进排气开启角对气动发动机的影响及其优化设计

Influence of inlet and outlet valve's open timing on pneumatic engine and their optimal design

为解决气动发动机在高转速下动力性和经济性恶化的问题,对进排气阀开启角进行优化.基于热力学理论建立了气动发动机缸内过程模型,通过计算分别得到进排气阀开启角对气动发动机动力性和经济性的影响.计算结果表明,在排气阀开启角不变的情况下,适当的进气提前有利于动力性和经济性的提高,在进气阀开启角不变的情况下,适当的排气提前有利于动力性和经济性的提高,并利用试验验证了模型的正确性.最后以功率和气耗率为优化目标,利用已建立的模型,采用降维法优化计算.优化结果表明,不同的转速下,最优的进排气提前角不同.在高转速下,动力性和经济性提高显著.当转速大于2 000 r/min,功率提高20%以上,气耗率下降25%以上.

To solve dynamic and economic performance deterioration of pneumatic engine under high speed, the open timing of inlet valve and outlet valve was optimized. Based on thermodynamics, the model of pneumatic engine inner process was established, which obtained the influence of inlet valve and outlet valve＇s open timing on pneumatic engine＇s dynamic and economic performances separately. The results show that the dynamic and economic performances are improved when the inlet valve was opened earlier appropriately and the open timing of outlet valve is constant. And they are improved also when the outlet valve was opened earlier appropriately and the open timing of inlet valve is constant. The correctness of this model is validated by experiments. Finally, by taking power and gas loss rate as optimization objective, and utilizing the above established model, dimension-reduction algorithm is adopted for optimization calculation. The result of optimization indicates that for different speeds, the optimal open timing of inlet and outlet valve are different. At high speed, dynamic and economic performances are greatly enhanced. When rotating speed is higher than 2 000 r/min, power is increased by more than 20% while gas loss rate decreases more than 25 %.