Shock Tube Studies of RP Series Fuel Surrogates and RP Fuel Thermal Stability

Fuel Summit at USC, September, 15-17, 2009

R K H M E M D ld D F D idR. K. Hanson, M. E. MacDonald, D. F. DavidsonHigh Temperature Gasdynamics Laboratory

Mechanical Engineering DepartmentStanford University, Stanford CA

Background & Experimental Approach Fuel Stability Studies Fuel Stability Studies RP-Fuel Surrogate Studies

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This work sponsored by ERC, Inc. at the Air Force Research Laboratory, Edwards AFB, Matthew Billingsley, contract monitor.

Motivation: Improving High TemperatureThermal Stability of RP fuelsy

Future jet/rocket engine designs will likely i l hi h f l t t hinvolve higher fuel temperatures, however this may promote fuel decomposition and coking in fuel lines

To reduce fuel decomposition (and coking) improved understanding of the kinetics of jet fuels (and surrogates) are needed RP-1 RP fuels: RP-1/-2 (narrow distillation cut fuels) n-dodecane (single component RP-1 surrogate) Methylcyclohexane (2nd RP surrogate component) C12H26

Do existing thermal stability additives (i.e. hydrogen donors such as THQ) work at higher temperatures (i e above 800 K)?higher temperatures (i.e. above 800 K)?

1,2,3,4-Tetrahydroquinoline

2THQ

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Overview: Coke formation processes andfuel decompositionfuel decomposition

Different coke formation mechanisms at different T

Oxidation (T < 600 K) Oxidation (T < 600 K) Fuel reaction with trace impurities

Catalytic or Filament (650 K < T < 1750 K) Fuel reaction with heat exchanger walls Fuel reaction with heat exchanger walls Filamental carbon deposits on walls

Condensation or Dehydrogenation (T > 850 K) Fuel decomposition Fuel decomposition Amorphous particles formation in the flow Similar to sooting, formation of PAHs

This study addresses first step of high temperature coke formation: fuel decomposition and role of additives to slow this process

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RP Fuels Stability Studies Strategy:Measure decomposition rates with shock tubes/laser absorptionp / p

Pyrolysis via Reflected Shock Wave Heating:l ( h ) d l h k b conventional (gas phase) and aerosol shock tubes

Laser Absorption Diagnostics: 3.39 m mid-IR: Fuel concentration

10 57 m mid IR: ethylene alkenes 10.57 m mid-IR: ethylene, alkenes 650 nm visible: droplet extinction

Fuels & Additives: RP-1, RP-2, n-dodecane, MCH, THQRP 1, RP 2, n dodecane, MCH, THQ

(RP-1 Cetane No. = 38.6: high cyclo-alkane content)

Experimental Conditions: 1050-1300 K, 2-8 atm, 0.05-0.5% fuel/Argon

Measurement Targets: Fuel half-lives Species concentration time-histories: fuel, C2H4

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Experimental Setup: Aerosol shock tube (AST) with laser diagnostics

AST enables study of low-vapor-pressure fuels Load aerosols pre-shock

Full evaporation after incident shock Full evaporation after incident shock High T test conditions after reflected shock

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Example AST/Laser Absorption Experiment:RP-1 Pyrolysisy y

Three wavelengthsExcellent SNR

1.5

0.45% RP-1/Ar Excellent SNR

10.57 m: absorption by th l d th lk

1.0

rban

ce

0.45% RP 1/Ar1238K, 6.7 atm

10 57 m ethylene and other alkenes 3.39 m: absorption by fuel 650 nm: extinction by

0.5Abs

or

3.39 m

10.57 m

droplets

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0

0.0650 nm

Complete evaporation of RP-1 droplets behind incident shock wave

Time [ms]

Strong evidence of conversion of RP-1 fuel components to ethylene and higher alkenes

6

Example Half-Life Measurements:n-Dodecane Pyrolysisy y

Strong temperature d d f l

10000

10 57 m dependence to fuel decomposition rate as expected1000

us]

10.57 m 3.39 m

Close agreement between 10.57 m absorption (by ethylene) and 3.39 m: b i (b f l)

10

100

Hal

f-Life

[u

absorption (by fuel)

0.6 0.7 0.8 0.9 1.01

1000/T [1/K]

0.25% Dodecane/Ar7 atm

Direct comparison of RP fuels and surrogate half-life measurements

1000/T [1/K]

possible with and without thermal stablility additives

7

Comparison of Fuel Half-Life Measurements:RP-1, RP-2 and n-Dodecane Pyrolysis, y y

RP-1 and RP-2 have 10000

RP-1

similar pyrolysis half-lives

N d d h lf lif 3

1000

us]

RP-2n-Dodecane

N-dodecane half-life ~3x RP-fuel half life

10

100

Hal

f-Life

[

0 25% F l/A

0.6 0.7 0.8 0.9 1.01

1000/T [1/K]

0.25% Fuel/Ar7 atm

Measurements consistent with earlierdecomposition rate study (2008)

1000/T [1/K]

faster decomposition rate, shorter half-life

Thermal Stability Additives: Hydrogen donors - THQy g Q

THQ: proposed hydrogen + R• + R

•

Q p p y gdonor additive for high temperature fuel stabilization

+ R• + R

1,2,3,4-Tetrahydroquinoline

Fuel Stabilization Process: Simple H-abstraction from hydrogen donor (i.e. THQ) by Sequential hydrogen donation to alkyl hydrogen donor (i.e. THQ) by alkyl radicals (i.e. dodecyl C12H25•) should stabilize early fuel decomposition products

radicals by THQ (adapted from Yoon et al.)

fuel decomposition products and slow overall fuel decomposition rate

.

9

.

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Comparison of Fuel Half-Life Measurements:Effect of Thermal Stability Additive THQy Q

10000

10000

n-Dodecane

RP-1 + THQ N-Dodecane + THQ

1000

s]

RP-1RP-1 + 5% THQ

1000

s]

n Dodecane n-Dodecane + 5% THQ

10

100

Hal

f-Life

[us

10

100

Hal

f-Life

[us

0.6 0.7 0.8 0.9 1.01

100.25% Fuel/Ar7 atm

0.6 0.7 0.8 0.9 1.01

100.25% Dodecane/Ar7 atm

Preliminary measurement show evidence of THQ slowing RP-1 decomposition Stabilizing effect not seen in n-dodecane (down to 1100 K)

0.6 0.7 0.8 0.9 1.01000/T [1/K] 1000/T [1/K]

Stabilizing effect not seen in n dodecane (down to 1100 K) Yoon et al. (1996) sees effect with dodecane/10%THQ at 660-740K

RP Fuel Thermal Stability Studies: Statusy

Pyrolysis half-life measurements provide simple test of fuel stability Good agreement between ethylene formation

and fuel decomposition half livesand fuel decomposition half-lives

Pyrolysis half-lives measured for:RP 1 RP 2 n dodecane RP-1, RP-2, n-dodecane

RP-1 and n-dodecane + THQ

Further low temperature studies needed to Further low temperature studies needed to confirm effect of THQ addition

11

Multi-Component RP-Fuel Surrogates andComposition of Various Aviation Fuels

Higher fidelity simulation of kerosene-based fuels will require multi-component surrogatesq p g

JP-8″ th ″ i

JP-7″ th ″ i

RP-1″ th ″ i

RP-2″ h ″ i l• ″other″ is

aromatics/olefins (18/2 vol%)• 500 ppmtotal sulfur

• ″other″ is aromatics• 60 ppm total sulfur

• ″other″ is aromatics• 30 ppm totalsulfur (max)

• ″other″ is mostly aromatics• 0.1 ppmtotal sulfur (max)

12

Testing and Validation of RP-Fuel Surrogate Pyrolysis Mechanismsg y y

Problem:Problem: Intermediate temperature (600-1200K) pyrolysis mechanisms

needed to describe first steps of RP fuel decomposition

Stanford Strategy: Multi-species testing of single component RP-fuel surrogate:Multi species testing of single component RP fuel surrogate:

n-Dodecane Multi-species testing of possible second component of RP-fuel

surrogate: Methylcyclohexanesu ogate et y cyc o e a e Test JetSurF 1.1: possible RP-fuel surrogate mechanism for

pyrolysis

13

Testing and Development of a Single Component Surrogate for RP Series Fuels: N-Dodecane:g

N-Dodecane oxidation mechanisms are currently being validatedThi k f l i h i t This work focuses on pyrolysis chemistry

Multi-species laser absorption studies of n-dodecane pyrolysis :3.39 m (dodecane), 10.57 m (ethylene)

Dodecane (and ethylene) measurements provide test of overall fuel decomposition ratep

Ethylene measurements provide test of fuel decomposition branching ratios

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N-Dodecane Pyrolysis:Laser Absorption Time-Historiesp

High SNR measurementSt i ti f

400 ppm n-Dodecane/Ar, 2.4 atm

Strong variation of decomposition rate with temperatureR id l b ti t l

0.8

1.0

1159KAbs

orba

nce 1098K

Residual absorption at long time from product species (large alkenes)0.4

0.6

1235K1189K

1159K

ed 3

.39 m

A

0.0

0.2 Corrected

1235K

Nor

mal

ize

JetSurF 1.1ResidualAbsorption

JetSurF 1 1 model may slightly overpredict n-dodecane removal rate

0 500 1000 1500 2000

Time [s]

JetSurF 1.1 model may slightly overpredict n dodecane removal rate

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Ethylene Formation during N-Dodecane Pyrolysis: 10.57 m Laser Absorptiony y p

High signal/noise ratio t

400 ppm n-Dodecane/Ar, 2.4 atm2000

measurement Near constant ethylene

yield over 1250-1736K1500

1391K

ctio

n [

ppm

]

400 ppm N-Dodecane/Ar, 2.4 atm

yield over 1250 1736K temperature range:(2.980.05) C2H4 per C H molecule

10001288K

1252K

ne M

ole

Frac

C12H26 molecule

0 500 1000 1500 20000

500

Eth

yle

1736K

Direct comparison with JetSurF model predictions provides

0 500 1000 1500 2000Time [s]

Direct comparison with JetSurF model predictions provides check on branching ratios of decomposition pathways

16

Ethylene Formation during N-Dodecane Pyrolysis: Comparison with Modely y p

Constant ethylene yield (2 98 0 05) ith T

Experiment vs. JetSurF Mech.1500

(2.980.05) with T (1250-1736K)

JetSurF mechanism1000

500Mech. Yield =3.10x

on

[ppm

]

EthyleneExpt. Yield =2.97x

JetSurF mechanism predicts gradual rise in ethylene yield (3.1x-3.4x)

500

1000

Mol

e Fr

actio

1252 K 2 54 t Good agreement with

product formation time scales

500

Eth

ylen

e 1252 K, 2.54 atm430 ppm C12H26/ArJetSurF 1.1 (2009)Dodecane

Current n-dodecane decomposition rates and pathways (JetSurF)

scales0 500 1000 1500 2000

0

Time [s]

Current n dodecane decomposition rates and pathways (JetSurF) sufficiently accurate to predict major product (C2H4) formation rates

17

N-Dodecane Decomposition Channelsp

JetSurF mechanism ff ti l

1000 1052K 1212K

uses effectively constant branching ratios (1050-1250K) for 100

C3H7+C9H192C6H13te

[1/

s]

N-Dodecane = Products

( )C12H26 decomposition

J S F b hi i10

2C6H13C4H9+C8H17

C H +C H

posi

tion

Rat

JetSurF branching ratios consistent with current experiments1

C5H11+C7H15C2H5+C10H21D

ecom

CH3+C11H23 p

Next Steps: 1) investigate higher alkane/alkene product yields in C12H26

0.80 0.85 0.90 0.951

1000/T [1/K]

p ) g g / p y 12 26

2) Extend investigations to multi-component surrogates18

Conclusions and Future Work

Thermal Stability Studiesy Measurements of RP-1/RP-2 decomposition in AST Possible evidence of RP-1 thermal stabilization by THQ at high T Kinetic model needed for THQ chemistry Kinetic model needed for THQ chemistry

RP fuel surrogate pyrolysis mechanism developmentM lti i t di f d d l i Multi-species studies of n-dodecane pyrolysis

Initial multi-species studies of MCH pyrolysis Development/refinement of RP-fuel surrogate mechanism

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