路试状态汽油机缸内热功转换过程性能及影响因素的检测与分析

Diagnostics and analysis of heat to work conversion process and major influencing parameters of IC engine under road test conditions

提出一种能对整车实际路试工况下汽油机的多项运行及性能参数进行连续检测与诊断的方法,应用于某车辆的实际路试工况,获得汽油机瞬态参数,并对该样机进行系统的稳态台架试验。研究结果表明:无论是台架稳定工况还是实车瞬变工况,汽油机缸内热功转换效率主要与50%放热量的位置以及过量空气系数相关;当50%放热量的位置出现在上止点后10°左右(高速略早、低速略晚)时,高压循环热效率达到峰值;而影响50%放热量的位置有点火提前角、转速、负荷、缸内残余废气系数和过量空气系数等参数;该样机标定时由于对缸内残余废气系数的变化缺乏了解,瞬变工况下的过量空气系数与理想值有偏差,从而影响实际热效率;某些过渡工况下点火提前角变化异常,导致热效率偏离理想值。

A new approach was demonstrated which enables continuous detection and judgment of multi controlling and performance parameters in an automotive IC engine under actual road testing conditions. The transient performance parameters of engine were obtained from the typical road testing operations. Steady state engine tests were conducted to help understanding what were observed during the transient tests. The results show that 50% burning position and the relative air-fuel ratio （AFR） are the two most important key factors for the heat to work conversion efficiency in both conditions. The high pressure loop thermal efficiency produces a peak when 50% burning position is located at about 10~ crank angle after the top dead center. In addition to the influencing trend of the spark timing over the 50% burning position, other parameters such as engine speed, load, burnt mass fraction and relative AFR also have significant influence. The relative air-fuel ratio errors observed during the transient tests are caused by the poor estimation of the residual gas fraction in the cylinder, and the spark timing is also identified to exercise dramatic and unreasonable changes under certain circumstances, resulting in significant drop in the thermal efficiency.