Investigation On The Oxidation Kinetics Of Diesel Particulate

The emission of the diesel particulate is the main reason that causes the serious fog and haze, which must be controlled effectively. Diesel particulate filter(DPF) is an effective way to lower particulate emission from diesel engine, which based on physically captures diesel particulates. The efficient and reliable regeneration of collected diesel particulate in DPF is the critical factor that matters the widespread application of DPF. However, there are a lot of factors that could influence the regeneration of diesel particulate, the oxidation characteristic of diesel particle is a main influence factors to affect the DPF regeneration performance,which has important significance to investigate on it.In this paper, three typical thermal analysis methods are compared based on thermal experimental data of simulating diesel particulate. When the reaction order n is 1, the integration method(Coats-Redfern) can not only calculate the intrinsic activation energy of the particulate, but also calculate the apparent activation energy of the sample. However, it is the intrinsic activation energy of particulate based on Arrhenius and differential(ABSW)methods.The influence of heating rates(10~100 K/min) on the oxidation behavior of particulates is explored. TG and DTG curves gradually shift to higher temperature range and the characterisitic temperature of all particulates increase with the increase of heating rates. The“rapid oxidation” phenomenon of particulate will be appeared randomly and the relative reaction rate increase sharply when the heaing rate is greater than 50 K/min. Compared with low heating rate, more thermal energy is applied to oxidize the carbon black per unit of time under higher heating rate. So, the values of apparent activity energy of particulate decrease with the increase of heating rates.In order to study the influence of SOF on diesel particulate, carbon black and diesel fuel(0#) are used to simulate the SOF content and dry diesel soot. And the real diesel particulates are collected under different operating conditions based on engine condition. There are two oxidation stages during the combustion of simulating particulate, the oxidation of simulated SOF has slight effect on oxidation of carbon black when the simulated SOF content is smaller than 40%. While, the SOF of real diesel soot can promote the oxidation reaction of dry soot and the apparent activity energies of it decrease with the increase of SOF. The reaction order of diesel particulate is about 0.7. The whole oxidation of diesel particulate is divided into two stages: the oxidation of easily oxidized material, for example SOF and the reaction of residual particulate and other easily oxidable content. However, the oxidation of carbon black is a single-stage process and the reaction order is about 1. Compared with carbon black, the ignition temperature of diesel particulate is lower and the oxidation reaction rate is morerapidly. The oxidation characteristics are very similar between the dry soot and carbon black.There is little difference of apparent activity energy between them, so the diesel particulate can be simulated and replaced by carbon black to some extent.The oxidation behaviors are also different if the microstructures of carbon particles are different. Relatively lower ignition temperature and apparent activity energy can be appeared if the ratio between the initial surface area and primary particle size of carbon black was higher. The internal microstructure would get changed when carbon black are applied to different heating treatment. The cumulative surface area of particles would increase when there are more shorter crystallite chain in carbon black. It would be more easily oxidized to carbon black with higher cumulative surface area and shorter crystalline length, which lead to increase the oxidation activity of carbon particles, low the ignition temperature and decrease the apparent activity energy at the same time. The carbon black would sequentially take four oxidation steps during combustion: volatile substance evaporation, amorphous carbon oxidation, graphitization, and combustion finally. Each step can affect carbon black oxidation characteristic.