Physical and Chemical Properties Division
THE OXIDATION OF FUEL RADICALS(the treatment of chemical activation processes)
Wing TsangNational Institute of Standards and Technology
Gaithersburg, MD 20899
Multi Agency Coordination Committee for Combustion Research [MACCCR]
Fuel Research ReviewArgonne National Laboratory
September 21, 2011
Physical and Chemical Properties Division
MOTIVATION
Contribute to the development of a fundamentally based combustion kinetics database for the simulation of combustion phenomena
Serve as a basis for the development of correlationsProvide a test of theory
Development of mixing rules for mixtures
Experimental studies on larger molecules and structuresreal fuels
Pay particular attention to oxygen attack to larger radicals
Develop methodology for treating chemical activation reactions
Physical and Chemical Properties Division
Mechanism For Fuel Breakdown During Combustion
FuelRadical attack
Fuel Radical 1-olefin + smaller alkyl radical
Radical O2 attack
1-olefinyl H, methylEthylenePropene
Fuel –O2 allyl dienes
Olefin + HO2
QOOH β-bond scission
Cyclic Ether + OH O2
O2QOOH
Ketohydroperoxide +OH
Fuel => Fuel Radical => Smaller Radical + 1-olefin => 1-olefinyl radical =>olefins, diene and cyclic radicals.
Chemical activation process
Thermal activation processes
Physical and Chemical Properties Division
Kinetics Modules in Databases
GRIMECH - methane (light hydrocarbon) combustion
Pyrolysis of fuels
Oxidation of larger fuels
Soot formation
Recent NIST experimental and data
evaluation programTarget of most models Focus of current
NIST work
Widely used Problems with rich
mixtures
Many models, begin with unsaturates
7
Physical and Chemical Properties Division
Thermodynamic PropertiesEnthalpiesEntropies
As a function of temperature
Rate ExpressionsAs a function of temperature and
pressure
CONTENTS OF DATABASE
Physical and Chemical Properties Division
CHEMICAL ACTIVATED REACTIONS
Consequence of the unimolecular reactions of molecules with non-thermal energy distribution function
Usually occurs through the formation of excited molecule from combination of two reactive species
Important in combustion environments
Neglected in all combustion kinetics databases
Physical and Chemical Properties Division
Special Features of Chemical Activation Processes
Non-thermal (Boltzmann) energy distribution
Collisions will lead to thermal distributiom: measure of energy transfer(a) stabilization
(b) Thermal decomposition
Consequences: time dependent distribution function
Direct pertinence to combustion
How does one describe processes in terms of rate constants
Physical and Chemical Properties Division
RELEVANT RELATIONS
k (T, P) = Σ k(E) ρ (E) dE
Macroscopic rate constant
RRKM expression for specific rate
Experimental data from chemical activation
Physical and Chemical Properties DivisionP h ys ic a l a n d C h e m ic a l P ro p e rtie s D iv i s io n
TYPICAL WINDOW FOR MASTER EQUATION SOLVER (CHEMRATE)
Physical and Chemical Properties Division
PAST WORK
Extensive experimental work by Rabinovitch and coworkersEmphasis of H+olefin reactions
Most studies at room temperature and low pressuresClean systems very reliable experiments
Structure for treating results in terms of stabilizatiom to decompositiom ratiosRRKM theory and energy transfer model
Leading to prohibitively large step-size down paramter
Knyazev and Tsang demonstrated that actual values for step sizes down were really much smaller for s-butyl
Due to errors in thermochemistry and high pressure rate expressions
Physical and Chemical Properties Division
Log [P, torr]0.0 0.2 0.4 0.6 0.8 1.0
Log
[Sta
biliz
atio
/Dec
ompo
sitio
n]
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
120 cm-1
150 cm-1
180 cm-1
H2-exponential down
400 cm-1-step ladder[Tardy and Rabinovitch]
Log [P, torr]0.0 0.2 0.4 0.6 0.8
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Log
[Sta
iliatio
n/D
ecom
posi
tion]
CH4-exponenial down
300 cm-1360 cm-1
400 cm-1
1500 cm-1 step ladder(Tardy and Rabinovitch}
Log [ P,torr]0.0 0.2 0.4 0.6 0.8 1.0
Log
[Sta
biliz
atio
n/D
ecom
posi
tion]
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
210 cm-1
240 cm-1
270 cm-1
N2-exponential down
800cm-1step ladder [Tardy and Rabinovitch]
Log P[torr]0.0 0.2 0.4 0.6 0.8 1.0
Log
[Sta
biliz
atio
n/D
ecom
posi
tion]
0.8
1.0
1.2
1.4
1.6
1.8
2.0
360
420
480
CF4-exponential down
>3000cm-1 step ladder(Tardy and Rabinovitch}
COMPARISON BETWEEN EXPERIMENTSL AND CALCULATED RESULTS ON THE CHEMICALLY ACTIVATED DECOMPOSITION OF HEXYL-2
Physical and Chemical Properties Division
STRATEGY FOR STUDYING RADICAL OXIDATION
Generate radicals as in pyrolysis experiments
Dilute concentrations of radicals
Vast excess of chemical inhibitor
Add sufficient amount of oxygen molecules to change reaction direction from pyrolysis to oxidation
Determine cracking patterns as function of oxygen concentration
Reproduce oxidative cracking pattern through solution of the master equation for chemical activation process
Physical and Chemical Properties Division
RADICALS STUDIED
C H3CH2CH2CH2CH2*
CH3CH2CH2CH2CH2CH2*
CH3CH2CH2CH2CH2CH2CH2*
CH3CH2CH2CH2CH2CH2CH2CH2*
CH2=CHCH2CH2CH2*
CH2=CHCHCH2CH2CH2*
CYCLOHEXYL
CYCLOPENTYL
CH3CH(CH3)CH2CH2CH2*
CH3CH(CH3)CH2CH2CH2CH2*
Physical and Chemical Properties Division
CH3CH2CH2CH2 + O2 CH3CH2CH2CH2OO CH3CH2CH=CH2+HO2
CH2CH2CH2CH2OOH CH3CHCH2CH2OOH
oHO + C2H4 + CH2CH2OOH C2H4 + HO2
C3H6+ CH2OOH
CH2O + OH
Oxidative Decomposition of n-Butyl Radical
CH3CH2CH2CH2ICH3CH2CH=CH2 +HI CH3CH2CH2CH2
CH3CH2 + C2H4
C2H4 + H
Pyrolytic Decomposition of n-Butyl Radical (through n-Butyl Iodide)
Physical and Chemical Properties Division
Molecular Properties Necessary for the Analysis of Chemical Activation Results
Properties of reactants and productsVery little experimental data on peroxy compounds nnd radicals
How good are ab initio calculations?.
Properties of transition statesLeading to rate expressions for unimolecular reactions
No experimental data on oxygenatesDependent on ab initio calculations
Energy transferred on collisions for bath moleculeStep size down
Physical and Chemical Properties Division
SOURCES OF ALKYL RADICAL
RCH2CH22CH2--I = RCH2CH2=* + I source of radicalI = RCH2CH2=* + I source of radicalRCH=CH2 + HI parallel processRCH=CH2 + HI parallel process
Interference for 1Interference for 1--butene production from oxidation of radicalbutene production from oxidation of radicalR = CH3 CH2R = CH3 CH2
RCH2CH2CH2CH2ONO = NO + RCH2CH2CH2CH2O*=RCH2CH2CH2*+ CH2ORadical source
RCH=CH2 + CH2=CH2 + OHInterference for propene formation from oxidation of radical
R = CH3
Physical and Chemical Properties Division
E xpan sion fan
In ciden t sh ock
R eflec ted shock
D istan ce
Tim
e
In terface
L ow pressureH igh pressure
D iaphragm
Tim
e
P ressu re T em p eratu re
E xpan sion fan
P artic le pa th
S am pling port
D um p tank
2
1
3
4
5
SINGLE PULSE SHOCK TUBE AND ASSOCIATED WAVE PROCESSES
Physical and Chemical Properties Division
800 850 900 950 1000 1050 1100
LOG
[MO
L-FR
AC
TIO
N]
-1.0
-0.5
0.0
0.5
1.0
800 850 900 950 1000 1050 1100
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
800 850 900 950 1000 1050 1100
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
150 torr O % O2150 torr 1.54% O2 150 torr 4.07% O2150 torr 9.21% O2300 torr 10.35% O2600 torr 10.15% O2
800 850 900 950 1000 1050 1100
-3.0
-2.5
-2.0
-1.5
-1.0
800 850 900 950 1000 1050 1100-3.5
-3.0
-2.5
-2.0
-1.5
-1.0-0.5
LOG
[MO
L-FR
AC
TIO
N]
LOG
[MO
L-FR
AC
TIO
N]
LOG
[MO
L-FR
AC
TIO
N]
LOG
[MO
L-FR
AC
TIO
N]
Ethylene
Propene
1-Butene
Butanal
THF
Temp [K} Temp [K}
Temp [K} Temp [K}
Temp [K}
PRODUCT YIELDS FROM THE OXIDATIVE DECOMPOSITIOM OF BUTYL RADICALS FROM BUTYL
IODIDE
Physical and Chemical Properties Division
850 900 950 1000 1050
Log
[mol
e-fr
actio
n]
-1.0
-0.5
0.0
0.5
1.0
850 900 950 1000 1050
-2.0
-1.5
-1.0
-0.5
0.0
850 900 950 1000 1050-2.5
-2.0
-1.5
-1.0
-0.5
850 900 950 1000 1050
-2.5
-2.0
-1.5
-1.0
850 900 950 1000 1050
-3.0
-2.5
-2.0
-1.5
-1.0
150 torr 0% O2150 torr 1.25% O2150 torr 3.13% O2150 torr 6.05% O2150 torr 10.1% O2150 torr 22.6% O2
Ethylene
Log
[mol
e-fr
actio
n]Lo
g [m
ole-
fract
ion]
Log
[mol
e-fr
actio
n]Lo
g [m
ole-
frac
tion]
Propene
1-Butene
Butanal
THF
PRODUCT YIELDS FROM THE OXIDATIVE DECOMPOSITIOM OF BUTYL RADICALS FROM
PENTYL NITRITE
Physical and Chemical Properties Division
1000 /T0 .90 0 .95 1 .00 1 .05 1 .10 1 .15 1 .20
Log[
C3H
6/TH
F]
0 .0
0 .5
1 .0
1 .5
2 .0
150 , 1 .54%
150 .4 .04%
150 , 9 .15%300 ,10 .35% 600 .10 .15%
PROPENE/THF RATIOS AS A FUNCTION OF TEMPERATURE AND OXYGEN CONCENTRATION
Log [C3H6/THF] = 2.92 -2120/T= .64 (930K)
Physical and Chemical Properties Divisionlog[time,s]
-10 -8 -6 -4
log[
bran
chin
g ra
tio]
-4
-3
-2
-1
0
C4H9OO
C4H9 +O2
1-C4H9OO 3-C4H9OO2-C4H9OOH
1-butanal
THF
1-butene
ethylene
propene
BRANCHING RATIOS FROM THE CHEMICALLY ACTIVATED DECOMPOSITION 0F BUTYLPEROXYL
RADICAL FROM OXYGEN ADDITION TO BUTYL
Physical and Chemical Properties Division
1000/T[K]0.8 1.0 1.2 1.4 1.6 1.8 2.0
LOG
[k,c
c/m
ol-s
]
11.0
11.5
12.0
12.5
13.0
13.5
HEXYL-2
CIS-BUTENE-2
RATE CONSTANTS FOR ADDITION AND ABSTRACTION TO OLEFINS (LABELS ARE
FOR PRODUCTS)
Physical and Chemical Properties Division
Log [time,s]-10 -8 -6 -4 -2 0
Log
[bra
nchi
ng ra
tio]
-3
-2
-1
0
s-butyl =propene+methyl
s-butyl =cis-butene-2 + H
s-butyl600 K, 0.1 bar
-10 -8 -6 -4 -2 0-3
-2
-1
0
Log [time,s]
s-butyl
s-butyl =propene+methyl
s-butyl =cis-butene-2 + H
Log
[bra
nchi
ng ra
tio]
1400 K, 10 bar
TEMPORAL BEHAVIOR OF S-BUTYL RADICALS AND PRODUCTS FORM FROM H + CIS-BUTENE-
2
Physical and Chemical Properties Division
Energy(kcal/mol]0 20 40 60 80 100
Log
[con
cent
ratio
n]
-20
-18
-16
-14
-12
-10
-8
-6
-4
--12-11
-10
-9
-8
-7-6-5-4
-3
-2 - 0
Distribution function for s-butyl radicalat 600 K and 1 bar
S-BUTYL RADICAL DISTRIBUTION FUNCTION FROM H + CIS-BUTENENE-2
Physical and Chemical Properties Division
0.8 1.0 1.2 1.4 1.6
Log
[cc/
mol
-s]
10
11
12
13
1000/T[K]
s-C4H9
10
0.1
CH3 + C3H6
10
1.0
0.11.0
H + c-C4H8-2
0.1
1.0
10
RATE CONSTANTS FOR THE CHEMICALLY ACTIVATED REACTIONS OF S-BUTYL RADICAL FROM H + CIS-BUTENE-2
Physical and Chemical Properties Division
1000/T0.96 0.98 1.00 1.02 1.04 1.06 1.08 1.10
log(
olef
ini/ Σ
olef
ini)
-2.0
-1.8
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
C2H4
C3H6
1-C4H8
1-C5H10
EXPERIMENTAL OLEFINIC BRANCHING RATIOS FROM 1-HEXYL RADICAL DECOMPOSITION
1-hexyl
2-hexyl 3-hexyl
C2H4 + 1-C4H9
C3H6 + 1-C3H7 1-C4H8 + C2H5
1-C5H10 + CH3
Physical and Chemical Properties Division
TEMPORAL BEHAVIOR OF HEXYL-2 RADICAL AND PRODUCTS FORMED FROM H+HEXENE-1 AT 800 K AND 1 BAR PRESSURE
Log [time, s]
-10 -8 -6 -4
Log
[bra
nchi
ng ra
tio]
-4
-3
-2
-1
0
-10 -8 -6 -4-4
-3
-2
-1
0
-10 -8 -6 -4-4
-3
-2
-1
02-hexyl
1-hexyl
3-hexyl
2-hexyl = propene+ propyl
2-hexyl = hexene-2 +H
1-hexyl = ethylene +butyl
3-hexyl = 1-butene + ethyl
3-hexyl = 1-pentene + methyl
Log [time, s]Log [time, s]Lo
g [b
ranc
hing
ratio
]
Log
[bra
nchi
ng ra
tio]
Physical and Chemical Properties Division
SUMMARY and CONCLUSIONS
Chemical activation reactions are very important components of combustion processes .
Can be treated in the context of unimolecular rate theory
Added complication in converting results to rate constants for combustion conditions is the necessity of considering three distinct processes:
stabilization, reaction from excited species and thermal processing
Theory must be considered in the interpretation of experimental data
Need for fundamental information on molecular properties of non-hydrocarbon (OXYGENATES} compounds and
transition states