气动发动机活塞运动轨迹的优化设计

Optimal piston trajectory design of air powered engine

为解决高转速下动力与经济性能的下降,提出一种新的气动发动机曲轴连杆机构.通过建立气动发动机的进气模型和缸内工作过程模型,以压缩空气的比输出功最大为目标函数,给出优化的活塞运动轨迹曲线.分析了进气阀与活塞运动之间新的匹配关系.设计了复曲轴连杆结构,并得到调节进排气门的开关时刻与持续时间的方法.结果表明,在该机构实现的优化轨迹曲线中,在缸内压力达到进气压力之前,活塞的运动速度应该保持静止;缸内高压建立后,活塞的运动速度应与进气门的截面积保持线性关系;进气门关闭后,活塞速度应保持匀速运动.采用新机构后的压缩空气比输出功比原系统提高了一倍.

To solve the poor economic and dynamic performance at high engine speed, a new crank shaft mechanism of air powered engine was proposed. After the intake model and the cylinder work process model of air powered engine were built, the maximal specific work output of compressed air was taken as object function, and an optimal piston trajectory was obtained. After the matching relationship between inlet valve and piston trajectory was analyzed, a dual crank shaft mechanism was designed, and method of adjusting the valves between their on-off time and continuance time was obtained. Results show that in the optimal trajectory realized by the mechanism, the piston speed remains zero before cylinder pressure reaches intake pressure, piston speed remains linear with cross-section area of intake valve after the establishment of high cylinder pressure, and that the piston runs in uniform speed after the inlet valve closes Specific work output of compressed air using the proposed mechanism is twice than that applying original system.