............................................................17

Figure 2-6 Emission standards for a diesel locomotive engine as per EPA ................19

Figure 2-7 EPA NOx and PM forecast for 2010 .........................................................19

Figure 2-8 Spray formation process ............................................................................22

Figure 3-1 Photograph of 2.5 L DDC engine ..............................................................24

Figure 3-2 AVL CEB II Combustion emissions bench ...............................................28

Figure 3-3 BG-3 Particulate sampling system .............................................................29

ix

Figure 3-4 Humidity control chamber and Sartorius micro-balance for measuring

particulate sample filter mass.....................................................................30

Figure 3-5 Facility for bulk sampling, vacuum pump with sample collector ..............31

Figure 3-6 TGA-MS; TA instruments 2050 ................................................................32

Figure 4-1 Engine NOx map on a brake specific basis at 1500 rpm, 40% load ..........35


Figure 4-3 Engine NOx map on a brake specific basis at 2100 rpm,40% load ...........36

Figure 4-4 Variation of bulk temperature with injection timing at fixed rail pressure

(425 bar) .....................................................................................................38

Figure 4-5 Effect of rail pressure on bulk temperature at fixed injection timing (4 deg

BTDC)........................................................................................................39

Figure 4-6 Effect of injection timing and rail pressure on BSNOx at 1500 rpm, 40%

load .............................................................................................................40

Figure 4-7 Effect of injection timing and rail pressure on BSNOx at 1800 rpm, 40%

load .............................................................................................................40

Figure 4-8 Effect of injection timing and rail pressure on brake specific fuel

consumption at 1500 rpm, 40% load .........................................................41

x





Figure 4-11 Effect of engine speed on brake specific fuel consumption at 425 bar rail

pressure ......................................................................................................44


pressure ......................................................................................................45


pressure ......................................................................................................45

Figure 4-14 Plot showing the variation of BSFC vs. BSPM at constant NOx and load,

varying speeds, injection timing and rail pressure .....................................47

Figure 4-15 Heat release profile comparisons for three selected points at 500 bar rail

pressure ......................................................................................................50

Figure 4-16 Weight loss curves from TGA at 425 bar rail pressure .............................53

Figure 4-17 Weight loss curves from TGA at 500 bar rail pressure .............................53

Figure 4-18 Multi-peak fitting for Raman Spectra depicting 5 first order peaks ..........56

Figure 4-19 Variation of ID1/IG at 425 bar rail pressure for 3 test conditions obtained

at constant NOx..........................................................................................57

xi

Figure 4-20 Variation of ID1/IG at 500 bar rail pressure for 3 test conditions obtained

at constant NOx..........................................................................................58

Figure 4-21 Variation of ID1/IG for 2 test conditions at constant NOx at different

locations .....................................................................................................59


Figure 5-2 Engine NOx map on a brake specific basis at 1800 rpm, 47.5% load .......61


Figure 5-4 Effect of load on brake specific fuel consumption at 425 bar rail pressure

and various injection timings .....................................................................63





Figure 5-7 Variation of BSFC vs. BSPM at constant NOx at different rail pressures

and constant speed .....................................................................................66

Figure 5-8 Comparison of heat release rates for various loads at constant rail pressure

(500 bar) .....................................................................................................67

Figure 5-9 Comparison of heat release rates for various loads at constant rail pressure

(575 bar) .....................................................................................................67

xii

Figure 5-10 Effect of load on bulk temperature at 575 bar rail pressure .......................68

Figure B-1 Variation of MAF with Pressure Difference (dP) ......................................83

Figure B-2 New MAF Calibration Curve.....................................................................84

Figure C-1 TGA results for 1500rpm, 425 bar, 6 deg BTDC sample ..........................86

Figure C-2 TGA results from 1500 rpm, 500 bar and 4 deg BTDC sample ................87



Figure C-5 TGA results from 2100 rpm, 425 bar and 14 deg BTDC sample ..............90

Figure C-6 TGA results from 2100 rpm, 500 bar and 10 deg BTDC sample ..............91

xiii

LIST OF TABLES

Table 3-1 2.5 L DDC/VM Motori engine specifications ...........................................23

Table 3-2 Engine test conditions ................................................................................34

Table 4-1 Effect of engine speed on solids formation and oxidation ........................51

Table 4-2 Comparison of NOx values at four different loads, 425 bar rail pressure

and 4 deg before top dead center ...............................................................62

Table 5-2 Effect of engine load on solids formation and oxidation ...........................69

Table A-1 Ultra low sulfur diesel specifications .........................................................79

Table B-1 Standard modes for MAF calibration ........................................................81

Table B-2 Flow element calibration............................................................................82

Table B-3 Present and previous MAF comparison .....................................................83

Table B-4 Difference between BG-2 and BG-3 readings ...........................................85

Table C-1 Processed Raman data at 425 bar rail pressure ..........................................92

Table C-2 Processed Raman data at 500 bar rail pressure ..........................................93

xiv

NOMENCLATURE

Acronym Description

AHR Apparent heat release

ATDC After top dead center

BSFC Brake specific fuel consumption

BSNOx Brake specific nitrogen oxides

BSPM Brake specific particulate matter

BTDC Before top dead center

CI Compression ignition

DDC Detroit Diesel Corporation

Deg Degrees

DI Direct injection

ECU Electronic control unit

EGR Exhaust gas recirculation

EPA Environmental protection agency

HC Hydrocarbon

HRTEM High resolution transmission electron microscopy

I.C Internal combustion

IDI Indirect injection

MAF Mass of air flow

M.S Mass spectroscopy

NOx Nitrogen oxides

xv

PAH Polycyclic aromatic hydrocarbons

PM Particulate matter

PPM Parts per million

RPM Revolutions per minute

SI Spark ignited

SLPM Standard liters per minute

SOF Soluble organic fraction

SOI Start of injection

TDC Top dead center

TGA Thermogravimetric analysis

ULSD Ultra low sulfur diesel

XPS X-ray photoelectron spectroscopy

XRD X-ray diffraction

xvi

ACKNOWLEDGEMENTS

This thesis work has given me a wonderful research experience and exposure. I

would like to take this opportunity to express my sincere gratitude to those who were

involved with me during the course of this work. First and foremost, I would like to thank

Dr. André Boehman, my adviser, who trusted me in full and gave me the opportunity to

work under him. He has always been an excellent motivator and has encouraged me to

think out of the box. I am always indebted to him. I would like to thank Dr. Haworth and

Dr. Thole for their time and effort in reviewing and critiquing my thesis

Special thanks to Dr. Dave Walker and Dr. Tony Dean at GE Global Research

and the US-Department of Energy (DOE) for financially supporting this project and

providing good fuel for experiments.

Many thanks to Vince Zello, whose expertise with machines and tools reward in

sorting issues out. Thanks to Joe Stitt at MRI for letting me use Raman Spectroscopy

under his guidance and many thanks to Magda Salama at MCL for helping me with TGA.

Thanks to my lab-mates Greg, Hee Je, Kuen, Yu Zhang and Peng Ye who have helped

me directly or indirectly, maintaining a scholarly environment in the lab.

Last but not the least, countless thanks to my dad-L.D Prabhakar and mom-

Gayathri Prabhakar for taking a bold step in sending me to Penn State University from

India, and for motivating me at every step in my life. Special thanks to my sister Kavita

and brother in law Karthik, for their support and encouragement.

1

Chapter 1

Introduction

1.1 General Introduction

The automotive industry worldwide is experiencing tremendous changes day by

day. Spark-ignition (SI) engines were favored for a long time because of their relatively

simple design and their performance. But with increasing cost of fuel and stricter

emission legislations, engine alternatives have become a necessity. Even though

considerable progress has been made towards the development of hybrid vehicles, they

have not penetrated much of the automotive market because of their high initial

investment and lack of sufficient manufacturing capacity to meet the demand. Hence

diesel engines are an attractive choice and invariably continue to gain more interest in the

automotive sector.

1.2 Pros and cons of a diesel engine

Diesel engines have several advantages over conventional spark ignited engines:

Diesel engines have a higher maximum efficiency compared to gasoline engines

because of higher compression ratios employed in the combustion process [1].

Diesel engines are rugged and more reliable in their operation [2].

2

Since diesel engines burn lean and are more fuel efficient, they produce less

carbon dioxide emissions per unit of work produced, which reduces their

contribution to the greenhouse effect [2].

The part load specific fuel consumption of a diesel engine with direct injection

rises less rapidly than for an indirect diesel injection engine (IDI) and a spark

ignition engine as shown in Figure 1-1.

____________________________________________________________________

Figure 1-1: Comparison of part load specific fuel consumption for spark ignited, direct

and indirect injection diesel engines [3].

________________________________________________________________________

3

Even though diesel engines produce less nitrogen oxides (NOx) than gasoline

engines [4], both NOx and particulate matter (PM) emissions are still a major concern for

diesel engines. Several techniques like retarded injection timing and exhaust gas

recirculation (EGR) have been incorporated to reduce NOx from diesel engines.

Similarly, fuel injection at higher rail pressures has been used to reduce PM. However,

reducing NOx and PM from the engine at the same time has been a daunting task. Most

of the in-cylinder techniques used to reduce NOx tend to invariably increase PM, as seen

in Figure 1-2 for different levels of intake swirl. Particulate traps and oxidation catalysts

have been quite successful in curtailing PM emitted into the atmosphere. As one

example, Yoshida et al. [5] at Toyota Motor Corporation have shown that PM and NOx

can now be simultaneously reduced in diesel exhaust gas with a sulfur trap catalyst

system. However, this research is still in its elementary stages.

Figure 1-2: Variation of NOx vs. PM for different levels of intake swirl [3].

________________________________________________________________________

4

Emissions on the 2010 heavy-duty vehicles [6] will be controlled by

implementing selective catalytic reduction (SCR) systems with diesel particulate filters

(DPF). Further investigation into DPF’s revealed that oxide DPF’s can save more energy

in regeneration, and installation of a soot filtration membrane can keep soot out of the

wall for a reduced delta pressure (Δp) across the filter. HC-deNOx systems show a lot of

progress, with new formulations and configurations for controlling emissions.

Incorporating advanced air handling systems with EGR within vehicles reduces CO2 and

other emissions without sacrificing their performance.

1.3 Motivation and thesis overview

The goal of this project was to determine the effect of rail pressure on the

variation of brake specific fuel consumption (BSFC) versus brake specific particulate

matter (BSPM) at constant NOx. From a literature review, it was found that a majority of

the previous tests conducted used a similar approach as that employed here, but none of

them were at a constant level of NOx emissions. The unique aspect of this research was

adding this constraint to the experiments.

To find the points of constant NOx emissions, an engine map was created at

different loads, speeds, rail pressures and injection timing. NOx parity was maintained by

varying the injection timing (retard/advance) at different rail pressures. The injection

strategy was limited to a single pulse main injection, as multiple injections would have

posed greater problems in identifying points of similar NOx. By comparing the soot

5

characteristics and building a relationship between BSFC and BSPM, the effect of fuel

spray momentum on particulate mass and soot character was examined. With the same

test procedure, the effect of speed and load on emissions, BSFC and other parameters

such as exhaust temperature, heat release rate, etc., were determined and verified with

test results from the literature.

All experiments were performed on a 2.5 L Detroit Diesel Corporation

(DDC)/VM Motori turbocharged, common rail direct injection (DI) engine. A detailed

description of the experimental setup can be found in Chapter 3. Fuel used for the

experiment was an ultra low sulfur diesel (ULSD) whose details can be found in

Appendix A. A literature review, presented in Chapter 2, discusses the effects of engine

operating conditions including speed and load, and more importantly in-cylinder

parameters including rail pressure, injection timing, etc., on NOx, PM, and BSFC. Some

important characteristics of fuel sprays are discussed, as they play a major role in

combustion. Experimental setup and test conditions are discussed in Chapter 3. Results

are presented in Chapters 4 and 5. Conclusions and recommendations for future work are

presented in Chapter 6.

6

1.4 Objectives

This research work has been divided into different tasks and subtasks as

mentioned below. Results from the subtasks can be found in Appendix B.

1.4.1 Tasks

1. To see the effect of rail pressure on BSFC vs. BSPM at different speeds (1500

rpm, 1800 rpm, and 2100 rpm), fixed load (40 percent) and constant NOx

(referred to as Test 1).

2. To see the effect of rail pressure on BSFC vs. BSPM at different loads (40, 47.5,

and 55 percent), fixed speed (1800 rpm) and constant NOx (referred to as Test 2).

3. To collect bulk particulate matter samples from six conditions at constant load

and analyze their oxidation behavior using Thermogravimetric analysis (TGA).

4. To perform Raman spectroscopy to delve deeper into soot reactivity to support the

results from thermogravimetric analysis.

1.4.2 Subtasks

1. Compare Sierra Instruments BG-2 and BG-3 particulate partial flow sampling

systems- readings for the same face velocity across the filter.

2. Check the existing calibration on the mass of air flow sensor and recalibrate if

necessary.

7

Chapter 2

Literature Review

2.1 Diesel engine operating principles

Rudolph Diesel in the year 1897 invented the diesel engine, which operates using

a compression ignition (CI) process. The diesel engine differs from the gasoline powered

Otto cycle by using a higher compression of the air to ignite the fuel rather than using a

spark plug. The idealized diesel cycle, as shown in Figure 2-1, has a constant pressure

heat addition process as compared to a constant volume heat addition in the idealized

Otto cycle.

________________________________________________________________________

Figure 2-1: Diesel engine operating cycle 1

________________________________________________________________________

1 www.dimec.unisa.it

8

The diesel engine has 4 strokes of operation as discussed below.

1. Intake stroke: (e to a) Atmospheric air after passing through the air filter gets

inducted into the engine through the intake valve while the exhaust valve remains

closed. This happens during the downward motion of the piston.

2. Compression stroke: (a to b) Inducted air gets compressed adiabatically (without

heat loss- under ideal cycle) into the clearance volume as the piston moves

upwards completing the second stroke. While this happens, both intake and

exhaust valves remain closed. Typical compression ratios (ratio between the

volume of the cylinder and combustion chamber when the piston is at the bottom

of its stroke, and the volume of the combustion chamber when the piston is at the

top of its stroke) are between 16 and 24.

3. Expansion stroke: (b to c and c to d) Due to high compression ratios, the

temperature at the end of compression is sufficiently high to auto ignite the fuel.

Fuel injection starts near the end of the compression stroke. In an ideal cycle, the

rate of injection is such that the combustion maintains the pressure constant in

spite of the piston movement during the expansion stroke which increases the

chamber volume. Heat is assumed to have been added at constant pressure. After

the injection of fuel is completed, the products of combustion expand. Both valves

are closed during this operation.

http://en.wikipedia.org/wiki/Ratio

http://en.wikipedia.org/wiki/Cylinder_%28engine%29

http://en.wikipedia.org/wiki/Piston

9

4. Exhaust stroke: (d to a and a to e) As the piston moves up again, it pushes the

burned combustion gases out through the exhaust valve, while the intake valve

remains closed until the next cycle starts. The pressure falls to atmospheric

pressure. Some residual gases are trapped in the clearance volume of the cylinder

which is carried over to the subsequent cycle.

Each cylinder of a four stroke engine completes the above four operations in two

engine revolutions, one revolution during which intake and compression processes occur,

and a second revolution during which the expansion and exhaust occur. Thus for one

complete cycle, there is only one power stroke while the crankshaft rotates through two

revolutions. A detailed overview of the strokes can be seen in Figure 2-2.

________________________________________________________________________

Figure 2-2: Four strokes of the diesel cycle.

________________________________________________________________________

10

2.2 Diesel combustion

Like most transportation fuels, diesel fuel is hydrocarbon based. C10.8H18.7 can be

considered a generic representation of the diesel fuel. A detailed specification of the ultra

low sulfur diesel (ULSD) fuel used in this study is given in Appendix A. Under ideal and

stoichiometric conditions (required amount of air for a given amount of fuel), with air as

the oxidizer, and under the assumption that only major products of combustion are

formed, fuel undergoes complete combustion [8], yielding carbon dioxide (CO2), water

(H2O) and un-reacted nitrogen (N2) as shown in Equation (1).

𝐶𝑎𝐻𝑏 + 𝑎 + 𝑏

4 𝑂2 + 3.76𝑁2 → 𝑎𝐶𝑂2 +

𝑏

2𝐻2𝑂 + 3.76 𝑎 +

𝑏

4 𝑁2 (1)

This is just a global reaction and does not happen in reality. There are hundreds of

elementary reactions that make up the entire combustion process [8]. Since the

composition of the combustion products is significantly different for lean and rich fuel

mixtures, and because stoichiometric fuel air ratio depends on the fuel composition,

another parameter called the equivalence ratio (Ф) becomes more convenient to define

the overall combustion conditions, as given in Equation (2).

Ф = 𝐹𝐴 𝑎𝑐𝑡𝑢𝑎𝑙

𝐹𝐴 𝑠𝑡𝑜𝑖𝑐𝑕

(2)

11

Ф > 1 represents a rich mixture while Ф < 1 represents a lean mixture. With

increasing amounts of diesel fuel injected, problems with air utilization are created

leading to excessive amounts of soot [8]. Hence diesel engines usually burn lean (Ф <

1). This also leads to higher fuel conversion efficiency over a spark ignition engine.

There are different stages of diesel combustion, which are well explained by the

heat release profile shown in Figure 2-3.

________________________________________________________________________

Figure 2-3: Typical heat release profile of a diesel engine [1].

________________________________________________________________________

12

1. Ignition Delay: (a to b) This represents the time delay between start of injection

and actual start of combustion in the cylinder. During this process, the rate of heat

release drops below zero due to fuel absorbing heat while vaporizing.

2. Phase of rapid combustion or the premixed phase: (b to c) This process happens

over a small range of crank angles. The fuel mixes with air and burns rapidly,

resulting in a high heat-release rate, as seen by the sharp peak. The combustion

process appears to be like that when the reactants are premixed and hence is

termed the premixed combustion phase.

3. Phase of mixing controlled combustion: (c to d) There are several processes that

go on in this phase. The liquid fuel atomizes, vaporizes, and mixes with air and

finally burns with a diffusion flame. The rate of heat release is not as high as the

peak during the premixed phase, but it occurs over a larger range of crank angle.

4. Phase of late combustion: (d to e) This can be termed as the last stage of heat

release. It is very low in its release rate, and might occur due to several reasons. It

could be because of some leftover fuel, or some energy stored in soot and fuel

rich combustion products. This happens over a few crank angle degrees.

13

2.3 NOx emissions from internal combustion engines

The mixture of nitric oxide (NO) and nitrogen dioxide (NO2) is referred to as

NOx. Nitric oxide is by far the most dominant oxide of nitrogen formed during

combustion [1]. The exact amount depends upon the engine design and operating

conditions, but is typically in the range of 500-1000 ppm or 20 g/kg of fuel [3].

Subsequent oxidation of nitric oxide leads to nitrogen dioxide in the environment, which

reacts with hydrocarbons in the atmosphere to form smog. Smog and nitrogen oxides are

both dangerous as they can cause severe respiratory problems [9].

Nitric oxide is formed in flames by three mechanisms: the thermal or Zeldovich

mechanism, the prompt or Fennimore mechanism and the nitrous oxide (N2O)

intermediate mechanism. The thermal mechanism is the most referred to and is based on

the extended Zeldovich Mechanism [8] as shown in Equations (3), (4), and (5).

𝑂 + 𝑁 2 ↔ 𝑁𝑂 + 𝑁 (3)

𝑁 + 𝑂 2 ↔ 𝑁𝑂 + 𝑂 (4)

𝑁 + 𝑂𝐻 ↔ 𝑁𝑂 + 𝐻 (5)

Equations (3) and (4) were identified by Zeldovich (1946) and Equation (5) was added by

Lavoie et al. [10] as they showed that it contributed significantly under equilibrium

conditions.

14

NOx is formed in regions where enough energy is available for nitrogen to

oxidize. Hence NOx formation is governed by higher temperatures and the availability of

oxygen [10]. Several strategies have been adopted to reduce NOx emissions in an engine.

Campbell et al. [26] showed that a simple way to reduce NOx emissions was by retarding

the injection timing because it resulted in lower flame temperatures. Sasaki et al. [12]

showed that incorporating diluents in the intake, for example, exhaust gas recirculation

(EGR), helped in reducing NOx emissions as it would reduce the mean flame

temperature. Burning ultra-lean mixtures can minimize NOx formation, but may not be

applicable in the case of diesel engines as combustion might not be sustained. In

automotive applications, combustion system modifications alone are unable to reduce

NOx emissions to mandated levels, and hence use of catalytic converters in the exhaust

stream is a necessity.

2.4 Particulate matter emissions

Soot and particulate emissions from a diesel engine form due to incomplete

oxidation of the fuel. Formation of soot can be considered an intrinsic property of most

fuel rich flames. Because these particles are very small (of the order 15 to 30 nm [2]), it is

easy for them to enter the lungs through inhalation and cause severe respiratory problems.

Short term problems include dizziness and coughing, and in the long term it could lead to

lung cancer as well [13].

15

The composition of diesel particulates varies with operating conditions and the

type of collection system [3]. At diesel combustion temperatures above 500oC, individual

particles are principally clusters of many small spheres of carbon, with individual sphere

diameters of about 15 to 30 nm. As temperatures go below 500oC, particles get coated

with absorbed and condensed high molecular weight organic compounds which include

unburned hydrocarbons, oxygenated hydrocarbons and polycyclic aromatic hydrocarbons

(PAH) [3].

The objective of most particulate measurement techniques is to determine the

amount of particulate being emitted to the atmosphere. Measurement techniques range

from simple smoke meters to analyses using dilution tunnels. Most techniques require

lengthy sample collection periods because the emitted rates from the exhaust are usually

low. The physical conditions under which they are sampled are closely monitored as the

composition of the samples can easily get altered, depending on the sampling conditions,

either chemically or by interaction with the surroundings.

2.4.1 Stages of soot formation

From the most modern view, it is assumed that diesel engines have a diffusion

flame structure during the mixing controlled phase of combustion, since the reactants (air

and fuel) are not premixed. There are four stages that lead to the formation of soot [8].

16

1. Formation of precursor species: Polycyclic aromatic hydrocarbons are

considered to be important intermediates between the original fuel and primary

soot particle. Formation of ring structures and their growth via reactions with

acetylene have been identified as an important process.

2. Particle inception: This step involves the formation of small particles of a

critical size (3,000-10,000 atomic mass units) from growth by both chemical

means and coagulation. It is in this step that large molecules are transformed to, or

become identified as particles.

3. Surface growth and particle agglomeration: Throughout combustion,

more particles keep forming. When these primary particles get exposed to the

bath of species from the pyrolizing fuel, particle growth, which includes surface

growth, coagulation, and aggregation, is experienced. Surface growth, by which

the bulk of the solid-phase material is generated, involves the attachment of gas-

phase species to the surface of particles.

4. Particle oxidation: Particles agglomerated from the previous step get

oxidized in the flame.

17

Formation of soot within the flame is highly dependent on the fuel type. Smoke

point measurements help in experimentally determining the sooting tendency of a fuel.

The eventual emission of soot from the engine will depend on the balance between these

processes of formation and burnout. The phases of particulate matter formation can be

visualized as seen in Figure 2-4. Figure 2-5 shows the typical nanostructure of diesel soot

obtained using a high resolution transmission electron microscope.

________________________________________________________________________

Figure 2-4: Stages of soot formation within a diesel engine]2.

________________________________________________________________________

Figure 2-5: Typical diesel soot nanostructure [15].

________________________________________________________________________

2 www.forfbrf.lth.se

18

2.4.2 Reducing particulate matter formation/emissions

Increasingly stringent emission regulations require reduction of particulate

emissions. Incorporation of common rail direct injection systems with electronic control

have been helpful to improve fuel-air mixture preparation to lower PM, NOx, and noise.

Injecting fuel at higher pressure results in less PM as fuel gets atomized better leading to

improved mixing with air [16]. Use of alternative fuels or burning fuels in advanced

combustion modes can be good ways to reduce PM emissions, as well [17].

As with NOx, it is not entirely possible to reduce PM through in-cylinder

modifications alone, when operating on diesel fuel. Diesel particulate filters offer retrofit

opportunities [18]. Even though these filters can remove more than 90 percent of PM,

there are several issues related with their use. First, a high sustained exhaust temperature

is needed for regeneration to take place within the filter. Secondly, these filters typically

work well only with ultra low sulfur diesel fuels. Oxidation catalysts, which use chemical

processes to break down pollutants in the exhaust stream into less harmful components,

can be a good way to control PM emissions. However, they are quite expensive.

Figure 2-6 represents the emission levels for locomotive engines as set by the

Environmental Protection Agency (EPA). All values are listed on a brake specific basis.

Figure 2-7 represents the new NOx and PM levels requirements for the year 2010. EPA

mandates that all new vehicles follow these rules strictly.

19

________________________________________________________________________

Figure 2-6: Emission standards for a diesel locomotive engine as per EPA.

________________________________________________________________________

Figure 2-7: EPA NOx and PM forecast for 2010 heavy-duty vehicles [20].

________________________________________________________________________

20

2.5 Injection pressure, timing and common rail injection system

Common rail fuel injection systems decouple the pressure generation from the

injection process and have become popular because of the possibilities offered by

electronic control. With this kind of a system, higher injection pressures of up to 1400

bars can be achieved. The engine management system can divide the injection process

into multiple phases: for example, two pilot injections, main injection and post injection.

In addition to the usual inputs, the engine management system uses the fuel rail pressure

as an input. Hence, with engine speed and load fluctuations within a cycle, correct

metering of fuel is possible to obtain smooth torque output [21].

Badami et al. [22] showed that increasing injection pressure improved the

atomization of fuel. This aids in reducing PM emissions, at the expense of an increase in

NOx. Hence an optimum value of injection pressure is necessary to keep both PM and

NOx as low as possible. Wallace et al. [23] found that the effect of injection pressure was

much more marked at higher speeds on torque, power, and brake specific fuel

consumption. They were able to analytically show that BSFC decreased with increasing

injection pressures, while it increased with increasing speeds.

Desantes et al. [24] reported similar trends. They showed that NOx decreased

with retarded injection timing, while BSFC increased. They also found that dry soot

increases with retarded injection timing. These findings were similar to the work done by

Payri et al. [26] who concluded that retarded fuel injection produced very low levels of

21

NOx and significantly lower emissions of soot as well. The same conditions resulted in

higher carbon monoxide and unburned hydrocarbons, and a significant fuel efficiency

penalty. Their main idea was to delay the injection to an extent that the first phase of

combustion occurred in premixed conditions.

2.6 Spray and droplet characteristics

Spray formation is a critical process during liquid fuel combustion. There are

various stages of spray formation [2] in an engine, as shown in Figure 2-8.

1. Formation of droplets: At the start of fuel injection, the pressure difference

across the orifice is low and hence droplets are formed (a).

2. A stream of fuel emerges from the nozzle (b).

3. The stream encounters aerodynamic resistance from the dense air present in

the combustion chamber and breaks into a spray. The place where this

happens is called the breakup point (c, d).

4. With increasing pressure difference, the break-up distance decreases and the

cone angle increases until a full spray is formed at the orifice (e, f).

22

________________________________________________________________________

Figure 2-8: Spray formation process [2].

________________________________________________________________________

The spray from a circular orifice is surrounded by a cone of droplets of various

sizes. Larger droplets provide a deeper penetration into the chamber but smaller droplets

are required for quick mixing and evaporation of the fuel. Droplet size decreases with

increasing injection pressure and air density, and increases with fuel viscosity and orifice

size increase.

23

Chapter 3

Experimental Setup

3.1 Engine and engine related information

A heavily instrumented 2.5L Detroit Diesel Corporation (DDC)/VM-Motori

engine was used for these experiments. Engine specifications are given in Table 3-1 and

the general engine layout is shown in Figure 3-1.

________________________________________________________________________

Table 3-1: 2.5 L DDC/VM Motori engine specifications

Engine DDC 2.5 L Turbo-charged, Direct Injection(DI)

Number of valves 4 valves/cylinder

Displacement 2.5 L

Bore 92 mm

Stroke 94 mm

Compression ratio 17.5

Length of the connecting rod 159 mm

Rated power 103 kW@ 4000 rpm

Peak torque 340 Nm@1800 rpm

Injection system Bosch common rail injection

________________________________________________________________________

24

________________________________________________________________________

Figure 3-1: Photograph of 2.5 L DDC/VM Motori engine.

________________________________________________________________________

3.2 Load generation and dynamometer

The load on the engine was generated using a 250 Hp Eaton eddy current

dynamometer coupled to the engine. The dynamometer was water cooled and the cooling

water was mixed with L5139 (Lycorine Hydrochloride-a selective inhibitor) and TK

2354 chemicals to prevent scaling due to water flow within the dynamometer. The engine

and the dynamometer were controlled by adjusting the settings on a Digalog Testmate

25

dyno and throttle controller. Cooling water temperatures were monitored during the test

to prevent overheating of the dynamometer.

3.3 Engine control and the ECU

Engine operating parameters were controlled using an unlocked Electronic

Control Unit (ECU). The ECU was connected to an ETAS MAC 2 unit via ETK

connection, which was connected to a computer running INCA software, version 4.0. All

programming modifications to the engine were performed using this interface. The

parameters that were varied during the test procedure were fuel rail pressure, pilot

injection shut off, and main injection timing.

3.4 Data acquisition

Real time engine data acquisition was possible with custom programs written in

National Instruments LabView VII. Signals such as mass of air flow (MAF), diesel fuel

flow rate, emissions, temperatures etc., were read by a series of FieldPoint modules. The

data were saved in a format that could be easily processed in Microsoft Excel and Matlab.

For most conditions, a sampling interval of 2 seconds was selected with a total sampling

time of 3-4 minutes, once steady state conditions were achieved.

26

3.5 Pressure trace and needle lift sensor

Cylinder pressure signals were measured using AVL GU12P pressure transducers.

The voltages from these transducers were amplified by a set of Kistler type 5010 dual

mode amplifiers. The signals were read by an AVL Indimodul 621 data acquisition

system. Needle lift data were obtained from a Wolff Controls Inc. Hall effect needle lift

sensor, which was placed on the injector of cylinder 1. This signal was read by the AVL

Indimodul, which was triggered by a crank angle signal from an AVL 365 C angle

encoder placed on the crank shaft. The Indicom interface recorded these signals over a

0.1 degree crank angle resolution and averaged them over 200 cycles.

3.6 Mass of air flow (MAF) and diesel fuel flow rate

The mass of air entering the engine at any given condition was calculated based

on the voltage reading on the MAF sensor. This sensor was calibrated using a laminar

flow element at room temperature, which was assumed to be 300 K; details are discussed

in Appendix B.

The diesel fuel consumption was measured using a Sartorius electronic

microbalance. LabView was programmed to calculate the actual flow rate based on 100

measurements of the fuel tank mass, while it tracked small changes in mass over 60

seconds.

27

3.7 Engine emissions measurement

Engine gaseous emissions were measured using an AVL CEB II combustion

emissions bench. Hot exhaust was sampled through head-line filters into an insulated

heated line which was maintained at 190oC. The gases were again filtered through

smaller filters to ensure particulate free exhaust entered the bench. Before data collection,

the bench was switched on at least 1-2 hrs in advance to let the analyzers warm up. Every

day, the bench was recalibrated by flowing the span gas and zero air for sufficient

duration.

NOx and NO were measured in parts per million (ppm) using an Ecophysics

chemiluminescence analyzer. NO2 concentration was assumed to be the difference of the

two. Carbon monoxide (CO, ppm) and carbon dioxide (CO2, %) were measured using

two separate Rosemount infrared analyzers and oxygen (O2, %) was measured using a

Rosemount paramagnetic analyzer. The emission bench also has the capability to

measure total hydrocarbons (THC) and methane in the exhaust. THC values were

recorded, but methane was not pertinent to this part of the research. A photograph of the

bench is shown in Figure 3-2.

28

________________________________________________________________________

Figure 3-2: AVL CEB II combustion emissions bench.3

________________________________________________________________________

3.8 Particulate matter emissions: BG-3 sampling system

Particulate emissions from the engine were sampled using a Sierra Instruments

BG-3 particulate partial flow sampling system, as shown in Figure 3-3. Earlier versions

of this instrument were the BG-2 and BG-1. The engine exhaust was drawn and diluted

and chilled with a known quantity of dry, hydrocarbon-free air (at 100 psig.) and passed

through a pair of filter membranes for sample collection. The dilution occurred in the

3 www.avl.com

29

micro-dilution chamber. A sample flow of 75 standard liters per minute (slpm) was set

and a dilution ratio of 10 was maintained throughout the sampling. The samples were

collected on a 47 mm PallFlex filter (Pall Life Sciences- Emfab TX40HI20-WW). A set

of 4 filters was used per mode and the duration of sampling was 5 minutes. Particulate

matter sampling on BG-3 cannot be performed simultaneously with AVL emission

measurements, as purge air from the bench gets mixed with the emissions from the

engine leading to erroneous PM measurements.

________________________________________________________________________

Figure 3-3: BG-3 particulate sampling system.4

________________________________________________________________________

The filters were prepared in a humidity controlled chamber at 25oC and 45

percent relative humidity for 48 hours prior to sampling, as seen in Figure 3-4. These

4 www.sierrrainstruments.com

30

were weighed on a Sartorius M5P electronic microbalance before and after sampling. The

difference in weight was the amount of PM deposited at that particular condition.

________________________________________________________________________

Figure 3-4: Humidity control chamber and Sartorius micro-balance for measuring

particulate sampling filter mass.

________________________________________________________________________

3.9 Facility for bulk sampling

Bulk samples were extracted from the engine exhaust using a vacuum pump to

perform further testing on the soot, as seen in Figure 3-5. Soot was collected on a Teflo

filter (Pall Life Sciences, P/N R2PL047) for several hours depending upon the engine

condition. The contents were then scraped off from the filter and collected on a static-free

31

paper. This was transferred to a glass bottle and weighed on a Sartorius Precision

balance.

________________________________________________________________________

Figure 3-5: Facility for bulk sampling, vacuum pump with sample collector shown.

________________________________________________________________________

3.10 Thermogravimetric Analysis (TGA)

Mass loss (oxidation) curves on various soot samples were obtained by

thermogravimetric analysis as shown in Figure 3-6. To extract volatile organic fraction

(VOF), bulk samples from exhaust were placed in the pre-cleaned alumina crucible and

heated at a constant rate of 10oC per minute from room temperature to 500

oC in Nitrogen

gas. Curves were then plotted in the TGA Manager.

Exhaust

32

________________________________________________________________________

Figure 3-6: TGA-MS, TA instruments 2050 TGA.

________________________________________________________________________

3.11 Raman spectroscopy

Raman spectra of soot samples were obtained on a WITec Confocal Raman

Microscope CRM 200. Soot samples were placed on a 25 mm square micro-cover glass

and placed under observation. A 40X magnification objective lens and primary white

light were used to obtain the primary focus; however, for greater magnification, the lens

was switched over to a 100X objective. The white light was turned off and a He-Ne laser

of 514.5 nm wavelength was directed to the sample using a beam splitter.

33

Laser power was set to 25-40% of the maximum to avoid overheating and burning

the sample. The scattered light was collected by the objective lens and passed through a

holographic notch filter to eliminate Rayleigh scattering. It was then focused into a

multimode fiber and directed to a spectrometer equipped with a CCD camera and photon

counting APD.

Spectra were obtained at fifteen different locations for each sample. Plots were

obtained on Igor Pro software and the average from different locations was used for final

data analysis.

3.12 Test conditions

Several combinations of speed and load were tested before settling at the

conditions given in Table 3-2. Based on the engine map in INCA, rail pressures of 425-

500-575 bar were selected to be within a safe working range. Based on a range of tests

for load condition, 40% load was selected as the operating condition for the experiments

at varying speeds. Various speeds (1500 rpm, 1800 rpm, 2100 rpm and 2400 rpm) were

tested and finally narrowed down to operate at first three of the four speeds. While

performing the constant speed and varying load test, a load of 30 percent was tried. Even

though collection of PM was possible, limitations in injection timing on the INCA map

prevented us from attaining points of constant NOx. Loads of 60% and 70% were

attempted, but it was difficult to operate at these conditions because of combustion

instabilities. The engine would frequently shut down to prevent any further damage.

34

Hence the other two possible loads at which the engine could be operated safely were at

55 percent and 47.5 percent.

________________________________________________________________________

Table 3-2: Engine test conditions

Test 1 Test 2

Engine speeds 1500 rpm, 1800 rpm, 2100 rpm 1800 rpm, fixed

Engine load 40%, fixed 40%, 47.5%, 55%

Rail pressure 425 bar, 500 bar, 575 bar 425 bar, 500 bar, 575 bar

Injection

timing

10 deg before TDC to 4 deg

before TDC, sweep

10 deg before TDC to 4 deg

before TDC, sweep

Injection mode Single pulse injection, no pilot Single pulse injection, no pilot

________________________________________________________________________

35

Chapter 4

Results and Discussion-Part 1

Results and discussion from the test at constant load (Test 1) are presented in this

chapter. Results include the variation of NOx emissions with speed and rail pressure, the

effect of injection timing on brake specific fuel consumption, and the effect of rail

pressure on the relationship between BSFC and BSPM at constant NOx levels.

4.1 Engine NOx emissions map

An engine map was created to identify points of constant NOx. This can be seen

in Figures 4-1, 4-2 and 4-3.

________________________________________________________________________

Figure 4-1: Engine NOx emissions map on a brake specific basis at 1500 rpm, 40%

load.

________________________________________________________________________

425

500

5753

5

7

9

108

64

Rai

l Pre

ssu

re, b

ar

BSN

Ox,

g/k

Wh

Injection Timing, °BTDC

7-9 5-7 3-5

36

________________________________________________________________________


load.

________________________________________________________________________


load. Data available only for two rail pressures (500, 575 bar).

________________________________________________________________________

425

500

575

3

5

7

9

108

64

Rai

l Pre

ssu

re, b

ar

BSN

Ox,

g/k

Wh


7-9 5-7 3-5

500

5753

5

7

9

108

64

Rai

l Pre

ssu

re, b

ar

BSN

Ox,

g/k

Wh


7-9 5-7 3-5

37

For the engine map at 2100 rpm and 40% load, data for only two rail pressures

have been plotted. This was because at 425 bar pressure, the point of desired NOx was

outside the given crank angle sweep for the injection timing range of 4-10 degrees before

top dead center. Comparing Figures 4-1 to 4-3, it is evident that increasing the speed

helps in reducing brake-specific NOx. Maximum NOx of 7.9 g/kWh was observed for the

condition at 1500 rpm with a rail pressure of 575 bar and an injection timing of 10

degrees before TDC while a minimum of 3.39 g/kWh was obtained for 2100 rpm, 500

bar rail pressure (data for 425 bar unavailable) and an injection timing of 4 degrees

before TDC.

As the engine speed is increased, air swirl and squish velocities are increased. In

addition, cycle time is decreased leading to increased wall temperatures and reduced time

for heat loss, thereby increasing the air temperature. These effects would in turn result in

shorter ignition delays, increased reaction rates and reduced time for reaction to occur

[26]. NOx decreases at higher speeds because of the fact that the residence time of the

mixture within the cylinder gets reduced, or in other words, there is less time available

(shorter time scale) for the formation of NOx. These results are consistent with the

findings from Glassman [9].

It can be inferred that brake-specific NOx increases with increasing rail pressure

and decreases with retarded injection timing. The reason for this can be explained on the

basis of NOx formation, which has been widely discussed in the literature [1, 3, 10].

Formation of nitrogen oxides in an engine is favored by high temperature. By retarding

38

the injection timing, the peak temperatures within the engine are reduced, which thereby

reduces the formation of NOx. A direct way to visualize this would be by looking at the

bulk temperature within the engine by calculating the heat release from the data obtained

from the cylinder pressure sensor. The bulk temperature for 1500 rpm, 425 bar and 40%

load is plotted for different injection timings as seen in Figure 4-4.

________________________________________________________________________

Figure 4-4: Variation of bulk temperature with injection timing at fixed rail pressure

(425 bar).

________________________________________________________________________

Bulk temperature was increased by advancing the injection timing. When the start

of injection was 4 degrees before the top dead center, the maximum temperature reached

was about 1580 K but when the start of injection was 10 degrees before the top dead

center, the maximum temperature attained was about 1630 K. Results are in accordance

600

800

1000

1200

1400

1600

1800

50 100 150 200

Bu

lk T

em

pe

ratu

re, K

Crank Angle, °ATDC

4 deg BTDC

6 deg BDTC

8 deg BTDC

10 deg BTDC

39

with the findings from Szybist et al. [11] who observed that NOx emissions were high

when the maximum cylinder temperature occurred earlier. To see the effect of rail

pressure on bulk temperature, variations were plotted holding the injection timing fixed at

4 deg before top dead center and maintaining the same speed and load, as shown in

Figure 4-5.

________________________________________________________________________

Figure 4-5: Effect of rail pressure on bulk temperature at fixed injection timing.

________________________________________________________________________

By increasing the rail pressure from 425 bar to 575 bar, the bulk temperature

increased from 1580 K to about 1625 K. Hence it can be concluded that NOx increases

with increasing rail pressure and advancing injection timings. These trends could be

clearly seen in Figure 4-6 and Figure 4-7 for two such speeds. Similar profiles were also

observed by Shimada et al. [27]. Acar [28] showed similar trends for two different fuels

(ULSD and FT fuel).

850

950

1050

1150

1250

1350

1450

1550

1650

1750

100 120 140 160 180

Bu

lk T

em

pe

ratu

re, K

Crank Angle, °ATDC

425 bar

500 bar

575 bar

Injection timing : 4 °BTDC

40

________________________________________________________________________

Figure 4-6: Effect of injection timing and rail pressure on BSNOx at 1500 rpm, 40%

load.

________________________________________________________________________

Figure 4-7: Effect of injection timing and rail pressure on BSNOx at 1800 rpm, 40%

load.

________________________________________________________________________

3

4

5

6

7

8

9

0 2 4 6 8 10 12

BSN

Ox,

g/k

Wh


425 bar

500 bar

575 bar

3

3.5

4

4.5

5

5.5

6

6.5

0 2 4 6 8 10 12

BSN

Ox,

g/kW

h


425 bar

500 bar

575 bar

41

4.2 Effect of injection timing and rail pressure on BSFC at constant load

Experiments were performed to see the effect of injection timing on the brake-

specific fuel consumption at different speeds in an engine. The results are shown below

in Figures 4-8, 4-9 and 4-10.

_______________________________________________________________________

Figure 4-8: Effect of injection timing on BSFC at 1500 rpm, 40% Load.

________________________________________________________________________

150

160

170

180

190

200

210

220

230

4 6 8 10

BSF

C, g

/kW

h


425 bar 500 bar 575 bar

42

________________________________________________________________________


________________________________________________________________________


________________________________________________________________________

150

160

170

180

190

200

210

220

230

4 6 8 10

BSF

C, g

/kW

h


425 bar 500 bar 575 bar

150

160

170

180

190

200

210

220

230

4 6 8 10

BSF

C, g

/kW

h

Injection Timing , °BTDC

500 bar 575 bar

43

These results show that brake specific fuel consumption deteriorated (increased)

with retarded injection timing. From Figure 4-8, at 1500 rpm and 500 bar rail pressure, a

6 degree change in injection timing from 10 deg BDTC to 4 deg BTDC increased the

BSFC from 214 to 218.5 g/kWh, more than a 2 percent change. A maximum change was

seen for the profiles at 2100 rpm and 500 bar rail pressure, with a change in BSFC from

208.5 g/kWh to 220.1 g/kWh accounting for nearly a 4% increase. Trends are in

agreement with those of Campbell et al. [26].

In a conventional diesel engine (with no major modifications to the injection

system), retarded injection timing tends to make the ignition delay shorter thereby

reducing the fuel-air mixing time before ignition. Fuel air mixing is an important stage in

combustion. With better atomization of fuel and better mixing, the combustion process is

smoother and the efficiency of the engine is usually higher. With less mixing of fuel and

air, more fuel gets consumed for the same quantity of air, increasing the brake specific

fuel consumption. However, with an increase in rail pressure, some fuel-wetting of the

cylinder walls might take place, which could result in higher values of fuel consumption.

It is speculated that BSFC increased with rail pressure (as in Figures 4-8 to 4-10) for the

above reason, although it cannot be visualized with the existing engine configuration.

Under such conditions, the total hydrocarbon (THC) emissions also increase. Su et al.

[19] investigated the effect of injection parameters on the specific fuel consumption

under HCCI mode and found that over-penetration of fuel resulted in higher specific fuel

consumption.

44

4.3 Effect of speed at constant load on BSFC

Experiments were performed to see the effect of speed on brake specific fuel

consumption. While doing so, the rail pressure and injection timing were held constant so

that the direct influence of speed could be visualized. The results can be seen in Figures

4-11, 4-12 and 4-13 for various injection timings.

________________________________________________________________________

Figure 4-11: Effect of engine speed at constant load on BSFC at 425 bar rail pressure

Data for 2100 rpm, 425 bar not available.

________________________________________________________________________

150

160

170

180

190

200

210

220

230

1500 1800

BSF

C, g

/kW

h

Speed , rpm

4 btdc 6 btdc 8 btdc 10 btdc

45

________________________________________________________________________

Figure 4-12: Effect of engine speed at constant load on BSFC at 500 bar rail pressure.

________________________________________________________________________

Figure 4-13: Effect of engine speed at constant load on BSFC at 575 bar rail pressure.

________________________________________________________________________

150

160

170

180

190

200

210

220

230

1500 1800 2100

BSF

C, g

/kW

h

Speed , rpm


150

160

170

180

190

200

210

220

230

1500 1800 2100

BSF

C, g

/kW

h

Speed, rpm

4 BDTC 6 BTDC 8 BTDC 10 BDTC

46

Some trends concerning speed, injection timing and BSFC are described below.

With an increase in speed from 1500 rpm to 2100 rpm, the BSFC values

decreased. The reason for this decrease could be explained in terms of heat

transfer within the engine. At low speeds there is a higher heat exchange from the

burnt gas to the combustion chamber walls, thereby reducing the combustion

efficiency resulting in higher fuel consumption. However, at higher speeds, the

frictional power increases at a much rapid rate than the power output at the

corresponding speed and load. In order to match up with the output power,

additional fuel is injected into the cylinder and hence a higher BSFC is observed.

These trends were seen by Zaid [29], who concluded that BSFC reduces initially

but increases at higher engine speeds. Along a similar line, we can reason out that

during this transition of speeds, BSFC decreases from 1500 rpm to 2100 rpm.

However, with variations in BSFC with speed being so small, the results cannot

be statistically significant. A maximum of 8 % coefficient of variation (COV) was

observed for the operating condition at 1500 rpm, 500 bar rail pressure and an

injection timing of 4 degrees before top dead center, which was greater than the

error in measurement.

A second argument for a decrease in BSFC with speed can be made on the basis

of the pressure curve, which rephases itself with a change in speed.

47

4.4 Effect of rail pressure on BSFC vs. BSPM at NOx parity (Test 1)

In this part of the test, operating points of constant NOx were determined at three

rail pressures, while the load was maintained constant and speed was varied. A plot

showing the variation of BSFC with BSPM at constant NOx is shown in Figure 4-14.

________________________________________________________________________

Figure 4-14: Effect of speed and rail pressure on BSFC vs. BPSM at constant NOx and

load.

________________________________________________________________________

1500,6

1800 , 8

2100 ,14

1500,4

1800,8

2100,10

0

0.03

0.06

0.09

0.12

200 205 210 215 220 225 230

BSP

M, g

/kW

h

BSFC, g/kWh

425 bar

500 bar

575 bar

2100,9 1800,6

1500, 1.75

48

Several interesting observations can be made from Figure 4-14. First, it was

apparent that with an increase in rail pressure from 425 bar to 575 bar, the brake-specific

particulate matter was reduced, which was in accordance with the literature [21, 26]. This

was because a higher injection pressure would have resulted in enhanced atomization (as

discussed in Chapter 2) of the fuel resulting in shorter droplet lifetimes, less pyrolysis,

and greater air utilization.

However, the trends were not as straight-forward to be explained on the basis of a

single parameter. Several parameters were varied at the same time to maintain constant

NOx emission level, including speed, rail pressure and injection timing. Individual

explanations are needed to describe the trends in Figure 4-14.

Along a constant rail pressure line, say 425 bar, speed and injection timing were

varied with speed decreasing from 2100 rpm to 1500 rpm, while injection timing was

retarded to maintain constant NOx. While this happened, the brake specific fuel

consumption increased from left to right; however, the brake specific particulate matter

reduced initially and increased again. At 425 bar, 2100 rpm and 14 deg BTDC the BSPM

was 0.089 g/kWh; at 1800 rpm and 8 deg BTDC the BSPM was 0.067 g/kWh; and at

1500 rpm and 6 deg BTDC the BSPM was 0.083 g/kWh. Further analysis was necessary

to determine which of the parameters was more significant.

49

Desantes et al. [24] showed that retarding injection increased dry soot, while

research from Campbell et al. [26] showed that the general effect of increasing speed was

to reduce NO and NO2 while increasing the soluble organic fraction in particulate matter

and BSFC. The overall effect of increasing speed was to increase the formation of solids

within the engine. However, none of these studies were performed at constant NOx.

Based on individual explanations, one could reason that at low speeds, injection

timing was more dominant and hence a retarded injection timing resulted in higher

particulate matter concentration (as seen at 1500 rpm, 6 degrees before top dead center);

at higher speeds and advanced injection timings (2100 rpm and 14 degrees before top

dead center), speed by itself was more dominant to give greater particulate matter. The

condition in the middle (1800 rpm and 8 degrees before TDC) appeared to be an

optimum point between the other two operating conditions along the same rail pressure of

425 bar.

With an increase in rail pressure, it was observed that there was a shift of the

trend-lines to the right, i.e., toward higher BSFC. This was because injection timing was

changed to match the NOx levels. This eventually resulted in an increase in the brake

specific fuel consumption, as discussed earlier. At 575 bar and 1500 rpm, the desired

brake specific NOx condition could not be achieved due to limitations in the injection

timing map in the INCA software. Hence a discrepancy in the data was observed, where

the PM value was higher. The heat release profile along the same rail pressure was

plotted for three points of constant NOx, as shown in Figure 4-15.

50

________________________________________________________________________

Figure 4-15: Heat release profile comparisons for three selected points at 500 bar rail

pressure.

________________________________________________________________________

Figure 4-15 shows that the rate of heat release was maximum for 1500 rpm and 4

degrees BTDC, while it was the minimum for 2100 rpm and 10 degrees before TDC.

Research has shown that with more premixed combustion [30], less particulate matter is

emitted. As the injection timing was retarded, the ignition delay is reduced. A longer

ignition delay will cause more fuel to be burned during premixed combustion and will

reduce the percentage of fuel burned during diffusion type combustion. Based on this

argument, we conclude that the time available for mixing of fuel and air was reduced

which resulted in an increase of particulate matter.

-50

0

50

100

150

200

-5 0 5 10 15 20

He

at R

ele

ase

Rat

e, J

/de

g

Crank Angle, °ATDC

1500rpm, 4 btdc

1800 rpm, 8 btdc

2100 rpm, 10 btdc

51

It might be expected from the heat release diagram that, the 1500 rpm and 4

degrees before top dead center condition (which appears to have the maximum zone of

premixed combustion) should have the least PM. However, such a comparison was

difficult to make here because injection timing and speed were much different for each of

the profiles. Similar comparisons are made in the next chapter where speed was constant;

there little variation existed in the injection timing while the load was varied. Campbell et

al. [26] configured their study to see the effect of speed on particulate or insoluble

emissions, as shown in Table 4-1.

________________________________________________________________________

Table 4-1: Effect of engine speed on solids formation and oxidation [26]

Engine Speed + Solids

Formation Oxidation

Mixing Rates + - +

Cycle Temperatures + + +

Ignition Delay - + *

Time for Reactions - * -

Overall Effect + +

+ indicates an increase, - indicates a decrease, * indicates not applicable

________________________________________________________________________

Hence the conclusion that can be drawn is that at high speeds and advanced

injection timings, speed results in high PM while at low speeds and retarded injection

timings, the injection timing results in high PM.

52

4.5 Thermogravimetric analysis

To delve deeper into the particulate matter study, and find a relationship between

speed, rail pressure and soot reactivity, and if possible a justification for the trends shown

in Figure 4-14, oxidation tests were performed on a few bulk samples. Oxidation rates,

however, are probably more important than formation rates as carbon is nearly always

formed during diesel combustion, and oxidation controls the amount of particulate

exhausted from the cylinder. A major factor controlling oxidation appears to be the local

oxygen partial pressure.

To perform this test, the following procedure was followed. The particulate matter

sample collected from different engine conditions was pretreated in nitrogen gas

(assumed inert) at 30 0C for 30 minutes The temperature was then increased to 500

0C at

a rate of 10 degrees per minute and was held constant at this point for the sample to

stabilize and to remove any volatile matter present, if any. The temperature was then

increased to 550 0C at a rate of 5 degrees per minute. After devolatilization, the samples

were exposed to an air flow to obtain the mass-loss curves (upon oxidation) in the TGA.

The results of the test are shown in Figures 4-16 and 4-17.

53

________________________________________________________________________

Figure 4-16: Weight Loss curves from TGA at 425 bar rail pressure.

________________________________________________________________________

________________________________________________________________________

Figure 4-17: Weight loss curve from TGA at 500 bar rail pressure.

________________________________________________________________________

54

From Figures 4-16 and 4-17, it can be seen that soot from 2100 rpm was the most

reactive, followed by soot from 1500 rpm, while soot from 1800 rpm appeared to be least

reactive. While performing the experiment, some mass change was observed during the

process of pretreatment and stabilization. This was because the soot samples were quite

volatile in nature and contained moisture. Soot at 1500 rpm, 425 bar and 6 degrees BTDC

seemed to have the least residue compared to all other conditions. All other samples had

significant residue in the form of ash. A reason for such high content of ash can be

attributed to the mixing of fuel with the lube from the engine. X-ray studies of soot from

elsewhere [32] showed that the remnant ash from soot oxidation consisted of Ca, P, and

sulfur, which is the ash from the combusted engine lubricant oil. However, additional

experiments need to be performed for this to be conclusive.

With an increase in rail pressure from 425 bar to 500 bar, the reactivity of soot

increased. At 500 bar, 2100 rpm, time taken to oxidize (and stabilize) on a weight basis,

was about 17 minutes, while, at 425 bar and the same speed, the time taken was about 36

minutes. At 500 bar and 1500 rpm, soot oxidation took 40 minutes versus 60 minutes for

the same speed and 425 bar. This shows that increasing the rail pressure made the soot

more reactive. It can be concluded that parameters including speed, injection timing and

rail pressure have a great influence on soot reactivity. Individual plots can be found in

Appendix C.

Zhu et al. [31] observed out that morphological properties of diesel PM are

important parameters required for understanding the complex particulate formation and

55

oxidation mechanisms. They suggested that the effect of speed (or characteristic time)

was relatively less important for particle growth. However, combustion temperature was

a more important parameter. Engine load also seemed to be an important parameter. At

low load, many particulates appeared to be non-distinct (boundaries between particulates

unclear) in morphology while at high load conditions, particulates appeared to be

distinctive and well separated. A greater degree of disorder of PM would enhance the

oxidative reactivity. Muller et al. [32] suggested that a reduction of rail pressure leads to

significant differences in soot microstructure, which cannot be explained by changes in

engine speed or load. The findings in the present study, however, suggest that speed, rail

pressure and load have significant impact on soot reactivity.

4-6 Raman spectroscopy

Raman spectra were obtained for each of the six samples at two rail pressures. For

the analysis and determination of spectral parameters, different combinations of bands

have been cited in literature [33, 34]. Most of the earlier Raman spectra considered only

three bands, G, D1, and either D2 or D3. However, in this case, five bands were fit to the

original spectrum, namely G, D1, D2, D3 and D4. The goodness of fit was achieved

through several iterations and the final results were based on the best fit. Several

combinations of fits are discussed in literature [33, 34]; here, due to simplicity, only

Lorentzian fits were employed. Sadezky et al. [33] suggested that 4 Lorentzian and 1

Gaussian would be the best fit for diesel soot. However, the problem with including a

56

Gaussian fit is the difficulty in processing the curves. A simple curve fit example is

shown in Figure 4-18.

________________________________________________________________________

Figure 4-18: Multi-peak fitting for Raman spectra depicting 5 first order peaks.

________________________________________________________________________

The first order spectra of soot generally exhibit two broad and strongly

overlapping peaks with intensity maxima at about 1350 cm-1

and 1585 cm-1 [33]. Raman

spectra of soot are analogous to those of graphite. The G band refers to the graphite band,

which usually occurs at 1580 cm-1

had the sample been fully graphitic. Diesel soot,

however, is not fully graphitized and several other defect bands, known as the D bands,

are found. The most intensive of them is the D1 band, which appears at about 1360 cm-1

and corresponds to a graphitic lattice vibration. Jawahari et al. [35] suggested that the

peak at 1585 cm-1

comprises not only the G but also the D2 band which occurs due to

graphitic lattices. A third defect band called the D3 band appears at about 1500 cm-1

,

57

which originates from the amorphous carbon fraction of soot [36]. A fourth defect band

called the D4 appears at about 1200 cm-1

, and was initially observed by Dippel et al. [37].

This originates from sp2-sp

3 bonds or C-C or C=C stretching vibrations of polyene-like

structures. The intensity was normalized and curves were plotted in the region of interest

(800-2000 cm-1

). Residuals were plotted to verify the quality of the fit.

The parameter ID1/IG is a good indication of the degree of disorder within the

material. If the ratio is lower, the sample is more graphitized. Full width at half maximum

(FWHM) is also a good parameter: where decreasing values of FWHM indicate

increasing degree of graphitization. A comparison of the Raman spectral parameter

(ID1/IG) was made for the six samples and can be seen in Figures 4-19 and 4-20.

________________________________________________________________________

Figure 4-19: Variation of ID1/IG at 425 bar rail pressure for 3 test conditions obtained

at constant NOx.

________________________________________________________________________

4.5

4.6

4.7

4.8

4.9

5

5.1

5.2

5.3

1500rpm,6 btdc 1800rpm,8 btdc 2100rpm,14 btdc

ID1

/IG

58

________________________________________________________________________

Figure 4-20: Variation of ID1/IG at 500 bar rail pressure for 3 test conditions obtained

at constant NOx.

________________________________________________________________________

From the variations in ID1/IG for three samples for a fixed rail pressure of 425

bar and 500 bar respectively, it can be observed that the soot sample at 2100 rpm has the

maximum ID1/IG ratio followed by the sample at 1500 rpm and finally the sample at

1800 rpm. A higher D to G ratio indicates that the sample is less graphitic and more

reactive. This supports the claims made in the previous section about the reactivity curves

from TGA. Full width at half maximum was compared for the samples at the same rail

pressure, details of which can be found in Appendix C. No conclusions could be drawn

using FWHM for the reason given in the next paragraph.

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

5

5.1

1500 rpm, 4 btdc 1800 rpm, 8 btdc 2100 rpm, 10 btdc

ID1

/IG

59

Bayessac et al. [38] reported that structural heterogeneity of carbonaceous

materials like natural coal, cokes and anthracite limit the use of Raman spectroscopy.

Even in our research, variations in D to G ratio could be found at different locations for

the same sample. The variations for two speeds (1500 and 1800 rpm) at different

locations can be seen in Figure 4-21. This uncertainty in results from multi-peak fitting

brings into question the value of the Raman data.

________________________________________________________________________

Figure 4-21: Variation of ID1/IG for two samples at different locations.

________________________________________________________________________

3

3.5

4

4.5

5

5.5

Position 1 Position 2 Position 3 Position 4

ID1

/IG

1500 rpm

1800 rpm

60

Chapter 5

Results and Discussion-Part II

This chapter presents results and discussion from the constant speed testing, also

referred to as Test 2. The results include consideration of the variation of NOx emissions

with load and rail pressure, effect of load on BSFC at constant speed, and the effect of

rail pressure on the relationship between BSFC and BSPM at constant NOx level.

5.1 Engine NOx map at constant speed.

As in Chapter 4, an engine map was created at 1800 rpm and three different loads

to identify points of constant NOx. These are shown in Figures 5-1, 5-2 and 5-3.

________________________________________________________________________

Figure 5-1: Engine NOx map on a brake specific basis at 1800 rpm, 40% Load.

________________________________________________________________________

425

500

575

3

5

7

9

108

64

Rai

l Pre

ssu

re, b

ar

BSN

Ox,

g/k

Wh


7-9 5-7 3-5

61

________________________________________________________________________

Figure 5-2: Engine NOx map on a brake specific basis at 1800 rpm, 47.5% Load.

________________________________________________________________________

Figure 5-3: Engine NOx map on brake specific basis at 1800 rpm, 55% Load.

________________________________________________________________________

425

500

575

3

5

7

9

108

64

Rai

l Pre

ssu

re, b

ar

BSN

Ox,

g/k

Wh

Injection Timing,°BTDC

7-9 5-7 3-5

425

500

575

3

5

7

9

108

64

Rai

l Pre

ssu

re, b

ar

BSN

Ox,

g/k

Wh


7-9 5-7 3-5

62

It is a well documented [1, 2, 26] that engine NOx emissions increase on a dry

basis with an increase in load. This is because with an increase in load on the engine,

more fuel is consumed and the mean flame temperatures are higher, which is the most

important factor for the formation of NOx. However, most emissions decrease with load

on a brake-specific basis [39]. This decrease in NOx may be attributed to the nature of

diesel combustion, where much of the fuel burns at near stoichiometric conditions, and

thus the effect of air-fuel ratio is minimized. A comparison of brake power and NOx

values is made for four load conditions and can be seen in Table 5-1.

________________________________________________________________________

Table 5-1: Comparison of NOx values at four loads, 425 bar rail pressure, 4 deg

before top dead center.

Case Power

kW

NOx

ppm

NO

ppm

NO2

ppm

BSNOx

g/kWh

BSNO

g/kWh

BSNO2

g/kWh

40% 23.87 495 479 16 3.83 3.65 0.18

47.5% 28.67 578 538 40 4.12 3.70 0.42

55% 32.93 589 556 33 3.69 3.48 0.21

70% 39.68 639 599 40 3.65 3.42 0.23

________________________________________________________________________

The observations seen in Table 5-1 do not correlate to the trends seen by Vittal et

al. [39]. It appears that under fixed conditions of rail pressure, speed and injection timing,

a particular threshold level in load exists beyond which the BSNOx values decrease, as

observed in Table 5-1. Similar trends were observed for other values of rail pressures and

injection timings.

63

5.2 Effect of load on BSFC at constant speed

The effect of load on brake specific fuel consumption is presented for various rail

pressures as shown in Figures 5-4, 5-5 and 5-6. Speed was held constant at 1800 rpm

throughout these tests. Injection timing was varied from 10 degrees to 4 degrees before

top dead center.

________________________________________________________________________

Figure 5-4: Effect of load on brake specific fuel consumption at 425 bar rail pressure.

________________________________________________________________________

150

160

170

180

190

200

210

220

230

240

40 47.5 55

BSF

C, g

/kW

h

Load, %


64

________________________________________________________________________


________________________________________________________________________


________________________________________________________________________

150

160

170

180

190

200

210

220

230

40 47.5 55

BSF

C, g

/kW

-hr

Load, %


150

160

170

180

190

200

210

220

230

40 47.5 55

BSF

C, g

/kW

-hr

Load, %


65

For most cases, the brake specific fuel consumption increased with a change in

load from 40% to 47.5% load, while it decreased for a further increase in load to 55%.

However, these trends may not be statistically significant because the variation of BSFC

with load was quite small. Campbell et al. [26] discussed the effect of load on engine

emissions and performance. They concluded that the general effect of load at

intermediate speeds was to increase NOx, smoke and solid emissions while reducing

BSFC and SOF emissions. Reasons for this could be from increased Ф and temperatures

at higher loads.

5.3 Effect of rail pressure on BSFC vs. BSPM at NOx parity (Test 2)

Points of constant NOx were determined from the engine map, and brake specific

fuel consumption was plotted with the corresponding brake specific particulate matter as

shown in Figure 5-7. Speed was maintained constant at 1800 rpm. Load and fuel injection

timings have been marked on the figure. As discussed earlier in Section 5.1, NOx

emissions on a brake specific basis at fixed values of rail pressure, speed and injection

timing increased with an increase in load from 40 to 47.5%, and decreased with a further

increase in load to 55%. Hence along a constant rail pressure line, injection timing had to

be varied only slightly. This was different in the case of a constant load test (Test 1),

where significant changes in injection timing were needed at the same rail pressure.

66

________________________________________________________________________

Figure 5-7: Variation of BSFC vs. BSPM at various rail pressures and constant NOx

and speed.

________________________________________________________________________

In Figure 5-7, a reduction in particulate matter formation was observed for

increasing rail pressure values. With an increase in rail pressure, the curves shifted to the

right because injection timing was retarded to maintain constant NOx, which

inadvertently increased BSFC. At the same rail pressure, it could be seen that an increase

in load from 40 percent to 47.5 percent increased PM and BSFC, while a further increase

in load from 47.5 percent to 55 percent reduced both PM and BSFC. Understanding this

behavior requires consideration of heat release, as seen in Figures 5-8 and 5-9.

0.03

0.04

0.05

0.06

0.07

0.08

0.09

210 212 214 216 218 220 222

BSP

M, g

/kW

h

BSFC, g/kWh

425 bar

500bar

575 bar

55,8.3

47.5,7.9

40,8

55,6

47.5, 5.8

40,8

55,4.4

47.5,4

40,6

67

________________________________________________________________________

Figure 5-8: Comparison of heat release rates for various loads at 575 bar rail pressure.

________________________________________________________________________

Figure 5-9: Comparison of heat release rates for various loads at 500 bar rail pressure.

________________________________________________________________________

-20

0

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30

Rat

e o

f H

eat

Re

leas

e, J

/de

g

Crank Angle , °ATDC

40 % Load

47.5 % Load

55 % Load

-20

0

20

40

60

80

100

120

0 5 10 15 20 25 30

Rat

e o

f H

eat

Re

leas

e, J

/de

g

Crank Angle, °ATDC

40 % Load

47.5 % Load

55 % Load

68

From the heat release profiles, the zone of premixed combustion spans the

greatest area for 40% load, followed by 47.5% load and finally 55% load. It is well

known that soot is typically formed in the diffusion flame and a greater area of premixed

zone of combustion results in less formation of soot. This explains why 40% load had the

least PM formation. Following this reasoning, the 55% load condition should have had

the highest PM but is not reflected in the plots. This could be explained in terms of the

bulk temperature within the engine at the respective conditions, as plotted in Figure 5-10.

________________________________________________________________________

Figure 5-10: Effect of load on bulk temperature at 575 bar rail pressure.

________________________________________________________________________

Bulk cylinder temperature can be used as an indicator for emissions in an engine.

From Figure 5-10, it can be seen that the bulk temperature within the cylinder increased

with an increase in load. The maximum temperature was about 1675 K at 55% load,

600

800

1000

1200

1400

1600

1800

0 20 40 60 80 100

Bu

lk T

em

pe

ratu

re ,K

Crank Angle, °ATDC

47.5%Load

55 % Load

69

while it was 1620 K at 47.5% load. A higher temperature could also mean greater

oxidation of particulate matter. PM exhausted from an engine is a competition between

the processes of formation and oxidation. Hence it could have been possible that when

the temperature was higher, more particulate matter was oxidized leading to a less PM

emissions. This can explain why at 55% load, lesser PM is emitted than for 47.5% load.

Campbell et al. [26] suggested a table which indicated the effect of load on the

formation and oxidation of the solids part of PM, as shown in Table 5-2.

________________________________________________________________________

Table 5-2: Effect of engine load on solids formation and oxidation [26].

Engine Load + Solids

Formation Oxidation

Cycle Temperature + + +

Ф + + -

Overall Effect + -

+ indicates an increase, - indicates a decrease

________________________________________________________________________

In conclusion, engine load, rail pressure and injection timing play a significant

role in determining the emissions and performance of an engine. Soot formation may be

dominant under certain conditions of operation while oxidation might be dominant under

others. Hence a better understanding of the soot formation process is necessary, where a

critical temperature separating the two would determine the emissions of PM.

70

Chapter 6

Conclusions

6.1 Conclusions

This thesis involves a study of the effect of rail pressure on the variation in brake

specific fuel consumption versus brake specific particulate matter while maintaining NOx

parity under two operating modes: variable speed at constant load, and variable load at

constant speed. While performing these tests, several other variations in engine

performance were determined with speed, load, rail pressure and injection timing. The

following conclusions were drawn from this work.

Trends in NOx emissions

NOx emissions from the engine reduced with an increase in the engine speed due

to reduced time available for the formation of NOx.

NOx emissions from the engine increased on a dry basis as the load on the engine

increased. This was due to increased temperatures within the engine at higher

loads.

Increasing the common rail pressure increased the formation of NOx. This was

attributed to increase in the bulk temperature within the engine.

71

Trends in BSFC and BSPM

Retarding injection timing increased the BSFC at different speeds and loads. An

explanation for this observation is that retarded injection timing reduces ignition

delay, which thereby reduces the time available for mixing of air and fuel within

the engine.

An increase in speed from 1500 rpm to 2100 rpm decreased the specific fuel

consumption. This trend was explained considering the heat transfer process

within the engine at low and high speeds.

The effect of load on BSFC was not consistent with earlier literature. BSFC

increased initially with a change in load from 40% to 47.5% and decreased when

the load was increased to 55%.

Trends at constant NOx (Results from Test 1 and Test 2)

At constant NOx and constant load (Test 1), BSFC increased as the speed was

reduced, while BSPM decreased initially and increased with further reduction of

speed. This behavior was explained on the basis of dominance of either speed or

injection timing, which was varied to maintain constant NOx levels.

At constant NOx and constant speed (Test 2) and for a particular rail pressure, a

decrease in load from 55% to 47.5% increased BSFC and BSPM, while a further

reduction to 40% reduced BSFC and BSPM. Trends in PM were explained on the

72

basis of heat release and bulk temperature while trends in BSFC were explained

on the basis of injection timing.

With an increase in rail pressure (during both tests), the curves moved towards

high BSFC and low BSPM. The reduction in PM was explained on the basis of

rail pressure, while increase in BSFC was explained on the basis of injection

timing.

Trends in soot reactivity

Increasing the rail pressure made soot more reactive, as observed in the oxidation

data from the TGA.

For a fixed rail pressure and at the respective injection timings, soot at 2100 rpm

appeared to be most reactive followed by soot at 1500 rpm and finally the soot at

1800 rpm. This showed that soot reactivity was governed by several parameters in

the engine and followed similar trends like its formation.

73

6.2 Recommendations for future work

During the course of experiments, several ideas for additional experiments were

generated. Some of these are listed below.

1. Explore the effect of rail pressures on BSFC with BSPM at constant NOx with

multiple injection strategies.

2. Repeat the same study with exhaust gas recirculation enabled. This would give us

more relevant results as EGR is being implemented in most vehicles for NOx

reduction.

3. Numerical simulations could provide better understanding of the physical

behavior of the engine under various operating conditions. This could help us to

understand better the particle formation for various speeds, loads and injection

parameters.

4. This project was limited to three speeds and three loads. However, to get a better

understanding, more speeds and loads need to be studied.

5. Soot samples from the constant speed testing could be collected and further

analysis could be performed using HRTEM, XPS etc. to delve deeper into soot

reactivity.

74

REFERENCES

1. Heywood, J.B, Internal Combustion Engine Fundamentals, 1988, McGraw-Hill

Science Publication.

2. Ganesan, V., Internal Combustion Engines, 1996, McGraw Hill Publications, New

York.

3. Stone, R., Introduction to Internal Combustion Engines, 1999, McMillan

Publications.

4. Ralbovsky, E., An introduction to compact and automotive diesels, 1996, Cengage

Learning Publications.

5. Yoshida, K., Takamitsu, A., Hiromasa, M., Kotaro, H., Shinya, H., Development of

PM and NOx simultaneous-reduction system in diesel exhaust gas with sulfur trap

catalyst, 2006 JSAE Annual Congress, Vol. 85-06.

6. Johnson, T., Diesel Emissions control technologies in review, 2008, Deer

conference, Dearborn, Michigan.

7. Celikten, I., An experimental investigation of the effect of injection pressure on

engine performance and exhaust emission in indirect injection diesel engines, 2003,

Applied Thermal Engineering, p:2051-2060, Elsevier Publications.

8. Turns, S.R., Introduction to Combustion, 2nd

ed., 2000, McGraw Hill Publications.

9. Glassman, I., Physical and chemical aspects of combustion, 1997, Combustion

Science and Technology, Gordon and Breach Science Publishers.

75

10. Lavoie, G.A., Heywood, J. B., Keck, J. C., Experimental and theoretical study of

nitric oxide formation in internal combustion engines, 1970, Combustion Science

and Technology, Issue 4 , pages 313 - 326

11. Szybist, J.P., Kirby, S.R., Boehman, A.L., NOx emissions of alternate diesel fuels:

A comparative analysis of biodiesel and FT diesel, 2005, Energy and Fuels.

12. Sasaki, M., Kishi, Y., Hyuga, T., Okazaki, K., Tanaka, M., Kurihara, I., The effect

of EGR on Diesel Engine Oil and its countermeasures, 1997, SAE Technical Paper

971695.

13. Taymaz, I., The effect of thermal barrier coatings on diesel engine performance,

2006, Surface Coatings and Technology, p:5249-5252, Elsevier Publications

14. Arregle J., Pastor, J.V., Ruiz, S., The Influence of Injection Parameters on Diesel

Spray Characteristics, 1999, SAE Technical Paper, 01-0200.

15. Boehman, A.L., Song J., Alam, M., Characterization of diesel and biodiesel soot,

2004, ACS Fuel Chemistry Division Reprints, 767-769

16. Nishimura, T., Effects of Fuel Injection Rate of Combustion and Emission in a DI

Diesel Engine, 1998, SAE Technical Paper 981929

17. Lilik, G.K., Hydrogen Assisted Diesel Combustion, 2008, Master’s Thesis,

Department of Energy and Geo-Engineering, The Pennsylvania State University

18. Song, J., Effect of fuel formulation on soot properties and regeneration on diesel

particulate filters, 2005, Doctor of Philosophy, Department of Energy and Geo-

Engineering, The Pennsylvania State University

19. Su, W., Liu, B., Wang, H., Huang, H., Effects of multi-injection mode on diesel

homogenous charge compression ignition combustion, 2007, JEGTP.

76

20. McGeehan, J.A., Sheila, Y., Melvin, C., Andreas, H., Bengt, O., Andrew, W.,

Philip, B., On the road to 2010 emissions: Field Test Results and Analysis with

DPF-SCR System and Ultra Low Sulfur Diesel Fuel, 2005, SAE Technical Paper.

21. Tenison, P.J., Reitz, R., An experimental Investigation of the effects of common rail

injection system parameters on Emissions and Performance in a High Speed Direct

Injection Diesel Engine, 2001, Journal of Engineering for Gas Turbines and Power,

ASME.

22. Badami, M., Nuccio, P., Trucco, G., Influence of Injection Pressure on the

Performance of a DI Diesel Engine with a Common Rail Fuel Injection System,

1999, SAE Technical Paper 01-0193

23. Wallace, F.J., Hawley J.G., Analysis of the effect of variations in fuel line pressure

in high speed direct injection diesel engines, with high pressure common rail fuel

injection systems, on heat release, cylinder pressure, performance, and NOx

emissions, 2004, Proc. IMechE. Vol. 219 Part D: Automobile Engineering.

24. Desantes, J.M., Benajes, J., Molina, S., Gonzalez, C.A., The modification of the fuel

injection rate in heavy-duty diesel engines Part 2: Effects on Combustion, 2004,

Applied Thermal Engineering, p: 2715-2726, Elsevier Publications.

25. Payri, F., Benajes, J., Arregle, J., Riesco, J.M., Combustion and Exhaust Emissions

in a Heavy Duty Diesel Engine with Increased Premixed Combustion Phase by

Means of Injection Retarding, 2006, Vol. 61 p:247-258, Oil & Gas Science and

Technology.

26. Campbell, J., Scholl, J., Hibbler, F., Bagley, S., Leddy, D., Abata, D., Johnson, J,

The effect of fuel injection rate and timing on the physical, chemical and biological

77

character of particulate emissions from a direct injection diesel. SAE Technical

Publications, 810996.

27. Shimada, T., Shoji, T., Takeda,Y., The effect of Fuel Injection Pressure on Diesel

Engine Performance, SAE Technical Paper 891919.

28. Acar, J., Effect of Engine operating parameters and Fuel Characteristics on Diesel

Engine Emissions, 2005, Master’s of Science, Department of Mechanical

Engineering, Massachusetts Institute of Technology

29. Abu-Zaid, M., Performance of single cylinder, direct injection Diesel engine using

water fuel emulsions, 2003, Energy Conversion and Management, p:697-705,

Elsevier Publications.

30. Dec, J.E., A Conceptual Model of DI Diesel Combustion Based on Laser Sheet

Imaging, 1997, SAE paper 970873

31. .Zhu, J., Lee, K.O., Yozgatligil. A., Choi, M.Y., Effects of engine operating

conditions on morphology, microstructure, and fractal geometry of light duty diesel

engine particulates, 2005, Elsevier Publications.

32. Muller, J.O., Su, D.S., Jentoft, R.E., Krohnert, J., Jentoft, F.C, Scholgl, R.,

Morphology-controlled reactivity of carbonaceous materials towards oxidation,

2005, Elsevier Publications.

33. Sadezky, A., Muckenhuber, H., Grothe, H., Niessner, R., Poschl, U., Raman micro-

spectroscopy of soot and related carbonaceous materials: Spectral analysis and

structural information, 2005, Elsevier Publications, Carbon 43, p: 1731-1742.

34. Dipper B.H., Soot characterization in atmospheric particles from different sources

by NIR FT Raman Spectroscopy, 1999, Journal of Aerosol Science.

78

35. .Jawahari, T.R., Roid, A., Casado, J., Raman Spectroscopic characterization of

some commercially available carbon black materials, 1995, Carbon, p: 923-927.

36. Cuesta, A., Dhamelincourt, P., Laureyns, J., Martinez-Alonso, A., Tascon, J. M.D.,

Raman Microprobe studies on carbon materials, 1994, Carbon p: 1523-32.

37. Dippel, B., Jander, H., Heitzenberg, J., NIR FT Raman Spectroscopic study of flame

soot, 1999, Phys. Chem. , p: 4707-12.

38. Bayessac, O., Goffe, B., Petitet, J.P., Froigneux, E., Moreau, M., Rouzaud, J.N., On

the characterization of disordered and heterogeneous carbonaceous materials by

Raman Spectroscopy, 2003, Spectrochim Acta Part A, p: 2267-76.

39. Vittal, M., Borek, J.A., Marks, D.A., Boehman, A.L., The effect of thermal barrier

coatings on diesel engine emissions, 1999, ASME, Vol. 121.

40. Moffat, R.J, Describing the uncertainties in experimental results, Experimental

Thermal and Fluid Science, 1988, Elsevier Publications

41. Esangbedo, C., Characterization of Diesel Engine Soot that lead to excessive oil

thickening, 2007, Master’s Thesis, Department of Chemical Engineering, The

Pennsylvania State University.

42. Martyr, A.J., Plint, M.A., Engine Testing, 3rd

ed., 2007, SAE International.

43. Thermo and fluid-dynamic processes in diesel engines: Selected papers from the

Thiesel 2000 conference held in Valencia, Spain.

79

Appendix A

Fuel Specifications

Detailed specification of fuel is shown in Table A-1.

Name: GE Ultra Low Sulfur Diesel

Company: Chevron Phillips

Material Code: 1069147

________________________________________________________________________

Table A-1: GE Ultra Low Sulfur Diesel Specifications

Property Test Method Specification Value Unit

Specific Gravity ASTM D-4052 0.8400-0.8550 0.8466

API Gravity ASTM D-4052 34.0-37.0 35.6

Particulate Matter ASTM D-6217 <=15.0 1.1 mg/l

Cloud Point ASTM D-2500 2 FAH

Flash Point, PM ASTM D-93 >=130 155 FAH

Pour Point ASTM D-97 -5 FAH

Sulfur ASTM D-5453 7.0-15.0 9.7 ppm

Viscosity @40 C ASTM D-445 2.0-3.0 2.5 cSt

Hydrogen ASTM D-3343 13.2 WT%

Carbon Calculated 86.8 WT%

Poly Nuclear

Aromatics ASTM D-5186 9.0 WT%

SFC Aromatics ASTM D-5186 30.0 WT%

Heat of Comb ASTM D-3338 18444 BTU/LB

Cetane Number ASTM D-613 43-47 45

80

Cetane Index ASTM D-976 42.0-48.0 45.3

HFFR Lubricity ASTM D-6079 <=0.4 0.3 mm

Distillation- IBP ASTM D-86 340-400 364 FAH

Distillation- 5 % ASTM D-86 394 FAH

Distillation- 10 % ASTM D-86 400-460 413 FAH










Distillation- EP % ASTM D-86 610-690 657 FAH

Distillation- Loss ASTM D-86 0.9 ML

Distillation-

Residue ASTM D-86 1.2 ML

Aromatics ASTM D-1319 28.0-32.0 28.8 LV %

Olefins ASTM D-1319 3.4 LV %

Saturates ASTM D-1319 67.8 LV %

________________________________________________________________________

The data set forth herein have been carefully compiled by Chevron Phillips

Chemical Company LP.

81

Appendix B

Results from Subtask I and II

1. Mass of Air Flow (MAF) Calibration

The calibration on the mass of air flow sensor was checked to ensure that the

correct amount of air was entering the system at a given engine condition. A laminar flow

meter was used to make the calibration, the details of which are discussed below.

1.1 Lab condition:

Ambient Pressure: 30.7 inches of Hg (101828.7 Pa),

Pressure Correction Factor, Pcf= 1.005013, Molecular Weight of Air = 28.9643 g/mol

The modes tested for mass of air flow calibration are presented in Table B-1.

________________________________________________________________________

Table B-1: Standard Modes for MAF calibration

Mode Speed Load dP T at MAF MAF

(RPM) (ft.lb) (in.water) (°C) (°F) (V)

1 1000 15.6 0.73 25 77 5.71

2 1330 46.4 1.02 24 75.2 6.01

3 1630 153.3 1.66 24 75.2 6.55

4 1960 206.2 2.51 23 73.4 7.04

5 3000 71.8 3.29 23 73.4 7.39

6 3000 160 4.07 23 73.4 7.69

________________________________________________________________________

82

1.2 Flow element calibration

The laminar flow element itself has to be calibrated for various modes of

operation as the density of air changes with temperature. The details of flow element

calibration are shown in Table B-2.

________________________________________________________________________

Table B-2: Flow element calibration

Mode Rho (Air) Tcf Air Flow

kg/m3 CFM SCFM ACFM g/s

1 1.1897018 0.977 39.5 38.784973 38.99745 21.89657

2 1.1937055 0.9828 55 54.324993 54.43951 30.66996

3 1.1937055 0.9828 88.5 87.413852 87.59812 49.35075

4 1.1977363 0.9888 132.5 131.67283 131.5066 74.33796

5 1.1977363 0.9888 172 170.92624 170.7105 96.49908

6 1.1977363 0.9888 212.8 211.47154 211.2046 119.3896

________________________________________________________________________

1.3 Comparison of present and previous mass of air flow

The present mass of air flow was compared with a previous student’s (Yu Zhang)

work, the details of which are in Table B-3. MAF is plotted with change in pressure

across the flow element (dP) as shown in Figure B-1 and the new calibration curve is

shown in Figure B-2.

83

________________________________________________________________________

Table B-3: Present and previous MAF’s comparison

MAF

present

MAF

former

MAF

Yu's

MAF

Yu's

MAF

dP (V) g/s g/s (V) g/s

0.73 5.71 21.89657 16.1 2.903711 23.05986

1.02 6.01 30.66996 27.37 3.05207 29.54107

1.66 6.55 49.35075 51.55 3.322053 47.46213

2.51 7.04 74.33796 76.25 3.584353 72.18821

3.29 7.39 96.49908 95.64 3.761595 92.82786

4.07 7.69 119.3896 118.9 3.911831 112.7266

________________________________________________________________________

Figure B-1: Variation of MAF with pressure difference (dP)

________________________________________________________________________

0

20

40

60

80

100

120

140

0 1 2 3 4 5

MA

F (g

/s)

dP (in H2O)

Yu's calibration

present calibration

New calibration

84

________________________________________________________________________

Figure B-2: New MAF calibration curve

________________________________________________________________________

2. Difference between BG-2 and BG-3 readings

Tests were performed to check the difference in readings between two generations

of particulate matter sampling instruments, BG-2 and BG-3. To make sure that the flow

rates were scaled correctly between the instruments, the face velocity (defined as the ratio

of volumetric flow rate to the wetting area) was maintained the same.

MAF = 2.4565x3 - 34.7801x2 + 182.0183x - 340.6190R² = 1.0000; x= MAF(v)

0

20

40

60

80

100

120

140

5 6 7 8

MA

F (g

/s)

MAF (v)

85

BG2 has a standard flow rate setting of 110 slpm and uses a 97 mm filter while

BG3 has a standard setting of 75 slpm and uses a 47 mm filter. However, to match the

face velocities, the wetting area ratio was determined and was equal to 4. Hence a flow

rate of 110/4 = 27.5 slpm was set on BG 3 and dilution ratio of 10 was maintained in both

cases. It is very critical that the dilution ratio be the same, as it determines the amount of

shop air that gets mixed with a known quantity of exhaust gas.

Two conditions were tested, whose results are given in Table B-4.

________________________________________________________________________

Table B-4: Difference between BG 2 and BG 3 readings

• Condition 1

BG2 PM reading= 0.123 g/kWh


Difference = 0.04 g/kWh

Percentage Difference= 32.52 %

• Condition 2

BG2 PM reading= 0.09g/kWh


Difference = 0.023 g/kWh

Percentage Difference= 25.56 %

________________________________________________________________________

There could be several reasons for the difference obtained in the two readings.

1. Method of sampling between the two instruments.

2. Design of the sampling probe.

3. Internal changes within BG2 and BG3 that calls for different standard flow

rates and filter sizes.

86

Appendix C

Additional Results from TGA and Raman Spectroscopy

C-1: Results from TGA experiments are displayed in figures below.

________________________________________________________________________

Figure C-1: TGA results for 1500rpm, 425 bar, 6 deg BTDC sample.

________________________________________________________________________

87

________________________________________________________________________

Figure C-2: TGA results from 1500 rpm, 500 bar and 4 deg BTDC sample.

________________________________________________________________________

88

________________________________________________________________________


________________________________________________________________________

89

________________________________________________________________________


________________________________________________________________________

90

________________________________________________________________________


________________________________________________________________________

91

________________________________________________________________________

Figure C-6: TGA results from 2100 rpm, 500 bar and 10 deg BTDC sample

________________________________________________________________________

92

C-2: Raman Spectra Results

________________________________________________________________________

Table C-1: Processed Raman Data at 425 bar rail pressure

________________________________________________________________________

Sample

G D1 D2 D3 D4 D1/G D2/G D3/G D4/G R2

1500_425_1 58.564 172.79 50.033 118.42 185.42 4.79078 0.64014 1.05729 0.66499 0.74496

1500_425_2 69.19 151.8 62.082 107.18 247 6.16204 2.08225 1.06965 1.68688 0.66658

1500_425_3 67.903 165.15 56.544 127.09 258.97 5.08764 1.20952 1.15785 1.12747 0.69721

1500_425_4 68.768 164.06 52.469 116.4 207.02 4.00742 0.71536 0.75358 0.72069 0.70026

Averages 66.1063 163.45 55.282 117.273 224.603 5.01197 1.16182 1.00959 1.05001 0.70225

1800_425_1 64.4425 171.759 48.722 122.956 248.945 4.22451 0.6141 1.05952 0.80871 0.72355

1800_425_2 75.0106 155.179 60.0181 126.115 264.751 4.19305 1.23376 1.00343 1.40907 0.65243

1800_425_3 66.504 167.595 57.1128 116.673 230.977 5.12782 1.32553 1.0155 0.90506 0.68799

1800_425_4 61.3352 168.691 57.2448 115.035 342.771 5.52931 1.34646 1.32735 1.91994 0.70207

Averages 66.8231 165.806 55.7744 120.195 271.861 4.76867 1.12996 1.10145 1.26069 0.69151

2100_425_1 69.0516 182.803 55.7317 122.727 250.616 4.68614 0.90516 0.9451 0.9183 0.71096

2100_425_2 71.1347 178.642 59.7153 116.018 242.625 5.97537 1.52414 0.97867 1.0735 0.70303

2100_425_3 71.7266 167.762 63.8633 115.44 275.101 6.31071 2.0256 1.15077 1.80698 0.67593

2100_425_4 71.7817 176.74 56.2063 119.332 242.077 3.84083 0.71701 0.7375 0.72972 0.69106

Averages 70.9237 176.487 58.8792 118.379 252.605 5.20326 1.29298 0.95301 1.13212 0.69525

FWHM Ratio

93

________________________________________________________________________

Table C-2: Processed Raman Data at 500 bar rail pressure

________________________________________________________________________

Sample

G D1 D2 D3 D4 D1/G D2/G D3/G D4/G R2

1500_500_1 61.2711 157.719 44.199 119.588 202.517 4.04541 0.57851 1.07607 0.65031 0.71932

1500_500_2 69.6935 152.07 58.7788 111.761 242.96 5.28112 1.79255 1.01134 1.20832 0.65412

1500_500_3 61.2847 157.719 44.1957 119.58 202.492 4.04372 0.57812 1.07532 0.64993 0.71929

1500_500_4 62.7109 165.191 46.4052 124.329 230.279 4.62126 0.69007 1.18279 0.82906 0.73222

Averages 63.7401 158.175 48.3947 118.815 219.562 4.49787 0.90981 1.08638 0.83441 0.70624

1800_500_1 72.3273 163.457 59.9051 118.541 232.312 4.51747 2.42179 1.21884 0.79218 0.569

1800_500_2 71.5352 163.603 54.806 121.53 282.651 3.82987 0.82494 0.85152 1.07548 0.67728

1800_500_3 73.1052 169.123 62.0981 114.457 288.808 5.0678 1.49201 0.91262 1.35228 0.67036

1800_500_4 72.3622 163.46 59.8939 118.518 232.3 4.51252 1.21678 0.79081 0.95803 0.67058

Averages 72.3325 164.911 59.1758 118.262 259.018 4.48192 1.48888 0.94345 1.04449 0.6468

2100_500_1 69.9892 171.592 59.7723 115.462 250.522 5.32837 1.43735 1.10061 1.24766 0.68614

2100_500_2 68.5116 175.947 61.2042 112.603 224.917 6.45952 1.77801 1.23062 1.16663 0.69927

2100_500_3 67.7116 166.501 54.399 120.098 297.186 4.63338 1.01105 1.06889 1.33038 0.69733

2100_500_4 65.847 172.482 48.4421 127.137 244.237 3.63403 0.42753 0.88819 0.70019 0.71797

Averages 68.0149 171.631 55.9544 118.825 254.216 5.01382 1.16349 1.07208 1.11122 0.70018

RatioFWHM

94

Appendix D

Brake Specific Emissions Calculations

1. NOx Emissions

1.1 𝐿𝑒𝑡 𝐴𝑉𝐿 𝑁𝑂 𝑏𝑒 𝑋 𝑝𝑝𝑚 𝑎𝑛𝑑 𝐸𝑥𝑕𝑎𝑢𝑠𝑡 𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑏𝑒 𝑇 deg𝐶.

1.2 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝐴𝑖𝑟 = 1.2 𝑘𝑔/𝑚3

1.3 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝐸𝑥𝑕𝑎𝑢𝑠𝑡 =300 ∗ 1.2

(273 + 𝑇) (𝑘𝑔

𝑚3)

1.4 𝑉𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 𝐹𝑙𝑜𝑤 = 𝑀𝑓 + 𝑀𝑎 ∗ 1000

𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝐸𝑥𝑕𝑎𝑢𝑠𝑡 (

𝑙

𝑕𝑟)

𝑤𝑕𝑒𝑟𝑒 𝑀𝑓 𝑖𝑠 𝑀𝑎𝑠𝑠 𝑜𝑓 𝐹𝑢𝑒𝑙 𝐹𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑎𝑛𝑑 𝑀𝑎 𝑖𝑠 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑎𝑖𝑟 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒.

1.5 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑁𝑂 =𝑋

106∗

101325

831430 ∗ (273 + 𝑇)

(𝑘𝑔

𝑚3)

1.6 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑁𝑂2 =(𝐴𝑉𝐿 𝑁𝑂𝑋 − 𝑋)

106∗

101325

831446 ∗ (273 + 𝑇)

(𝑘𝑔

𝑚3)

1.7 𝑁𝑂 𝑔

𝑕𝑟 = 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑁𝑂 ∗ 𝑉𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 𝐹𝑙𝑜𝑤

1.8 𝑁𝑂2 𝑔

𝑕𝑟 = 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑁𝑂2 ∗ 𝑉𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 𝐹𝑙𝑜𝑤

1.9 𝐵𝑟𝑎𝑘𝑒 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑁𝑂 =𝑁𝑂

𝑔𝑕𝑟

𝐵𝑟𝑎𝑘𝑒𝑃𝑜𝑤𝑒𝑟(

𝑔

𝑘𝑊.𝑕𝑟)

95

1.10 𝐵𝑟𝑎𝑘𝑒 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑁𝑂2 =𝑁𝑂2

𝑔𝑕𝑟

𝐵𝑟𝑎𝑘𝑒𝑃𝑜𝑤𝑒𝑟 (

𝑔

𝑘𝑊.𝑕𝑟)

1.11 𝐵𝑟𝑎𝑘𝑒 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑁𝑂𝑥

= 𝐵𝑟𝑎𝑘𝑒 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑁𝑂 + 𝐵𝑟𝑎𝑘𝑒 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑁𝑂2 (𝑔

𝑘𝑊.𝑕𝑟)

2. Particulate Matter Emissions

2.1 𝐿𝑒𝑡 𝑡𝑕𝑒 𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑃𝑀 𝑑𝑒𝑝𝑜𝑠𝑖𝑡𝑒𝑑 𝑜𝑛 𝑓𝑖𝑙𝑡𝑒𝑟 𝑏𝑒 𝑌 𝑚𝑔

2.2 𝐴𝑖𝑟 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑎𝑡 300 𝐾 = 1173.58 𝑔

𝑚3

2.3 𝐵𝑟𝑎𝑘𝑒 𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑃𝑀

=𝑌

1000∗

3600

𝑡∗

1

𝑃𝑜𝑤𝑒𝑟∗ 𝐷𝑖𝑙𝑢𝑡𝑖𝑜𝑛 𝑅𝑎𝑡𝑖𝑜 ∗

𝑀𝑓 + 𝑀𝑎

𝐴𝑖𝑟 𝐷𝑒𝑛𝑠𝑖𝑡𝑦∗ 1000

∗ 1

𝑠𝑙𝑝𝑚 ∗ 60 (

𝑔

𝑘𝑊.𝑕𝑟)

𝑤𝑕𝑒𝑟𝑒 𝑡 𝑖𝑠 𝑡𝑕𝑒 𝑡𝑖𝑚𝑒 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑖𝑛𝑔,𝐷𝑖𝑙𝑢𝑡𝑖𝑜𝑛 𝑅𝑎𝑡𝑖𝑜 𝑖𝑠 10

𝑎𝑛𝑑 𝑠𝑙𝑝𝑚 𝑖𝑠 𝑠𝑒𝑡 𝑡𝑜 75 𝑖𝑓 𝐵𝐺𝐼𝐼𝐼, 110 𝑖𝑓 𝐵𝐺𝐼𝐼.

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