1

Kinetic Mechanism Development for

Hydrocarbons and Oxygenated Fuels

Dr. Henry Curran and Dr. Philippe Dagaut

Combustion Chemistry Centre, NUI Galway, Ireland

CNRS Orleans, France

Lecture

1st Workshop on Flame Chemistry July 28th, 2012

Future HC fuels - many sources

Some petroleum will still be available

Oil sands, oil shale

Coal-to-liquids

Fischer – Tropsch

Natural gas

Hydrogen

Bio-derived fuels

Ethanol, butanol, algae

Biodiesel from vegetable and animal oils

Chemical kinetics to understand and simulate

complex behaviour (ignition, NTC, cool flames…)

reactivity (extent of conversion, heat release)

product / pollutant formation 2

0.0 0.1 0.2 0.3 0.4 0.50

5

10

15

20

25P

erc

en

tag

e o

f fu

el

ca

rbo

n

co

nv

ert

ed

to

so

ot

pre

cu

rso

rs

Fraction of oxygen in fuel by mass

MB

DMM

TPGME

Ethanol

Methanol

DME

Dibuthylmaleate

How well an oxygenated fuel works depends on its

molecular structure

Miyamoto et al. Paper No. SAE 980506 (1998).

Westbrook et al. J. Phys. Chem. A (2006) 110: 6912–6922.

Reference fuel mixed with:

3

Oxygenated fuels

Alcohols (methanol, ethanol, propanol, butanol)

Ethers (DME, DEE, EME, MTBE, ETBE)

Esters (methyl and ethyl esters)

Ketones (acetone, EMK, DEK)

Furans (methyl furan, di-methyl furan)

4

Fuel

Ṙ RO2 smaller molecules β-scission

High temperature

+ O2

QOOH chain

branching + O2

Intermediate temperature

Low temperature

olefins,

cyclic ethers,

β-scission

+ O2

General reaction scheme

5

∙

∙

Fuel decomposition reactions

6

5.0 5.5 6.0 6.5 7.0 7.5

100

1000 iso -propanol

n -propanolIg

nitio

n d

ela

y t

ime

(s)

104 K / T

Propanol isomers: Comparison of reactivity

0.5% fuel, 2.25% O2, f = 1.0, P = 1 atm

Johnson et al. Energy & Fuels (2009) 23 5886–5898.

7

Alcohol molecular elimination

k = 3.52 x 1013 0. 67300. s-1

k = 2.11 x 1014 0. 67300. s-1

Tsang, W. Int. J. Chem. Kinet. (1976) 8: 173–192.

n-propanol propene + water

+ OHH

C OH

C

H3C

H

H

H

H

iso-propanol propene + water

+ OHH

C OH

C

H

H

H

H3C

H

8

Water elimination is much more important for iso-

propanol

H3C CH2 CH2 OH

(nC3H7OH)

H3C CH CH2 + H2O

(29%)

CH2 OHCHH3COH (10%)

H (3%)(2C3H6OH)

(13%)

OH+ H3C CH CH2

(5%)

CH3 + H2C CH2 OH

+

(18.5%)

(3C3H6OH)CH2 OHCH2H2C

H2C OHH2C CH2

OH (7.6%)

H (10.9%)

CH OHCHH3C(1C3H6OH)

(14%)

+

H (7.8%)OH (4.7%)

CHH2C OH CH3

-H (1.5%)

H3C CH2 CH2 O(nC3H7O)

0.5% n-propanol

f = 1.0, T = 1600 K

30% fuel consumed

(iC3H7OH)

H3C CH CH2 + H2O

(63%)

OHCHH3C

CH2H (10%)

OH (5.2%)(iC3H6OH)

(11.5%)

OH+ H3C CH CH2

(5.6%)

CH3 + H3C CH OH

+

(7.2%)

(tC3H6OH)

C OHH3C

CH3

H3C C CH3

O

OH (5.8%)

H (7.7%)OHCH

CH3

H3C

O (1.6%)

H2C CH OH + CH3

(5.5%)

H

H2C C OH

CH3

H +

(5.6%)

(iC3H5OH)(C2H3OH) (sC2H4OH)

(C3H6) (C3H6) (CH3COCH3)

0.5% iso-propanol

f = 1.0, T = 1600 K

30% fuel consumed

Johnson et al. Energy & Fuels (2009) 23: 5886–5898.

9

Fuel

Ṙ RO2 smaller molecules β-scission

High temperature

+ O2

QOOH chain

branching + O2

Intermediate temperature

Low temperature

olefins,

cyclic ethers,

β-scission

+ O2

General reaction scheme

10

∙

∙

Sub-mechanism

11

Reactivity of ethers ● 1% H2, 1% O2 in Ar, p5 = 1.4–2.6 atm

○ 0.1% iso-C4H8

■ 0.1% MTBE

□ 0.1% ETBE

▲ 0.1% DEE

△ 0.1% EME

Yasunaga et al. Comb. Flame (2011) 158: 1032–1036.

12

Ether molecular elimination

k = 1.70 x 1014 0. 60800. s-1

k = 1.70 x 1014 0. 60600. s-1

MP4/cc-pVTZ//MP2/cc-pVTZ level of theory with zero point corrections

MTBE isobutene + methanol

+C O

C

H

H

H3C

H3C

H

CH3

H3C OH

C O

C

H

HH

CH2 CH3

H3C

H3C +

ETBE isobutene + ethanol

H3C CH2 OH

Yasunaga et al. Comb. Flame (2011) 158: 1032–1036.

13

Ether molecular elimination

k = 5.0 x 1013 0. 63400. s-1

k = 5.0 x 1013 0. 65200. s-1

MP4/cc-pVTZ//MP2/cc-pVTZ level of theory with zero point corrections

+

DEE ethylene + ethanol

H2C CH2O CH2H2C

C HH

H

CH3 H3C CH2 OH

H3

C O CH2

C CH

HH

H3C

H3C+

ETBE tert-butanol + ethylene

H2C CH2C OH

H3C

C

H3C

H3

+

EME ethylene + methanol

H2C CH2 C OH

H

H

H

O CH3H2C

C HH

H

Yasunaga et al. Comb. Flame (2011) 158: 1032–1036.

14

Ethylene is very fast to ignite

6.0 6.5 7.0 7.5 8.0 8.5 9.010

1

102

103

104

105

/ s

104 K / T

C2H

4

C3H

6

i-C4H

8

C2H

6

C3H

8

i-C4H

10

1700 1600 1500 1400 1300 1200 1100

1.0% fuel, f = 1.0

15

Fuel

Ṙ RO2 smaller molecules β-scission

High temperature

+ O2

QOOH chain

branching + O2

Intermediate temperature

Low temperature

olefins,

cyclic ethers,

β-scission

+ O2

General reaction scheme

H-atom abstraction

16

∙

∙

H-atom abstraction reactions

17

H3C CH

3

O

C

CH3CO CH

3

CO CH3

C2H

6

CH3COCH

2

CH3COCH

2

CH3COCH

2 CH4

CH3 CH

2CO

C2H

6

+

+

+ H2O

17% (f = 0.5)17% (f = 1.0)17% (f = 2.0)

+ H2

26% (f = 0.5)14% (f = 1.0)8% (f = 2.0)

+ OH

+ H

++ CH3

4% (f = 0.5)5% (f = 1.0)5% (f = 2.0)

53% (f = 0.5)64% (f = 1.0)70% (f = 2.0)

+

Acetone: Low p, High T

1.25% fuel, 22% fuel conversion, T = 1400 K, p = 1 atm

18

1 2 3 4 5

1E11

1E12

k (

cm

3 m

ol-1

s-1)

1000 K / T

This study

Gierczak et al. 03 (PLIF)

Wollenhaupt et al. 00 (PLIF)

Yamada et al. 03 (PLIF)

Vasudevan et al. 05

CH3COCH3 + OH = CH3COCH2 + H2O

19

CH3OCH3 + OH = CH3OCH2 + H2O

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

1E12

1E13

k (

cm

3 m

ol-1

s-1)

1000 K / T

Curran et al. 00

Ogura et al. 07

Bonard et al. 02

Tranter/Walker 01

Atkinson 97

Arif et al. 97

Mellouki et al. 95

Nelson et al. 90

Wallington et al. 88

Tully/Droege 87

Perry et al. 77

20

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

1E12

1E13

k (

cm

3 m

ol-1

s-1)

1000 K / T

Cook et al. 09

Curran et al. 00

Ogura et al. 07

Bonard et al. 02

Tranter/Walker 01

Atkinson 97

Arif et al. 97

Mellouki et al. 95

Nelson et al. 90

Wallington et al. 88

Tully/Droege 87

Perry et al. 77

CH3OCH3 + OH = CH3OCH2 + H2O

21

H-atom Abstraction

Ethers + OH

'

' '

'

DME EME iPME

n-Butanol + OH/HO2

C-W. Zhou, J. M. Simmie, H. J. Curran. Combust. & Flame, 2011 158 726−731.

C-W. Zhou, J. M. Simmie, H. J. Curran. Int. J. Chem. Kinet., 2012 44 155−164.

C-W. Zhou, J.M. Simmie, H.J. Curran

Phys. Chem. Chem. Phys. 2010 12 7221−7233.

n-Butanol + ĊH3 (Imperial College London: Prof. Alex Taylor )

D. Katsikadakos, C-W. Zhou, J. M. Simmie, H. J. Curran, P.A. Hunt,

Y. Hardalupas, A.M.K.P. Taylor. Proc. Comb. Inst., 2012. Paper 4D03 Thursday 2nd August.

22

H-atom Abstraction

' '

'

'

DMK EMK iPMK

Ketones + OH

C-W. Zhou, J. M. Simmie, H. J. Curran. Phys. Chem. Chem. Phys. 2011 13 11175−11192.

iso-Butanol decomposition and related (CH3)2ĊH + ĊH2OH

reaction (Argonne National Laboratory: Dr. Stephen Klippenstein)

'

+

23

C-W. Zhou, S. J. Klippenstein, J. M. Simmie, H. J. Curran

Proc. Comb. Inst., 2012 in press

Paper : 4D05 Thursday 2nd August

CH3OH + HO2CH2OH + H2O2

0.5 1.0 1.5 2.04

6

8

10

122000 1000 667 500

T / K

log (

k /

cm

3m

ol-1

s-1)

1000 K / T

Zhou

Klippenstein

Curran

Li

A n E

Zhou 6.24E-05 4.89 1.05E+04

Klippenstein 2.28E-05 5.06 1.02E+04

Curran 1.08E+04 2.55 1.05E+04

Li 3.98E+13 0.00 1.94E+04

--- in cm3, mol, s, cal units

)R/exp( TEATk n

Klippenstein, S J.; Harding, L B.; Davis, M J. et al. Proc. Comb. Inst. 2011 33 351−358. Li, J.; Zhao, Z.; Kazakov, A.; Chaos, M.; Dryer, F L. et al. Int. J. Chem. Kinet. 2007 39 109−136.

24

Acetone: α' hydrogen reactivity

TS1a

TS2a RC1a

DMK + OH RC1a

CH3COCH2 + H2O

0.0

TS2a

TS1a

-4.5

2.3

3.4

-26.2

-22.0PC1a

in kcal/mol

25

Acetone: α' hydrogen reactivity

0.5 1.0 1.5 2.0

1E11

1E12

2000 1000 667 500

T / K

k /

cm

3 m

ol-1

s-1

1000 K / T

Outofplane

Inplane

500 1000 1500 2000

0.2

0.4

0.6

0.8

1.0

Bra

nc

hin

g R

ati

o

T / K

Outofplane

Inplane

∆ECT

= 2.0 kcal/mol

C C

O

H

H

H

H

H

H

∆ECT

= 0.0 kcal/mol

Electron delocalization from π(CO) to σ*(CHin) and σ*(CHout) is different

26

α' hydrogen reactivity in DME

∆ECT

= 4.9 kcal/mol

0.5 1.0 1.5 2.0

1E11

1E12

1E13

2000 1000 667 500

T / K

k /

cm

3 m

ol-1

s-1

1000 K / T

Outofplane

Inplane

500 1000 1500 2000

0.2

0.4

0.6

0.8

1.0

Bra

nc

hin

g R

ati

o

T / K

Outofplane

Inplane

CO

CH

H

H

H

H

H

∆ECT

= 1.7 kcal/mol

Electron delocalization from oxygen lone pairs to σ*(CHout) weaken the BDE of out-of-plane CH bond by 5.0 kcal/mol.

27

α' Reactivity Compared to Alkanes

Ethers

Oxygen lone pairs accelerate reactivity of ’ hydrogen compared to alkane

Growing size of the -side has no influence on reactivity of ’ hydrogen atoms

Ketones

’ H-atom is less reactive than primary H-atom in alkanes

Growing size of the -side will accelerate reactivity of ’ H-atoms

0.5 1.0 1.5 2.0

1E11

1E12

1E13

2000 1000 667 500

T / K

k /

cm

3 m

ol-1

s-1

1000 K / T

Ketones

Ethers

Michael et al.

28

Comparative Reactivity

0.5 1.0 1.5 2.0

1E11

1E12

1E13

2000 1000 667 500

T / K

k /

cm

3 m

ol-1

s-1

1000 K / T

Ketones

Ethers

Michael et al.

1 2 3 4 5

1E10

1E11

1E12

1E13

k (

cm

3 m

ol-1

s-1)

1000 K / T

Acetone

DME

29

General reaction scheme

Fuel

Ṙ RO2 Smaller molecules β-scission

High temperature

+ O2

QOOH + O2

Intermediate temperature

Low temperature

olefins,

cyclic ethers,

β-scission

+ O2

H-atom abstraction

30

∙

∙

Low-temperature chemistry

31

Alcohol Oxidation

O2

+ OH + H2OOH

O

OO

H

OH

+ HO2O

OO

H

O

Aldehyde formation from -radical + O2

32

Alcohol Oxidation

O2

+ OH + H2OOH

O

OO

H

OH

O

OO

HO + CH2O + OH

Waddington mechanism (-radical + O2)

33

Comparison: Alcohol/Alkane Oxidation

0.01

0.1

1

10

100

1000

0.6 0.8 1 1.2 1.4 1.6

t ign

[ms]

1000/T [1/K]

n-butanol 15 bar

n-butane 18 bar

34

Effect of chain length

35

Alcohol Oxidation

Effect of chain length on influence of functional group

0.01

0.1

1

10

100

1000

0.6 0.8 1 1.2 1.4 1.6

t ign

[ms]

1000/T [1/K]

n-butanol 15 bar

n-butane 18 bar

n-Pentanol vs n-Pentane n-Butanol vs n-Butane

Heufer et al. Proc. Comb. Inst. (2012) in press.

Paper 4D06, Thursday 2nd August

0.01

0.1

1

10

100

1000

0.7 0.9 1.1 1.3 1.5

t ign

[ms]

1000/T [1/K]

n-pentanol 9 bar

n-pentane 8 - 11 bar

36

Soybean and rapeseed derived biodiesels have

only 5 principal components

0

10

20

30

40

50

60

70

C16:0 C18:0 C18:1 C18:2 C18:3

%

Soybean

Rapeseed

Methyl Palmitate (C16:0)

Methyl Stearate (C18:0)

Methyl Oleate (C18:1)

Methyl Linoleate (C18:2)

Methyl Linolenate (C18:3)

triglyceride

methanolmethyl ester glycerol

OO

O

O

O

O

R

R R

+ 3 CH 3OHOH

OH

OH

CH3

O

O

R

3 +

triglyceride

methanolmethyl ester glycerol

OO

O

O

O

O

R

R R

+ 3 CH 3OHOH

OH

OH

CH3

O

O

R

3 +

Fatty acid methyl esters (FAMEs):

Westbrook et al. Proc. Comb. Inst. (2012) in press.

Paper 3D03 Wednesday 1st August 37

Biodiesel components ignite in order of number of

double bonds

0.1

1

10

100

0.8 1 1.2 1.4 1.6

Ign

ition

delay -

ms

1000/T - K

stearate

linoleate

palmitate

oleate

linolenate

Engine-like conditions:

13.5 bar Stoichiometric

fuel/air mixtures

Westbrook et al. Proc. Comb. Inst. (2012) in press.

Paper 3D03 Wednesday 1st August 38

C = C double bonds reduce low T reactivity

s s a v v a s s

- C – C – C – C = C – C – C – C -

s s a a s s Inserting one C=C double bonds changes the reactivity of 4

carbons atoms in the C chain

Allylic C – H bond sites are weaker than most others

Therefore they are preferentially abstracted by radicals

O2 is also very weakly bound at allylic sites and falls off

rapidly, inhibiting low T reactivity

Westbrook et al. Proc. Comb. Inst. (2012) in press.

Paper 3D03 Wednesday 1st August

39

Observed same effect in hydrocarbon fuels: hexenes

3-Hexene

2-Hexene

1-Hexene

0

20

40

60

80

100

650 700 750 800 850 900

T [K]

Ign

itio

n d

ela

y t

ime

[m

s]

3-Hexene

2-Hexene

1-Hexene

0

20

40

60

80

100

650 700 750 800 850 900

T [K]

Ign

itio

n d

ela

y t

ime

[m

s]

Ignition delay times in a rapid compression

machine of hexene isomers

(0.86-1.09 MPa, Φ=1):

C = C - C - C - C - C 1-hexene

C - C = C - C - C - C 2-hexene

C - C - C = C - C - C 3-hexene

RO2 isomerization initiates

low temperature reactivity

Moving the double bond towards the center

of the molecule “inhibits” RO2 kinetics Experimental data: Vanhove et al. PCI 2005

Simulations: Mehl, Vanhove, Pitz, Ranzi Combustion

and Flame 155 (2008) 756—772.

40

Novel fuels

41

Furans vs bio-ethanol

Promising Next Generation Biofuels

Roman-Leshkov et al., Nature (2007) 447:

982-985. (2nd generation)

Novel renewable production process

Biomass (lignocellulosic) feedstock not

destined for human/animal consumption

Highly efficient

Large scale and low cost

Desirable physicochemical properties

Higher energy density (40%)

Direct combustion in unmodified engine

RON = 119

Lower aqueous solubility and less volatile

Laminar Flame Speed Measurements of DMF, Ethanol

and Gasoline, Tian et al., Energy Fuels, 2010

Energy Densities:

Gasoline: 35 MJ/L

2,5-DMF: 31 MJ/L

Bio-Ethanol: 23 MJ/L

Session 1: Monday morning: “Kinetics of Cyclic Ethers”

42

43

2MF: Unimolecular Decomposition

Energies (0 K, kJ / mol) CBS-QB3, CBS-APNO, G3 Somers et al. Comb. Inst. (2012) in press. Paper1D01 Monday 30th July

Conclusions

General chemical reaction schemes of HCs can

be applied to oxygenated fuels

Details of oxygenated fuel combustion are quite

different!

44