Experimental Investigation of Detonation Re-initiation Mechanisms

following a Mach Reflection of a Quenched Detonation

Rohit R. Bhattacharjee

M.A.Sc candidate

Matei I. Radulescu Advisor

MCG seminar Date – November 9th, 2012

Introduction

• Detonation waves are supersonic combustion waves

– Compression waves (p1~=20p0)

– Supersonic (M~=6)

• Practical applications include

– Detonation arrestors

– Pulse detonation engines

• Fundamental theory on detonations

– Zel’dovich-von Neumann-Doering (ZND) Theory

Ideal (ZND) Detonation Wave

Real detonations

Mach Reflection

Forward jetting slipline

Kelvin-Helmholtz Instability

Richtmyer-Meshkov Instability

Propagation mechanism

• Real detonations are different from ideal model

– 3D, transient, unsteady, cellular

– Multiple shock structure

– K-H, R-M instabilities, forward jet

• What is the propagation mechanism?

– Adiabatic shock compression

– Turbulent mixing

• Mechanisms involved in the detonation cell evolution

Self-propagating detonation cell cycle

Self-propagating detonation cell cycle

Self-propagating detonation cell cycle

Self-propagating detonation cell cycle

Self-propagating detonation cell cycle

Detonation re-initiation

Decoupled incident

shock flame complex

Re-initiated Mach

shock

Stochastic behaviour

a b c

Experiment 1

Experiment 2

a b c

p0 = 3.5 kPa

CH4+2O2

p0 = 3.5 kPa

CH4+2O2

Diffraction around obstacles

Diffraction around obstacles

Diffraction around obstacles

Diffraction around obstacles

Diffraction around obstacles

Diffraction around obstacles

Diffraction around obstacles

Mach reflection behind

obstacle

Mach reflection in

planar detonation

Diffraction around obstacles

• Detonation diffraction around an obstacle

– Quenches detonation wave

– Forms a decoupled shock-flame complex

– Shock front reflects to form a Mach reflection

• Benefits of detonation diffracting around obstacles

– Improve temporal and spatial resolutions

– More reproducible

– Retain main features of cellular gas dynamics

• Adopt technique to study re-initiation mechanisms

Detonation diffraction and re-initiation – Past study example 1

Teodorczyk, A., J.H.S. Lee, and R. Knystautas. 1991. Prog. Astronaut. and Aeronaut. 133:223–240.

T. Obara, J. Sentanuhady, Y. Tsukada, S. Ohyagi, Reinitiation process of detonation wave behind a slit-plate,

Shock Waves 18 (2) (2008) 117–127.

Detonation diffraction and re-initiation – Past study example 2

Detonation diffraction and re-initiation – Past study example 3

M. I. Radulescu, B. M. Maxwell, The mechanism of detonation attenuation by a porous medium and its

subsequent re-initiation, Journal of Fluid Mechanics 667 (2011) 96–134.

Objective

• Past results have identified several ignition mechanisms

– Adiabatic shock compression behind Mach stem,

– Kelvin-Helmholtz instability along the slipline,

– Richtmyer-Meshkov instability along the flame,

– Rapid combustion behind transverse wave

– The strong forward jetting of slipline behind Mach stem

• However, the key re-ignition mechanisms leading to re-initiation have not yet been clarified

• Isolate re-ignition mechanisms that lead to re-initiation following a Mach reflection of a shock-flame complex

Experimental Setup

M. Drolet, Design of an experiment to study the instability of

detonation waves, undergraduate thesis, University of Ottawa,

Mechanical Engineering Department, 2008.

L. Maley, Shock reflections in reactive gases, undergraduate

thesis, University of Ottawa, Mechanical Engineering

Department, 2012.

Experimental Setup (cont’d)

Courtesy – Thanos Drivas

Inert shock reflections

Roughness induced ignition

t = t1 t = t1+90µsec t = t1+70µsec Courtesy – Logan Maley,

Kadeem Deniese

Roughness induced ignition

Mach reflection with self-ignition

Mach reflection with self-ignition

Mach reflection with self-ignition

Mach reflection with self-ignition

Detonation re-initiation

Detonation re-initiation

Detonation re-initiation

Detonation re-initiation

Detonation re-initiation

Conclusion

• Forward jetting behind the Mach stem was found to be an important mechanism in increasing combustion rates

• For sufficiently strong Mach stem, re-initiation first appears along the Mach stem

• Rapid ignition of the tongue of unburnt gas via turbulent mixing (shock ignition, KH instability) could lead to re-initiation of transverse wave

Acknowledgements