fuel chemistry and cetane effects on hcci performance ......chemistry in hcci combustion – current...

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Fuel Chemistry and Cetane Effectson HCCI Performance,

Combustion, and Emissions

presentation for DEER 2005

Bruce G. Bunting, Craig Wildman, Jim Szybist, Sam Lewis, and John Storey

Oak Ridge National LaboratoryFuels, Engines, and Emissions Research Center


Outline of talk

• Purpose of research• Engine and experimental procedure• Results• Conclusions• Future work• Acknowledgements


Purpose of research

• To provide simple comparisons of the performance of diesel range fuels differing in properties and chemistry in HCCI combustion

– Current study covers commercial fuels• cetane range of 40 to 73• aromatics range of 0% to 33%• includes 100% biodiesel and Fischer-Tropsch fuels

– A second study covers diesel secondary reference fuels• 18 to 76 cetane• will be presented at SAE HCCI Symposium


Example diesel fuel composition (GC/MS)

0

100000

200000

300000

400000

500000

600000

700000

5 10 15 20 25 30

Elution Time

Con

cent

ratio

n (a

.u.)

C25

C24

C22

C21C20

C19

C18

C17C16

C15

C14

C13

C12

C23

Mixture of Aromatics & Branched Alkenes and Alkanes

Sulfur Compound :4(1)dimethylethyl-2-methyl Benzenethiol

Polyaromatic

Distinct peaks are straight-chain saturated compounds; i.e., Alkanes. Broad HC envelop is composed of everything else; i.e., branched alkanes, alkenes, aromatics…Broad range of straight-chain alkanes.

C9C10

C11

Normal paraffins with a carbon number range of 8 to 25

Iso-paraffins, cyclo-paraffins, olefins, and aromatics

2004 #2 pump fuel45 cetane

33% aromatic67% paraffin

0% olefin


15 fuels evaluated

10 Commercial fuels• 2004 fuels• 2007 fuels

• 5 diesel secondary reference blends

• Cetane range • 41 to 73

• Aromatics range • 0 to 33%

Fuel Cetane Aromatics (%)

A (2007) 45.4 23.5B (#2 Cert) 47.9 30.5

C (2004) 47.9 15.7D (2007) 50.5 12.0E (2007) 50.5 26.4F (2007) 50.5 32.8G (2007) 50.5 29.9

H (B100D) 53.2 0I (California) 53.6 21.4

J (FT) 73.0 0.9K (37%T/63%U) 40.7 15.8L (46%T/54%U) 46.7 15.0M (54%T/46%U) 50.5 14.4N (63%T/37%U) 53.6 13.6O (72%T/28%U) 60.7 13.0


Engine used for experiments

• Based on Hatz 1D50Z– Single cylinder, air cooled– 2 valve, naturally aspirated– 517 cc, 97 mm bore, 70 mm stroke– Selected modifications made to engine

• 10.5 C/R• Port fuel injection with heated atomizer• Intake air heater


- Standard tube fittings- 400 watt cartridge heater- Slight air purge- Operated at 375 deg.C- Mounted between air heaterand intake port

- Fuel controlled by laboratorymetering pump

- Provides very uniform fuel mixing

Heated atomizer


Engine and test stand

MODIFIED PISTONWITH SPHERICAL

COMBUSTION BOWL

INTAKE AIR HEATER

ATOMIZINGINJECTOR

ENGINE

BELT DRIVE

INDUCTION MOTOR

METERING PUMP


IMEP vs. MFB50%

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

3.6

350 355 360 365 370 375

MFB50% (CAD)

IMEP

(bar

)

Experimental procedure• Intake temperature used to

alter combustion phasing• MFB50 correlates best to

block temperature and Φ• Combustion phasing

bounds established– Retarded timing limited

by COV IMEP of 10% – Advanced timing limited

by rate of pressure rise of 25 bar/deg

• Point of best efficiency used for all comparisons

Operating Conditions• 1800 RPM• Stock valve timing• ~3 bar net IMEP• 15 mL/min fuel flow• 0.3 < Φ < 0.46

dP/dCA limit COV limit

Best eff.


Cetane and aromatic range covered

0

5

10

15

20

25

30

35

40 45 50 55 60 65 70 75

Cetane number

% a

rom

atic

s

B100 FT

Olefins ranged from0.7 to 2.3%

Lower heating valuesof fuels were within ±2%except B100 and FT, which were lower


Maximum IMEP

Max IMEP does not appear to depend in cetane or aromatics

B100 and FT were lowest

40 45 50 55 60 65 70 75Cetane Number

0

5

10

15

20

25

30

35

Aro

mat

ics

(%)

3.6

3.5

3.53.4

3.5

3.5

3.3

3.2

3.5

3.5

3.2

3.5 3.5

3.02.9

2.9 bar

3.0 bar

3.1 bar

3.2 bar

3.3 bar

3.4 bar

3.5 bar

3.6 bar


MBT combustion phasingCombustion phasing correlates with cetane number but

not with aromatics. Higher cetane requires earlier MFB50

40 45 50 55 60 65 70 75Cetane Number

0

5

10

15

20

25

30

35

Aro

mat

ics

(%)

365.5

364

368.6364.7

364

367.9

363

360.2

362.5

362.9

360.3

362.6 359.7

353.8352.5

353.0 CAD

357.0 CAD

361.0 CAD

365.0 CAD

369.0 CAD

50% MFB vs. Cetane

352.0

354.0

356.0

358.0

360.0

362.0

364.0

366.0

368.0

370.0

40 50 60 70

Cetane Number

MFB

50%

(CA

D)

Highest IMEP: SRFs Highest IMEP: All Data


Maximum rate of pressure rise

Rate increases with aromatics

Cetane number appears to have little effect

B100 is highest and does not fit trend

40 45 50 55 60 65 70 75Cetane Number

0

5

10

15

20

25

30

35

Aro

mat

ics

(%)

4.5

5.5

3.75.2

9.4

5.0

6.2

7.6

6.5

5.6

6.2

4.6 5.6

4.810.4

3.5 bar/deg

4.5 bar/deg

5.5 bar/deg

6.5 bar/deg

7.5 bar/deg

8.5 bar/deg

9.5 bar/deg

10.5 bar/deg


NOx emissions

NOx is below 10ppm for all

Highest NOxoccurs at high aromatics and low cetane

B100 highest NOx

40 45 50 55 60 65 70 75Cetane Number

0

5

10

15

20

25

30

35

Aro

mat

ics

(%)

3.7

4.4

3.84.1

8.9

4.2

5.0

7.9

4.1

3.0

3.3

2.1 2.3

2.410.1

2.0 ppm

3.0 ppm

4.0 ppm

5.0 ppm

6.0 ppm

7.0 ppm

8.0 ppm

9.0 ppm

10.0 ppm


HC emissions

HC increase with aromatics

Analyzer and sample train were seriously contaminated by B100

40 45 50 55 60 65 70 75Cetane Number

0

5

10

15

20

25

30

35

Aro

mat

ics

(%)

1927

1735

17871411

2047

2256

2332

2348

2061

1726

2403

1661 1474

17272607

1400 ppm

1600 ppm

1800 ppm

2000 ppm

2200 ppm

2400 ppm


NOx corresponds to rate ofpressure rise for all data

NOx vs. Max Rate of Pressure Rise

0102030405060708090

0.0 5.0 10.0 15.0 20.0 25.0

dp/dCA (bar/deg)

NO

x (p

pm)

REGION OF RETARDEDAND OPTIMUM TIMING

TIMING ADVANCEDFROM OPTIMUM


LTHR % of totalLow temperature heat release magnitude increases with cetane, no aromatic effect

40 45 50 55 60 65 70 75Cetane Number

0

5

10

15

20

25

30

35

Aro

mat

ics

(%)

3.4

3.0

1.91.4

1.8

1.5

2.9

3.3

3.8

4.5

4.1

6.7 7.7

10.92.6

1 %

2 %

3 %

4 %

5 %

6 %

7 %

8 %

9 %

10 %

11 %

Cumulative Heat Release vs. Crank Angle

0

50

100

150

200

250

300

350

400

330 340 350 360 370 380 390

Crank Angle (deg)

Cum

ulat

ive

Hea

t Rel

ease

(J)

LTHR


Summary of results at best timingVARIABLE HIGHER

CETANEHIGHER AROMATICS B100 FT

Max IMEP ---- ---- ↓ ↓Optimum MFB50 advances ---- Follows cetane

trendFollows cetane

trendMaximum rate of pressure rise ---- ↑ ↑ ----

CA10-90 ---- ---- ↓ Longer (LTHR>10%)

COV IMEP ---- ---- ---- ----NOX emissions ↓ ↑ ↑ Follows cetane and

aromatic trend

HC emissions ---- ↑ ↑ ↑CO emissions ---- ---- ↑ ----

LTHR rate ↑ ---- ↓ Follows cetanetrend

LTHR % of total HR ↑ ---- ↓ Follows cetane

trendLTHR-HTHR spacing ↓ ---- ↓ Follows cetane

trend


Conclusions

• Diesel fuels of 41 to 73 cetane and 0 to 33% aromatics were successfully operated in an HCCI engine at 3.5 bar and 1800 rpm

• B100 operated but produced high HC emissions and did not fit other trends of the fuels

• Heated atomizer worked for port fuel injection of diesel fuel

• Much of fuel behavior can be explained by cetane number

• Aromatics did affect rate of pressure rise, NOx, and HC


Future work

• Apply statistical analysis to data to further understand trends and significance

• Continue fuel studies– Oxygenate and bio-diesel blends– Cycloparaffin and aromatic study– Separate effects of intake temperature and fuel/air

ratio to gain better ability to control engine. We are also considering EGR, throttling, VVT, and pressure boosting in future builds

• Continue related work with gasoline range fuels and spark augmented HCCI


Acknowledgements

• The work is supported by DOE’s Office of FreedomCAR and Vehicles Technology under the Fuels Technologies Program

• Steve Goguen and Kevin Stork are DOE’s program managers for this research

• Others at ORNL who contributed to this project include Jimmy Wade, Jim Tassitano, and Eric Nafziger

• Fuel samples were analyzed by Southwest Research Institute

• FT fuel was supplied by NREL

fuel chemistry and cetane effects on hcci performance ......chemistry in hcci combustion – current...

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