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.