Effect Of Injecting Methanol At Intake And Exhaust Pipes On The Active And Passive Regeneration Of DPF

In order to meet the emission limit of particulate number（PN）in the China VI emission regulations,diesel engines need to be equipped with diesel particulate filters（DPFs）.In practical applications,DPF needs the periodic active regeneration,which will increase diesel consumption.Injecting methanol into intake gas（IMIG）can reduce the emissions of nitrogen oxides（NOx）and particulate matter（PM）in the cylinder and promote the generation of nitrogen dioxide,which can help the passive regeneration of the DPF and then reduce the frequency of active regeneration.Methanol,due to its low price,easy evaporation and no sulfur,has great advantages as an external energy source for active regeneration.However,the effect of injecting methanol into exhaust gas（IMEG）on the active regeneration of DPF is unclear.Therefore,it is necessary to study the effect of IMIG and IMEG on the active and passive regeneration performance of DPF.Based on the above requirements,this subject carried out detailed experimental research on a turbocharged and intercooled high-pressure common rail four-cylinder diesel engine equipped with the system of IMIG.The engine is equipped with a set of IMEG on the original catalytic continuously regeneration trap（CCRT）system.The main research contents and conclusions are as follows:（1）A route is proposed to achieve the active and passive regeneration of DPF by the IMIG and IMEG.The research about this route conducted on the engine shows that IMIG can greatly reduce the emission of PM in the exhaust gas and reduce the pressure of PM accumulation on the DPF.The IMEG can increase the DPF inlet temperature and provide suitable conditions for the active and passive regeneration of DPF.This route not only provides a new technical route for DPF to achieve the active and passive regeneration,but also can reduce the diesel consumption and carbon dioxide（CO₂）emission.This work studies the engine performance of pure diesel and IMIG mode（the substitution rate of methanol to diesel is 40%）.The passive regeneration of IMIG combined with the CCRT system is the main way,and the IMEG to assist the active regeneration is as a supplement.Combining the steady-state test data and the passive regeneration balance model based on the Arrhenius equation,it is found that the continuous passive regeneration conditions of the diesel engine equipped with IMIG system account for 61.5%under the premise of meeting the China VI emission standards,which is 14.3%higher than those of the pure diesel mode.It effectively reduces the frequency and energy consumption of active regeneration.Compared with other methods,the IMEG can achieve higher regeneration temperature and lower fuel consumption.In comparison,the fuel consumption can be reduced by 2.45%at the maximum.（2）The law of the influence of diesel oxidation catalyst（DOC）on the regeneration process is obtained and the thermal management control strategies are proposed.The experiment compares the effect of two DOCs with different ratios of catalytic volume to displacement on various import and export parameters.The DOC with the high ratio of catalytic volume to displacement can improve the performance of active and passive regeneration.The control strategies of thermal management are as follows:1)At medium and low loads,the engine preferentially uses the intake and exhaust throttling to increase the DOC inlet temperature.Result shows that the heating effect of intake throttling is stronger than that of exhaust throttling.2)The close-post injection and late-post injection strategy are introduced.Result shows that the effect of increasing the quality of close-post injection on increasing the DOC inlet temperature is better than that of delaying the close-post injection timing.According to the test results,the best close-post injection timing is 35°CA ATDC.The late-post injection strategy has little effect on the DOC inlet temperature,while the quality of late-post injection has a greater influence on the DOC outlet temperature.3)Adopting IMEG can increase the DOC outlet temperature,which is beneficial to the regeneration of the DPF.Result shows that the IMEG combined with the phased heating strategy can achieve ultra-low secondary pollutant emissions,and does not need to use the heating measures of DOC inlet temperature at low loads,which can expand the operating range.4)The combination of IMIG and the above-mentioned thermal management methods can further increase the DOC outlet temperature and greatly reduce NOx and PM emissions.Result shows that IMIG is more resistant to the throttle of the intake and exhaust.When the opening of the intake throttle and exhaust back pressure valve is less than 30%,as the opening decreases,the PM emissions in IMIG mode first increase and then decrease,while the PM emissions in pure diesel mode increase significantly.（3）The IMIG has an important influence on the carbon loading,regeneration balance and passive regeneration performance.Result shows that IMIG can effectively extend the carbon loading time of CDPF,and expand the operating boundary of continuous passive regeneration.The balance point temperature used to evaluate the passive regeneration performance parameters decreases with the increase of the amount of IMIG,and the maximum decrease is 9.64%.During passive regeneration,with the increase of the amount of IMIG,a large amount of PM in the soot cake layer in the CDPF will be oxidized and burned.Although the filter efficiency of PM will be reduced,the efficiency and rate of passive regeneration will be improved.（4）The IMIG and IMEG have an important influence on the performance of active regeneration.Results shows that the IMIG and IMEG can effectively reduce regeneration energy consumption and CO₂ emission,and improve the efficiency energy ratio of regeneration.After IMIG and IMEG are used,the DOC will increase the inlet temperature of CDPF,thereby increasing the efficiency,rate and efficiency energy ratio of active regeneration.Considering regeneration safety and energy consumption,it is recommended that the CDPF inlet temperature is 550℃during active regeneration.During active regeneration,with the increase of the amount of IMIG,the emissions of PM in the exhaust gas are reduced,and the filter efficiency of PM in the CDPF is increased.The study points out that during the active regeneration of CDPF,when the concentration of PM after the CDPF suddenly increases,the proportion of accumulation mode in particulates increases significantly.The position where the maximum temperature and the maximum temperature gradient appear in the CDPF is mainly affected by the initial carbon loading,and is slightly affected by the IMIG and IMEG.At the same regeneration temperature,the IMIG has little effect on the maximum temperature and maximum temperature gradient in the CDPF.