Influence of nozzle hole diameter on combustion and emission characteristics of diesel engine under pilot injection mode

Abstract

Present work was divided in two different parts. In first part, an experimental study was carried out to analyze the effect of dwell on diesel engine combustion and emission characteristics. Experimental data showed that shorter dwell results in improved specific fuel consumption (SFC) but with increased smoke emissions penalty. To overcome the disadvantage of higher smoke emissions associated with shorter dwell, an effort was made to reduce smoke emissions under pilot injection mode by changing nozzle hole diameter (NHD) while keeping rest of the injection parameters unchanged. In second part, this was done numerically by using commercial Converge 3-D computational fluid dynamics (CFD) tool. In addition to baseline NHD (0.120 mm), two other NHDs i.e. 0.08 mm and 0.160 mm were considered. Numerical results showed that for given injection parameters, lower NHD resulted in faster evaporation of injected fuel as well as greater homogeneity of the mixture prepared due to better air entrainment inside fuel spray and hence led to overall faster combustion process. This faster combustion process subsequently reduced the time available for spray interactions. Therefore, in spite of getting further shortening of dwell in case of 0.08 mm NHD compared to other two cases, soot emissions were reduced by 87.2% when NHD was reduced from 0.160 mm to 0.08 mm. However, nitric oxide (NO) emission was found to increase by around 43% when NHD was reduced from 0.160 mm to 0.08 mm.