基于超声速气流中凹腔主动喷注的强迫点火方案研究

Investigation of Forced Ignition Scheme Based on Active Cavity Injection in a Supersonic Flow

关键词:  点火  主动喷注  图像处理  数值仿真

Key words:  Ignition  Active injection  Image processing  Numerical simulation

摘要:

为了进一步研究在入口来流Ma=2.1和[T0=846K, p0=0.7MPa]的条件下凹腔主动喷注对点火的影响，通过分析高速摄影拍摄的瞬态图像和合成后的统计图像对比了采用凹腔前壁面喷注、后壁面喷注等组合方式的三种乙烯点火方案，并对采用凹腔前壁和后壁面喷注相结合的组合喷注方式开展点火前冷态流场数值仿真分析。研究表明，在此工况条件下，凹腔前壁面喷注容易使燃料在凹腔角回流区内和火花塞处聚集，而凹腔后壁面喷注更加利于点火产生的初始火核在凹腔内传播，但在相同喷前压力下凹腔后壁面的喷注压降要更低；为了使燃料主动喷注后在凹腔内分布更加均匀，凹腔前壁面喷注位置应该设置在靠近剪切层处，而凹腔后壁面喷注位置应该设置在靠近凹腔底壁处；采用凹腔前壁喷注和后壁面喷注相结合的喷注方式相比于单采用前壁喷注和单采用后壁面喷注的喷注方式，凹腔的燃料分布更加均匀，点火后凹腔内火焰更加均匀稳定。当凹腔主动喷注当量比达到0.03、全局当量比达到0.14时，火焰就能穿过剪切层引燃凹腔下游横向射流，在串联凹腔中稳定地燃烧。

Abstract:

To investigate the effects of active cavity injection on ignition at the inflow conditions of Ma=2.1 with stagnation state[T0=846K, p0=0.7MPa]，transient images taken by high speed photography and synthetic images made by statistical processing were used to study the ethylene ignition scheme of using the parallel injection alone，using the ramp injection alone and using the parallel and ramp injection together，and numerical simulation was carried out to study the steady flow field before ignition of the scheme of using parallel injection and ramp injection together. It is revealed that under the ignition working conditions in this paper，the parallel injection will make the fuel conglomerated in the cavity angular recirculation zone and around the spark plug easily. The ramp injection is good for the initial flame kernel to propagate in the cavity，although the ramp injection pressure drop is lower at the same injection pressure. In order to make the fuel distribution more even in the cavity，the injection position in the parallel edge should be near the shear layer while in the ramp edge should be near the cavity bottom wall. By comparison，using the parallel injection and the ramp injection together in the cavity will make the fuel distribution more even and the flame in the cavity is more stable after ignition. Besides，the flame will penetrate the shear layer，ignite the transverse jet downstream of the cavity and form a stable combustion in the cavities at the active injection equivalent ratio of 0.03 and the overall equivalent ratio of 0.14.