为了适用不同飞行工况的需求，超燃冲压发动机要求具备变工况下稳定工作的能力，然而作为一个复杂的力学系统，在变工况过程中会表现出发动机流动及推力性能的非线性演化特性，变速度下燃烧稳焰模式的转换过程、燃烧过强诱发的进气道不起动/再起动过程都存在着与燃烧关联的典型突变和迟滞问题。该类现象对于发动机的稳定工作至关重要，然而目前对于此两类问题的研究还多停留在定马赫数或者未考虑燃烧与进气道流动的耦合，对其现象及流动机理的理解亟待加强。

论文利用高焓变马赫数推进风洞及直连试验平台，从燃烧的视角，探索稳焰模式转换过程及燃烧驱动进气道不起动/再起动过程的突变与迟滞现象。结合对火焰特性的光学观测，揭示了来流马赫数变化对稳焰模式及推力的影响机制，提出并深入研究了多燃烧区调控抑制推力突变的方法。通过真实模拟发动机燃烧驱动的不起动/再起动过程，分析了燃烧与进气道流动的耦合作用及对起动迟滞的影响，并获得了来流变马赫数变化速率对发动机再起动特性的影响规律。

基于变马赫数风洞，对发动机稳焰模式转换过程中推力变化及迟滞特性进行了研究。试验发现，来流马赫数变化会导致压力和推力出现一次甚至两次的突变，这与以往只出现一次突变的认知不同。直连台试验进一步揭示了突变次数由稳焰模式转换过程决定，受当量比变化速率和来流马赫数变化方向的影响，三种稳焰-凹腔内稳焰、凹腔剪切层稳焰和射流尾迹稳焰之间会表现出不同的稳焰模式转换过程，导致突变次数的差异及推力迟滞现象。

论文进一步开展了推力突变抑制方法的试验探索，提出并验证了利用多燃烧区耦合抑制推力突变的方法。在发动机双排凹腔同时喷注燃料工况下，稳焰模式转换时壁面压力仍存在明显的突变和迟滞现象，然而由于两燃烧区的耦合作用，不同区域压力突升与突降之间的互补，发动机推力未表现出明显的突变及迟滞。利用直连试验进一步探究了双排凹腔不同喷注策略的影响，发现，若仅在上游凹腔喷注、依靠自身释热实现稳焰模式转换时，沿程压力突变幅值和迟滞环较大；引入下游凹腔燃烧并产生耦合作用后，会使得稳焰模式转换的迟滞环减小，压力突变幅值降低，而且迟滞环随下游凹腔燃烧对上游凹腔燃烧的影响增强而缩小。

试验中还发现，上游凹腔由凹腔剪切层稳焰转换到射流尾迹稳焰时，当上游当量比低于迟滞环下限时，在上下游燃烧耦合作用下，火焰会在两种稳焰模式间振荡；当上游凹腔当量比进一步增加达到一定值，火焰会稳定在射流尾迹稳焰模式；继续增加上游凹腔当量比，火焰会依次出现随机不对称和闪回现象。数值结果表明火焰不对称是由于非对称激波串诱导的涡结构对燃料的卷吸/燃烧导致的。

针对燃烧过强导致的发动机不起动/再起动研究，发现燃烧与进气道流动的耦合会导致进气道不起动/再起动过程出现两类新的迟滞，一类发生在不起动程度较轻的工况，认为源于激波-燃烧的双解特性，一类发生在不起动程度较深的工况，认为源于局部倒流出现的历史效应，两类起动迟滞现象与发动机当量比变化范围息息相关。与几何节流相比，燃烧的耦合作用下进气道的再起动能力会削弱，而进气道不起动后流场结构需要更长的稳定时间。同时发现，无论是进气道不起动或是再起动时刻均不会引起发动机推力的突变。论文进一步开展了马赫数变化引起进气道再起动的试验研究，发现当量比不变条件下来流马赫数的增加可以实现进气道再起动，且马赫数变化速率越快，发动机再起动马赫数越低，而随着马赫数变化速率逐渐减慢，发动机再起动马赫数趋近于某个固定值。

To adapt to different flight conditions, scramjet is required to have the ability to operate stably with varying conditions. As a complex mechanical system, scramjet will have nonlinear evolution characteristics of flow and thrust performance with varying conditions. There are typical abrupt changes and hysteresis related to flame stabilization mode transition under variable speed conditions and the inlet unstart/restart induced by excessive combustion, which is very important for the stable operation of the scramjet. At present, the study on abrupt changes and hysteresis is carried out with fixed Mach number inflow or does not consider the coupling between combustion and inlet, so a better understanding of the phenomenon and flow mechanism needs to be acquired.
The variable Mach number wind tunnel and the direct-connect facility are used to explore the abrupt change and hysteresis phenomena of flame stabilization mode transition and combustion-driven inlet unstart/restart. Based on the optical observation of flame, the influence of inflow with varying Mach numbers on flame stabilization mode and thrust is revealed, and the method of controlling the abrupt change of thrust by multi-combustion zone is proposed and studied. The coupling effect of combustion and inlet and hysteresis are analyzed by simulating the combustion-driven unstart/restart process of the scramjet, and the influence rule of the change rate of inflow Mach number on the inlet restart is obtained.

The abrupt change and hysteresis characteristics during the transition flame stabilization mode were studied by variable Mach number wind tunnel. It is found that the change of inflow Mach number will lead to one or even two abrupt changes in pressure and thrust, which is different from the previous cognition that there is only one abrupt change. The direct-connect facility further revealed that the number of abrupt changes is determined by the flame stabilization mode transition. Influenced by the rate of equivalence ratio change and the direction of incoming Mach number change, the three flame stabilization modes: flame inside the cavity, cavity shear-layer stabilized combustion and jet-wake stabilized combustion will show different flame stabilization mode transition processes, resulting in the difference of the number of abrupt changes and hysteresis.
The paper further carried out the experimental exploration of the suppression method of abrupt change in thrust and proposed and verified the method of using multi-combustion zone coupling to suppress the abrupt change in thrust. Under the condition of simultaneous injection of fuel into the double-row cavity of the engine, there is an abrupt change and hysteresis of the wall pressure when the flame stabilization mode transition. However, due to the coupling effect of the two combustion zones and the complementarity between the abrupt pressure rise and drop in different areas, the thrust does not show abrupt change and hysteresis. Using the direct connection test to explore the influence of different injection strategies of double-row cavities. If only the upstream cavity injection and self-heat release are used to achieve flame stabilization mode transition, the abrupt change amplitude and hysteresis loop of pressure are large. When the downstream cavity combustion is introduced and the coupling effect is generated, the hysteresis loop of flame stabilization mode transition will be reduced, the amplitude of abrupt change in pressure will be reduced, and the hysteresis loop will be reduced with the increase of the influence of the combustion of the downstream cavity on the upstream cavity.
It is also found in the experiment that when the flame stabilization mode of the upstream cavity transitions from cavity shear-layer stabilized combustion to jet-wake stabilized combustion when the upstream equivalence ratio is lower than the lower limit of the hysteresis loop, the flame will oscillate between the two flame stabilization modes under the coupling effect of upstream and downstream combustion. When the equivalence ratio of the upstream cavity further increases to a certain value, the flame will be in the jet wake stabilized combustion. If the equivalence ratio of the upstream cavity continues to increase, the flame will appear with random asymmetry and flashback in turn. The numerical results show that the asymmetry of flame is due to the entrainment/combustion of fuel caused by the vortex structure induced by the asymmetric shock train.

The study of scramjet unstart/restart caused by excessive combustion shows that the coupling of combustion and inlet flow will lead to two kinds of new hysteresis in the process of engine unstart/restart. One type of hysteresis occurs with a low degree of unstart, which is believed to be caused by the shock combustion double solution characteristic, and the other occurs with a high degree of unstart, which is believed to be caused by the historical effect of reverse flow. The two types of hysteresis are closely related to the variation range of the equivalence ratio. Compared with geometric throttling, the restart ability of the inlet will be weakened under the coupling effect of combustion, and the flow field structure of the inlet will require a longer stabilization time when the inlet in unstart. At the same time, it should be noted that the abrupt change of thrust will not occur either at the time of unstart or restart. The paper further carried out experimental research on inlet restart caused by Mach number change, and found that inlet restart can be achieved by increasing the flow Mach number under the condition of constant equivalence ratio, and the faster Mach number changes, the lower Mach number required for engine restart, but as the Mach number change rate gradually slows down, the engine restart Mach number tends to a certain fixed value.