Oxidation Characteristics Of Particulate Matters From Diesel Engine

Due to the increasing demand of engines in transportation applications,diesel engine has become a major source of particulate matter(PM)pollutions in atmosphere.Diesel particulate filter(DPF)has high efficiency for PM filtration,hence it becomes the necessary aftertreatment device for diesel engine.However,the DPF requires regeneration and ash elimination.The regeneration of DPF is one of the problems to be solved,as the efficiency of regeneration involves fuel economy,DPF lifetime and engine reliability.The objective of this research is to provide ideas for improving DPF regeneration performance by analyzing the PM oxidation characteristics.Based on an experimental diesel engine,PM emissions are measured under various control strategies with different fuels.The effects of various operating strategies on PM oxidation are analyzed.Furthermore,the mechanism of oxidation reactivity variations is elucidated by physicochemical characterizations,and the different oxidation modes are also explained.(1)The effects of thermogravimetric procedures on the PM oxidation reactivity are analyzed.It is found that the optimal sample mass is between 0.5-3 mg,as the variation of mass in this range has minimum influence on measurements.Non-isothermal method has better repeatability and precision than isothermal method.A moderate temperature ramping rate should be applied,because higher rate results in lower precision temperature control,while too low rate results in low experimental efficiency.As to the sample state,PM sample which is trapped on quartz filters causes higher bias.The soot sample separated from any other supporter has better stability in thermogravimetric analyses.(2)The effects of engine control strategies on PM oxidation reactivity are analyzed.It is found that the PM generated at low load has higher reactivity.With the post-injection,the produced PM has lower oxidation reactivity than that from single injection.As the post-injection interval increases,the oxidation reactivity becomes lower.With the application of DOC and POC,the oxidation reactivity of generated PM increases.(3)The oxidation characteristics of PM from biodiesel,China-III diesel and China-V diesel are compared by analyzing the specific area,functional groups on the surface and nanostructures.Two different oxidation modes are found.It is found that the oxidation reactivity of biodiesel particulates is higher than diesel particulates.Particulates from China-V diesel has slightly higher reactivity than that from China-V diesel.The biodiesel particles have higher specific surface area and contain more amorphous carbon.Based on the morphology analyses by HRTEM,it is found that particles from all three fuels can show interior oxidation at certain oxidation degrees.Biodiesel particles tend to be interior oxidation mode more notably than diesel particles.Diesel particles tend to be surface oxidation mode because the interior oxidation only occurs at very late stage.Based on the fringe length analyses,it is found that during the oxidation processes,graphitization occurs in different extend.The biodiesel particles experiences more notable graphitization than diesel particles.