NUMERICAL ANALYSIS OF HOT JET INJECTION AND PREMIXED FLAME PROPAGATION IN A CHANNEL Dhruv Baronia Graduate Research Assistant Department of Mechanical

NUMERICAL ANALYSIS OF HOT JET INJECTION NUMERICAL ANALYSIS OF HOT JET INJECTION AND PREMIXED FLAME PROPAGATION IN A AND PREMIXED FLAME PROPAGATION IN A

CHANNELCHANNEL

Dhruv BaroniaDhruv BaroniaGraduate Research AssistantGraduate Research Assistant

Department of Mechanical EngineeringDepartment of Mechanical EngineeringPurdue School of Engineering and Technology, IUPUIPurdue School of Engineering and Technology, IUPUI

Graphics: Rolls RoyceGraphics: Rolls Royce Source: ABBSource: ABB

Source: NASASource: NASA

Purdue School of Engineering and Technology, Indianapolis, IN

● Design of Experiment (DOE)

● Numerical Simulations Using Star-CD

OutlineOutline

●Single Channel Test Rig

● Conclusions and Recommendation

● Motivation


MotivationMotivation

High cost of experiments

Guide future experiments on Single Channel Rig for efficient data collection

Optimize wave rotor performance


IUPUI Single-Channel Internal Combustion Wave Rotor

Premixed

Chamber

Supersonic Injection Nozzle

Pyrex Window


Previous Experimental ResultsPrevious Experimental Results


Numerical Simulation in Single Channel Numerical Simulation in Single Channel Test Rig With Star-CDTest Rig With Star-CD

Star-CD is a commercial Computational Fluid Dynamics (CFD) code

It is a finite-volume solver and is selected because of relatively advanced modeling of transient and propagating combustion phenomena

It is a pressure-based solver hence it is not expected to capture shock waves sharply

Used extensively in IC engine and gas turbine combustion simulations


Combustion ModelingCombustion Modeling

Hundreds of elementary reactions

Simplified models to predict overall temperature, pressure and enthalpy changes

Reaction rates determined by both mixing and kinetics


Numerical Combustion ModelingNumerical Combustion Modeling

Computation Cellflame front

averaged thermodynamic, species and turbulence values

turbulent flame thickness ~ 0.3mm

burnedunburned

minimum cell size 0.5mm


Single Channel Test Rig Simulation: Single Channel Test Rig Simulation: Geometry And Grid For NumericalGeometry And Grid For Numerical

A 2D geometry is created to preserve the volume ratio to maintain realism of mass, energy and pressure history


Body fitted grid with refinement near the boundary and in the shear layer

Single Channel Test Rig Simulation: Single Channel Test Rig Simulation: Geometry And Grid For NumericalGeometry And Grid For Numerical


Initial ConditionsInitial ConditionsThermodynamic Properties and

Mass FractionTest Cell Prechamber

Equivalence Ratio (prior to burn) 1.34 1.5

Propane 0.079096 0.0219

Oxygen 0.214663 0.0

Carbon Dioxide 0.0 0.1759

Water Vapor 0.0 0.0957

Nitrogen 0.706241 0.6994

Pressure (abs, Pa) 1.0E05 8.4E05

Temperature (K) 298 1950

Turbulence Kinetic Energy (m2/s2) 0.0 0.0

Eddy Dissipation (m2/s3) 0.0 0.0


Combustion ModelsCombustion Models

One-step combustion reaction with combined (kinetic & turbulent) time scale model

Four-step combustion reaction [Glassman] based on pure kinetics

Four-step combustion reaction [Glassman] with hybrid reaction modeling


One-Step Reaction With Combined Time One-Step Reaction With Combined Time ScaleScale

Reaction time scale is a sum of turbulence time and kinetic time

Activation energy, pre-exponent factor, etc. are calculated by Westbrook and validated for laminar flames

Model will not predict ignition delay time


Baroclinic EffectBaroclinic Effect

grad p

Incident shock wave

ρ2 ρ1 ρ2 > ρ1

grad ρ

grad ρ

Interface

vorticity

I

II

III

Initial configuration

Vorticity generation

Deformation


Results for One-Step Reaction With Combined Results for One-Step Reaction With Combined TimeTime

Acceleration and stretching of the flame front on interaction with shock wave

Some amount of fuel/air mixture is left unburned at the left end of the channel


Comparison With Non-reacting CaseComparison With Non-reacting Case

Pressure wave moving ahead

Stretching of the flame front due to baroclinic effect

No Combustion

Combustion


Baroclinic Effect on Reacting and Non-Baroclinic Effect on Reacting and Non-Reacting CasesReacting Cases

Combustion No combustionexp(grad ρ)

exp(grad p)

Density gradient

Pressure gradient

combustion front

shock wave


Combustion EffectsCombustion Effects

higher mass injection in no combustion case


Four-Step Reaction Four-Step Reaction

OHOH

COOCO

HCOOHC

HHCHC

222

22

2242

24283

2

12

1

222

3

OHOH

COOCO

HCOOHC

HHCHC

222

22

2242

24283

2

12

1

222

3

OHOH

COOCO

HCOOHC

HHCHC

222

22

2242

24283

2

12

1

222

3

OHOH

COOCO

HCOOHC

HHCHC

222

22

2242

24283

2

12

1

222

3

Initiation

Propagation

Oxidation

Oxidation


Four Step ReactionFour Step Reaction

4444

3333

1222

1111

][][])[/exp(10][

)48.2exp(93.7][][])[/exp(10][

][][])[/exp(10][

][][])[/exp(10][

422242

223

83242242

42283183

cbax

cbax

cbax

cbax

HCOHRTEdt

Hd

OHOCORTEdt

COd

HCOHCRTEdt

HCd

HCOHCRTEdt

HCd

1 2 3 4

x 17.32 14.7 14.6 13.52

Ea/R (K) 24962 25164 20131 20634

a 0.5 0.9 1.0 0.85

b 1.07 1.18 0.25 1.42

c 0.4 -0.37 0.50 -0.56

Note: negative exponent


Validation of Four-Step ReactionValidation of Four-Step Reaction

Geometry: 5X5X5 cells with symmetry boundary on all sides

Initial Conditions: p=1 atm, T=1200 K, φ=1.34


ResultsResults

0

0.02

0.04

0.06

0.08

0.1

0.12

0 1 2 3 4 5 6 7 8

Time(ms)

Mas

s F

ract

ion

C3H8 C2H4 H2 CO CO2 H2O O2/3 Temperature/20000


ObservationsObservations

Ignition delay time of 6.2 ms which is in good agreement with experimental data

Dissociation of propane is endothermic

Oxidation of hydrogen takes place at all temperatures

All propane is dissociated in ethylene


ResultsResults

Geometry, BCs and ICs (expect for φ=1.34 in test cell) are similar to the previous one step reaction

Reflected shock wave initiates autoignition resulting in further compression waves to complete the combustion


Key IssuesKey Issues

One-step global reaction is too coarse assumption Four-step reaction (pure kinetics) is able to simulate low

temperature chemistry before ignition, which is purely based on kinetics

Four-step reaction (kinetics + turbulence mixing) includes the influence of turbulence and can model the

turbulent flame propagation after auto-ignition

These inferences call for a hybrid reaction model that can switch between pure kinetics and

combined time (kinetics + turbulence mixing)


Hybrid Reaction ModelHybrid Reaction Model

For (T < Tign) Use reaction rates (for all four reactions) based on kinetics

For (T > Tign) Reaction time scale is a sum of kinetic time scale and turbulent

mixing time scaletlc f

Where ‘ f ’ (0.0 < f < 1.0) is a delay constant that simulates the influence of turbulence on combustion after ignition [Kong]

632.0

1 ref

species reactive total

products ofamount r

The choice of Tign is arbitrary and some experimentation will be required


Hybrid Reaction Model: Initial ConditionsHybrid Reaction Model: Initial Conditions Hybrid model I : Tign=1200 K

Hybrid model II : Tign=1500 K Initial conditions inside the prechamber is calculated using mole balance and water

gas shift reaction

Thermodynamic Properties and Mass Fractions Test Cell Prechamber

Equivalence Ratio (prior to burn) 1.0 1.5

Propane 0.0624 0.0

Oxygen 0.219 0.0

Carbon Dioxide 0.0 0.0834

Water Vapor 0.0 0.0973

Nitrogen 0.7186 0.69965

Ethylene 0.0 1.0E-18

Hydrogen 0.0 0.00515

Carbon Monoxide 0.0 0.1145

Pressure (abs, Pa) 1.0E+05 8.4E+05

Initial Turbulence Kinetic Energy (m2/s2) 0.0 0.0


Propane Mass Fraction ContoursPropane Mass Fraction Contours

Tign = 1200 K Tign = 1500 K

Stretching of flame front


Temperature ContoursTemperature Contours

Tign = 1200 K Tign = 1500 K


Ethylene Mass Fraction ContoursEthylene Mass Fraction Contours

No oxygen in this region


Propane Consumption PlotsPropane Consumption Plots

0.00E+00

5.00E-08

1.00E-07

1.50E-07

2.00E-07

2.50E-07

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Time (ms)

Rat

e o

f p

rop

ane

con

sum

pti

on

(kg

/ms)

Tign = 1200K

Tign = 1500K

5.00E-07

5.50E-07

6.00E-07

6.50E-07

7.00E-07

7.50E-07

8.00E-07

8.50E-07

9.00E-07

9.50E-07

1.00E-06

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Time (ms)

Pro

pan

e M

ass

(kg

)

Tign = 1200K

Tign = 1500K


Hybrid Reaction Model: ResultsHybrid Reaction Model: Results

With the 1500K threshold temperature ignition occurs as soon as the hot gas jet mixes with cold gas whereas with 1200K threshold temperature it happens upon second compression by the reflected shock wave

Hybrid model II shows the stretching of the flame front due to baroclinic effect

In hybrid model II, the peak pressure inside the test channel is about 2 atmospheres higher and average pressure is about 1.5 atmospheres higher


Key IssuesKey Issues

Two model options predicted different combustion behavior

Effects of equivalence ratio and initial turbulence are not evaluated


Design of Experiment (DOE)Design of Experiment (DOE)

DOE is a statistical method to do the numerical experiments

DOE provides information about the interactions of parameters and shows how parameters affect the combustion model

Box Behnken Model: Individual and Combined effect of design parameters


DOE :Design and model parametersDOE :Design and model parameters

Design Parameter Low Value Mid Value High Value

Equivalence Ratio 1.0 1.17 1.34

Initial Turbulence Kinetic Energy (m2/s2) 0.0 1125 2250

Threshold Temperature (Tign , K) 1200 1350 1500


Propane Consumption PlotsPropane Consumption Plots

Different Ignition delay


DOE : ResultsDOE : Results


DOE: ResultsDOE: Results

t = 0.5ms

t = 1.0ms

t = 2.0ms


Conclusion and RecommendationsConclusion and Recommendations

Combustion regimes inside the channel is studied numerically using available combustion models

Hybrid model is proposed which was able to predict autoignition and subsequent turbulent flame propagation

Hybrid model was found to be more sensitive to model parameter Tign


Conclusion and RecommendationsConclusion and Recommendations

Hybrid model needs further development to be predictive of combustion effects

Suggested model parameter: entropy


PublicationsPublications

Akbari P., Baronia D., Nalim M. R., 2006, “Single-Tube Simulation of a Semi-Intermittent Pressure-Gain Combustor”, appears in ASME Turbo-Expo 2006, GT-2006_91061


AcknowledgementAcknowledgement

Department of Mechanical Engineering, IUPUI

Computer Network Center

CD-Adapco

Colleagues and friends


Thank you …Thank you …

Questions?Questions?

Documents

NUMERICAL ANALYSIS OF HOT JET INJECTION AND PREMIXED FLAME PROPAGATION IN A CHANNEL Dhruv Baronia Graduate Research Assistant Department of Mechanical