Effects Of Hybrid EGR And Regulated Two Stage Turbocharging System On The Combustion And Emissions Of A Diesel Engine

More and more stringent emission regulations is being put forward for reducingdiesel engine NOx and particulate (PM) emissions. Therefore, how to maintain goodeconomy to reduce PM and NOx emissions to achieve high efficient andlow-pollution diesel engine to meet increasingly stringent emission regulations hasbecome a common problem and challenge faced by the diesel combustion technology.Two-stage turbocharging and exhaust gas recirculation technology are considered asone of the most important and efficient technical routes to meet the EURO IV andmore stringent emission standards.This research was carried out on a two-stage turbocharging electronicallycontrolled high pressure common rail diesel engine. Firstly, a group of experimentsabout the comparison of different EGR styles were carried out to have a goodknowledge of these EGR,s different effect on the diesel engines economy andemissions.The research shows that: In low-speed and large load conditions, the use ofthe low pressure EGR, a higher oxygen ignition equivalence ratio、a better trade-offrelationship between NOx and Soot and a lower fuel consumption can be obtained.While in small load condition, compared wit the pure low-pressure EGR, the use ofhigh-pressure EGR can reduce the pumping losses by reducing the eddy and thedifferential pressure after throttling and achieve a longer ignition delay andcombustion duration shorter to reduce the fuel consumption rate and improve thetrade-off relationship between NOx and Soot; In Large load and medium speedcondition, high-pressure EGR can achieve both a lower BSFC and a better trade-offrelationship between NOx and Soot; Then in medium or large load and high speedcondition, the hybrid EGR can achieve a better trade-off relationship between NOxand Soot than either the pure high pressure EGR or the pure low pressureEGR,though the BSFC increases with the increasing of the proportion of thelow-pressure EGR in total EGR rate.Based on the comparative study among different EGR styles, the research ofbypass valve coupling with EGR was carried out. The research shows that: moderateopening of the bypass valve in the fresh intake air quantity sufficient conditions caneffectively reduce BSFC and improve emissions, such as in high-speed small loadconditions; Relatively, in lack of fresh gas conditions, the opening of the bypass valvewill result in double deterioration of BSFC and emissions, such as in low speed andhigh load conditions; By using low-pressure EGR, the opening of the bypass valvecan effectively improve the economy in both small load condition and high-speedconditions, without causing a significant deterioration of the emissions, even can reduce emissions of soot and NOx in small load condition; In high-speed and largeload condition, Hybrid EGR coupling with bypass valve,keeping NOx emissioncontrol EURO V level,the bypass valve opening will result in a rising of sootemission while a slight variation on BSFC.