基于可变气门定时策略的HCCI汽油机试验研究

在电控气口喷射四冲程单缸试验机上,利用特殊设计的小包角配气凸轮,通过负气门重叠角实现了由内部残余废气控制的汽油HCCI燃烧,详细研究了气门定时参数对HCCI燃烧的影响.结果表明,就进排气门定时比较而言,排气门关闭时刻对内部EGR率和负荷的影响更大,而进气门开启时刻对HCCI燃烧的影响相对较小.在进排气门相位对称条件下,随着气门重叠负角的减小,最大压力升高率增加,着火时刻提前,负荷也增大.随着转速的增加,内部EGR率增加,排气温度升高,着火时刻也提前.通过调整气门定时,在不需要进气加热的条件下,可在转速880～4 000 r/min,负荷0.25～0.75 MPa（pIMEP）的范围实现HCCI燃烧.

Experimental Investigation of HCCI Gasoline Engine Based on Variable Valve Timings

In a 4-stroke,port injection,single cylinder gasoline engine,through a set of intake and exhaust valve cams with specially designed profile and short lift,HCCI combustion based on trapped internal residual gases is implemented at room intake temperature with a conventional gasoline engine compression ratio.The effects of intake and exhaust valve timing,including the negative valve overlap interval,on HCCI combustion were experimentally investigated.The results showed that the exhaust valve closure timing(EVC) has a greater influence on internal EGR rate,auto-ignition timing and heat release rate compared with the influence from the intake valve opening timing(IVO).In the case of symmetrical setting of intake and exhaust valve timing,with decreasing of negative valve overlap interval,the peak pressure,the maximum rate of pressure rise and indicated mean effective pressure(p_(IMEP)) will increase along with the advancement of auto-ignition timing.For fixed valve timing,with the increase of engine speed,exhaust temperature will increase and earlier auto ignition will occur due to higher EGR rate and less heat loss.Through the adjustment of valve timing,wide HCCI operation region with engine speed from 880 r/min to 4 000 r/min and p_(IMEP) from 0.25 MPa to 0.75 MPa can be obtained without intake charge heating.