Characteristics of Dynamic Pressures in Liquid Rocket Thrust Chambers

Abstract

The objective of this paper is to characterize dynamic pressure traces measured at various experimental conditions of liquid rocket thrust chambers. Stability rating test and self-excited combustion instability results for subscale and full-scale thrust chambers show various aspects of dynamic behavior of the pressure field depending on combustion system hardware and operating conditions. External perturbations facilitated by a shock wave generated from an explosion of solid material are able to alter the stable combusting flow to an unstable one when it has lack of dynamic stability margin. The direct comparison of pressure traces for self-excited and perturbed high frequency instabilities suggests that coupling mechanisms behind these two cases are totally different from each other. Naturally occurring combustion instability seems to be first coupled with a low frequency wave that affects flame more vigorously with the smaller phase difference between heat release rate and acoustics than a high frequency wave. However, for the artificial perturbation, the combusting flow triggered by a shock wave becomes located at physical conditions irrelevant to those before the perturbation.