| For the automotive industry,one of the most important thing is the engine,which must have low cost,high performance,the owners willingness to accept and optimization performance,to meet the most stringent emission requirements,and good economy.This is a systematic project,and the essence is to use various ways to tap the full potential of the engine,then develop a new generation of high-performance engines.The traditional port injection gasoline engine inject fuel to intake port and inlet valve wall.The fuel absorbs heat from intake port and inlet valve wall,and volatilize to a uniform mixture into the combustion chamber.While gasoline direct injection engine inject fuel directly into the combustion chamber.The fuel is gasified in the combustion chamber.Endothermic gasification makes the intake air cooled,so the air density increases and the charging efficiency improves.Meanwhile combustion chamber is cooled,and the engine knock tendency is reduced.In this thesis,the research object is a gasoline engine named CA4 GA.It's a new ideas,that the port fuel injection engine inject fuel in the intake stroke to achieve high power output at full load conditions.It makes engine power improve by changing the fuel injection strategy.The injection of fuel into the cylinder of the port fuel injection engine is considered in four ways: stripping atomization,spray atomization,oil film extrusion,oil film deposition at the bottom of the valve and the cylinder head.The fuel injection process of the fuel port gasoline engine has a significant influence on the combustion process in the cylinder.In the closed valve injection mode,the mixture distribution in the cylinder is uniform at compressed dead center.In the open valve injection mode,most of the fuel vapor is in the cylinder,but the fuel droplets and wall film form have emerged.At the ignition time,the cylinder air-fuel ratio changes greatly and obvious layering.In addition,under the full load condition the influence of the intake air velocity on the fuel injection can not be ignored.When using the open valve injection,the fuel wall phenomenon is more obvious,and only half of the fuel is in the cylinder.It is very important to match the fuel injection time with the airflow velocity under this condition.In this thesis,to solve the problem of uneven fuel atomization when the valve is opened,the improved design and simulation analysis of the fuel injection system are carried out,and then the test is carried out to verify the influence of the opening valve injection on the power and emission.The effects of injector parameters on the mixture preparation process are investigated by using simulation on a port fuel injection engine.The effects of fuel injection timing on power and emission performance under full-load condition are investigated by using experiment.The results show that: after improving the design of injector,homogeneous mixture witch open-valve injection need can be produced by optimizing the injector's spray angle,installation angle and installation position.There is a best EOI(End Of Injection)at speed of 1200r/min~5600r/min.When EOI is 420°CA,comparing with the closed-valve injection,the optimized open-valve injection makes the power performance increasing by 1%~2%,and has little impact on THC(Total Hydrocarbons)emission.While at speed of 6000 r/min,the closed-valve injection has better power performance. |
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