kinetic effects of blended n-alkane and aromatic fuel ...€¦ · kinetic coupling between toluene...
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Kinetic effects of blended n-alkane and aromatic fuel mixtures on the extinction limits of diffusion Flames
& A new dynamic multi time scale algorithm andA new dynamic multi-time scale algorithm and
path flux analysis method for mechanism reduction
Sang Hee Won, Wenting Sun, Xiaolong Gou, Yiguang Ju*
Department of Mechanical and Aerospace EngineeringPrinceton University
Sept.14-17, 2009
Introduction: Surrogate Fuel Model DevelopmentS th ti f l h t b d b bl di ith j t f l• Synthetic fuels have to be used by blending with jet fuel: – normal, branched, and cyclo alkanes, and aromatics
• MURI team selected surrogate jet fuel components• MURI team selected surrogate jet fuel components– n-decane, methyl-cyclohexane, n-propyl- and trimethyl- benzenes,
toluene…By matching H/C ratio, sooting index, burning rates, ignition time…
• Example: Gasoline Surrogate model (PRF+1)– Blending of toluene to n-heptane and iso-octane to match both
burning and soot formation targets• Challenge 1:• Challenge 1:
How does the kinetic coupling between aromatics and alkanesaffect burning rate and extinction limit? g
How can we predict burning limits, flame speeds from mixing rule?• Challenge 2: g
How to generate robust, efficient, & user friendly reduced kinetic models?
1. Experimental Studies of Kinetic Effects of Diffusion Flame Extinction Limits
(Fuel Vaporization and Counterflow Burner)
• Experimental setup of the measurements of n-decane/aromatics extinction limits– Using FTIR measurements to check thermal decomposition and
concentration variation: Concentration fluctuation < 1%concentration variation: Concentration fluctuation < 1%
Heater & insulation
Nitrogen
Heater & insulationHeater
Fuel
T1 T2
To burner
Schematics of evaporation system
Experimental Measurements of OH Concentration b i l i d d flby using laser induced fluorescence
• Nd:YAG Laser : Quanta-Ray (532 nm), Cobra-stretch dye laser• ICCD Camera : PIMAX-Gen II (Princeton Instrument)• PLIF: Q1(6) transition (282.93 nm), linear regime, beam height 80 mm
Quenching correction n decaneQuenching correction n‐decane
OH PLIF(a)
blended fuelOH
OH PLIF( )
blended fuelPAH
OH PLIF(b)
Schematic photo for Rayleigh scattering and PLIF PAH PLIF(c)
Extinction limits of toluene blended n-decane–air Mixtures
224n-decane80% n-decane & 20% toluene60% n-decane & 40% toluene/s
]
192
40% n-decane & 60% toluenetolueneJet-A, Ref [5]JP-8, Ref [5]ra
te [
1/
160
stra
in r
n-decane
128
nctio
n s n-decane
l
96Extin toluene
0.15 0.2 0.25 0.3 0.35
Fuel mass fraction YFF
Validation of n-decane-toluene mechanism: Extinction Limits
250
s]
n-decane (present)n-decane (Seshadri, 2007)
LIF tested condition
200e
a E[1
/s toluene (present)toluene (Seshadri, 2007)calculation (present)80% n-decane + 20% toluene60% n-decane + 40% toluene
150
rain
rate 60% n-decane + 40% toluene
40% n-decane +60% toluene
100ctio
n st
rEx
tinc
500.02 0.06 0.1 0.14
Fuel mole fraction Xf Chaos et al. 2005
Kinetic coupling between toluene fragment H abstraction reactions with chain-branching reactions
C6H5CH3+H<=>C6H5CH2+H2n-decane, Xf = 0.0580% n-decane + 20% toluene, Xf = 0.06
C6H5O+H(+M)<=>C6H5OH(+M)
C6H5CH2+H<=>C6H5CH360% n-decane + 40% toluene, Xf = 0.08toluene, Xf = 0.10
CH3+H(+M)=CH4(+M)
( ) ( )
HCO+M=H+CO+M
H+O2(+M)=HO2(+M)
H+O2=O+OH
CO+OH=CO2+H
-0.7 -0.5 -0.3 -0.1 0.1 0.3 0.5 0.7
Sensitivity of extinction strain rate
Kinetic coupling between toluene fragment H abstraction reactions with chain-branching reactions
1500
1800
1.00E-04
1.50E-04
]
60 % n-decane + 40 % toluene near extinction, Xf = 0.1, a = 176 1/s
1200
1500
5.00E-05 Tem
ole/
cm3 s
C6H5CH2+ H = C6H5CH3
900
-5.00E-05
0.00E+00
mperaturra
te [m
o
overall decomposition of n-decane
600-1.00E-04
5.00E 05 re [K]
actio
n r
C10H22=C2H5+C8H17 1
of n decane
overall decomposition of toluene
0
300
-2 00E-04
-1.50E-04Re
C10H22=C2H5+C8H17-1C10H22=nC3H7+C7H15-1C10H22=CH3+C9H19-1C6H5CH3+H<=>C6H5CH2+H2C6H5CH3+OH<=>C6H5CH2+H2OC6H5CH3+H<=>A1+CH3
0.1 mm
0-2.00E-040.85 0.9 0.95 1 1.05 1.1
Axial coordinate [cm]
Validation of Kinetic Mechanism (OH concentration)( )
2E-082
O
80% n-decane + 20% toluene,Xf = 0.07
1.8E-081.8O
H conc[a.u
.]
1.6E-081.6
centrationt
ensi
ty [
1.4E-081.4
on [mole/
OH
LIF
in
80% n-decane + 20% toluene,
1E 08
1.2E-08
1
1.2
/cm3]
O
n-decane, Xf = 0.05
,Xf = 0.06
1E-08150 100 150 200
Strain rate a [1/s] OH and HOver prediction of H abstraction?Over prediction of H abstraction?
Thermal and Kinetic effects on Extinction Limits
4E-081800 Ma]
Xf = 0.100.09
N2/n-decane4E-081800 M
a]
Toluene/n-decane
3E-08
1600
1700
ax. concentrure
T max
[K]
0.08
0.06
[OH]
3E-08
1600
1700
ax. concentrure
T max
[K]
[OH]
increasing toluene blending
1E-08
2E-08
1400
1500
ration [molex.
tem
pera
tu
[H]1E-08
2E-08
1400
1500
ration [molex.
tem
pera
tu
n-decane
[H]80% n-decane+ 20% toluene
extinction limit
01300
1400
2.5 3.5 4.5 5.5
e/cm3]M
ax
M h t l t / t i t [J/ 3]
n-decane
decreasing fuel mole fraction
extinction limit01300
1400
2.5 3.5 4.5 5.5
e/cm3]
Max
Ma heat release rate / strain rate [J/cm3]
toluene Xf = 0.1
[ ]+ 20% toluene60% n-decane+ 40% toluene 40% n-decane
+ 60% toluene
Max. heat release rate / strain rate [J/cm3] Max. heat release rate / strain rate [J/cm3]
Low dimensional correlation between strain rate and heat release200
1000
1200
Max
of rem3 s
] overall heat release rateheat release rate from CO + OH = CO2 + H
n-decane
150
800
000
x. heat reeaction ra
te [J
/cm
80% n-decane+ 20% toluene
60% n-decaneextinction
100600
elease raC
O + O
Helea
se r 60% n-decane
+ 40% toluene
40% n-decane+ 60% toluene
50
400
ate [J/cmH = C
O2.
heat
re
toluene
00
200
m3s]
+ H Max
.
0 100 200 300 400
Strain rate a [1/s]
50% h t l i l di tl i OH~50% heat release involves directly in OH
Linear Correlations between OH concentration and extinction limit
2E-08
cm3 ] near extinction
1.5E-08
[mol
e/c
n-decane
80% n-decane20% l
1E-08
trat
ion [OH] + 20% toluene
60% n-decane+ 40% toluene
40% n-decane+ 60% toluene
5E-09conc
ent
toluene+ 60% toluene
0
Max
. c
[H]
00 100 200 300 400
Extinction strain rate aE [1/s]
Linear correlation of extinction limits for toluene-n-decane mixtures
300
/s]
n-decane80% n-decane + 20% toluene60% n-decane + 40% toluene
250at
e a E
[1/
40% n-decance + 60% toluenetoluenelinear fit
R² = 9.703E-01200
stra
in ra
100
150
nctio
n s
50
100
Exti
500.001 0.0013 0.0016 0.0019 0.0022 0.0025
Xf ·(H/C ratio)2 / mean fuel molecular weight
Update of toluene kinetic mechanismp
500n-decane_exp.toluene exp.
400e
a E[1
/s] toluene_exp.
n-decane_num.updated toluene_num.previous toluene_num.
300
rain
rate
200
nctio
n st
r
0
100
Extin
00 0.05 0.1 0.15 0.2 0.25
Fuel mole fraction Xf
2. A Dynamic Multi-Time Scale (MTS) Method with2. A Dynamic Multi Time Scale (MTS) Method with Path Flux Analysis (PFA) for Mechanism Reduction
– Dynamic (Hybrid) Multi Timescale Method (MTS/HMTS) – A Path Flux Analysis (PFA) Method for Mechanism Reduction– Validations of MTS using ignition, steady/unsteady flames
Reduced mechanisms generated by existing approaches remainReduced mechanisms generated by existing approaches remain •Very large •Broad reaction timescale distributions and physical interests•Quasi steady assumption ILDM only apply to limited conditions•Quasi-steady assumption, ILDM only apply to limited conditions.
Can we develop a simple, rigorous, time accurate method?
Multi Timescale (MTS) Method
35
40
t = 0.1 ms
The Basic Idea of Multi-Time Scale Method: timescale changes!
25
30
35
spec
ies
t = 0.2 ms t = 0.3 ms
ΔtF
10
15
20
Num
ber o
f FastestGroup
Medial Groups
ΔtMk
t
kk eKY τ−
=
-1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -130
5
Log10
(characteristic time / s)
Groups
Sl tΔtS g
10( )Slowest
Group
0Ti
Δt1 2
Diagram of multi time scale scheme
ΔtF is the time step of the fastest group, ΔtM is the time step of the medial group and Δt is the time step of the slowest group
Time
group, and ΔtS is the time step of the slowest group
MTS to HMTSHybrid Multi Timescale (HMTS) Method
ΔtF = basetImplicit Euler Method
Fastest Group
Intermediate Groups
ΔtM
Fastest Groups
Intermediate Groups
ΔtM
base
E li it
Groups
ΔtS
Groups
ΔtS Explicit Euler Method
Slowest Group
0 t
ΔtSSlowest Group
0 t
ΔtS
0.06
ctio
n VODE MTSHMTS 1
0 Time tbase0 Time t
0.04m
ass
frac HMTS-1
HMTS-3 HMTS-5
0.02
C10
H22
m
0.0 0.1 0.2 0.30.00
C
Time /ms
Validation by homogeneous ignition
Ignition in
n-decane/air 121 species (M. Chaos, IJCK, 2007)
Ignition inhomogeneous
mixture
5 2 62.8temperature 2.0
) VODE
100
105
2.22.42.6
OH
tion
CO2
1000
K)
1.0
1.5
time
(ms) MTS
HMTS1atm
10-10
10-5
1 61.82.0
Mas
s fra
ct ODE MTSHMTS m
pera
ture
(
0 0
0.5
20atm
tion
dela
y 0 1 2 3 4 5
10-20
10-15
1.21.41.6
C10H22
M HMTS T
em0.5 0.6 0.7 0.8 0.9
-0.5
0.0
Igni
Temperature and species profiles
0 1 2 3 4 5Time (0.1 ms)
Ignition delay time for n decane air
1000/Initial temperature (1/K)
Temperature and species profiles Ignition delay time for n-decane-air
Computation efficiency: comparison with ODE solverp y p
Normalized by the computation time of ODE solver
1.5 ODE
1.5 ODE
1.0
ratio
MTS HMTS 1.0
ratio
MTS HMTS
0.5
CP
U ti
me
0.5
CP
U ti
me
0.5 0.6 0.7 0.8 0.90.0
C
0.5 0.6 0.7 0.8 0.90.0
1000/I iti l t t (1/K)C
1atm
1000/Initial temperature (1/K) 1000/Initial temperature (1/K)
20atm
7~10 times faster
Validation by propagation of unsteady spherical flamesy p p g y pDetailed Mechanism
Outwardly propagating spherical n-decane flames (ASURF-1D Princeton)
Flame front
Ignition pointIgnition point
Can we further reduce the computation time?
A Path Flux Analysis (PFA) Method forM h i R d ti
p
Mechanism Reduction
Reaction path, DRG & DRGEP
∑ δ 1 if the th elementary reactioni⎧
•Only direct relation;•r is not conservative;•Multi-path reaction?
AA
ABAB
Ii iiA
Ii BiiiAAB CP
CPv
vr
++
=≡∑∑
=
=
,1 ,
,1 ,
ω
δωDRG: ,
1 if the th elementary reaction involves speceis B0 otherwise
B i
iδ
⎧⎪= ⎨⎪⎩ A
)()(,1 , ABABIi BiiiA
AB CPCP
CP
vr −
=≡∑ =
δω CAB PAB
•Net reaction rate;
Mi
),max(),max( AAAAAB CPCPDRGEP:
)(max BMAMMpathsallAB ii
i
rrr ⋅≡
;•Consider strongest indirect path•Catalytic reactions? B
Path Flux Analysis Method• Both forward and backward
flfluxes• Both direct and indirect relations
r are conservativeM lti ti fl
A B
1pro st ABAB
Pr − = 1con st ABAB
Cr − =
• Multi-generation fluxes• Multi-reaction pathways
max( , )ABA A
rP C max( , )AB
A AP C
A M B
∑=− ×=
IiBMAMndpro
ABii
CPP
CPP
r,1
2 ])max()max(
[ ∑=− ×=
IiBMAMndcon
ABii
CPC
CPC
r,1
2 ])max()max(
[
ndconndprostconstpro 2211 −−−− +++
MMAA iiCPCP ),max(),max( MMAA ii
CPCP ),max(),max(
ndconAB
ndproAB
stconAB
stproABAB rrrrr 2211 +++=
22
Validation by n-decane homogeneous ignitionIgnition delay times Perfect Stirred Reactor
23
Skeletal mechanisms of different sizesComparison of PFA with DRG
0 01T0=1200 K
0.01
g (s)
detail DRG PFA
1E-3
τ ig
1 atm
50 60 70 80 90
1E-3
20
τ ig (s
)
50 60 70 80 901E-4
20 atm
Number of species in skeletal mechnism
24
Integration of HMTS & PFA : Comparison of ODE & HTMS
Outwardly propagating spherical n-decane/air flame
Reduced mechanism
Flame front
1.00
n decane air φ 1
Outwardly propagating spherical n decane/air flame Flame front
0.75
on (c
m) n-decane-air,φ=1
Reduced mechanism
0.50 t loc
atio
0.25
me
front
ODEHMTS
0 000 0 002 0 004 0 006 0 0080.00
Flam
HMTSIgnition point
0.000 0.002 0.004 0.006 0.008Time (s)
ConclusionKi ti li ff t t l th ti ti li it f bl d d lk d• Kinetic coupling affects strongly the extinction limits of blended alkane and aromatic fuel mixtures.
• Measurements of aromatic fuel fragments and OH concentration are important g pto develop validated kinetic mechanisms for blended fuel mixtures.
• The extinction limits of toluene blended n-decane mixtures are found linearly d d t th i OH t ti ti di l i ddependent on the maximum OH concentration, suggesting as a radical index.
• A simple linear correlation between extinction limits and fuel properties is obtained for n-decane/toluene blended fuel mixtures.obtained for n decane/toluene blended fuel mixtures.
• A new dynamic multi-timescale (MTS) model and a hybrid MTS model are developed. Both MTS and HMTS methods have excellent accuracy and i d i ffi i f i i i d fl i h d il d h iimproved computation efficiency for ignition and flames with detailed chemistry.
• A Path flux analysis (PFA) method is developed for mechanism reduction. The method has better model accuracy in a broad temperature and pressure ranges.method has better model accuracy in a broad temperature and pressure ranges.
• The integration of MTS/HMTS with PFA mechanism reduction can dramatically enhance the computation efficiency.
F t kFuture work:•Kinetic effects on extinction limits of n-decane/n-dodecanewith trymethylbenzene n propylbenzenewith trymethylbenzene, n-propylbenzene•Development of radical index to construct extinction correlation•Experimental data of flame speeds at elevated pressures •Reduced mechanism development using MTS/PFA for aromatic fuels
Thanks Dr. Tishkoff for the MURI research grantg
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