气动发动机进气过程流动损失分析

Analysis of Intake Flow Loss in Pneumatic Engine

作为一种清洁能源动力装置,气动发动机以高压空气为储能介质,进入气缸膨胀做功,其进气过程流动特性对整机效率影响显著。针对气动发动机旋转阀进气机构的流动损失,根据计算流体力学理论,建立了气动发动机进气过程数学模型,利用动网格技术分析了进气过程不同时刻进气道速度场及瞬态流动特性,并计算了压力损失及其随气动发动机工况的变化规律。研究结果表明:进气阀开度较小时,流体局部湍流较强,压力损失严重,而随着进气阀开度增加,压力损失逐渐减少;在进气过程初期,压缩空气压力损失下降较快,而随着进气过程持续,压力损失趋于平稳;当运行工况改变时,气动发动机进气过程压力损失比例随转速上升而上升,随进气压力变化趋势则不明显。对进气机构及进气流动方式进行优化,是降低气动发动机进气损失的首要工作。

Intake flow characteristics has significant influence on pneumatic engine efficiency. The pneumatic engine intake process was modeled according to CFD theory to examine flow loss of intake compressed-air at the rotational valve mechanism and intake port velocity fields, instantaneous flow characteristics at different times in intake process based on dynamic mesh theory,and to calculate pressure loss and its variation rule with engine conditions. Simulation results show that the pressure loss increases at small intake valve opening due to strong local turbulence and it decreases with the valve opening adding. Compressed-air pressure loss decreases rapidly in intake early period, and becomes steady thereafter. The pressure loss percentage increases with engine speed rising and slightly fluctuates with intake pressure changing. Optimization of valve mechanism design and intake flow pattern are the keys to reduce engine intake flow loss.