Stability Characteristics of an Actively-valved Pulse Combustor

Abstract

This work describes the stability characteristics of an actively-valved pulse combustor through experimental methods. An ion probe detected the combustion events and a pressure sensor measured the pressure wave in the combustion chamber. By decreasing the injected fuel flow rate to approach near blow-out limit and fixing the value frequency to 270 Hz, the stability characteristics of the pulse combustor was studied systematically. The time and frequency domains of the ion and pressure data show that with decreased fuel flow rate, the ion and pressure signals amplitude decrease, time traces show some discontinuity, and low frequency oscillations appear. We then quantified the stability characteristics by introducing two indexes: the integrated power spectrum density (PSD) and PSD ratio. The indexes provide direct evidence showing that the low frequency oscillation governs the combustion dynamics when approaching blowout limit. The strong low frequency oscillation is treated as the symptom of the near blowout. The present study can be used to guide the operation of the pulse combustor and avoid low frequency oscillations.