INSTABILITIES OF SUPERSONIC COMBUSTION AT PLASMA-BASED FLAMEHOLDING

Abstract

Two types of supersonic combustion instabilities identi¦ed in a M = 2 reacting §ow at direct injection of gaseous hydrocarbon fuel and Quasi-DC plasma assistance are considered: a dynamic (global) instability triggered by a mechanism of §ow combustion plasma coupling and a fast instability of a thermoacoustic nature. The experiments were performed at SBR-50 supersonic combustion facility at variable conditions: pressure P0 = 1 4 bar; temperature T0 = 300 750 K; and fuel mass §ow rate ‘m = 1 8.5 g/s. Diagnostics included pressure measurements, ¦ltered fast camera imaging, schlieren visualization, and spectroscopic observations. The dynamic instability develops with a characteristic time of about 10 ms and is related to the interaction of the combustion-based separation zone with the re§ected shock wave and electric discharge. It is shown that this instability could be e¨ectively controlled by electrical discharge power. The thermoacoustic instability is developed with a characteristic time < 1 ms. The analysis of pressure data reveals a resonant acoustic wave presence in the combustion zone between fuel injection ports and the test section di¨user.