Study On Structure And Characteristic Parameters Of Laminar Premixed Flame In Low Pressure

As the simplest flame in the nature, the laminar premixed flame is the base of studying turbulent diffusion flame. The thickness of flame front will be widened in low pressure, which makes it possible to obtain a more comprehensive and detailed flame structure through optical measurement techniques. The combustion in high-altitude ramjet engine is low and prone to combustion instability due to the low pressure or negative pressure. This paper focus on the study of laminar premixed flame structure and characteristic parameters in low pressure mainly by experiment means, supplemented by numerical simulation.In order to study the effect of pressure, equivalence ratio and strain rate on the structure of methane air laminar premixed flame in low pressure, a planner burner and a opposed jet burner which had the ability to produce flame in low pressure was designed and spontaneous emission and OH-PLIF optical measurement system was set up. Numerical simulation adopts Chemkin software and GRI-Mech3.0 methane air combustion reaction model, and adds the reaction mechanism of excited state particles such as OH*, CH* and C2*, mainly analyzes the effect of pressure, equivalence ratio, and the strain rate on concentration distribution of excited state particles.Based on the results of the numerical simulation, the effect of pressure, equivalence ratio and strain rate on the structure of laminar premixed flame was investigated by the spontaneous emission and OH-PLIF optical measurement system. Studies have found that OH* and CH* varies with pressure, while C2* keeps unchanged. As the equivalence ratio increases, the peak intensity of OH* first increased and then decreased and CH* varies with no rule, while the C2* increases and OH decreases. The peak intensity of OH*, CH*, C2* and OH radicals first increased and then decreased as the strain rate increases.The characteristic parameters such as heat release rate and flame equivalence ratio of the laminar flame in low pressure was studied by means of the spontaneous emission and flame spectrum of spontaneous radiation. Studies have found that OH* can be used to identify the heat release rate in flat flame and opposed jet flame conditions and CH* can also identify the heat release rate in the some flame, while C2* cannot. Studying of flame equivalence ratio found that OH*/CH* ratio can be used to infer the local equivalence ratio of fuel rich methane air flames, and the ratio of C2*/CH* can be used to infer the local equivalence rati of poor burning methane air flames.