Effect Of EGR On Performance And Cyclic Variation Of Port Fuel Injection Engine

Energy conversion and reduce emissions have always been directions of engineresearchers. EGR technique, as one of effective measures to reduce NO_Xformation,was firstly adopted in diesel engines. But with the growing energy and environmentproblems, EGR has been commonly used also in gasoline engines together with otheradvanced techniques. At present, the application of EGR in gasoline engine is notvery mature. The main reason is that engine performance will decrease after usingEGR, and cyclic variation will increase with the increase of EGR ratio. Accordingly, itis necessary to research the effect of EGR on engine performance and cyclic variation.This paper transforms a carburetor engine to a PFI engine, and established a externalEGR system on this basis, then carry out experiment to research the effect of EGR onengine performance. Last, the effect of EGR on engine cyclic variation and themethod to reduce it is studied by simulation method.Relative to the traditional method to produce initial MAP, this paper establish amathematic model to gain initial injection MAP, it is a new method. Mean valueengine model of Ricardo E6engine is established in MATLAB/SIMULINKenvironment, the initial MAP is obtained by simulation. Then, import it to MOTECECU as the basic injection pulse; it can keep the engine operation, so it is reasonableto produce initial MAP by simulation method. The engine calibration is made on thisbasis which stoichiometric air-fuel ratio is as a target, and then the work of changecarburetor engine to PFI engine is done. At last, the experiment is done to test theexternal characteristic at different air to fuel ratio of the engine, and obtained thechange of torque and power with engine speed.The external EGR system is established at the Ricardo E6single cylinder engine,this system include EGR pipe, EGR valve and EGR cooler. The experiment is doneunder different throttle opening and EGR ratio, to get the change of engine torque,power, fuel consumption, cylinder pressure and NO_Xemissions. In addition, thecomparison is made at wide open throttle and different compression ratios, the changeof BMEP and NO_Xemissions with EGR ratios. The obtained results show that whenthe throttle angle is constant, engine torque, power and maximum cylinder pressurewill decrease with the increase of EGR ratios, but NO_Xemissions will decrease. Inaddition, the combine of EGR and compression ratio can achieve a balance ofperformance and NO_Xemissions.The operation of gasoline engine is largely limited by cyclic variation, especiallyunder high EGR dilution; therefore it is necessary to research the effect of EGR oncyclic variation of gasoline engine. This paper using CFD simulation by FIRE code,considering influencing factors of cyclic variation under EGR condition, in addition,the method to reduce cyclic variation is discussed. First, AVL-BOOST software isused to construct the whole engine model of Ricardo E6single cylinder engine, theexperiment validation is made and obtain the initial and boundary condition by simulation. UG software is used to construct solid model of the engine includingintake port, combustion chamber and exhaust port, then this model in imported toFIRE code to generate moving mesh, then take the combustion simulation underdifferent EGR ratio, compression ratio and boost pressure. The obtained results showthat cyclic variation is increased with the increase of EGR ratio, but it is decreased byincreasing the compression ratio and boost pressure.