Influence Of Residual Ash On DPF Regeneration By Non-thermal Plasma Technology

Diesel particulate filter?DPF?is an efficient technology in the field of particulate matter?PM?emission control.The timely regeneration and ash removal are the key problems of DPF.Based on non-thermal plasma?NTP?technology,the residual ash deposition test project was designed and completed.The effects of residual ash on DPF capture and regeneration,the physicochemical properties of residual ash were studied in this paper.The main researches are as follows:?1?Different initial content of ash was loading in the DPF filter channel for PM capture and oxidation.The influence of residual ash on DPF backpressure,trapping ratio,regeneration duration,peak temperature of measuring point and carbon removal mass was explored.The results indicated that the trapping ratio of particle with smaller size was significantly improved due to the existence of residual ash,but the backpressure of DPF was increased.DPF regeneration by NTP technology was gradually achieving from DPF front-end to back-end which illustrated the high utilization rate of NTP.With the raise of ash content,regeneration duration,peak temperature of measuring point and carbon removal mass increased.Therefore,in practical application,the ash content in DPF should be controlled in a reasonable range to improve PM capture rate and prevent DPF from overpressure or long regeneration time due to excessive ash content.?2?An energy dispersive spectrometer?EDS?and a laser Raman spectrometer was applied to investigate the elements composition,chemical heterogeneity,graphitization degree and amorphous carbon content of ash which was remains of DPF regeneration by NTP technology.The results showed that the residual ash is grey brown.The ash is mainly powder in light load engine conditions,but the major shape of ash became strip in heavy engine load.When the engine load increased to 100%,more strip ash with size from 6 mm to 10 mm appears.Besides C,O and S,there were some Na,Ca and other metal elements contained in the ash.The values of I_D1/I_G ranged from 1.5 to 1.8,and the values of I_D3/I_G ranged from 0.4 to 0.7.The values of I_D1/I_G and I_D3/I_G decreased with the increase of engine load,which indicated that the graphitization degree increased,and content of amorphous carbon decreased.When the engine load increased,the full width at half maximum of D1 peak ash sample increased gradually,while that of G peak increased first and then decreased.In general,the chemical heterogeneity of ash increased,and the structure of ash sample was more diversified.?3?In order to reveal the physicochemical properties,the surface functional groups and occurrence forms,proportion of elements were analyzed by means of Fourier transform infrared spectrometer?FTIR?and X-ray photoelectron spectrometer?XPS?.It was found that the ash contained alkyl and some oxygen-containing functional groups such as O-H?C-O?C=O.The XPS survey scan patterns of ash showed that the total molar proportion of C and O was about80%,and the molar ratio of C and O was 0.657 to 0.839.The total molar proportion of metal element?such as Ca and Na,et al?was 13.96%to 14.67%,and the molar proportion of S was2.98%to 3.67%.There were three occurrence state of elements C,C-C,C-OH and O-C=O,with the ratios of 49.6%⁵1.5%,13.9%¹5.9%,33.8%³6.1%,respectively.Elements S occurred in the form of SO₄^2-and SO₃^2-.The ratio of SO₄^2-was about 40%,and the rest was SO₃^2-.The molar proportion of S element in the ash obtained from 75%load reached a higher value,stated that more inorganic salt occurred in this sample.The molar proportion of O element was about 43.64%to 48.11%with the 25.79%to 30.81%molar proportion of organic O.Besides SO₄^2-and SO₃^2-,some inorganic oxygen occurred in ash in the form of metal oxides.