传热对微型发动机预混催化燃烧特性影响的研究 *

Effects of Heat Transfer on Premixed Catalytic Combustion Characteristics of Micro Engine

关键词:  微型发动机  传热  催化燃烧  燃烧特性  预混燃烧  微推进系统

Key words:  Micro engine  Heat transfer  Catalytic combustion  Combustion characteristics  Premixed combustion  Micro-propulsion systems

摘要:

为了研究传热对微型发动机燃烧室内甲烷催化燃烧特性的影响，采用CH4和空气的预混合气体，对在活塞上表面和燃烧室顶部涂有Pt-La/γ-Al2O3催化剂的传热情况下的微型发动机的催化燃烧特性进行了实验研究及数值模拟，详细对比分析了3种典型的管壁材料(Si，Fe和矾土)，有、无催化涂层及绝热与传热情况下的微型发动机燃烧室内CH4的催化燃烧特性。结果表明:对于Pt-La/γ-Al2O3催化下自由活塞式的微型发动机，受尺度减小引起的传热损失对催化燃烧过程影响不大；有催化情况下的燃烧效率明显高于无催化，催化燃烧具有更高的燃烧室内温度，可以实现更高的动力和电能输出，微型发动机(MEMS微推进系统)具有更高的输出功率和能量密度；管壁材料为导热系数较小的矾土的催化燃烧效率略高于导热系数较大的Si；微型发动机燃烧室的壁面材料应采用具有承受应力高、适应温度广、机械性能及抗变形能力强等优点的耐火陶瓷。

Abstract:

To understand the effects of heat transfer on the methane catalytic combustion characteristics inside combustion chamber of micro engine，catalytic combustion characteristics of premixed methane/air mixture inside combustion chamber of micro engine were experimentally and numerically investigated by using the catalysts (Pt-La/γ-Al2O3) which were coated at the upper surface of piston and the top of chamber in heat transfer case. For three kinds of characteristic wall materials (Si，Fe and alumina)，with and without catalytic coatings，adiabatic and heat transfer case，the comparative studies were carried out to clarify methane catalytic combustion characteristics of the micro engine. The results show that the heat loss caused by the scale decreases has little effect on the catalytic combustion process for catalytic (Pt-La/γ-Al2O3) micro free-piston engine. The combustion efficiency and the temperature inside combustion chamber can be improved greatly by catalytic combustion. The output power and the energy density of micro engine (MEMS micro-propulsion systems) can be improved by catalytic combustion. The catalytic combustion efficiency of alumina (smaller thermal conductivity) is slightly higher than that of the Si (larger thermal conductivity). The refractory ceramics with advantages of withstanding high stress，adapting to wide temperature，strong mechanical properties and resistance to deformation，etc. should be used as the wall material of micro engine combustion chamber.