A STUDY OF THE OPERATING CHARACTERISTICS OF A HELMHOLTZ-TYPE PULSATING COMBUSTOR

Abstract

This paper describes the results of an experimental study of the spontaneous operating mechanism, the mixing process and the heat-release rate model in the Helmholtz-type pulsating combustor with a flapper valve. To investigate the operating response, the air intake rate and the moving velocity of the flame front were measured with various fuel-flow rates. The effects of the mixing time and flame-length on the pulsating operation were observed with four tried fuel nozzles and with stabilisers of two sizes. And the positive-ion current measurement technique was adopted to suggest the space- and time-resolved heat-release rate model. The operating frequency and the moving velocity of the flame front have a linear variation with the actual fuel-consumption rate. The fuel consumed during a cycle and the flame propagating length become constant in a given pulsating burner system. And the fuel nozzle geometry is proved to be an important design parameter for stable ignition and flame stabilisation, which arise from the mixing of the cold reactants and the residual flame. The result of the Rayleigh stability criterion shows that, in spite of stable operation, there is a locally unstable region upstream of the combustion chamber; this is caused by the initial active reaction including the ignition at negative gauge pressure.