The Properties Of Ultrafine Particulate Emission In Common-rail Diesel Engine

The world car ownership has grown rapidly with the rapid development of theeconomy. Diesel engines have been widely used due to its high thermalefficiency，good adaptability，economy and high power output，but diesel nitrogenoxides(NOx) and particulate matter (PM) emissions have caused more and morewidespread concern at the same time. With the evolution of emission regulations，a growing number of new technologies have gradually been applied on a dieselengine. Application of new technologies changed the particles formation andevolution process，high-temperature reaction thermodynamics and kinetics andalso their physical and chemical properties, which result inCombustion-generated particles with smaller size，more complex composition，higher degree of ultrafine and greater harm on environment and human. Europeanemission regulations from EU-5b put a limit on the quantity of particulateemission on the basis of particle mass emission limit. Therefore，the studyon the ultrafine particle(Dp≤100nm) emission of a new generation high-pressurecommon rail diesel engine has important practical significance.In this study, a high-pressure common-rail diesel engine measurement andcontrol system was established for engine transient cycle test. Also, we havedeveloped a partial flow dilution sampling system for diesel engine exhaustparticulates and a two-stage dilution sampling system for particle sizedistribution test. The straight-run diesel was blended with Hydrogenated dieseland Kerosene for different cetane number and volatility fuel. We have determinedthe optimum dilution ratio for engine particle size distribution test and thebasic law of particle size distribution for high-pressure common-rail dieselengine during cruise and transient cycles. We also studied the effect of exhaustgas recirculation (EGR) and fuel properties on particle size distribution andtopography characteristics.The results showed that the particle size distributions for high-pressure common-rail diesel engine were bi-modal with nano-peaks at10nm to15nm andaccumulation-peaks at50nm to100nmr during the cruise cycles. During transientcycles, it was single-peak structure, quite different from that during cruisecycles. EGR could reduce both the number of nano-particles and the totalparticles at low load and increase the total particles emission and nano-particles at high load during cruise cycles. For transient cycles, EGR couldlower the percentage of the nano-particles and the number of total particleemissions but increase the number concentration of the accumulation particles.The ultrafine particles and nano-particles increased rapidly as the sulfurin fuel increased. Lower the sulfur in fuel can reduce the ultrafine particleemissions. An appropriate increase of cetane number in fuel can shorten thecombustion lagging period, reduce premix combustion, increase diffusioncombustion, it could help to reduce the nano-particulate emissions, but a highcetane number would lead to an increase of the accumulation particles. Usually,it is appropriate to select the cetane number from55to60. Improveing thevolatility of fuel helps to improve fuel and air mixing, which reduces thequality of particulate emissions, but will lead to increase in the percentageof SOF and ultrafine particulate emissions. Topography characteristicsobtained using high-resolution electron microscopy is in good agreement withthe particle size analyzer measurement results, it would be an effective methodto analysis the characteristics of ultrafine particulate emissions.