Investigation of combustion characteristics of a diesel

Shanghai Jiao Tong University

7th Asian DME Conference

Qiao Xinqi

School of Mechanical Engineering

Shanghai Jiao Tong University, China

Investigation of combustion characteristics of a

diesel engine fueled with DME-biodiesel blends



Outline

1. Introduction

2. Research approach

3. Experimental apparatus

4. Results and discussion

5. Conclusions



Biodiesel

High viscosity and

surface tension

DME

Low viscosity and

surface tension

Proper Lubricity, atomization, heat

value and combustion , performance.

Blended

1. Introduction



2. Research approach

Combustion

experiment

for measuring

engine

performance

Heat release analysis In-cylinder pressure

pressure rise rate

In-cylinder temperature

Heat release rate

DWT(discrete wavelet

transform) analysis Amplitude of subsignal

Wavelet relative energy



DWT analysis

Wavelet layer Frequency band (kHz)

1 ( D1) 5-10

2 ( D2 ) 2.5-5

3 ( D3 ) 1.25-2.5

4 ( D4 ) 0.625-1.25

4 ( A4 ) 0-0.625

Table.1 Frequency band of each layer

With Daubechies 10 as wavelet, in-cylinder pressure is

decomposed into four layers that contain four details D1, D2,

D3, D4 and an approximation A4.



To quantify intensity of pressure oscillation

The amplitude of pressure subsignal pDj at layer j is defined as half of the

difference between its maximum and minimum.

Wavelet relative energy Rj at layer j is defined as the ratio of detail energy Ej

of the in-cylinder pressure signal to the total detail energy E of the four layers

[14], expressed as

4

1j

j

jj

j

E

E

E

ER

jN

k

kjj dE1

2

,

Where, k is an integer as the coefficient ordinal number, and Nj the number

of detail coefficient dj,k at layer j.



3. Experimental apparatus

Parameter biodiesel DME

Density g/cm3(20˚C) 0.875 0.660

Kinematic viscosity

mm2/s(40˚C) 4.185 0.185

Surface tension kg/s2

(40˚C) 0.028 0.012

Low heat value MJ/kg 38.4 28.6

Cetane number 51 55~66

Table 3. Properties of test biodiesel and DME

bore / stroke / mm 135/145

Compression ratio 16.5

Rated speed /(r·min-1) 1500

Rated power/ kW 29.4

Fuel delivery advance angle / oCA BTDC 28

Nozzle orifice number× diameter (mm) 4×0.35

Nozzle opening pressure / MPa 19

Table 2. Specifications of test diesel engine

In view of low heat value and excellent atomization of DME, for

blends containing more than 50% of DME, nozzle orifice

number×diameter is changed from 4×0.35 mm to 5×0.43 mm, and

nozzle opening pressure is decreased from 19 to 15 MPa to increase

fuel injection supply.



4. Results and discussion

-40 -30 -20 -10 0 10 20 30 40 500

1

2

3

4

5

6

7

0

100

200

300

400BMEP=0.135MPa

Crank Angle/oCA

p /

MP

a

DME0

DME20

DME50

DME70

DME100

He

at

Re

lea

se

Ra

te

/ J

/ oC

A

-40 -30 -20 -10 0 10 20 30 40 500

1

2

3

4

5

6

7

0

100

200

300

400

500BMEP=0.27MPa

Crank Angle/oCA

p /

MP

a

DME0

DME20

DME50

DME70

DME100

He

at

Re

lea

se

Ra

te

/ J

/ oC

A

With the increase of DME proportion, the peak in-cylinder pressure decreases with

retarded peak pressure phase. But DME20 is the exception.

At two BMEP, increased DME proportion causes reduced premixed combustion, the

peak heat release rate and retarded phasing, but increased diffusive combustion and

the peak heat release in diffusive combustion increases.

Effect of DME proportion on in-cylinder pressure and heat release rate



-30 -20 -10 0 10 20 30 40 50

-0.2

0.0

0.2

0.4

0.6

BMEP=0.135MPa

Crank Angle/oCA

Pre

ssure

Ris

e R

ate

/（M

Pa/

oC

A） DME0

DME20

DME50

DME70

DME100

-30 -20 -10 0 10 20 30 40 50

-0.2

0.0

0.2

0.4

0.6

0.8

BMEP=0.27MPa

Crank Angle/oCA

Pre

ssure

Ris

e R

ate

/（M

Pa/

oC

A）

DME0

DME20

DME50

DME70

DME100

Effect of DME proportion on in-cylinder pressure rise rate

Increased DME proportion reduces the peak pressure rise rate and retards

phase, thus producing a soft engine operation.



Effect of DME proportion on in-cylinder temperature

-40 -30 -20 -10 0 10 20 30 40 50400

600

800

1000

1200

1400BMEP=0.135MPa

In-C

yli

nd

er T

emp

erat

ure

/ K

Crank Angle/oCA

DME0

DME20

DME50

DME70

DME100

-40 -30 -20 -10 0 10 20 30 40 50400

600

800

1000

1200

1400

1600BMEP=0.27MPa

In-C

yli

nd

er T

emp

erat

ure

/ K

Crank Angle/oCA

DME0

DME20

DME50

DME70

DME100

With increased DME proportion, the peak in-cylinder temperature decreases, and

their phase retards.



0.0 0.1 0.2 0.3 0.4

0

2

4

6

8

10

12

14

16

BMEP / MPa

Sm

oke

Op

acity

/ %

DME0

DME20

DME50

DME70

DME100

0.0 0.1 0.2 0.3 0.4

200

400

600

800

1000

1200

1400

BMEP / MPa

NO

x /

10

-6

DME0

DME20

DME50

DME70

DME100

Effect of DME proportion on smoke emissions and NOx emissions

As BMEP increases, smoke emission increases, but changes little for blended

fuels containing more than 50% of DME.

At the same BMEP, the increased DME proportion reduces smoke emissions,

especially at high BMEP.

NOx emissions increase with increased BMEP

At the same BMEP, NOx emissions decrease with increased DME proportion.



DME0 DME20

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-0.3

0.0

0.3-0.2

0.0

0.2-0.2

0.0

0.2-0.2

0.0

0.2

Crank Angle/oCA

pD

3 /

MP

ap

D2 /

MP

ap

D1 /

MP

a

p

D4 /

MP

a

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-0.3

0.0

0.3-0.2

0.0

0.2-0.2

0.0

0.2-0.2

0.0

0.2

Crank Angle/oCA

pD

3 /

MP

ap

D2 /

MP

ap

D1/

MP

a

p

D4 /

MP

a

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-0.3

0.0

0.3-0.2

0.0

0.2-0.2

0.0

0.2-0.2

0.0

0.2

Crank Angle/oCA

pD

3 /

MP

ap

D2 /

MP

ap

D1 /

MP

a

p

D4 /

MP

a

DME50

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-0.3

0.0

0.3-0.2

0.0

0.2-0.2

0.0

0.2-0.2

0.0

0.2

Crank Angle/oCA

pD

3 /

MP

ap

D2 /

MP

ap

D1 /

MP

a

p

D4 /

MP

a

DME70

BMEP=0.135 MPa

Wavelet decomposition of in-cylinder pressure



-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-0.3

0.0

0.3-0.2

0.0

0.2-0.2

0.0

0.2-0.2

0.0

0.2

Crank Angle/oCA

pD

3 /

MP

ap

D2 /

MP

ap

D1 /

MP

a

p

D4 /

MP

a

DME100

BMEP=0.135 MPa

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-0.3

0.0

0.3-0.2

0.0

0.2-0.2

0.0

0.2-0.2

0.0

0.2

Crank Angle/oCA

pD

3/

MP

ap

D2/

MP

ap

D1/

MP

a

p

D4/

MP

a

DME0

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-0.3

0.0

0.3-0.2

0.0

0.2-0.2

0.0

0.2-0.2

0.0

0.2

Crank Angle/oCA

pD

3/

MP

ap

D2/

MP

ap

D1/

MP

a

p

D4/

MP

a

DME20




-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-0.3

0.0

0.3-0.2

0.0

0.2-0.2

0.0

0.2-0.2

0.0

0.2

Crank Angle/oCA

pD

3 /

MP

ap

D2 /

MP

ap

D1/

MP

a

p

D4 /

MP

a

DME50

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-0.3

0.0

0.3-0.2

0.0

0.2-0.2

0.0

0.2-0.2

0.0

0.2

Crank Angle/oCA

pD

3 /

MP

ap

D2 /

MP

ap

D1 /

MP

a

p

D4 /

MP

a

DME70

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-0.3

0.0

0.3-0.2

0.0

0.2-0.2

0.0

0.2-0.2

0.0

0.2

Crank Angle/oCA

pD

3 /

MP

ap

D2 /

MP

ap

D1 /

MP

a

p

D4 /

MP

a

DME100

BMEP=0.27 MPa


BMEP=0.27 MPa



0.0

0.1

0.2

0.3

0.4

DME20 DME100DME70DME50

Am

pli

tud

e /

MP

a

DME0

pD1

pD2

pD3

pD4

BMEP=0.135MPa

0.0

0.1

0.2

0.3

0.4


Am

pli

tud

e /

MP

a

DME0

pD1

pD2

pD3

pD4

BMEP=0.27MPa

Effect of DME proportion on amplitude of subsignal

At 0.135 MPa BMEP, the amplitude of pD4 is obviously greater than those of pD1,

pD2 and pD3.

With decreased DME proportion from DME 100 to DME70, DME50, the amplitude

of pD4 gradually increases. As fuel changes from DME50 to DME20, the amplitude

of pD4 decreases, but the amplitude of pD3 increases. As DME20 changes to DME0,

the amplitude of pD3 and pD4 both increase.



0

20

40

60

80

100


Wav

elet

R

elat

ive

En

erg

y /

％

DME0

D1 D2

D3 D4

0

20

40

60

80

100


Wav

elet

R

elat

ive

En

erg

y /

％

DME0

D1 D2

D3 D4

Wavelet relative energy of in-cylinder pressure with blend fuels

The wavelet relative energy at detail D4 is the largest for all five test fuels .

With increased DME proportion in fuel blends, the relative energy at D4 increases,

with a reduction of relative energy at D1, D2 and D3.

As BMEP increases from 0.135MPa to 0.27MPa, the relative energy at D4 is still

the largest for all five test fuels, relative energy at others are still small.

BMEP=0.135 MPa BMEP=0.135 MPa



-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-0.3

0.0

0.3-0.2

0.0

0.2

0.4

0

50

100

150

Crank Angle/oCA

PR

A/(

MP

a/ o

CA

2)

PR

R/(

MP

a/ o

CA)

HR

R/(

J/ o

CA)

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-0.3

0.0

0.3-0.2

0.0

0.2-0.2

0.0

0.2-0.2

0.0

0.2

Crank Angle/oCA

pD

3 /

MP

ap

D2 /

MP

ap

D1 /

MP

a

p

D4 /

MP

a

Just as the peak heat release rate, pressure rise rate and pressure rise acceleration, so

the peak amplitudes of subsignals at four layers are located within premixed combustion

phase. The peaks of subsignals represent pressure oscillation of premixed combustion.

Relation of heat release analysis and wavelet analysis



5. Conclusions ① With the increase of DME proportion, the peak in-cylinder pressure and

pressure rise rate decrease with retarded phase, thus producing a soft engine

operation. A two-stage combustion of DME-biodiesel blends is exhibited,

including premixed combustion and diffusive combustion. Increased DME

proportion causes reduced premixed combustion, the peak heat release rate

and retarded phasing, but increased diffusive combustion and the peak heat

release in diffusive combustion increases.

② As BMEP increases, smoke emissions increase, but change little for blended

fuels containing more than 50% of DME. At the same BMEP, the increased DME

proportion reduces smoke emissions, especially at high BMEP. NOx emissions

increases with increased BMEP, and at the same BMEP, NOx emissions

decrease with increased DME proportion.

③ The curves of pD3 and pD4 change slowly with relatively large oscillation

amplitude, but rapidly change of pD1 and pD2 with small oscillation amplitude.

The heat release analysis is associated with in-cylinder pressure four-layer

wavelet analysis of blended fuels. Just as the peak heat release rate, pressure

rise rate and pressure rise acceleration, so the peak amplitudes of subsignals at

four layers are located within premixed combustion phase. The amplitudes of

subsignals represent pressure oscillation of premixed combustion.



④ The wavelet relative energy at fourth layer is the largest. With the increase of

DME proportion, wavelet relative energy at fourth layer increases, but wavelet

relative energy at other layers decreases.



Documents

Investigation of combustion characteristics of a diesel