传热对微型摆式发动机性能的影响机制分析

建立了微型摆式发动机(Micro internal combustion swing engine,MICSE)的计算模型,揭示了传热及其尺度效应对微型摆式发动机性能的影响机制。结果表明:壳体仅在一个较薄的热缓存层内与工质气体进行周期性热交换。在进气过程中,热缓存层对气体的传热会提高气体温度,从而降低进气质量和压缩比;在做功过程中,气体对热缓存层的传热减少做功,这两方面都会降低系统热效率。尺寸越小,进气气体在热缓存层传热下的温升越大,相对进气质量和压缩比越低;做功过程中的气体向热缓存层的传热量占燃气总化学能的比值越高。因此尺寸越小,传热效应增强,热效率越低。

Influence of Heat Transfer on Performance of Micro Internal Combustion Swing Engine

A computational model of a micro internal combustion swing engine (MICSE) is established. The mechanism of the heat transfer and its scale effect on the system performance are analyzed. The results show that the heat exchange between the gas and the solid wall occurs in a thin thermal buffer layer close to the contact area. In the intake process, the hot thermal buffer layer heats the intake gas, thereby reducing the intake air mass, resulting in a compression ratio drop. While in the power process, the heat transfer from the gas to the thermal buffer layer reduces the work output. Hence the thermal efficiency declines. The smaller the engine scale is, the gas temperature in the intake stroke increases for the influence of the thermal buffer layer, the less the dimensionless inlet air mass and the compression ratio will be. While in the power process, the ratio of the thermal transferred from the gas to thermal buffer layer to the fuel chemical energy increases with the reduction of engine scale. Therefore, the heat transfer enhances and the thermal efficiency drops with the reduction of the engine scale.