调控燃烧室燃料初始分布建立稳定旋转爆轰波的方法

旋转爆轰发动机具有比传统航空航天发动机更高的燃烧效率,近年来引起人们的关注。其中,点火启动过程尤为重要。为达到一次点火就能在燃烧室内建立稳定旋转爆轰波的目的,本文提出通过控制点火前燃料初始分布来建立稳定旋转爆轰波的方法,并基于纳维-斯托克斯方程与10组分27可逆反应基元化学反应模型的数值模拟验证了该方法的可行性。对旋转爆轰波传播特性的研究表明,燃料在发动机燃烧室中的分布是影响旋转爆轰波建立的关键。在燃料喷注压力较低时此影响尤为明显,它决定了爆轰波发展第一周期内波前燃料层厚度。而波前燃料层与波的稳定传播密切相关。基于该方法,本文对燃烧室初始流速为360 m/s,喷注总压0.4 MPa的旋转爆轰发动机实现了点火至稳定爆轰,得到的爆轰波传播平均速度为1 604 m/s,频率为5 347.6 Hz。此外,燃料初始填充率作为燃料初始分布的量化指标,文中给出了它建立稳定旋转爆轰时的临界范围。

Method based on controlling initial fuel distribution to establish stable rotating detonation wave in combustion chamber

In recent years, Rotary Detonation Engine(RDE) has attracted more and more attention because of their higher combustion efficiency than conventional aerospace engines. For the key problems, ignition technique is particularly important. In order to establish a steady rotating detonation wave under one single ignition in a combustion chamber, a method based on controlling initial fuel distribution is proposed to start a rotating detonation engine under 0.4 MPa injection total pressure using hydrogen/air mixture as its propellant. Two-dimensional reactive Navier-Stokes equation coupled with the Arrhenius kinetic model andκ-ε model are used to simulate detonation process. Elementary chemical reaction model with 9 species 27 reversible reactions is applied to describe the evolution of reaction components. The finite volume method is conducted, and flux terms are solved by using the monotonic upstream-centered scheme for conservation laws, and the time integration is performed by using Euler method. Grid numbers are 600(azimuthal direction) ×200(axial direction), with mesh size of about 0.5 mm. Initial fuel filling rate(φ) is used to quantify the initial fuel distribution. The numerical study on the propagation characteristics of rotating detonation wave shows that the initial fuel filling rate is the key to the establishment of rotary detonation wave. This effect is particularly evident when the fuel injection pressure is low, which determines the height of the fuel layer(hf) for the first cycle of detonation wave development. When RDE operating steadily, hf is a function of the mixture sensitivity to detonation. But in initial stage, hf is affected by the fuel distribution and this affection can last more than one period. Once detonation wave or deflagration wave formed, it can either maintain rotating or die down, which is determined by the height of mixture layer ahead of it. Thus, keeping hf in an appropriate range by adjusting the initial fuel filling rate is the key to establish and maintain a rotating detonation wave in initial stage. Also, in this stage DW faces maximum possibility of extinguish.Based on this strategy, a rotating detonation wave is established successfully in combustion chamber with diameter of 95.5 mm and the length of chamber is 100 mm. The computed results give the rotating detonation wave has a velocity of 1 604 m/s and operational frequency is 5347.6 Hz. Furthermore, there are four operation modes of the engine due to different initial fuel filling rate, which are failed initiation of the detonation(0%-13.3%), stable rotating detonation(13.3%-20%), unstable detonation(20%-26.6%) and dying detonation(26.7%-100%). So the critical range of the initial fuel filling rate for steady rotating detonation is obtained. Moreover, the initial fuel distribution also influences the delay time of fuel deflagration to detonation transition.