Low Temperature Heat Release BehaviorLow Temperature Heat Release Behavior of Conventional and Alternative Fuels in aof Conventional and Alternative Fuels in a

Motored EngineMotored Engine

James P. Szybist* and AndrJames P. Szybist* and Andréé L. BoehmanL. BoehmanPenn State UniversityPenn State University

*Now at Oak Ridge National Laboratory*Now at Oak Ridge National Laboratory

2006 DEER Conference2006 DEER Conference

Are the growing interests in alternative diesel fuelsAre the growing interests in alternative diesel fuels and advanced combustion techniques compatible?and advanced combustion techniques compatible?

National Biodiesel Board (nbb.org)

Biodiesel productionBiodiesel production

CoalCoal--derived FT programs in PA and MTderived FT programs in PA and MT

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.00 0.20 0.40 0.60 0.80 1.00 1.20

NOx Emissions (g/mi)

PM E

mis

sion

s (g

/mi)

0

0.01

0.02

0.03

0.04

0.05

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70

NOx Emissions (g/km)

PM E

mis

sion

s (g

/km

)

U.S. Tier 2 2004+

Bin 8

Bin 5

Euro 4 2005

Euro 3

2000 U.S. Tier 1 1994-2003

Reduced emission standardsReduced emission standards

Advanced combustion techniquesAdvanced combustion techniques

Reproduced from Ryan

Tier 2 emission standards

Are advanced combustion techniques sensitive toAre advanced combustion techniques sensitive to fuel composition?fuel composition?

…it is almost certain that future, advanced combustion engine technologies will show a greater [performance and

emissions] sensitivity to [fuel-property] variations… (section 4.7.1 of the FreedomCAR Multi-Year Program Plan)

•• Lack of direct control of combustion timingLack of direct control of combustion timing– No spark initiation in most cases – Limited control with fuel injection timing (combustion strategy

dependent) – Combustion is kinetically initiated

•• Traditional fuel ignition properties may not be sufficientTraditional fuel ignition properties may not be sufficient indicators of advanced combustion performanceindicators of advanced combustion performance– Influence of “physical” vs. “chemical” cetane number

Low temperature heat releaseLow temperature heat release

Reproduced from Christensen et al.

Gasoline HCCIGasoline HCCI

Reproduced from Christensen et al.

Diesel HCCIDiesel HCCI

With increasing temperature at constant pressure Non-Explosive → Explosive → Non-Explosive → Explosive

Reproduced from Glassman, 1996

•• What is formedWhat is formed during LTHR?during LTHR?

•• Alternative fuelAlternative fuel differences?differences?

Experimental platform and fuel matrixExperimental platform and fuel matrixGDI Injector

Main Air HeaterHeating Tape

Vacuum Pump

FTIR

Ice Bath Up to 260˚ C

Φ=0.25 to 2.0

Compression

In-house combustion analysis system

Variable Compression

Ratio CFR Engine

Exhaust

-

246

280

-

T90 (°C)

22449.5methyl decanoate (biodiesel surrogate)

-65.5FT diesel-light cut

-39.4#2 diesel-light cut

9852.6n-heptane

BP (°C)DCNFuel

Ratio=4.0-13.75

Fuels progressed from only LTHR at low CR toFuels progressed from only LTHR at low CR to LTHR and HTHR at higher CRLTHR and HTHR at higher CR

0.005 1200 0.004 1100

10000.003 900 0.002 800CR = 4.47 7000.001

6000 500 Exhaust ofExhaust of

-0.001 400300 320 340 360 380 400 LTHRLTHRCrank Angle

0.005 1200 productsproducts0.004 1100 1000

0.003 900 onlyonly0.002 800 0.001 CR = 5.70 700

6000 500

-0.001 400300 320 340 360 380 400LTHR Crank Angle

0.025 2500

0.02 2000 HTHR 0.015 CR = 6.52

1500 0.01

0.005 1000

0 500 300 320 340 360 380 400

Crank Angle 0.05 2500

0.04 CR = 7.04 2000

0.03 1500

0.02 10000.01

0 500 300 320 340 360 380 400

Crank Angle

Hea

t Rel

ease

(kJ/

deg)

Hea

t Rel

ease

(kJ/

deg)

Hea

t Rel

ease

(kJ/

deg)

Hea

t Rel

ease

(kJ/

deg) Tem

perature (K)

Temperature (K

) Tem

perature (K)

Temperature (K

)

LTHR magnitude is dependent on CN andLTHR magnitude is dependent on CN and equivalence ratioequivalence ratio

0

5

10

15

0.0 0.5 1.0 1.5 2.0

LTH

R (%

of t

otal

)

Equivalence ratio

○ #2 diesel-light cut ◊ FT diesel-light cut ■ methyl decanoate

CH3

O

O

CH3

methyl decanoate

•• LTHR magnitude trends with derivedLTHR magnitude trends with derived cetanecetane numbernumberFT diesel-light cut > methyl decanoate > #2 diesel-light cut

•• MethylMethyl decanoatedecanoate LTHR likely overLTHR likely over--predicts LTHR ofpredicts LTHR of biodieselbiodiesel– Aliphatic chain is responsible for LTHR, not methyl ester – Over 50% of soy-based biodiesel is comprised of species with multiple

unsaturations – Unsaturated species exhibit less LTHR than saturated species

FTIR analysis ofFTIR analysis of nn--heptaneheptane exhaust revealsexhaust reveals CO andCO and aldehydesaldehydes are formed by LTHRare formed by LTHR

n-heptane, Φ=0.254 2000

■ acetaldehyde ○ formaldehyde

CH

O and C

H O

(ppm)

2 2

4

3 1500

2 1000

1 500

0 0 4 5 6 7 8 9 10

Compression Ratio

CO

and

CO

(%)

2

◊ carbon monoxide ▲ carbon dioxide

0.0050.0.0104 0.0350.0.0040080.03 0.0.0.003006025

8000000101675000090147008012650000

Hea

t Rel

ease

HHea

t Rel

ease

eat R

elea

se(k

J/de

g((k

J/de

g)kJ

/deg

)

Temperature (K

)TTem

perature (K)

emperature (K

)

• LTHR but no HTHR• LTHR a

nd H

THRNo reaction at low CR 0.02 700.0.002 600 00010004• 0.0150.0010.0020.01 550006080Aldehyde and COAldehyde and CO 500••• 0.005 0 506045000

-0.001 00 400404000

300 320 340 36030300 340 3600 320 340 360 380 400440000320 380380No exhaust aldehydesconcentrations plateauconcentrations dropor CO

• Negligible CO2

Crank AngleCrCrank Angleank Angle

• CO2 increases

2,52,5 heptanedioneheptanedione identified inidentified in nn--heptaneheptaneexhaust condensateexhaust condensate

CH3

CH CH3

CH3 CH3

Hydrogen Abstraction

O2 Addition

CH3 CH3

O O

CH3

CH3O O

Six-Membered-Ring Transition State

CH3 CH CH3

O OH

O2 Addition

CH3 CH3

O OH

O O

CH3

CH3

O

OH

O O

CH3 CH3

O

O OH

CH3 CH3

O

O

+ OH

Internal Isomerization

Internal Isomerization

Dehydration

2,5-heptanedione

Hydroperoxy Radical

n-Heptane

Alkyl Radical

Hydroperoxide Radical

Six-Membered-Ring Transition State

Ketohydroperoxide

Additional Species Identified Butanal2,3 Butanedione

4-penten-2-one

2-pentanone

Butanoic acid

Pentanoic acid

2,5 hexanedione

2-pentanone, 5-(1,2-propadienyloxy)

Reaction scheme taken from Curran et al., 1998.

O (ppm

)

Conventional diesel and FT fuels showConventional diesel and FT fuels show trends similar totrends similar to nn--heptaneheptane

15 1800

•• Partially oxidizedPartially oxidized 12.5 1500 2 2

4C

H O

andC

H

species are formed byspecies are formed by LTHR, consumed byLTHR, consumed by main combustion eventmain combustion event at higher CRat higher CR

•• High MW oxygenatedHigh MW oxygenated species identified inspecies identified in exhaust condensateexhaust condensate – C7 to C15 straight-chain

aldehydes – C9 to C12 straight-chain

2-ketones– C5 to C11 straight-chain C

O2 a

nd C

O (%

)C

O2 a

nd C

O (%

)

10 1200

7.5 900

5 600

2.5 300

0 0 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8

Compression Ratio ■ acetaldehyde ○ formaldehyde ◊ carbon monoxide ▲ carbon dioxide8 2400

2 2

4 C

H O

and C H

6 1800

4 1200

O (ppm

)

2 600

organic acids 0 0

4.4 4.6 4.8 5 5.2 5.4 Compression Ratio

DecarboxylationDecarboxylation of methylof methyl decanoatedecanoateproduces COproduces CO22 during LTHRduring LTHR

10 2000

7.5 1500

5 1000

2.5 500

0 0 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8

Compression Ratio

•• Comparable levels of CO and COComparable levels of CO and CO22 are formed by LTHRare formed by LTHR– Temperatures are insufficient to oxidize CO to CO2– CO2 is a product of decarboxylation

•• DecarboxylationDecarboxylation is undesirable from sootis undesirable from soot--suppression standpointsuppression standpoint– Under-utilization of fuel-bound oxygen to remove carbon from soot-precursor

reactions – Better oxygen utilization could be realized by oxygenates with ether functional

groups

CO

and

CO

(%)

2

CH

O and C

H O

(ppm)

2 2

4

LTHR reactions of aliphatic chain occurLTHR reactions of aliphatic chain occur prior toprior to decarboxylationdecarboxylation

29.50methyl decanoate

28.83 + 4 othersMethyl decenoate (isomers)

25.90Methyl nonanoate

22.12, 25.85Methyl nonenoate (isomers)

22.06Methyl octanoate

21.72Methyl octenoate

17.59Methyl heptenoate

17.45Methyl hexanoate

12.862-methyl butanoic acid methyl ester

Retention TimeMethyl esters

Methyl Decanoate

O

3

O

2 (3H) f ne-5ethyldihydroCH3

O O

4 ethyl ester

O C

O O O

5-mMethyl Decanoate

CH

urano3O CH

-oxopentanoic acid m

H3

ethoxycarbonylpentan-4-olide

OCH3

O

2 (3H) furanone-5ethyldihydroCH3O CH3

O O

4-oxopentanoic acid methyl ester

OCH3

O OO

5-methoxycarbonylpentan-4-olide

32.069-oxodecanoic acid methyl ester

30.032-oxodecanoic acid methyl ester

29.864-oxooctanoic acid methyl ester

25.446-oxoheptanoic acid methyl ester

20.905-oxohexanoic acid methyl ester

17.455-oxopentanoic acid methyl ester

16.454-oxopentanoic acid methyl ester

Retention TimeOxo-methyl ester

ConclusionsConclusions•• LTHR behavior of different fuels can be investigated in aLTHR behavior of different fuels can be investigated in a

motored enginemotored engine•• LTHR magnitude trends withLTHR magnitude trends with cetanecetane numbernumber•• The oxidation taking place during LTHR produces partiallyThe oxidation taking place during LTHR produces partially

oxidized species with only negligible amounts of COoxidized species with only negligible amounts of CO22– High concentrations of CO and aldehydes – 2,5-heptanedione, found in n-heptane exhaust condensate, can

be closely linked to LTHR mechanism •• If allowed to proceed through HTHR, partially oxidizedIf allowed to proceed through HTHR, partially oxidized

species largely converted to COspecies largely converted to CO22•• COCO22 produced during LTHR from methylproduced during LTHR from methyl decanoatedecanoate is ais a

product ofproduct of decarboxylationdecarboxylation– Decarboxylation is undesirable from a soot-suppression standpoint – LTHR reactions with aliphatic chain can occur before

decarboxylation, incorporating additional oxygen into themolecule

AcknowledgementsAcknowledgements

The authors wish to thank the Department ofThe authors wish to thank the Department of Energy for support under Contract No. DEEnergy for support under Contract No. DE--FC26FC26­-01NT41098.01NT41098.

The authors also wish to thank Doug Smith, KirkThe authors also wish to thank Doug Smith, Kirk Miller, Etop Esen, Jim Rockwell, RafaelMiller, Etop Esen, Espinoza,Jim Rockwell, Rafael Espinoza, Keith Lawson and Ed Casey of ConocoPhillips forKeith Lawson and Ed Casey of ConocoPhillips for their support of this work.their support of this work.