Study On The Effect Of EGR On The Operating Characteristics Of Oxygenated Diesel Engine At Different Elevations

Conventinal energy depleted and emission regulations increasingly strict forced internal combustion engine development direction toward to low pollution、low fuel consumption and high specific power. The focus of the diesel engine emission control NOx and PM emissions, due to the contradiction between NOx and PM generation mechanism, make diesel engine emission control technology from gasoline engine is more complicated. In order to guarantee the performance of diesel engine, reducing dependence on post-processing technology and cost saving, internal purification have been the core of the research and application of the emission control. Exhaust gas recirculation (EGR) technology is one of the most effective internal purification measures to reduced NOx emission, combined with oxygen fuel blending technology, both help to reduce the degree of elevation rise leads to the deterioration of the diesel engine performance, but also to solve the contradiction between NOx and particulate emissions; study the application of the EGR and multicomponent oxygenated fuel (BED) at different altitudes plateau region, have great significance to realize efficient low pollution combustion on diesel engine.Using atmospheric simulation system, experimental study on the influence of EGR on the performance, fuel economy, emission characteristics and combustion characteristic of diesel, B15E5(volume fraction of diesel、biodiesel and ethanol respectively is80%.15%and5%)fuel and B25E5(volume fraction of diesel. biodiesel and ethanol respectively is70%.25%and5%) fuel in81kPa and simulated100kPa; On the basis of experimental study, use CAE simulation software analysis the engine combustion process, research the influence of EGR on temperature field, spray development and NOx concentration in cylinder of engine combustion process under different altitudes.Analysis results shows:(1)The EGR decreased the power performance of diesel engine; the falling range of B15E5fuel and B25E5fuel greater than diesel; with the loss of atmospheric pressure, the influence of EGR on engine performance is more obvious.(2) The economy efficiency of diesel engine is worsen by using EGR technology; on the whole, the economy efficiency of BED fuel is worse than diesel; the economy efficiency is worse as the altitude higher; under the light load condition, the effective fuel consumption slightly down at81kPa.(3) After using EGR, NOx emissions significant reductions; NOx emissions of B25E5fuel drop to49.6%at2200r/min under81kPa; the NOx emissions reduction range caused by EGR under81kPa is higher than100kPa of4%-6%. Carbon smoke and CO emissions increased with the EGR, the emissions of B25E5fuel respective raised207.7%and79.8%at2200r/min under81kPa; the carbon smoke and CO emissions increased range caused by EGR under81kPais higher than100kPa respectively of30%-263%and45%. The influence of EGR on THC emissions is fluctuant.(4) The simulation calculation results shows:after using EGR, the high temperature distribution of cylinder is greater than without EGR at the same crank angle; in general, the temperature of B25E5fuel is lower than that of diesel; the temperature under high altitude is lower than the temperature of the low altitude. At the same crankshaft, NOx concentration with EGR is significantly lower than that without EGR in cylinder, gathered area is relatively small as well; the NOx concentration of B25E5fuel is slightly lower than diesel. The NOx concentration in the cylinder of81kPa is higher than100kPa.