添加高比例丁醇对柴油机燃烧和排放的影响

Effect of High-Ratio Butanol Addition on Combustion and Emissions of a Diesel Engine

通过试验结合数值模拟的方法,研究了1,400,r/min、平均指示压力1.0,MPa工况下柴油机采用丁醇/柴油混合直喷和双喷射两种方式的燃烧和排放特性.结果表明,双喷射方式的指示热效率降低且指示比油耗明显升高;混合直喷方式具有最长的滞燃期,而丁醇高的汽化潜热是滞燃期明显延长的主要原因.两种喷射方式的燃烧持续期均比纯柴油的短,混合直喷方式的燃烧持续期最短.与纯柴油相比,混合直喷和双喷射的NOx排放分别增长了28%和9%,燃烧过程中具有更宽的高温区域是混合直喷方式NOx排放升高的原因.混合直喷方式的碳烟排放比纯柴油方式降低约40%,其原因是掺混丁醇后降低了燃烧总体当量比和改善了局部当量比分布均匀性.双喷射由于局部当量比过浓,造成燃烧过程中碳烟峰值较高,而对碳烟最终排放的改善效果不如混合直喷方式.

The combustion and emission characteristics of a diesel engine, operating in high-ratio butanol/diesel blend direct-injection mode and dual-injection mode, were investigated at the speed of 1 400 r/min and IMEP of 1.0 MPa by experiment and numerical simulation. The results reveal that compared with pure diesel mode, the indicated thermal efficiency of dual-injection mode decreases with an obvious increase in indicated specific fuel consumption. Blend direct-injection mode has the longest ignition delay primarily due to the high heat of butanol evaporation. The combustion durations of these two injection modes are both shorter than that of pure diesel mode, and blend direct-injection mode has the shortest duration. Compared with pure diesel mode, NOx emissions of blend directinjection mode and dual-injection mode increase by 28% and 9%, respectively, and blend direct-injection mode has the highest NOx emissions due to its wider high-temperature region. Soot emissions of blend direct-injection mode are reduced by 40%, compared with pure diesel mode, due to the addition of butanol which can reduce the overall equivalence ratio and improve the local equivalence ratio distribution uniformity. However, as a result of local overrich mixture which will result in higher peak value of soot in combustion process, the dual-infection mode fails to achieve an obvious soot reduction.