油气比对超燃发动机点火过程的影响

Influence of Fuel-Air Ratio on Scramjet Ignition

关键词:  超燃冲压发动机  自点火  非定常计算  化学非平衡  点火延迟时间

Key words:  Scramjet  Self-ignition  Unsteady numerical method  Chemical non-equilibrium  Ignition delay time

摘要:

为了研究油气比对超燃发动机自点火性能的影响,利用二维非定常化学非平衡计算方法模拟了总温2000K,总压3.0MPa,入口马赫数3.0,煤油油气比为0.2和1.0时超燃发动机的自点火过程。具体可以得到以下结论:(1)总油气比越高,燃料传播速度越快；燃料首先沿着剪切层传播至凹槽后缘,之后在凹槽漩涡的带动下向凹槽上游和底部传播。(2)凹槽回流区温度高,点火延迟时间短,低油气比的气体一旦进入凹槽回流区后即可在凹槽后缘和上方点火。(3)火焰从凹槽的上沿和右边向凹槽底部和左边传播。(4)总油气比越高,点火越困难。

Abstract:

To study the influence of fuel-air ratio on the scramjet self-ignition, two self-ignition processes of kerosene fueled scramjet were simulated with 2D non-equilibrium unsteady numerical method, the total temperature, total pressure and Mach number of the incoming flow were 2000K, 3.0MPa and 3.0 respectively, the two cases had different fuel-air ratios, one was 1.0 and the other 0.2. Four conclusions can be reached. Firstly, the higher the fuel-air ratio is, the faster the fuel propagates; fuel propagates through the shear layer downstream first, and when achieving the rear cavity wall, kerosene will be propagated to the cavity upstream and bottom by the vortices. Secondly, the temperature in the cavity is high, so the ignition delay time is short, and as soon as the mixed gas with lower fuel-air ratio propagates into the cavity the ignition will occur downward and upward in the cavity. Thirdly, the flame propagates from top and right to bottom and left in the cavity. Fourthly, the higher the fuel-air ratio is, the more difficult the ignition is. 