Simulation Research On Effects Of Multiple Injections And EGR Rates To Biodiesel/Ethanol Blended Fuel Combustion And Emission Performance

Driven by environmental pollution and energy stress,biodiesel,a clean alternative fuel for diesel engines,has attracted extensive attention from domestic and foreign experts because of its excellent environmental protection and renewable properties.Meanwhile,to further reduce diesel engine emissions,the combination of multiple injection and EGR can be used to improve the NOx and soot emissions by improving the combustion process.Based on the six-cylinder turbocharged diesel engine,the different fuels(BD100,BD90E10,BD80E20,BD70E30)were bench-tested at 1600r/min,and their combustion and emission characteristics were analyzed.Based on which,this thesis,by using GT-power onedimensional simulation software,also made a further study of various injection strategies,including pilot-main spray,main-post injection,and pilot-main-post injection,and researched the effect of EGR Rate on Combustion and Emission performance of Diesel Engines.The test results show that the ignition delay period of biodiesel has been postponed along with the increasing of ethanol;besides,biodiesel can reduce soot emissions effectively.When ethanol waxed,soot waned,while the emissions of HC and NOx increased.Considering above,BD80E80 is a suitable mixed fuel proportion.The simulation yields that when using the pilot-main injection strategy,the soot and NOx can be improved as the interval was shorter.Contrally,NOx increased while soot decreased as the intervals were longer and pilot injection quantity was larger.When the mainpost injection strategy is adopted,NOx and soot emissions can be reduced simutaneously.When the load is small,a smaller main-post injection interval should be used,the load should be increased,the main-post injection interval should be increased properly,and the amount of post-injection should be increased.Both NOx and soot emissions are reduced.The results also indicate that the combustion and emission patterns of diesel engines under pilot-main-post injection strategies are consistent with the pilot-main injection and main-post injection strategies.Overall,multiple injection injection strategies can effectively improve the trade-off relationship between NOx and soot and reduce NOx and soot emissions.In a single injection,as the EGR rate increases,NOx emissions are greatly reduced while the soot increased,and the power and economy of the diesel engine are reduced as well.Therefore,the EGR rate should not be too high.When the EGR rate is around 0.2,the integrated emissions of NOx and soot perform well.When the EGR and the after-injection are coupled,the combustion and emission of the engine are similar to those of a single injection,and the after-injection has a little effect on NOx,but the soot emission is greatly reduced.