Numerical And Experimental Research For The Ignition Delay Time Of The Ethylene In The Scramjet

Hypersonic technology has important effects on the national defense and the aviation and aerospace, it has been noticed greatly by the human beings. Nowadays,its emphases are focused on the scramjet technology and the airframe/propulsion integration technology. Up to now, a great deal of accomplishment of scramjet has been reached, however, there are many other difficulties still existing, among which is the ignition process of the engine. To study the ignition process is to study the unsteady phenomena of the pressure, the temperature, the chemical components of the flow and so on in the engine from the time of fuel injection to the steady combustion of the engine, and the current technologies can't satisfy the above needs well. But it does not to say that there is no way to these problems, and researches on the ignition delay time of the engine are conducted with CFD and experiment in this paper. The paper is divided into 5 chapters. In chapter 1, the playground and the fundamental principles of scramjet are introduced. In chapter 2, the functions, turbulent model and chemical reaction model used in the computational program which is developed by the Airbreathing Hypersonics Laboratory of CARDC are listed. The program is validated by calculations for the 2-dimensional flows of cavity and combustor.In chapter 3, the engine configuration, the grid for computation, the conditions of inlet inflow and the fuel injection are all described. The results are analyzed in detail. Firstly, the shock and expansion wave systems, the streamlines, the vortex of the cold flow are analyzed and the conclusion that the vortex in the cavity is the key factor to automatical ignition is reached. Secondly, the reacting nonequilibrium steady flow is analyzed and a lot of phenomena different from the cold one are discovered. Thirdly, the pressures of 16 wall points with 6 in the cavity and 10 in the dilation part are tracked during the procedure of the flow from the cold state to the hot one and we know the ignition delay times of the wall points are approximately between 3 and 4 ms and that the ignition in the cavity is more complex than that in the expansion part from the pressure variation with time. Finally, the pressure distribution along the engine wall and the flow fields in different time steps are compared and the development history of the flow is gained.In chapter 4, the preparation for the experiment is described detailedly. Firstly, the principle of the experimental facility is studied. Secondly, the characteristics of the pressure sensor are investigated, several sensors are calibrated by shock tube and analyzed by the frequency analysis method and what kind of sensor should be suitable to the experiment is answered. Thirdly, as this experiment is more rigorous than previous, the delay of the engine model is studied and the result shows that the delay can be ignored only if the engine is modified. The modified engine outline is showed also.In the last chapter, the main researches of the paper are reviewed and the outlook of the future work are given.