Effect of cetane number on HCCI combustion efficiency and emissions

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Effect of cetane number on HCCI combustion efficiency and emissionsHosseini, Vahid; Neill, W. Stuart; Guo, Hongsheng; Chippior, Wallace L.; Fairbridge, Craig; Mitchell, Ken

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Effects of Cetane Number on HCCI Combustion Efficiency and Emissions

Vahid Hosseini, W. Stuart Neill, Hongsheng Guo, Wallace L. ChippiorNational Research Council Canada

Craig Fairbridge Ken MitchellNatural Resources Canada Shell Canada Limited, Canada

International Energy Agency31st Task Leaders Meeting on Energy Conservation

and Emissions Reduction in CombustionSeptember 20-24, 2009, Lake Louise, Canada

Outline

• Experimental Setup

• Fuels

• Experimental procedures

• Results

– Controlled Input Conditions

– Controlled Engine Outputs

• Conclusions

Outline


• Fuels


• Results



• Conclusions

Experimental Setup HCCI Engine laboratory

1 /19

Experimental Setup Enhanced fuel injector/vaporizer

•Enhanced fuel injector/vaporizer consisting of:

o OEM gasoline port fuel injectoro Air blast for improved atomizationo Heated section to improve vaporization

Port fuel injector

Air blast 2 /19

Outline


• Fuels


• Results



• Conclusions

Fuels Base fuel and CN enhancement

• A minimally processed and low cetane number (36.6) fuel derived from oil sands (OS-CN36) was used as the base fuel in the study.

• Three different methods were applied to modify the base fuel to achieve higher CN fuels:

• Hydroprocessing

• Addition of cetane improver

• Blending with a Supercetane™ renewable diesel fuel

3 /19

Fuels Hydroprocessing, cetane improver addition,

and blending with renewable diesel

• The base fuel (OS-CN36) was hydroprocessed in two stages.Cetane numbers were 39.4 (OS-CN39) and 41.4 (OS-CN41),respectively.

• Two fuels with 40.0 (2EHN-CN40) and 44.6 CN (2EHN-CN44)were produced by adding 0.05% and 0.23% by volume of 2-ethyl-hexyl-nitrate (2EHN) to the base fuel, respectively.

• The Supercetane™ was produced by hydrotreatingmustard seed oil at CanmetENERGY to produce a highcetane blending component with a DCN of 109. It wasblended at 5% and 10% volume fraction into the base fuelto produce fuels with CN of 39.6 (SCRD-CN39) and 41.9(SCRD-CN42), respectively.

4 /19

Outline


• Fuels


• Results



• Conclusions

Experimental Procedures

• It is a challenging task to compare the HCCI combustioncharacteristics of test fuels as each fuel requires different initialconditions to achieve optimal combustion behavior.

• Two sets of experiments were devised to evaluate each testfuel: one set employed controlled input conditions (EGR-AFR),while the other set employed controlled engine outputs (speed,load).

5 /19

Outline


• Fuels


• Results



• Conclusions

ResultsControlled Input Conditions

• Two of the input conditions, namely AFR and EGR, were changed and

the resultant engine combustion behavior (power, efficiency, emissions)

was measured.

• Other initial conditions were fixed for this experiment:

Fuel vaporizer temperature (Tvap, C) 220

Intake mixture temperature (Tmix, C) 75

Compression ratio 13:1

Engine speed (rpm) 900

MAP (kPa) 200

6 /19

Results Controlled Input Conditions

EGR-AFR Operating Region

• Hydroprocessing

The base fuel (OS-CN36)

7 /19



• Hydroprocessing

OS-CN39

7 /19



• Hydroprocessing

OS-CN41

7 /19



• Hydroprocessing

AFR15 20 25 30 35 40 45 50 55

EG

R (

%)

50

55

60

65

70

OS-CN36

OS-CN39

OS-CN41

OS-CN36

OS-CN39

OS-CN41

a.

7 /19



• Cetane improver (2EHN) addition

55AFR

10 15 20 25 30 35 40 45 50

EG

R (

%)

50

55

60

65

70

OS-CN36

2EHN-CN40

2EHN-CN44

OS-CN36

2EHN-CN402EHN-CN44

b.

8 /19



• Blending with SupercetaneTM

Renewable Diesel (SCRD)

AFR

AFR10 15 20 25 30 35 40 45

EG

R (

%)

50

55

60

65

70

75OS-CN36

SCRD-CN39

SCRD-CN42

OS-CN36

SCRD-CN39

SCRD-CN42

c.

9 /19



• Comparing fuels with similar cetane numbers

AFR

45

AFR10 15 20 25 30 35 40 45 50

EG

R (

%)

55

60

65

70

OS-CN39

2EHN-CN40

SCRD-CN39

OS-CN39

2EHN-Cn40

SCRD-CN39

d.

10/19


Power and Efficiency

AFR25 30 35 40 45 50

ISF

C (

g/k

Wh

)

260

280

300

320

OS-CN36

OS-CN39

OS-CN41

2EHN-CN40

2EHN-CN44

SCRD-CN39

SCRD-CN42

AFR25 30 35 40 45 50

IME

P (

bar)

2.5

3.0

3.5

4.0

4.5

OS-CN36

OS-CN39

OS-CN41

2EHN-CN40

2EHN-CN44

SCRD-CN39

SCRD-CN42

EGR=59.6% 1.5%

Hydroprocessing the base fuel was the only method that increased IMEP and reduced ISFC.

Efficiency Power

11/19


Combustion Characteristics

COVIMEP was decreased and KI was increased by increasing CN independent of the upgrading method.

Combustion cyclic variation Knocking intensity

AFR25 30 35 40 45 50

CO

V IM

EP

(%

)

2

3

4

5

6

OS-CN36

OS-CN39

OS-CN41

2EHN-CN40

2EHN-CN44

SCRD-CN39

SCRD-CN42

AFR25 30 35 40 45 50

KI (b

ar.

oC

A)

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0 OS-CN36

OS-CN39

OS-CN41

2EHN-CN40

2EHN-CN44

SCRD-CN39

SCRD-CN42

12/19


Regulated Emissions

•Increasing fuel’s CN improved CO emissions for all cases. The hydroprocessed fuelsproduced the lowest CO emissions.•Indicated specific HC emissions (isHC) in this case, blending with Supercetane™increased isHC emissions, while adding cetane improver did not clearly affect isHC.Hydroprocessing reduced isHC emissions.

AFR25 30 35 40 45 50

isC

O (

g/k

Wh

)

0

20

40

60

80

100

120

140OS-CN36

OS-CN39

OS-CN41

2EHN-CN40

2EHN-CN44

SCRD-CN39

SCRD-CN42

AFR25 30 35 40 45 50

isH

C (

g/k

Wh

)

4

5

6

7

8

OS-CN36

OS-CN39

OS-CN41

2EHN-CN40

2EHN-CN44

SCRD-CN39

SCRD-CN42

13/19


NOx

AFR25 30 35 40 45 50

isN

Ox(g

/kW

h)

0.00

0.02

0.04

0.06

0.08

0.10

OS-CN36

OS-CN39

OS-CN41

2EHN-CN40

2EHN-CN44

SCRD-CN39

SCRD-CN42

AFR25 30 35 40 45 50

NO

x (

pp

m)

0

2

4

6

8

10

12

14 OS-CN36

OS-CN39

OS-CN41

2EHN-CN40

2EHN-CN44

SCRD-CN39

SCRD-CN42

14/19

Outline


• Fuels


• Results



• Conclusions

ResultsControlled Engine Outputs

• A matrix of 9 speed/load

conditions, consisting of 3 IMEP

levels and 3 speed levels were

defined for the experiments,

considering the safe limits of

operation. Other initial

conditions were fixed for this

experiment:

Fuel vaporizer temperature (Tvap, C) 220

Intake mixture temperature (Tmix, C) 75

Compression ratio 13:1 15/19

Results Controlled Engine Outputs

Setting Initial Conditions

14

15

16

17

18

AF

R

17

21

25

36 38 40 42 44

30

40

50

60

Cetane Number

36 38 40 42 44 36 38 40 42 44

1

2

3

4

5

6

7

8

9

65

70

75

EG

R (

%)

50

55

60

65

70

36 38 40 42 44

02

04

06

0

Cetane Number

36 38 40 42 44 36 38 40 42 44

1

2

3

4

5

6

7

8

9

Cetane Improver Addition

Hydroprocessing

Blending w Supercetane

16/19


High Power limits

17/19


High Power limits

36 38 40 42 44

IME

P (

ba

r)

45

67

Cetane Number

36 38 40 42 44 36 38 40 42 44

1 4 7

17/19


Efficiency

220

240

260

280

Ind

icate

d S

pec

ific

Fu

el

Co

nsu

mp

tio

n, IS

FC

(g

/kW

h)

220

240

260

36 38 40 42 44

250

270

290

Cetane Number

36 38 40 42 44 36 38 40 42 44

1

2

3

4

5

6

7

8

9

Cetane Improver Addition

Hydroprocessing

Blending w Supercetane

• The only method that

improved ISFC was

hydroprocessing the

base fuel.

18/19

Outline


• Fuels


• Results



• Conclusions

Conclusions

• Increasing the fuel cetane number shifted the AFR-EGR operatingwindow for HCCI combustion towards higher AFR (leaner mixtures) andreduced the cyclic variations.

• Higher EGR rates were required to operate the higher cetane numberfuels at lower AFR (richer mixtures). This led to a significant decrease inthe maximum engine power produced for the higher cetane number fuelswith a fixed boost pressure.

• The hydroprocessed fuels had more stable and complete HCCIcombustion than the base fuel, which resulted in reduced CO, HC, andNOx emissions and lower ISFC.

• The addition of a nitrate cetane improver increased ISFC and led tosubstantially higher NOx emissions on a relative basis, but the absoluteemissions were still very low. Blending a renewable diesel componentincreased the ISFC and HC emissions.

19/19

Acknowledgement

• The authors would like to acknowledge the financial

support of the Government of Canada’sPERD/AFTER and ecoETI programs.

Thank you for your attention([email protected])

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Effect of cetane number on HCCI combustion efficiency and emissions