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ISSN Печать: 2150-766X
ISSN Онлайн: 2150-7678
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ACTIVE DAMPING OF COMBUSTION INSTABILITIES WITH OSCILLATORY LIQUID FUEL SPRAYS
Краткое описание
This paper describes an experimental investigation that employed optical techniques to determine the characteristics of the combustion process in an actively controlled, liquid-fueled, unstable combustor when the ACS (Active Control System) was "on" and "off". The objective of the study was to determine the differences in the characteristics of the combustion process during stable and unstable operation, and the manner in which the ACS modified the combustion process to significantly reduce the amplitude of the instability. During active control, the ACS used a liquid fuel injector actuator to modulate the flow rate of the fuel into the combustor and an adaptive control approach to determine the optimal control signal phase. Initially, this study investigated the characteristics of the oscillations under different combustor operating conditions that produced stable and unstable operation without active control. This study showed that large amplitude instabilities occurred when the phase difference between the heat addition and pressure oscillations changed little along the combustion zone. In contrast, stable operation with very small amplitude pressure oscillations was attained when the above-mentioned phase gradually varied along the combustion region, thus dividing the combustion zone into regions that alternately damped and drove combustor oscillations. The effects of these driving/damping regions tended to counter one another, which resulted in significant damping of the unstable oscillations. Subsequent studies of the characteristics of the combustion process in an actively controlled combustor revealed that the ACS dramatically modified the characteristics of the combustion process. Specifically, it changed the nearly flat phase distribution observed under unstable operating conditions (in the absence of active control) to obtain a gradually varying phase distribution similar to that observed in stable combustors. The adaptive ACS apparently modulates the fuel injection rate with a phase delay that modifies the phase distribution to produce stable operating conditions