Schlieren Visualization of Multicyclic Flame Acceleration Process in Valveless Pulsed Detonation Combustors

Abstract

Turbulent flame acceleration process has been studied in a two-dimensional valveless pulsed detonation combustor (PDC) using Schlieren flow visualization, ionization probes, and companion high-frequency pressure instrumentation. Experiments were conducted using near stoichiometric propane-air mixtures in a 76.2 mm × 76.2 mm, 1.68 m long modular detonation tube with the windowed combustor under multicyclic conditions within the PDC operating in a valveless mode. The effect of the presence of the obstacle was investigated at various stages of the flame acceleration process in aerodynamically confined environment. Amplification of the leading shock waves through the interaction of the obstacle enhances the flame acceleration process owing to the reduction of post-shock induction time and the hydrodynamic instabilities at the baroclinic interface. The internal configuration of the combustor including the obstacle plays a major role of the flame acceleration due to the shock amplification pattern. Sequences of schlieren images also show the flow drifting and blowdown processes confirming that the gasdynamic valves are successfully operative in the valveless PDC.

Keywords:

• Deflagration to detonation transition (ddt)
• Detonation
• Propane-air mixture
• Valveless pulsed detonation combustor (pdc)

This work was supported by a grant from the Indiana 21st Century Research and Technology Fund, and Rolls-Royce North America. We are grateful to Dr. Lynn Snyder at Rolls-Royce North American Technologies Inc. for his continuous support. We also thank senior engineer Scott Meyer, technician Rob McGuire and CAD operator Jerry Shepard at Purdue University Central Machine Shop for their helpful suggestions and assistance with the design, fabrication, and testing of the test articles.