小升程凸轮轴发动机HCCI燃烧特性的研究

为了在发动机的低速低负荷区实现均质充量压缩着火（HCCI）燃烧，设计了气门升程小和气门开启持续期短的进、排气门凸轮轴，并将其安装在Ricardo Hydra单缸汽油机上。试验研究了发动机使用理论空燃比混合气时的燃烧情况，结果表明，使用负气门重叠角可以在低速低负荷区实现HCCI燃烧。在HCCI燃烧方式下运行时的平均指示压力（PIMEP）依赖于气门定时和发动机转速。排气门关闭越早，缸内的残余废气量增加，每循环进气量减少，燃烧持续期变长，PIMEP减小，然而泵气损失减小；进气相位对PIMEP的影响小于排气相位的影响；高的发动机转速对燃烧过程的影响类似于排气门早关．

Study on the Combustion Characteristics of an HCCI Engine with Low Cam Lift and Short Cam Duration Camshafts

To achieve HCCI (Homogeneous Charge Compression Ignition) combustion in the range of low speeds and loads, the specially designed camshafts with low cam lift and short intake/exhaust cam duration were mounted in a Ricardo Hydra four-stroke single cylinder port-injection gasoline engine. HCCI combustion characteristics were investigated on the modified engine. The results show that HCCI combustion was achieved by controlling the amount of trapped residuals through negative valve overlap. Indicated mean effective pressure (IMEP) relies on valve timings and engine speeds. Early exhaust valve closing ( EVC ) timings result in high residual fractions in the cylinder, decreasing air mass in cylinder per cycle, increasing combustion duration, and decreasing IMEP while the pumping loss is decreased. Inlet valve o-pening timings have little effect on IMEP compared to EVC timings. Increasing engine speed on combustion characteristics has similar influence as that of early EVC timings.