This work was funded by the National Aeronautics and Space Administration underagreement numbers NNX15AV05A and NNX15AU96A, by the the US Air Force Office ofScientific Research under grant number FA9550-14-1-0235, and by the US FederalAviation Administration (FAA) Office of Environment and Energy, ASCENT Projects 25 and26 under FAA Award Numbers: 13-C-AJFE-SU-008 and 13-C-AJFE-SU-006. Any opinions,findings, and conclusions or recommendations expressed in this material are those ofthe authors and do not necessarily reflect the views of the FAA or other ASCENTSponsors.

ASCENT Projects 25, 26, 28a

Chemical Kinetics Working Group: Experiments, Modeling, Model Reduction

Project managers: Cecilia Shaw, FAA, Jeff Moder, NASALead investigators: Ron Hanson, Hai Wang (Stanford

University), Tiangfeng Lu (UCONN), Wenting Sun (Georgia Tech), Steve Zeppieri (UTRC)

Staff/Students: David Davidson, Rui Xu, Chiara Saggese(Stanford), Ji-Woong Park, Yang Gao (UCONN)

April 3-4, 2018

Motivation and Objectives

Methods and Materials

Conclusions and Next Steps

Motivations

o Next gen of jet engines will operate at higherpressures for fuel efficiency improvement.

o Use of new alternative fuels in commercial aviationis hindered by the lack of quick and inexpensivefuel certification methods.

oModeling methods are needed that accuratelydescribe the behavior of real fuels in gas turbines

Objectives

o Experiments: Extend optical methods for nearsimultaneous, time dependent, quantitativemeasurements of multiple products duringpyrolysis towards closure on mass balance(~80%+)

oModel: Build a Hybrid Chemical model (HyChem)and document method and procedures

oModel Reduction: Develop reduced kinetic modelsfrom HyChem that can capture fuel sensitivitiesand create advanced tools for application to CFDsimulations and interrogate solutions to understandlimiting behavior

HyChem Approach

o The kinetic rate of the overall pyrolysis is fast ascompared to oxidation, and the distribution of thepyrolysis products dominants heat release rates.

o Jet fuel reaction kinetics (HyChem) are created bycombining an experimentally constrained, lumpedpyrolysis model with a foundational chemistrymodel for the oxidation process of decompositionproducts (e.g., USC Mech II).

Results – Experiments

o Experiment: We have demonstrated that data neededfor the development of a HyChem model for any Jet fuelcan be completed using shock tube measurements.Next step: Relate fuel pyrolysis yields to DCN, IDT andfuel composition.

o Model: The HyChem approach provides a direct pathtowards real, liquid fuel combustion chemistry modeling.Work has been documented in upcoming publication

o Model Reduction: CEMA is applied to LES-LBO case toidentify important species/reactions. Next step: CEMAwill be applied to near LBO condition when available.

ReferencesA Physics-based approach to modeling real-fuel combustion chemistry: I. Evidence from experiments, and thermodynamic, chemical kinetic and statistical considerations & - II. Reaction kinetic models of jet and rocket fuels,Hai Wang, Rui Xu, and co-workers. Combustion and Flame, in Press.

Results – Model

Comparisons shown previously. Documentation complete, manuscript submitted for publication

C2H4 CH4 C3H6 iC4H8 1C4H8 C6H6 C7H80

20

40

60

80

100

Perc

ent o

f T

ota

l C

arb

on

Flow Reactor

HyChem Model

Least Squares Fit

0.4% JP-8/Argon1310 K, 1.6 atm

Shock Tube Measurements

o Selected jet fuels were pyrolyzed at 1310K and 1.6atm behind reflected shock waves, and the time-histories of the decomposition products weremonitored at 8 infrared wavelengths using laserabsorption.

o Utilizing an extensive absorption cross-sectiondatabase developed under this program, speciesmole fractions of the dominant pyrolysis products(as predicted by the HyChem model) weredetermined from the absorption measurements byleast-squares fitting.

o These measured species mole fractions comparewell with earlier Flow Reactor/GC measurementsand account for 80+% of the fuel carbon.

Results - Model Reduction

• Only a small portion of explosive mixture the flame seems still strongly burning

• Important species/reactions to near-LBO flame will be further analyzed when available

* Region with T<1000K is truncated

𝑠𝑖𝑔𝑛𝜆𝑒×𝑙𝑜𝑔10 (

𝜆𝑒+1)

+6

-6

0

0.3

1.5

𝑇/1000(𝐾)0.9

2.1𝐳 = 𝟎. 𝟎𝟒𝟎𝟔𝟒𝒎

o CEMA of the LES-LBO (Cat-A2 with 𝜙𝑔 = 0.096 at 𝑡 = 18 𝑚𝑠 from GaTech)

Perfectly Stirred Reactor (PSR)

Residence time, s

T/1

00

0, K

Blue color: non-explosive mixture or strongly burning

Red color: explosive mixture or near-extinction state

Zero-crossing of 𝜆𝑒 can distinguish extinction state

𝑷𝑰 : the contribution of reaction to explosive mode

PSR-LBO is controlled by oxidation of small molecules

Chemical Explosive Mode Analysis (CEMA)o CEMA is a systematic approach to identify limit phenomena

(ignition, extinction) and other critical features (Lu et al., JFM 2010)

o CEMA can identify important species/reactions to extinction state

𝒚: species concentrations and temperature𝝎: chemical source / 𝒔: non-chemical source𝐉𝛚: Chemical Jacobian / 𝜆𝑒: eigenvalue 𝒂𝒆(𝒃𝒆): right (left) eigenvectorS: Stoich. coeff. matrix / R: net reaction rates vector⨂: element-wise multiplication

Re(λe) = Re 𝐛𝐞 ∙ 𝐉𝛚 ∙ 𝒂𝒆

𝑷𝑰 =(𝐛𝐞 ∙ 𝐒)⨂𝐑

sum( (𝐛𝐞 ∙ 𝐒)⨂𝐑 )

D𝐲

Dt= 𝐠 𝐲 = 𝛚 𝐲 + 𝐬 𝐲 , 𝐉𝛚 =

𝜕𝛚

𝜕𝐲,

Extinction𝐶𝑂 + 𝑂𝐻 = 𝐶𝑂2 + 𝐻

𝐻 + 𝑂2 +𝑀 = 𝐻𝑂2(+𝑀)

𝐻 + 𝑂2 = 𝑂 + 𝑂𝐻

𝐻𝐶𝑂 + 𝑂2 = 𝐶𝑂 +𝐻𝑂2

𝐻𝐶𝑂 +𝑀 = 𝐶𝑂 + 𝐻 +𝑀

𝑷𝑰 at PSR-LBO

Participation Index, PI

Stable upper branch(𝑅𝑒(𝜆𝑒) < 0)

Unstable middle branch(𝑅𝑒(𝜆𝑒) > 0)

𝑝 = 2.04𝑎𝑡𝑚𝑇 = 394 𝐾𝜙 = 0.457