Study On Control Strategy For Electronically Controlled Common Rail Dimethyl Ether Engine Meeting National ? Emission Standard

Under the pressure of increasingly scarce oil resources and severe environmental problems,it is very important to find high efficiency and clean alternative energy sources for the engine.As an alternative fuel to diesel fuel,dimethyl ether?DME?can maintain the high thermal efficiency of the compression ignition engine and simultaneously realize soot-free emission.To develop a DME fueled engine meeting the National V stage emission regulations has important practical significance to improve the energy structure of vehicle fuel in China and environmental pollution environment.Based on the electronically controlled common rail injection system,this research has firstly investigated the influences of injection strategy and injection parameters on combustion,emission and performance of DME engine.The soft modulation of different combustion heat release modes was achieved by adjusting the injection strategy and changing injection parameters.On this basis,the high pressure exhaust gas recirculation?EGR?was used to reduce NOx emissions,and the effects of EGR rate on the different combustion modes were also studied,while taking the post-processing technology?Diesel Oxidation Catalyst:DOC?to solve the problem of HC and CO emissions caused by EGR.The research on different injection strategies showed that DME engine could perform three different combustion heat release modes under different injection strategies and different injection parameters.Postponing the main injection time and decreasing the injection pressure could reduce NOx emission of DME DICI engine and PPCCI engine,but it would cause an rise of HC and CO emissions.With the increase of interval_pilot-main,the DME engine would be transformed from the two stage combustion heat release mode into the PPCCI three stage combustion mode,and the NOx emission was significantly reduced,but the CO and HC emissions gradually increased.In addition,increasing the pilot-injection quantity at the low load could further reduce the NOx emissions of DME PPCCI engine,but it would raise the NOx emissions slightly at the medium load.Based on the DME DICI and PPCCI combustion heat release modes,the influence of EGR on the DME engine was further studied.It showed that EGR could effectively reduce the NOx emission,but the HC and CO concentrations were significantly increased,and with the increasing of load,the influence of EGR on the DME engine would be more significant.For the DICI mode,the proper EGR rate could improve the economy of the DME engine at the low load,For the PPCCI mode,at the low load,the increase of the pilot-injection quantity could further reduce the NOx emission at different EGR rates,but the change of pilot-injection quantity had little effect on the NOx emission at the medium load.The effects of diesel oxidation catalyst?DOC?on the emission characteristics of DME engine were also studied in this paper.The results showed that the DOC had a very good oxidation effect on HC and CO.Almost all the CO and the majority of HC in the DME engine exhaust gas could be oxidized by DOC.In order to make DME engine meet the National V stage emission regulations,the potential of different control strategies of the DME engine was further studied.Studies showed that,only using injection strategies and injection parameters optimization,DME engine could meet the National III stage emission regulations;but compared to the reference baseline(EBSFC_DME=213.05g/kWh),the EBSFC_DME increased by the rate of 2.34%.Using EGR+DOC+Injection strategy collaborative optimization,the DME engine could meet the National V stage emission regulations,but compared to the reference baseline(EBSFC_DME=213.05g/kWh),the EBSFC_DME increased by the rate of 4.20%.In addition,using the NH₃-SCR strategy?volume ratio,NH₃:NOx=0.8:1?in the best fuel economy(reference baseline,EBSFC_DME=213.05g/kWh),the NOx emissions of DME engine just a little higher?0.07g/kWh?than National V stage NOx emission limit.While,implementing the NH₃-SCR strategy?volume ratio,NH₃:NOx=1:1?in the best fuel economy(reference baseline,EBSFC_DME=213.05g/kWh),the DME engine could meet the National V stage emission regulations with much surplus.