燃燒室之燃料噴注方式、燃料與空氣之混合特性以及燃料反應過程等問題向來是超音速燃燒衝壓引擎相關研究中受關注的方向，本研究探討背階模型於超音速流場內對氫氣噴注之影響，並針對其流場結構與自燃性進行分析。
本研究使用雙隔板反射式震波風洞製造出高焓自由流，並搭配馬赫2噴嘴模擬超燃衝壓引擎於馬赫六飛行速度下之燃燒室入口條件（全溫1950 K，全壓9.2巴，動溫1220 K，動壓1.2巴）。常溫氫氣燃料於蓄壓鋼瓶內經高速電磁閥以音速噴注於馬赫2高焓自由流，噴注口位於背階模型之階梯下游兩倍階梯高度處。本研究並以高速攝影機搭配紋影法及OH自然螢光法觀察流場結構及燃燒區域分析。
紋影影像顯示，背階模型下游因震波產生之斜壓力矩有助於自由流與累積於模型表面之燃料混合，並且藉由OH自然螢光影像觀察發現，自燃反應出現於氫氣噴注頂端。

The efficient injection, mixing and combustion process inside the combustor have been the key elements of supersonic combustion ramjet (scramjet). This study is focused on how the backward-facing step model affects the mixing efficiency of free-stream and hydrogen jet in supersonic flow and the self-ignition process.
The study used the reflected shock tunnel re-equipped to double-diaphragm operation to replicate the scramjet combustor environment while the flight speed reaches Mach 6. The high enthalpy flow is provided by the impulse facility and by means of the Mach 2 nozzle, the test condition of free-stream is Mach 2, total temperature 1950 K, total pressure 9.2 bar, static temperature 1220 K, static pressure 1.2 bar. The hydrogen in room temperature is injected into supersonic flow by the high speed solenoid valve. The jet orifice is located at the bottom wall of the backward-facing step model and is 2 times of the step height away from the step corner. Schlieren image and OH-chemiluminescence methods are applied in this study to observe the flow feature and the combustion region.
The schlieren image shows that, the baroclinic torque induced by the recompression shock of the backward-facing step, rolls up the fuel on the model surface and thus has positive effect on the fuel-air mixing. And from the OH-chemiluminescence images, the ignition reactions take place at the top of the jet.

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