eric r. boyd, ryan w. houim and kenneth k. kuo- experimental and numerical investigation into the...

8/3/2019 Eric R. Boyd, Ryan W. Houim and Kenneth K. Kuo- Experimental and Numerical Investigation into the Ignition and Combustion of Aluminum Particles with TBX Applications

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Experimental and Numerical Investigation

into the Ignition and Combustion of

Aluminum Particles with TBX Applications

Eric R. Boyd, Ryan W. Houim, Dr. Kenneth K. Kuo

April 28, 2009

The Department of Mechanical and Nuclear Engineering

The Pennsylvania State University

University Park, PA 16802


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Acknowledgements

We would like to express our thanks to Jon Fox and Jan Mahar

for the support and administering the DTRA-SRAP program

under Contract No. DTRA01-03-D-001-0006.

We would also like to thank Prof. Alon Gany and Dr. Valery

Rosenband of Technion of Israel for supplying the Nickel coated

Al particles for a part of this investigation.


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Some Important Questions to be Answered

To what extent does the Ni-coating improve the ignition properties

of two different sizes of aluminum particles?

By varying the diluent flow rate of the multi-diffusion flat-flame burner, the

equilibrium flame temperature can be reduced to lower levels for determiningthe particles ignition behavior.

What are the effects of CO2, H2O, and O2 as oxidizing chemical

species to the Ni-coated Al particles?

By adjusting the flow rates of the fuels (mixtures of H2 and CO) and the

oxidizer (O2), systematic variation of product species can be achieved for

studying the strength of the oxidizers and their effect on the ignition and

combustion of the Ni-coated Al particles.

Does the Ni-coating inhibit any favorable combustion

characteristics of Al particles?

By comparing the combustion times of the Ni-coated and uncoated Al particles.


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Four batches of particles: Davg = 9 m and 32 m (two batches

with a 5-wt% coating of nickel) were tested.

SEM images show that the aluminum particles vary in shape andare covered with nano-sized Ni particles.

Not all of the particle were coated completely with some bare

spots apparent.

Ni-Coated Al Particle Results

5m

5 m

10m

10 m


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Experimental Apparatus for Single

Particle Ignition and Combustion Study

Particles ignite and combust inhot post-combustion zone of

the flat-flame burner. Current burner fuel mixture

contains both H2 and/or CO.

Burner oxidizer is O2.

N2 is used as a diluent.

The particles are injected usinga fluidized bed feeder.

Quartz tube is utilized toprevent entrainment andcontamination of the mixturein the post-flame zone from

the ambient air.

Particle

Breakup Jet

Particle

Entrainment

Gas

COH2N2 N2

Oxidizing

Mixture

Energetic Particle Flat-Flame

Multi-

Diffusion

Flat-Flame

Burner

Fluidized

Bed

Feeder

Fuel Mixture

COH2O2N2N2

Purge

Quartz Tube

Streak of

Ignited Particle


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Diagnostic System for Particle Burn

Time and Temperature Measurements

Ignition Temperature were measuredwith a go or no go criteria. N2diluent levels were increased until

particles can no longer be ignited. Thecorresponding equilibrium flametemperature was considered to be theignition temperature threshold.

Photo-multiplier tube is used inconjunction with a cylindrical lens tocollect data along the centerline for

deducing the burning time durations (tb)

Video images are taken as well forparticles that stretch past the viewing

range of the PMT (~5 cm above burnersurface).

PMT

Gain Control

InstruNet DAQ

Cylindrical

LensBurner

t

I

Camera for Streak

Imaging


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Measured Combustion Times of

9-m Particles

0

0.5

1

1.5

2

2.5

3

0 0.2 0.4 0.6 0.8 1 1.2

Equivalence Ratio ()

BurningTime,tb(ms)

Ni-Coated 100% H2 Fuel Ni Coated 50% H2 / 50% CO Ni-Coated 5% H2 / 95% CO

Bare Al 100% H2 Bare Al 50% H2 / 50% CO Bare Al 5% H2 / 95% CO

tb for DP < 5 m

tb for DP = 25 m

Data points lie almost

on top of one another.

Almost no distinction

in tbbetween the

coated and the

uncoated particles can

be established.

Trends cannot be

formed because of the

large amount of data

scatter due to theparticle size

distribution.


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Measured Combustion Times of

32-m particles

0

1

2

3

4

5

6

7

8

0 0.2 0.4 0.6 0.8 1 1.2Equivalence Ratio, ()

Burning

time,

tb(ms)

Ni-Coated 100% H2 Ni-Coated 50% H2 / 50% CO Ni-Coated 5% H2 / 95% CO

Bare Al 100 % H2 Bare Al 50% H2 / 50% CO Bare Al 5% H2 / 95% CO

tb for DP = 60 m

tb

for DP

= 4m

Data points lie almost on top of one another again. Indicating that the coating

does not affect the combustion behavior of the larger particles either.


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Comparison of tb(Dparticle) to other works

Correlation developed in

Becksteads (2005)

Summary of Aluminum

Combustion

Measured burning time for

32-m particles matches

well with correlated data.

Measured burning times

of 9-m particle are

longer due to importanceof chemical kinetics for

smaller sized particles.

Current Study


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Consideration of

Effective Oxidizer Mole Fraction In Becksteads summary of aluminum combustion, he stated

that the large variation in data was due to the relative strength of

different oxidizer species.

By correlating the data he found that O2 was the most effective

aluminum oxidizer, H2O was about half as effective, and CO2was about one fifth as effective.

Therefore, he developed the follow effective oxidizer mole

fraction:

2 2 2,0.5 0.22OX eff O H O COX X X X + +


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Correlated Ignition Temperature Data for

the 9-m sized Al Particles

0

500

1000

1500

2000

2500

3000

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Effective Oxidizer Coefficient, XOX,eff

IgitionTempe

rature,

Tign

(K)

Nickel-Coated

Un-coated

( )2 2 2

-0.266

953 0.5 0.22ign O H O CO

T X X X + +

( )2 2 2

-0.313

1078 0.5 0.22ign O H O COT X X X + +


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Correlated Ignition Temperature Data for

the 32-m sized Al Particles

0

500

1000

1500

2000

2500

3000

0 0.1 0.2 0.3 0.4 0.5 0.6

Effective Oxidizer Concentration, XOX,eff

IgnitionTemperture,

Tign

(K)

Nickel-Coated

Un-coated( )

2 2 2

-0.104

1868 0.5 0.22ign O H O COT X X X + +

( )2 2 2

-0.190

969 0.5 0.22ign O H O COT X X X + +


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Reasons for Lower Tign of

Ni-Coated Aluminum Particles

Based upon measurements, Ni-coated aluminum particles have

demonstrated lower ignition temperatures in comparison with bare

aluminum particles.

The intermetallic reactions between the Ni and Al release heat to heat the

particle near the Ni-Al interface.

This additional heat then causes the NixAly compounds to melt whichallows oxygen to diffuse to the interface.

The oxidizer species can attack the Al particle surface to release

significant amount of heat causing higher heterogeneous reaction rates atthe Al interface leading to chain reaction that causes full ignition.


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Conclusions from

Experimental Investigation1. Ni-coating on the aluminum particle surfaces made it possible for an ignition temperature

drop of ~750 K on average for the larger (32 m) particles. The smaller (9 m) particles

did not experience such a significant drop, but there was still a notable reduction in ignition

temperature of ~300 K.

2. Both sizes of the Ni-coated aluminum ignited and burned at temperatures as low as ~1100

K. The disparity is because the 9-m uncoated aluminum particle ignited at a lower

temperatures than the 32-m aluminum particles.

3. The mean combustion times for the coated and uncoated particles were almost identical.

4. The measured tb match reasonably well with previously reported data from other

experiments that tested aluminum particles of similar sizes.

5. The considerable data scatter for tb can be attributed to the relatively large particle size

variations. The primary controlling factor for aluminum particle combustion times is the

size of the particles. A broad size distribution of particle sizes can result in a large

variations in measured combustion times.


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Need for a Detailed Model ofAluminum Particle Combustion

Numerical simulation is the only effective method toexamine the combustion behavior of transitional Alparticles (Dp from about 1m to 20m) in detail.

Particles are simply too small to be observed indetail in practical experimental conditions

Modern numerical methods allow the gas-liquidinterface jumps to be accurately calculated,without the use of engineering correlations.

There is a lack of understanding how shock wavesinteract with reacting droplets and particles.

Fundamental understanding of shocked dropletignition and combustion would be a great benefitto the development of advanced thermobaricexplosives (TBX) as well as safety considerations.

Using modern surface capturing methods, effects ofshape change and particle breakup phenomena can besimulated directly

A detailed understanding of the physicochemicalprocesses on the combustion of transitional Alparticles and flakes can be achievable.

10m

SEM image

of a

Silberline

PC-8602Xaluminum

flake.

5 s

Calculation of a reacting Al flake.

N i l St d


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Numerical Study

Method of Approach (1/2)

The numerical schemes for treating the interface between different phases willbe treated using techniques based on the Level Set and Sharp Interface Methods.

Level Set method captures the location of the interface

The Sharp Interface Method imposes the jump conditions at the interface.

Chemistry is integrated using an operator-split approach by the freely availableCantera library (Developed by Dr. Dave Goodwin of CalTech)

The advection and diffusion operators are evolved separately from chemical

source terms This allows the choice of different solvers for fluid dynamics and chemistry,which typically have far different time scales.

Transport and thermodynamic properties are calculated using routines from

Cantera Mass diffusion can be changed from either mixture averaged formulation

with a correction velocity for mass conservation equation or multi-component system with thermal diffusion.

N i l St d


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Above: Numericalsolution of theRiemann problemsusing high-order

schemes.

Left: Numericalsolution of the DoublyPeriodic Vortex test

with AMR provided byParaMESH.

High-order numericalWeighted Essentially Non-Oscillatory (WENO)

schemes are used tocalculate the inviscidfluxes.

Adaptive mesh refinement(AMR) capability usingthe ParaMESH library(Peter MacNeice at DrexelUniv.) Increase computational

efficiency by placing thefinest cells only where theyare needed.

Numerical Study

Method of Approach (2/2)


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Benefits of the Modeling Approach

Treatment of multi-phase reacting fluid flows with phase change while avoidingthe use of empirical correlations

The level set method is applicable to any particle morphology

Spherical particles, oblong particles, and flake-shaped particles can besimulated by simply changing the initial conditions of the level set equation

Development of a highly valuable predictive tool that can facilitate bothfundamental understanding and engineering correlations in situations wheredetailed experimentation is difficult, expensive, or even impossible.

The developed model can be utilized to systematically vary

Particle geometry (size and shape),

Ambient environment (mixture of gaseous species, temperature, etc.),

Blast wave strength.

The proposed model and numerical scheme could be extended to calculate

detailed surface phenomena for many different types of multi-fluid flows. Theend product can be applied to non-traditional interfaces.

Some caveats are that a model of the surface phenomenon and equation ofstate are needed for the non-traditional material and the continuumassumption must be valid.


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Future Work

Future areas of interest for experimental investigation include:

Test the particles under rapid heating, high-pressure environments like

those that would be seen in a TBX blast

Test particles in complex shock wave environments to see how the

introduction of shock waves affects the particle ignition and

combustion.

Testing the particles as a propellant additive and in rocket motorenvironments would give additional useful information.

Future areas of interest for modeling investigation include: Implementing the level set method for compressible multi-fluid flows

Developing robust and accurate methods to calculate the effects of

phase change at the droplet/particle interface.


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Thank you very much for your attention

Any Questions?


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Additional Slides Follow


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Explanation for Large Variation of Al

Particle Burning Times

Particle size distribution for a mean size of 9 m and a standard deviation of 16 m.

Particle size distribution for a mean size of 32 m and a standard deviation of 29 m.

Using one std.

size deviation

above andbelow mean

size, burning

time bounds can

be found. Referring back

to the burning

time plots thecollected data

fits within the

bounds.


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Introduction

Aluminum releases a large amountof energy when combusted inoxygen environment. Thisincreases the total energy content

of aluminized energetic materialsand hence increases explosiveyield or propulsive thrust.

Al particles are very difficult to ignite,often requiring the removal of itsprotective oxide layer by melting at2327 K or mechanical cracking.

Different geometries (such asflakes) may alter the stresses on the

particle and aid ignition Apply coatings to the aluminumparticles

o Protective coatings with alower melting temperature

o Reactive coatings to initiate

particle ignition.

0

20

40

60

80

100

120

140

Aluminum(A

l)

Boron(B

)

Beryllium(Be)

Carbon(C

)

Iron(Fe)

Lithium(L

i)

Magnesium(Mg

)

Silicon(S

i)

Titanium(T

i)

Tungsten(W

)

Zirconium(Z

r)

HTP

B

Gravimetric Heat of Oxidation [kJ/gmfuel

]

Volumetric Heat of Oxidation [kJ/cm3

fuel]


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Motivation

Al particle are used in thermobaric weapons as a fuel additive to

fuel the destructive fireball and the resulting blast wave.

The detonation event that is necessary to ignite these particles is

very fast leaving a brief period for that particle ignition delay.

This could lead to a large number of particle being unburned

and adding nothing to the blast event.

There are many other application such as rocket motors or other

propellants that would benefit from a reduced particle ignition

temperature and shortened ignition delay.


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Nickel Aluminum Combustion

Several studies have been conducted showing a substantially lower

ignition temperature and ignition in inert atmospheres.

Andrzejak et. al. (2006) burned 2.5 mm particles coated with different

wt% of Ni. Ignition was characterized as low as ~1600 K in Ar and CO2atmospheres.

Rosenband et. al. (2007) placed bulk samples of 30m Al and Ni-Coated

Al on an electrically heated metal strip in air and noted ignition at ~1350

K of the Ni-coated Al particles and no ignition of the bare Al particles. Yagodnikov et. al. (1997) completed a study on the effect of a nickel

encapsulation on flame propagation in an aluminum particle aerosol.

They found that Al particles encapsulated with nickel had flame

propagation rates 1.5-4 times higher. Bocanegra et. al. (2007) carried out a study on coated and uncoated Al

particles using laser heating. They found that, particle ignited at reduced

temperatures even without a homogenous Ni coating.

M l i Diff i


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Multi-Diffusion

Flat Flame Burner

QuartzTube

CylindricalLens

Camera

PMTAssembly

BurnerSurface


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Prevention of Agglomerate Ignition

In order to study the single

particle ignition behavior, it

is important to avoidparticle agglomeration.

Glass beads sized 250 m

and 2 mm were placed in a

fluidized bed along with a

mesh screen to prevent

agglomerations fromentering the flow stream.

Streamlines

Large GlassBeads(dia.=2mm)

Aluminum Particles

Diffuser

Gas Outlet

Converging Nozzle

GasInlet

400 Mesh Filter

Small GlassBeads(dia.=250m)

T i l PMT i i f i l


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Typical PMT intensity traces for a singleintensely burning Al particle

Burning time is assumed to be when light intensity is collected until whenlight intensity drops off below noise levels.

0.7 ms

1.375 ms


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Burning Particle Streak

Burning streak length was

considered to begin when the light

was emitted until when light was

no long emitted

The particles are completing

combustion and potentially

continuing to radiate light. Visible particles are in fact burning

though. Al2O3particles were run

through the burner at ~2500 K and no

particles were visible.

This is a potential source of error in

the burn time analysis

Beginning of

Burning Time

End ofBurning Time


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CHEMKIN Simulation

Input the surface wall conditions in conjunction with input flow

rate into the CHEMKIN simulation

Output the flow field temperature profiles and velocity profiles

Burning times are found by dividing the recorded streak lengthby the gas velocity (particle velocity)

PSR

Oxidizer Inlet

Fuel Inlet

Quartz Tube

Equilibrium Products

Simulation Output

streakb

gas

Lt

u

=


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Instrumented Quartz Tube

25 m S-typeThermocouples

Flame

CeramicInsulation

SquareCopper SheetAttached toQuartz Wall

QuartzTube

The quartz tube for shielding the

combustion product gases has been

instrumented with five 25 m S-typethermocouples.

The purpose for these measurements is to

track the heat loss from the burner.

The temperatures are measured at 4locations on the outer wall of the quartz

tube and 1 along the centerline on the exit

plane of the quartz tube.

The heat loss rate is used as a boundary

condition that is needed as an input to the

CHEMKIN simulation.


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Velocity Results

Particles typically ignited and

completely combusted within 10

cm. Typical velocities were on

the order of 100 cm/s

The centerline velocity increases

due to the developing flow with

the cylindrical tube.

Temperature flow field

simulations were also run to

validate the model. Measuretemperatures were typically with

~100 K of the calculated

temperature.

Exit Planeof QuartzTube

Radius (cm)


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Ignition Temperature Test Matrix

Equivalence Ratio ()Composition ofFuel

0.25 0.5 1.0 1.5

H2=100% CO=0% Test 1 Test 2 Test 3 Test 4

H2=75% CO=25% Test 5 Test 6 Test 7 Test 8

H2=50% CO=50% Test 9 Test 10 - -

H2=40% CO=60% - - Test 11 Test 12

H2=25% CO=75% Test 13 Test 14 Test 15 Test 16H2=5% CO=95% Test 17 Test 18 Test 19 Test 20

Test conditions were selected to fully vary the product specie

levels of O2, H2O, and CO2by adjusting the fuel ratio andoxidizer content.

100% CO condition could not be studied because the OH radical

is necessary to create a stable flame in CO+O2

reaction.


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Combustion Time Test Matrix

Reduced in size to save in material costs and additional tests were not

necessary.

Captures the results that were necessary to see if the Ni-coating hadany effect on the Al combustion.

Equivalence RatioComposition of inFuel

0.25 0.5 1

H2=100% CO=0% Test 1 Test 2 Test 3

H2=50% CO=50% Test 4 Test 5 -

H2=40% CO=60% - - Test 6

H2=5% CO=95% Test 7 Test 8 Test 9


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Test Matrix

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0 10 20 30 40 50 60 70 80 90 100

Percent of Hydrogen in Fuel Mixture

Prod

uctMoleFraction

95% CO / 5%

H2 Fuel Mixture

75% CO / 25%

H2 Fuel Mixture

50% CO / 50%

H2 Fuel Mixture

25% CO / 75% H2Fuel Mixture

0% CO / 100%

H2 Fuel Mixture

Conditions were selected so that varying ratios of O2, H2O, and CO2were created in the product stream.

0.25=

CO2

H2O

O2


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9 m uncoated particle uncertainty

1000

1200

1400

1600

1800

2000

2200

2400

2600

1000 1200 1400 1600 1800 2000 2200 2400 2600

Correlated Ignition Temperature, Tign=1078(XOX,eff)-0.313

(K)

MeasuredIgnition

Temperature,

Tign

(K)

Ignition Temperature Correlation,Tign=1078(XOX,eff)

-0.313

Measured DataPoints

+10% Certainty Limit

-10% Certainty Limit


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9 m Ni-coated particle uncertainty

1000

1200

1400

1600

1800

2000

2200

2400

2600

1000 1200 1400 1600 1800 2000 2200 2400 2600

Correlated Ignition Temperature Tign=953(XOX,eff)

-0.266

(K)

MeasuredIgnition

Tempearature,

Tign

(K)


-0.266

Measured Data Points




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32 m uncoated particle uncertainty

1000

1200

1400

1600

1800

2000

2200

2400

2600

1000 1200 1400 1600 1800 2000 2200 2400 2600

Correlated Ignition Temperature, Tign=1869(XOX,eff)-0.104 (K)

MeasuredIgnitionTemperature,

Tign

(K)


-0.104

Measured Data Points



Xox,eff > 1so the correlation isno longer physicallypossible

32 Ni d i l i


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32 m Ni-coated particle uncertainty

1000

1200

1400

1600

1800

2000

2200

2400

2600

1000 1200 1400 1600 1800 2000 2200 2400 2600

Correlated Ignition Temperature, Tign=969(XOX,eff)

-0.190

MeasuredIgnitionTempeartureTign

Ignition TemperatureCorrelation, Tign=969(XOX,eff)

-0.313

Measured DataPoints



T P fil


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Temperature Profile

Exit Planeof QuartzTube

Measured exit

temperature was

880 K and the

calculated exit

temperature was

940 K.

Ni Al Ph Di


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Ni-Al Phase Diagram

Applications of PSU Model for


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pp

TBX Applications

The model will zoom in ona single reactive particle.

The particle will be impacted

with a strong shock wave orcontact surface

The ignition andcombustion will becalculated directly fromfirst principles.

Modern interface capturingtechniques will allow the jumpconditions at the gas-liquidsurface to be calculated

accurately.

.

..

. ..

.

.

.

.

..

..

.

.

.

.

Overall domain of a TBXdetonation, that is calculated using

traditional multiphase methods.

Some possible zoomed indomains for PSU model

development

Fuel ParticlesPrimary Shock

Detonation Product Contact Surface

Fuel Particle

eric r. boyd, ryan w. houim and kenneth k. kuo- experimental and numerical investigation into the...

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