柴油机燃烧模式切换过程燃烧特性变化试验

Diesel Engine Combustion Characteristics Variation Under Switching Process

为研究柴油机在传统燃烧与低温燃烧的燃烧模式切换过程中,如何识别缸内当前所处的燃烧模式,以及不同喷油参数在不同的燃烧模式对燃烧特性参数的影响,在一台高压共轨柴油机1 500r·min-1、30%负荷下采用燃油单次喷射、调节EGR率方式实现燃烧模式切换并进行了试验研究.结果表明,EGR率从0增加到55%,缸内燃烧起点位置稍有后移,但变化不大,当EGR率超过45%后,缸内开始进入低温燃烧模式,瞬时放热率曲线初始上升过程,由于冷焰反应持续期增加导致出现的二阶段滞燃,可以作为识别当前的燃烧模式的特征,控制缸内燃烧模式;喷油相位从-14°CA ATDC推迟到-7°CA ATDC,对传统燃烧模式滞燃期和燃烧持续期的影响较小,但对低温燃烧的燃烧持续期影响较大,同时,当喷油相位推迟到-7°CA ATDC时,缸内接近失火;喷油压力从75MPa提高到140MPa,在传统和低温燃烧模式均可以改善发动机的油气混合程度,缸内最大爆发压力及瞬时放热率峰值增加,指示热效率有所增加,但幅度变化不大.

In order to study the way how to identify the combustion region between conventional combustion and low temperature combustion （LTC） under combustion mode switching process in diesel engine, and the effect of different injection parameters on combustion characteristics, experimental investigations were carried out on a common rail diesel engine by single injection and EGR to switch combustion mode at 1 500 r · min-1 and 30% load condition. The results show that, with the promotion of exhaust gas reeireulation （EGR） from 0% to 55%, the position of start of combustion （SOC） is delayed a little but not too much. However, when the EGR ratio is over 45 %, the LTC region is attained. The point of inflection at the beginning of heat release rate （HRR） profile can be used as an indicator to identify the LTC region and control the combustion event. When the injection timing retards from -14℃A ATDC to -7℃A ATDC, it shows little effect on ignition delay and combustion duration on conventional combustion region, but it influences greatly on LTC region. What＇s more, it almost misses fire when the injection timing is tuned to -7℃A ATDC. With the fuel injection pressure increasing from 75 MPa to 140 MPa, it promotes the air-fuel mixing both in conventional combustion region and LTC region. The peak point of in-cylinder pressure and HRR are risen and the indicated heat efficiency slightlyincreased.