Effects of pintle injector on ethylene-air rocket-based continuous rotating detonation

Abstract

Continuous Rotating Detonation (CRD) shares many similarities with the High-Frequency Tangential Instability (HFTI) in liquid rocket engine, and it may be one cause of the HFTI. To investigate the self-sustaining mechanism of CRD/HFTI, a pintle-like injection scheme is adopted in this paper, and series of ethylene-air tests have been conducted. The pintle injector effects on the CRD operation range have been analyzed firstly. By decreasing the diameter of pintle injector, the lean equivalence ratio boundary increases, and the primary combustion mode transfers from CRD to sawtooth-wave mode. By increasing the insertion length, the enlarging of the head recirculation zone is helpful for the realization of multi-CRD waves. Based on the high-frequency pressure results, the propagation characteristics of single-wave, two-waves and sawtooth-wave modes are detailed. Theoretical intrinsic frequencies of the hollow chamber have been calculated and compared with the test results. The single-wave and two-waves modes show good agreements with the first tangential and second tangential theoretical results, respectively, with the relative deviations within just 6%. But the frequency of sawtooth-wave mode is much less than the first tangential theoretical value, and the deviation reaches about 20%. Because the diameter of traditional rocket pintle injector is much smaller than that of combustor, CRD cannot be achieved due to the propellant deficiency around the outer combustor, leading to the depress of HFTI. This paper could improve the understanding of the self-sustaining mechanisms of CRD and HFTI.