The Effect Of Combustion Boundary Conditions On Properties Of Particulate Emission In Diesel Engine

The past few decades have seen the rapid development of global automotive industry.Cars make our life more convenient, but meanwhile they also brought increasingly seriousenvironmental problems. In recent years, the community shows increasing attention onparticulate matter emissions from vehicles resulting from haze problem nationwide.Particulate emissions from diesel engine are many times more than that of gasoline engine,and these particulate emissions contain a variety of carcinogens, which bring damages tohuman organs, and related research shows that there is a close link between the degree of thedamages and the particle size, the ultrafine particles (DP≦100nm) are more harmful tohumans. This article mainly focus on the properties of particle emissions under differentconditions of fuel injection and EGR, and exploring the influence of the combustionboundary conditions on ultrafine particles size distribution.A state IV diesel engine test platform was established in this study, and we alsodesigned and developed three measuring devices, which include: electronically controlledfuel injection system and EGR system, two-stage exhaust particles dilution system. Theelectronically controlled fuel injection system and EGR system were used to control the keyinjection parameters and to adjust the composition and temperature of the engine intakerespectively. Two-stage exhaust particles dilution system was used to dilute and cool downthe exhaust air, only by this step can the exhaust air meet the measuring standards. With theabove three devices, the combustion boundaries could be adjusted effectively and theexhaust particles could get measured accurately, finally, the influence law of combustionboundaries could be drawn.The results shows that:1. The distribution area of most diesel engine particles was between5nm to200nm.Under different working conditions, the number of all modes particulates went downas the main timing advanced under light and medium load conditions, under heavy load conditions, it shows the opposite results. The number of all modes particles decreased withthe increases of premixed combustion proportion.2. For the effects of injection parameters, with the amount of pre-injection rising,number concentration and proportion of nucleate particles were both reduced, butaccumulated particles increased. As the interval between main injection and post injectionexpanded, the peak area of nucleate particles moved towards the smaller diameter direction,and peak area of accumulated particles moved towards bigger diameter direction. Except theaccumulation mode, Number concentration of all modes particles went down, the numberconcentration of accumulation mode particles rose up. With the number of injection stagesgoing up, the peak area of both nucleate and accumulation mode particles went towardssmaller diameter direction, number concentration of all modes particles went down,especially the accumulation mode particles, which were reduced by97.2%. If the injectionstrategy was chosen to be two-stage injection, then we adopted “Mi+Poi” injection strategyfor better particulate emissions reduction.3. For the effects of EGR, With EGR rate rising up, the number concentration ofaccumulated particles went up, but the other modes of particles all went down, when EGRtemperature increased, all modes particles increased, and the increases of their numberconcentrations were significant.