双模态冲压发动机以其自身的诸多优点是实现宽马赫数飞行有吸引力的选择。双模态冲压发动机的燃烧室是发动机的重要部件，其性能直接关系到发动机的总体性能。尤其是其中的双模态转换技术更是一个技术难点，亚燃超燃的明确定义以及如何实现模态转换的平稳和高效是近年来研究的重点方向。过去对于大部分的研究主要集中在定马赫数状态下的研究，其中模态转换主要通过调节当量比和供油位置实现。这与实际的飞行状态是不一致的。因此本文通过烧氢补氧加热器和喷管喉道截面的改变来实现来流马赫数和总温的动态改变，模拟飞行器在飞行过程中高度和马赫数的改变，使得能够研究动态过程中的模态转换特性。研究模态转换的路径问题和过程的稳定性问题。

    首先研究在固定马赫数和总温状态的实验中，燃烧室的模态和火焰的稳定性，通过改变供油方案实现了亚燃模态、超燃模态以及过渡模态。然后开展变马赫数实验，研究动态过程中模态的转换过程和火焰的形态，研究了供油策略对火焰稳定和模态的影响。

    在变马赫数过程中，与单极燃料布局相比，采用多级燃料布局使得燃烧稳定性有显著的提高，避免了单级燃料的不稳定和熄灭现象，模态转换过程中，过渡状态变得尤为重要。模态转换过程中，双级凹腔布局的燃烧室，转换过程是趋于稳定的或平稳过渡，单级的火焰稳定性较差，更易发生突变。

  The dual-mode scramjet is an attractive choice of realizing the wide range of flying Mach number because of its many advantages. As a significant component of the scramjet engine, the dual-mode scramjet combustor determines the overall performance of the engine. The transition of the combustion mode is the key to the dual-mode scramjet technology. How to exactly define the combustion mode and how to realize mode transition in a stable and efficient route is focused on by many researchers in latest years. However, most of past works are limited to the condition of a fixed inlet Mach number, in which combustion mode is changed by different equivalence ratio or position of the fuel injection, ignoring speed changed in the real flight. In this paper, a heater, which burns Hydrogen and adds Oxygen, is used to dynamically change total temperature of inlet flow and maintain stable mole fraction of Oxygen, and a nozzle with variable throat cross-section is used to change inlet Mach number, which simulates the change of altitude and velocity in the real flight process. The main content of this paper is the investigation of the route of the mode transition and the stability of the process.

  Firstly, stable experiments with fixed inlet Mach numbers and fixed inlet total temperatures are carried out in order to investigate the combustion mode of the dual-mode scramjet combustor and the stability of flame. In these experiments, ramjet mode, scramjet mode and transition mode are found with different arrangement of fuel injection. Then experiments with variable inlet Mach numbers are conducted to study the process of the mode transition and the pattern of flame stability in the dynamic process. The influence of fuel supplement on the flame stability and the combustion mode is also studied in variable inlet Mach number experiments.

  In the process of variable Ma number, compared with the single-level fuel arrangement, the multi-level fuel arrangement apparently enhances the stability of combustion and reduce the risk of extinction. In a two-cavity combustor, the transition mode plays a significant role in mode transition. In the process of mode transition, two-cavity layout restrains fluctuation and makes it smoother, while the flame in a single cavity shows poor stability and more possible changes suddenly.