Effect of cetane number on HCCI combustion efficiency and emissions

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Effect of cetane number on HCCI combustion efficiency and emissions

Hosseini, Vahid; Neill, W. Stuart; Guo, Hongsheng; Chippior, Wallace L.; Fairbridge, Craig; Mitchell, Ken

Effects of Cetane Number on HCCI Combustion

Efficiency and Emissions

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

Craig Fairbridge Ken Mitchell

Natural Resources Canada Shell Canada Limited, Canada

International Energy Agency 31st _{Task Leaders Meeting on Energy Conservation}

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

Outline

• Experimental Setup • Fuels

• Experimental procedures • Results

– Controlled Input Conditions – Controlled Engine Outputs

Outline

• Experimental Setup

• Fuels

• Experimental procedures • Results

– Controlled Input Conditions – Controlled Engine Outputs

Experimental Setup

Experimental Setup

•Enhanced fuel injector/vaporizer consisting of:

o _{OEM gasoline port fuel injector} o _{Air blast for improved atomization}

o _{Heated section to improve vaporization}

Port fuel injector

Outline

• Experimental Setup

• Fuels

• Experimental procedures • Results

– Controlled Input Conditions – Controlled Engine Outputs

Fuels

• 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

Fuels

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 hydrotreating

mustard seed oil at CanmetENERGY to produce a high

cetane blending component with a DCN of 109. It was

blended at 5% and 10% volume fraction into the base fuel

to produce fuels with CN of 39.6 (SCRD-CN39) and 41.9

(SCRD-CN42), respectively.

Outline

• Experimental Setup • Fuels

• Experimental procedures

• Results

– Controlled Input Conditions – Controlled Engine Outputs

Experimental Procedures

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

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

Outline

• Experimental Setup • Fuels

• Experimental procedures

• Results

– Controlled Input Conditions

– Controlled Engine Outputs

Results

• 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 (T_vap, C) 220 Intake mixture temperature (T_mix, C) 75

Compression ratio 13:1

Engine speed (rpm) 900

MAP (kPa) 200

Results

• Hydroprocessing

The base fuel (OS-CN36)

Results

• Hydroprocessing

OS-CN39

Results

• Hydroprocessing

OS-CN41

Results

• Hydroprocessing

a.

7 /19

Results

• Cetane improver

(2EHN) addition

b.

8 /19

Results

• Blending with

Supercetane

Renewable Diesel

(SCRD)

c.

9 /19

Results

• Comparing fuels

with similar cetane

numbers

d.

10/19

Results

Power and Efficiency

AFR 25 30 35 40 45 50 IS F C (g/ kW h ) 260 280 300 320 OS-CN36 OS-CN39 OS-CN41 2EHN-CN40 2EHN-CN44 SCRD-CN39 SCRD-CN42 AFR 25 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

Results

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

Combustion cyclic variation Knocking intensity

AFR 25 30 35 40 45 50 CO V I ME P ( % ) 2 3 4 5 6 OS-CN36 OS-CN39 OS-CN41 2EHN-CN40 2EHN-CN44 SCRD-CN39 SCRD-CN42 AFR 25 30 35 40 45 50 KI (bar . o CA ) 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

Results

Regulated Emissions

•Increasing fuel’s CN improved CO emissions for all cases. The hydroprocessed fuels produced 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.

AFR 25 30 35 40 45 50 isCO (g/ kW h ) 0 20 40 60 80 100 120 140 OS-CN36_OS-CN39 OS-CN41 2EHN-CN40 2EHN-CN44 SCRD-CN39 SCRD-CN42 AFR 25 30 35 40 45 50 isHC (g/ kW h ) 4 5 6 7 8 OS-CN36 OS-CN39 OS-CN41 2EHN-CN40 2EHN-CN44 SCRD-CN39 SCRD-CN42

13/19

Results

NOx AFR 25 30 35 40 45 50 isNO x(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 AFR 25 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

• Experimental Setup • Fuels

• Experimental procedures

• Results

– Controlled Input Conditions

– Controlled Engine Outputs

Results

• 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 (T_vap, C) 220 Intake mixture temperature (T_mix, C) 75

Results

Setting Initial Conditions

14 15 16 17 18 A FR 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 EGR (% ) 50 55 60 65 70 36 38 40 42 44 0 20 40 60 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

Results

High Power limits

Results

High Power limits

36 38 40 42 44 IMEP (ba r) 4 5 6 7 Cetane Number 36 38 40 42 44 36 38 40 42 44

1

4

7

17/19

Results

Efficiency 220 240 260 280 Indicat ed Spec ific Fuel C onsu mption, 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.

Outline

• Experimental Setup • Fuels

• Experimental procedures • Results

– Controlled Input Conditions – Controlled Engine Outputs

Conclusions

• Increasing the fuel cetane number shifted the AFR-EGR operating window for HCCI combustion towards higher AFR (leaner mixtures) and reduced the cyclic variations.

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

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

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

Acknowledgement

• The authors would like to acknowledge the financial

support

of

the

Government

of

Canada’s

Thank you for your attention

(vahid.hosseini@nrc-cnrc.gc.ca)