Investigation On Performances Of Gasoline Engine With Variable Valve Timing System

VVT is widely used as an important measure to improve the engine energy-savingand emission reduction. A well designed VVT can automatically change the valvetiming and valve lift with operation condition changing to increase volumetricefficiency, so that good engine combustion is reached to improve engine idle speedstability increase output power and reduce emission.An inline four-cylinder four-stroke gasoline engine was taken as the researchobjective and the influences of two different kinds of VVT system on the gasolineengine performances were compared based on the co-simulation platform withAVL-BOOST and Isight.Finally, a suitable VVT system for the engine was chosen; Anoptimal timing phase for chosen VVT system under different working conditions wasobtained by taken cam timing angle as control parameters and power performances asoptimization target; The in-cylinder flow fields, fuel densitydistributions etc. for theengine without and with VVT system wereobtained based on multidimensional modelunder3600r/min full load condition. The research results have important referencevalues for the practical application of VVT system to the engine.The main contents and conclusions are as follows:1）A one-dimensional simulation model of the engine working process wasestablished and calibrated with test data based on AVL-BOOST, then3parameters, startof combustion angle, during of combustion angle, combustion quality index, werepredictedrespectively.2）The engine performances with the two kinds of VVT system were obtainedunder full load based on the co-simulation platform with AVL-BOOST and Isight,combining with Multi-Island Genetic Algorithm. Finally scenario one was chosen as theVVT system of the engineconsidering the engine power performance and structurerealizability.3）The variations of throttle flow coefficient and pressure drop, air-fuel ratio,ignition advance angle and combustion quality index with the engine speed and loadwere determined, and then the optimal IVC and EVO under various operationconditions were obtained with Multi-Island Genetic Algorithm based on theco-simulation platform with AVL-BOOST and Isight. The results show that, enginepower performances were improved obviously, especially in low engine speeds, and the effective torque and effective power increase by10.6percent compared with theprototype engine.4）The in-cylinder flow fields, temperature fields, fuel and NO densitydistributionsfor the engine without and with VVT system wereobtained based on AVL-FIRE under3600r/min full load condition. The results show that, in-cylinder fuel densitydistributions are more uniform than those of the prototype engine, and in-cylinder NOemits29percent less than that of the prototype engine.