排气早开角对低散热Atkinson循环汽油机能量分配的影响

基于GT-Power软件建立某增压汽油机仿真模型,并通过试验验证模型的准确性。优化原模型配气机构,设计包角更大的进气凸轮以实现Atkinson循环,设计多组排气凸轮以得到20°~80°范围内的多个排气早开角(θ_(EVO)),改变传热模型实现缸内的低散热条件,模拟分析了1 500 r/min,40%负荷时,θ_(EVO)对低散热前后Atkinson循环增压汽油机能量分配的影响。结果表明:常规散热条件下,该汽油机的燃油经济性在θ_(EVO)为60°~70°范围内时较佳,而低散热条件下,该汽油机的燃油经济性在θ_(EVO)为50°~60°范围内时较佳;降低传热系数后,该汽油机散热损失的能量大幅减少,由此减少的能量在不同θ_(EVO)下转化为指示功的比例不同,θ_(EVO)为55°时转化比例为17.4%,此时指示热效率与原机相比提高了6.58%;而常规散热条件下Atkinson循环增压汽油机的指示热效率只比原机高3.79%,说明结合低散热技术能进一步增强Atkinson循环的节能效果。

Effects of Exhaust Valve Opening Angle on Energy Distribution of Gasoline Engine with Low Heat Rejection and Atkinson Cycle

The simulation model of supercharged gasoline engine was built with GT-Power software and was verified by the experiment.Atkinson cycle was first achieved by optimizing the valve train of original model through designing the intake cam with a larger angle,multiple exhaust valve open angles between 20°CA and 80°CA were acquired by designing multiple exhaust cams,the condition of low heat rejection in the cylinder was realized by changing the heat transfer model,and the effects of ex-haust valve opening angle on engine energy distribution were finally simulated and analyzed under the condition of 1 500 r/min and 40% load.The results show that gasoline engine has better fuel economy at the exhaust valve opening angle between 60°CA and 70°CA under the normal cooling condition and at the angle between 50°CA and 60°CA under the low heat rejection condi-tion.The energy loss owing to heat rejection reduces greatly after decreasing the heat transfer coefficient and hence the indicated work increases.The increased indicated work is different under different exhaust valve opening angles.The indicated thermal efficiency increases by 6.58% when the conversion ratio is 17.4% at the exhaust valve opening angle of 55°CA.However,the indicated thermal efficiency of supercharged gasoline engine with Atkinson cycle is only 3.79% higher than that of original en-gine under the normal cooling condition,which indicates that combining the technology of low heat rejection and Atkinson cycle can strengthen the effect of energy saving.