进气门早关对柴油机进气和燃烧特性的影响

在一台SD2100TA柴油机上安装了全可变液压气门机构,采用进气门早关(EIVC)的方式对进气量和有效压缩比进行调节,并对进气性能和燃烧性能进行了研究。试验研究结果表明:与节气门进气量调节方式相比,EIVC能有效降低泵气损失,且能够降低缸内工质温度,有利于实现低温燃烧。随进气门关闭时刻(IVCT)的提前,有效压缩比降低,压缩终点压力和温度下降,滞燃期增长,着火推迟,预混燃烧比例上升,扩散燃烧比例下降,由于工质总热容降低,燃烧后的缸内工质温度增加,导致排气温度显著提高。在保持指示热效率基本不变的前提下,EIVC可以有效地降低缸内峰值压力,拓宽柴油机负荷范围。在1 650r/min、平均指示压力(IMEP)为0.64MPa工况点,当IVCT从下止点后30°提前到下止点后-50°时,峰值压力降低了26%。

Effects of Early Intake Valve Closing Actuation on Intake and Combustion Characteristics on Diesel Engine

A fully variable hydraulic valve actuation using early intake valve closing (EIVC) mode was developed and assembled on a SD2100TA diesel engine to adjust intake mass flow and effective compression ratio in a large speed range. The intake and combustion characteristics of the modified engine were investigated. The experimental results show that, compared with the throttle valve control mode, the pumping loss is reduced substantially and the mean cylinder temperature is decreased in EIVC mode, which is beneficial to low temperature combustion (LTC). With the advance of intake valve closing timing (IVCT), the effective compression ratio is decreased, the cylinder pressure and temperature at the end of compression stroke are lowered, the ignition delay is increased, the start of heat release is delayed, the proportion of premixed combustion is increased, the proportion of diffusion combustion is decreased, and the exhaust temperature is decreased because of the reduction in the heat capacity. A significant reduction in the peak pressure is attained providing that there is little variation in indicated thermal efficiency, with which a larger output power is obtained. The peak pressure is reduced by 26% at 1 650 r/min and IMEP of 0.64 MPa when the IVCT is advanced from 30° to -50° in crank angle after BDC.