Analysis of knocking phenomena in a high performance engine · Analysis of knocking phenomena in a high performance ... engine low end torque performance, ... After a proper tuning

POLITECNICO DI TORINO - ENERGY DEPARTMENT

Federico Millo, Luciano Rolando

1st GTI Italian User Conference

March 18th , 2013 – Turin

Analysis of knocking phenomena in a high performance

engine


OUTLINE

2

• Introduction

• Experimental setup

• Results & discussion

• Conclusions


130 g/km CO2

Fleet standards 2015

Proposed fleet standards 2020 95 g/km CO2

Introduction

The main downsizing driver: CO2 reduction targets

130 g/km by 2015 95 g/km by 2020


Technologies for improving fuel economy of gasoline engines:

– Downsizing + Turbocharging

– Gasoline Direct Injection (GDI)

– Variable Valve Actuation (VVA)

– Electrification and Hybridization

– …..

Introduction


B

ME

P

Specific Brake Power [kW/dm3]

Introduction

BMEP vs. Specific Brake Power European Gasoline Engines 2009

Source: Indagine sui principali parametri prestazionali nei motori ad accensione comandata autoveicolistici di attuale produzione,

P. Paniccia, BSc Thesis, Politecnico di Torino, 2010

25 bar bmep

100 kW/ltr


The use of GDI in turbocharged engines allows a reduction of the octane request, thus permitting to increase

compression ratio, boost level, spark timing: significant performance improvements can thus be achieved, allowing

an effective engine downsizing.

However the low end torque of a turbocharged engine is usually limited by compressor surge.

The use of GDI, combined with VVT, allows a cylinder “scavenging” effect, with significant improvements in the

low-end torque performance.

SURGE

CHOKING

OVERSPEED

Introduction

Scavenging

(Source: Andriesse et al. The New 1.8 ltr DI Turbo-Jet Gasoline Engine from FPT,17. Aachener Kolloquium Fahrzeug und Motorentechnik, 2008)


Introduction

Knock

However, although the achievement of high boost levels at low engine speed definitely improves

engine low end torque performance, the likelihood of engine knock increases dramatically.

Furthermore, the risk of pre-ignition or mega knock, with pressure peaks reaching or exceeding 200

bars, is also significantly increased, due to the high power density.

Therefore, reliable knock predictive models are necessary to support the design and calibration

activities of new turbocharged high performance engines.

0

50

100

150

200

250

330 360 390

Mega knock: Immediate effects

causing damages to spark plug,

rings, piston.


Introduction

• Increase in the complexity of calibration of GDI turbocharged engines • Increase in the number of calibration parameters:

• Lambda

• Boost level

• Spark Advance

• Intake Valve Opening

• Exhaust Valve Opening

• Traditional “one parameter at a time” calibration approach unsuitable

• Interactions between calibration and design parameters choices (eg. between boost and compression ratio)

• Possibilities offered by the continuous development of CAE tools to carry out the system optimization on a “virtual test bench”


OUTLINE

9

• Introduction



• Conclusions


Experimental Setup Engine: FIAT T-Jet family

10

Racing Engine N° of cylinder 4 – In line Displacement 1368 cm3 Bore 72 mm Stroke 84 mm Injection System PFI Turbocharger FGT - Garrett GT 1446 Pistons Forged Compression Ratio 9.4 Max Nominal Torque 270 Nm@3000 RPM Max Nominal Power 180 CV@ 5750 RPM

Production Engine N° of cylinder 4 – In line Displacement 1368 cm3 Bore 72 mm Stroke 84 mm Injection System PFI Turbocharger IHI RHF3 Pistons Forged Compression Ratio 9.8 Max Nominal Torque 230 Nm@3000 RPM Max Nominal Power 150 CV@ 5750 RPM


4 Sensorized Spark Plugs: Kistler 6115

Accelerometer: Bosch 0261231148

Additional Sensors: • 4 Thermocouples (k-series) in the intake runners,

• 1 Lambda sensor mounted downstream of the turbine

• Turbocharger speed

Experimental Setup


Test Matrix

12

• Engine Speed: 2500 - 3000 - 3500 - 4000 - 5000 - 6000 [rpm]

• Relative A/F Ratio: 0.7 – 0.8 – 0.9 [-]

• Boost Pressure: 2000 – 2200 – 2400 [mbar]

For each operating conditions 3 different spark advance settings were tested :

• Knock Limited Spark Advance (KLSA),

• KLSA +2,

• KLSA -2

For each op.cond. and spark timing 200 consecutive engine cycles were acquired

0

0.5

1

1.5

2

2.5

3

1012141618202224

0 2 4 6 8 10 12 14 16

ID/I

Dm

[-]

BM

EP [

bar

]

Spark Advance [°]

Spark Advance

2000 3000 4000 5000 6000 2000

2200

2400

0.7

0.8

0.9

Rela

tive A

/F [-]

Engine Speed [RPM]

Boost Pressure [mbar]

Norm

Knock

intensity


Test Matrix

13

Additional tests were carried out evaluating the effects of:

• Different Gasoline:

Racing Gasoline

Composition [% m/m] Carbon: 83.72 % Hydrogen: 13% Oxygen: 3.28%

Lower Heating Value [MJ/kg] 41.41

Octan Number [R.O.N.] 102

Density [kg/m3] 758.4

Unleaded Gasoline

Composition [% m/m] Carbon: 86.45 % Hydrogen: 13.55%

Lower Heating Value [MJ/kg] 44.47

Octan Number [R.O.N.] 95.7

Density [kg/m3] 724.6

• Temperature of the intake manifold downstream of intercooler:

• T1 = 44° C

• T2 = 55° C


OUTLINE

14

• Introduction



• Conclusions


• Knocking phenomena were analyzed by means of the Three Pressures Analysis (TPA).

• The TPA represents a simulation based methodology to analyze experimental data and to

determine quantities that are difficult or impossible to measure directly, such as:

• Apparent burn rate

• Residual fraction

• Trapping ratio

• Valve mass flow profiles

• Focuses on a cylinder, cuts-off rest of system

• Replacing it by measured port pressures

• Input exp. cylinder pressure to get comb. rate

• Valid only for steady state operating points

• Single cylinder model (typically)

• Provides as output combustion and knock metrics such as, for instance:

• Crank angle at knock onset

• Unburned mass fraction at knock onset, etc.

Three Pressure Analysis (TPA)

15


Band pass filtered

pressure MAPO

Maximum

Amplitude

Pressure

Oscillation

Knock metrics

In cylinder pressure


Chun, Heywood, SAE-890156 Borg, Alkidas, SAE-2008-01-1088

Unburned Mass % at Knock Onset

MA

PO

(a

tm)

Unburned Mass Fraction

at Knock Onset

MA

PO

(b

ar)

MA

PO

(b

ar)


at Knock Onset

No correlation was initially found between

knock intensity and unburned mass fraction at

knock onset, in good agreement with

literature data.

Lack of correlation could be due to incorrect

knock metrics ?

Chun, Heywood, SAE-890156 Borg, Alkidas, SAE-2008-01-1088

Knock metrics: why use also engine

block vibration signal ?


fm,n [kHz] f1.0 f2.0 f0.1 f3.0 f4.0

theoretical 8.1 13.5 16.9 18.6 23.5

Knock free

Test results

Incipient

Knock

Light Knock

Heavy

Knock

Medium-

Heavy

Knock

Knock free Incipient

Knock

Light Knock

Medium

Knock

Heavy

Knock

Knock metrics: why use also engine block vibration signal ?

In cylinder pressure frequency spectra


Knock intensity: block vibration vs. in-cylinder pressure correlation

19

Engine Speed: 2500 RPM



Pboost = 2.2 [bar] - λ = 0.8 [-] – S.A: 4°

After a proper tuning of the bandpass filtering frequencies, a good correlation between block vibration based and in cylinder pressure based knock intensity measurements was found.


Chun, Heywood, SAE-890156

Unburned Mass % at Knock Onset

MA

PO

(a

tm)

Borg, Alkidas, SAE-2008-01-1088


at Knock Onset

MA

PO

(b

ar)

MA

PO

(b

ar)

Unburned Mass

Fraction at Knock Onset

Knock intensity vs. unburned mass fraction at knock onset

Engine Speed 2500 RPM Engine Speed 5000 RPM

A good correlation between knock intensity and unburned mass fraction at knock onset was also found, differently from data previously reported in literature.


Test Results – Statistics – Knock intensity thresholds

21

Knock Free - S.A. = 0

Incipient Knock - S.A. = 2

Light Knock - S.A. = 4

Knock threshold

Knock threshold

Knock threshold Knock threshold

Knock threshold

Knock threshold


Different models available in literature (Douaud&Eyzat, Franzke, Worret) have been included in the EngCylKnock object They are generally based on the assumption that end gas autoignition will occur when the condition ∫ dt/ = 1 will be reached (where t is the elapsed time from the start of end-gas compression and τ is the induction time)

- Mass fraction burned

- Induction time integral

- Mass fraction burned

- Induction time integral

Knocking cycle

Knock prediction: phenomenological models

Douaud & Eyzat

- MaMass fraction burned - MaMass fraction burned

Knock Free

cycle


Knock prediction: phenomenological models

Very good correlation between

prediction of crank angle at knock

onset based on Douaud&Eyzat

model and experimental values was

found.


Conclusions & Future Work

24

• After a proper tuning of the knock intensity metrics and of the knock

prediction models, a good correlation could be found between experimental

measurements and simulation results, both in terms of knock intensity ad in

terms of knock onset prediction.

• Further investigations will be carried out in order to evaluate the effects of:

• internal EGR

• different fuel properties (e.g. E85)

• mixture inhomogeneity


The valuable support provided to the research activity by Centro Ricerche

Fiat, Fiat Powertrain Technologies Racing, Kistler Italy and Gamma

Technologies is gratefully acknowledged.

The authors would also like to thank in particular mr. Fabrizio Mirandola

(formerly at FPT racing) for his precious and constant support during the

experimental activities.

AKNOWLEDGMENTS


Federico Millo, Luciano Rolando

1st GTI Italian User Conference

March 18th , 2013 – Turin

Analysis of knocking phenomena in a high performance

engine

Documents

Analysis of knocking phenomena in a high performance engine · Analysis of knocking phenomena in a high performance ... engine low end torque performance, ... After a proper tuning