Detonation Interaction with Sharp and Diffuse Interfaces

Abstract

Detonation interaction with an interface was investigated, where the interface separated a combustible from an oxidizing mixture. The ethylene-oxygen combustible mixture had a fuel-rich composition to promote secondary combustion with the oxidizer in the turbulent mixing zone that resulted from the interaction. Both sharp and diffuse interfaces were studied. Diffuse interfaces were created by the formation of a gravity current using a sliding valve that initially separated the test gas and combustible mixture. Opening the valve allowed a gravity current to develop before the detonation was initiated. By varying the delay between opening the valve and initiating the detonation it was possible to achieve a wide range of interface conditions. Sharp interfaces were created by using a nitro-cellulose membrane to separate the two mixtures. The membrane was destroyed by the detonation wave. The interface orientation and thickness with respect to the detonation wave have a profound effect on the outcome of the interaction. Diffuse interfaces result in curved detonation waves with a transmitted shock and following turbulent mixing zone. Sharp interfaces result in an interaction occurring at a node point similar to regular shock refraction (Henderson, 1989). The impulse was measured to quantify the degree of secondary combustion accounting for 5-6% of the total impulse. A model was developed that estimated the volume expansion of a fluid element due to combustion in the turbulent mixing zone (Dimotakis, 1991) to predict the impulse in the limit of infinite Damkohler number.