Effect of diaphragm height on the combustion characteristics of solid fuel ramjets

Combustion efficiency is a key performance metric for solid fuel ramjets (SFRJs) and is significantly affected by the combustion organization within the afterburning chamber. To enhance the combustion of pyrolysis fuel with air, a diaphragm structure is commonly utilized to control the flow field and to improve mixing. This paper utilizes numerical simulations to analyze the flow and combustion characteristics of SFRJs with various diaphragm heights and proposes a recommended design height range for this scale ramjet. The results indicate that diaphragms can effectively promote fuel–air mixing and improve combustion efficiency by inducing recirculation zones and increasing turbulence intensity. There is an upper limit to the improvement in combustion performance with increasing diaphragm height (≤0.873). Excessively high diaphragms reduce the effective flow area, increase flow velocity, and shorten the residence time of reactants, thereby limiting further enhancement. Based on the performance gain coefficient analysis, the recommended design range is identified as Hd/Rc (ratio of diaphragm height to combustion chamber radius) = 6/25 to 8/25. In addition, the diaphragm height shows minimal effect on the average regression rate, confirming its primary role as a flow control structure rather than a direct driver of fuel consumption. This study provides theoretical support and engineering guidance for the design of flow control structures in SFRJs.