超燃冲压发动机由于结构简单、不需携带额外的氧化剂以及在高飞行马赫数下推进性能优良而脱颖而出，如今中等马赫数超燃冲压发动机技术已经取得了全面突破，并逐步走向了工程应用。随着人们对更远射程、更强突防能力和更快飞行速度的追求，发展更高马赫数的超燃冲压发动机技术的需求日益迫切。然而，发动机研制过程中也面临各种各样的挑战，其中一个典型问题就是超高速、高焓条件下强烈的热力学非平衡效应。为此，本文以高马赫超燃冲压发动机内流混合与燃烧特性为背景，以热力学非平衡效应对超声速燃烧流场的影响为主线，开展了以下三个方面的研究。

针对超高速、高焓流场中的热化学非平衡流，开发了一套针对热化学非平衡流的数值求解平台。对于热力学非平衡的建模，采用双温模型体现分子振动模态激发，利用Landau-Teller模型来描述分子不同模态间的能量弛豫过程，通过Park修正的Millikan-White公式来计算分子的振动弛豫时间，而振动-化学耦合效应采用Park TTv模型来模拟。通过热浴、钝体绕流、激波诱导燃烧等系列典型算例对求解平台进行了数值验证。结果表明：求解平台不仅能准确预测高超声速流动中的流场结构、壁面压力、激波脱体距离和能量弛豫过程，并且在准确描述激波与超声速燃烧间的相互作用方面也能给出较为准确的结果。

在此基础上，针对来流Ma7.37的HyShot II超声速燃烧室，考察了热力学非平衡效应对燃料混合与燃烧特性的影响。通过冷、热态流场的对比研究发现，在燃料壁面横向喷流构型下，发动机内流在周向上始终存在明显的热力学状态分层。此外，对比考察了相同来流总焓、来流入口振动温度分别为688 K和1088 K的条件下，不同入口非平衡程度对稳焰特性及燃烧稳定性的影响。结果表明：在较高的燃烧室入口振动温度下，离解反应速率提高，从而缩短了点火距离。此外，在较高的入口振动温度条件下，发动机燃烧效率提高8%，但火焰变得更不稳定、燃烧释热以及局部静压波动更加剧烈。

进一步，针对来流Ma9.62下进气道支板与壁面直喷的组合喷注方式的高马赫数发动机的燃烧特性进行了系统研究。与HyShot II发动机仅采用直喷不同，支板提前喷注燃料不仅可以大幅降低燃烧室入口流速、促进下游射流剪切层失稳，同时可以提高燃烧室入口初始静温，提高离解反应速率、削弱热力学非平衡效应的影响。此外，还对比研究了ϕ = 0.416和 0.358两个当量比下燃烧室内的流场结构与燃烧性能，发现高当量比下燃烧反应更加充分，燃烧室内平动温度上升更快，两者最终的燃烧效率分别为55%和52%。

Scramjet engines stand out due to the simple structure, no need to carry additional oxidizer, and excellent propulsion performance at high flight Mach numbers. Today, medium Mach number scramjet engine technology has achieved a comprehensive breakthrough and is gradually moving towards engineering applications. But with the quest for longer range, better surprise defense capability, and faster flight speed, the need to develop higher Mach number scramjet technology is becoming increasingly urgent. However, the engine development process also faces various challenges, one of which is typically the strong thermal nonequilibrium effect under hyper-speed and high enthalpy conditions. In this thesis, the numerical simulation of the combustion in high Mach number scramjet engine is used as the background, and the effect of the thermal nonequilibrium effect on the supersonic combustion flow field is the main line. The main contributions of this thesis are summarized below.

A numerical solver is developed for thermochemical nonequilibrium flow in the hyper-speed, high-enthalpy flow field. For the modeling of thermal nonequilibrium, the two-temperature model is used to embody molecular vibrational mode excitation, the Landau-Teller model is used to describe the energy relaxation process between different modes of molecules, the vibrational relaxation timescale of molecules is calculated by Park's modified Millikan-White formula, and the vibrational-chemical coupling effect is modeled by the Park TTv model. The solver is verified numerically by a series of typical cases such as heat bath, blunted cone, and shock-induced combustion. The results show that the solver not only accurately predicts the flow field structure, wall pressure, shock stand-off distance, and energy relaxation processes in hypersonic flow, but also gives accurate results in describing the interaction between shocks and hypersonic combustion.

Based on this, the effect of thermal nonequilibrium effect on the fuel mixing and combustion characteristics is investigated for the HyShot II supersonic combustion chamber with an incoming flow of Ma7.37. The comparative analysis of the cold and hot flow fields reveals that there are always significant thermal state stratifications in the circumferential direction of the engine's internal flow with the transverse fuel injection configuration. Furthermore, the effect of different inlet nonequilibrium degrees on the flame characteristics and combustion stability are investigated under the same total incoming enthalpy and incoming inlet vibrational temperature of 688 K and 1088 K respectively. The results show that the dissociation reaction is enhanced and the ignition distance is reduced at higher inlet vibrational temperature. In addition, the engine combustion efficiency increases by 8% at higher inlet vibrational temperature, but the flame becomes more unstable, with more intense combustion heat release and local static pressure fluctuations.

Further, the combustion characteristics of the high Mach number engine are systematically investigated under a combination of intake strut injection and direct wall injection with an incoming flow of Ma9.62. In contrast to the HyShot II engine with direct injection only, the pre-injection of fuel by the strut not only dramatically reduces the combustion chamber inlet flow velocity and promotes the destabilization of the jet shear layer downstream, but also increases the initial static temperature of the combustion chamber inlet, enhances the dissociation reaction and weakens the effect of thermal nonequilibrium effect. In addition, the flow field structure and combustion performance in the combustion chamber at two equivalence ratios of ϕ = 0.416 and 0.358 are compared. It is found that the combustion reaction is more sufficient and the translational-rotational temperature in the combustion chamber rises faster at a higher equivalence ratio. The final combustion efficiency of the two cases is 55% and 52% respectively.