Study On Formative Histories And Morphological Properties Of Particulate Matter During Combustion Process

With the increase of diesel engines in the world, the pollution of particulateemissions from diesel engines, which are harmful to the atmosphere environment andhuman health, is getting more and more serious. Therefore, it has a great practicalsignificance to study the formation mechanism of the modem diesel particulates andthen work out the control techniques for them. To investigate the formation mechanismof the in-cylinder particulate and obtain the scientific basis to control the particulateemission from modem diesel engines, the research was carried out using the totalcylinder dumping system developed by predecessors, and its emphasis was on theformative histories and morphological properties of particulate matter duringcombustion process. The major achievements are listed as follows:1. The primary total cylinder dumpling system was optimized. Based on theimproved system, the scientific experimental scheme and sampling method wereestablished, meanwhile, the sampling process was calibrated.2. The disciplinarians of the in-cylinder particulate's mass formation history and itsnumber distribution were investigated by both filtration-weighing method and theElectrical Low Pressure Impactor (ELPI) detection method, meanwhile the SoxhletExtraction method was used to separate the soluble organic fraction (SOF) from thediesel particulates. Experiment results indicated that the particle mass (PM)concentration showed unimodal distribution with the crank angle (°CA). The peakpoint lied at about 13～15℃CA ATDC and the peak value of PM increased with the fuelinjection pressure increasing. During the combustion process, the total particle numberdistribution also presented unimodal distribution with the crank angle (°CA), andreached a peak between 14 and 18°CA ATDC, the particle number distribution waslognormal in form with the particle diameter, and the maximum value was lied atabout 100nm～200nm particle diameter. 3. The investigation on the morphology and microstructure of primary carbonparticle in-cylinder particulates were conducted on a field emission gun transmissionelectron microscopy (FEG TEM), and the results were analyzed by the imagetechnology. The results illustrated that in-cylinder particulates consist of tens tohundreds of near-spherical primary particles, and these aggregate particles exhibit avariety of different shapes, such as clustery, spherical, chain-like, branchlike andarmularity, and they all have fractal nature. A primary soot particle has tow distinctparts: an inner core and an outer shell. The outer shell is composed of graphiticstructure, and the inner core is amorphous structure. It was also found that the primaryparticles size distribution was Gauss distribution, and at the beginning of combustion,the primary particles has a diameter of 15N20nm, the diameter of primary particlesincreased with the processing of combustion, the peak of it was lied about 20～30nmdiameter meter. The average diameter was measured in a range of 16.3～29.7nm, andthe peak value present to 10～15℃CA ATDC. The fractal dimension of diesel sootmeasured was in a range of 1.2～1.74, and it declined at the early diffusive combustionperiod.