The Effect of Wall Heat Loss on the Flow Fields in a Pulse-Detonation Wave Engine

Abstract

The present study addresses the influence of convective heat losses on the flow field and performance of pulse detonation engines (PDE). We investigate the simplest PDE configuration of a straight detonation tube open at one end. The computations are carried out for stoichiometric hydrogen-oxygen, propane-oxygen and ethylene-oxygen mixtures at standard conditions using the method of characteristics for non-isentropic flows using a polytropic gas assumption. The thermodynamic foundation of this gas assumption is investigated. It is found that the model provides a very good approximation for an equilibrium flow. Previous heat flux measurements obtained immediately behind hydrogen-air and hydrogen-oxygen detonations are used to calibrate the assumed convective heat flux model. The calculations agree very well with experimental pressure and velocity profiles at various locations in the tube. The integrated impulse is also found in very good agreement with existing experimental results. The present study clarifies the previous observations of specific impulse deficits with increasing tube length. It is shown that the non-dimensional tube length L / D, where D is tube diameter, governs the amount of losses, the rate of pressure decay at the thrust wall, and hence the performance of PDE’s. The present study reveals that approximately 20% specific impulse losses are expected in typical tube geometries of L / D = 50, the losses varying quasi-linearly with L / D. Computations for ethylene-oxygen using the same heat loss model but including the exact thermo-chemical properties of the detonation products enabled validation of the polytropic gas calculations. Moreover, these finite rate calculations permitted comparisons with experimental temperature measurements, where excellent agreement is found. NOMENCLATURE