Comparison of thermodynamic efficiency and thrust characteristics of air-breathing jet engines with subsonic combustion and burning in stationary and nonstationary detonation waves

Abstract

Air-breathing jet engines (ABJE) with detonation combustion attract attention because of the widespread statements about a possible significant (by tens of percent) increase in their thrust characteristics in comparison with the ABJE with subsonic (“deflagration”) combustion, for example, with ramjet that perform combustion at constant pressure (in Brayton cycle). These statements are usually made on the basis of a comparison of the ideal thermal efficiency and the ideal specific thrusts and impulses calculated from such efficiency. In cases where the flow in the detonation chamber is nonstationary with shock waves, which appears from the reflection of the detonation wave from its narrowing (pre-nozzle) part, the determination of thrust characteristics by an ideal thermal efficiency that does not take into account the growth of entropy in unsteady shock waves overestimates the values of specific thrust and specific impulse. The validity of the aforementioned for multi-chamber pulsating detonation engines (PDE) confirmed the nonstationary calculations performed in this work. With the instant opening and closing of the valve at the entrance of the detonation chambers, the instantaneous initiation of the detonation wave, with the perfectly adjustable nozzle and shockless flow in its expanding part, the thrust characteristics of the PDE, starting from the small supersonic Mach numbers, are lower than the thrust characteristics of the RAMJET. Along with PDE, detonation engines with combustion in stationary detonation waves are considered.