提高高马赫数超燃冲压发动机推力的理论方法

斜爆轰发动机和激波诱导燃烧冲压发动机在高马赫数吸气式发动机中具有重要应用前景,但是斜爆轰发动机是否具有足够大的净推力,还是一个未知的问题,因此需要对高马赫数冲压发动机的推进性能以及提高推力的方法进行理论研究.本文主要分为3部分.第1部分理论研究了超燃冲压发动机中的爆燃波和爆轰波的传播特性.保证发动机稳定燃烧是提高推力的...

THE THEORETICAL METHOD TO INCREASE THE THRUST OF HIGH MACH NUMBER SCRAMJETS

The oblique detonation engines and shock-induced combustion ramjets have been proved to be practicable for high flight Mach number air-breathing engines in recent years. However, whether the oblique detonation engines and shock-induced combustion ramjets have enough thrust or not is unknown yet. In this paper, the combustion characteristics and propulsive performance of scramjets are discussed theoretically. Firstly, the mechanism of engine unstart of scramjets is discussed from the point of view of shock/shock interaction and deflagration-to-detonation transition. The results show that engine unstart process is very similar to the deflagration-to-detonation transition process. In the combustor of scramjets, the maximum velocity of the deflagration wave is very close to the detonation velocity. Therefore, the C-J detonation velocity is defined as the stable operation boundary of scramjets. Secondly, the formula of thrust produced by the divergent nozzle is put forth and key parameters influencing thrust are obtained. According to the thrust formula, supersonic combustion is beneficial for increasing the thrust. The main way to increase the thrust is to increase the pressure of combustion products. The propulsive performance of scramjets is theoretically analyzed by using C-J detonation theory, which is the critical condition when the engine is thermally choked. Finally, the theoretical method to increase the thrust is discussed. For high flight Mach number scramjets Ma ≥ 12, the velocity in the isolator is much faster than the C-J detonation velocity in the combustor and the problem of engine unstart disappears. Therefore, extra fuel and oxidizer can be injected into the combustor to increase the thrust further as long as the shock wave generated by the high pressure combustion products is slower than the air velocity in the isolator. The theoretical results agree well with the existing experimental and numerical results, which can be used as a baseline for the development of high Mach number scramjets.