Transient Simulation And Emission Performance Improvements Of Diesel Engine Using In Small Excavator

Diesel engine with low fuel consumption, high efficiency characteristics, have agood economy and dynamics performance. Diesel engine is widely used in engineeringmachinery because of its superiority in power. For these engines used in engineeringmachinery, most of their work processes are in transient conditions. In transientconditions, many characteristics of diesel engines deviat significantly compared withthe steady state environment. US and EU have implemented transient test cycles fordiesel engines to restrict the pollutant emissions, for example, US FTP(Federal TestProcedure) and EU ETC(European Transient Test Cycle).The combustion process has a significant impact on the power output, fueleconomy and emission behavior of the diesel engine in transient operating conditions,so the thesis based on a direct injection diesel4B2-38M34manufactured by AnhuiQuanjiao Diesel Engine Plant and using the coupling technology of Matlab/Simulinkand GT-Power software simulates two transient operations of the engine which inconstant speed and increasing torque, and constant torque and increasing speed. Alsowe analyze the results.At the same time, the thesis designs an internal EGR system in order to reduce NOxemissions of the diesel engine. The technology called the internal EGR is relying on thespecial design of valve tram to increase the amount of exhaust gas remained in cylinder.The main method to achieve internal EGR is changing valve overlap angle. Eitherclosing exhaust valve in advance to reduce the valve overlap angle or even zero to makepart of exhaust gas remain in cylinder which will participate in combustion in the nextcycle, to achieve internal EGR, or to delay closing the exhaust valve to increase thevalve overlap angle to make part of exhaust gas back into the cylinder so as to achieveinternal EGR.This paper uses a camshaft with bimodal exhaust cam. This kind of camshaft makesEGR exhaust cam open the exhaust valve slightly when piston close to the bottom deadcenter in suction stroke, and then the large vacuum degree will suck the exhaust gas inexhaust pipe into the cylinder, in order to achieve internal EGR. This paper simulatesthe whole work process of an excavator diesel engine to study the impacts of position,lift and cam angle of the little cam on engine power, fuel consumption ratio and NOxemission. Then the emission testing of the diesel engine under EPA eight conditions is made to identify the optimization result. Based on the coupling technology ofMatlab/Simulink and GT-Power，this paper simulates a transient operation of theengine.It is concluded that the emission of NOx reduced significantly after adopting thedouble-peak exhaust cam from the test result, at the same time, CO and HC emissionsdecreased a little, and it had not important impact on engine power and oil consumptionratio. In the torque increasing operation, with the increase of the rate of change oftorque, intake decreases and fuel consumption does not change obviously, as a result theair-fuel ratio decreases.