Research On Scavenging System Matching Method And Optimization Of Opposed-piston Two-stroke Engines

Scavenging process is essental in two stroke engines.Different from four stroke engines,burnt gas in cylinder is replaced by fresh air by pressure difference between intake ports and exhaust ports to accomplish the scavenging process in two stroke engines.During this process,not only the burnt gas and fresh air mixturation phonemenon will happen,but also the fresh air short circuited unavoidable exist.The choice of the scavenging parameters not only influences the cleaning situation of burnt gas in cylinder but also the engine working efficiency will be affected.So the investigation of matching and optimization of two stroke engines scavenging process should be carried out.In this paper,based on OP2S(Opposed Piston Two Stroke)principled sample engine which developed by the research group.The main investigations are including:1)The disscussion about OP2 S engines 1D-3D coupling simulation method is made.Accurate results can be got by untilizing the synthetic svavenging profile which is got by3 D CFD(Computational Fuild Dynamics)as 1D simulation boundary condtion.OP2 S engine experimental test bench is built and scaveing process validation and fuel consumption validation are respectively done by tracer gas method and weight type fuel consumption meter.2)The main scavenging parameters of OP2 S engines are pressure difference,exhaust pressure,the length and width of intake ports and exhaust ports.Scavenging process evaluation criterias are carried out by four aspects including scavenging over-all evalution parameters,gas mass trapped in cylinder,sub-scavenging periods accomplishment ratio and short circuited fresh air.On the basis of clearing the scaveing parameters and scavenging evaluation parameters,the influences of scavegnign parameters to scavenging evaluation parameters are investigated.3)The influences of intake and exhaust pressure to engine power and fuel consumption are investigated with the form of tandem compound supercharged OP2 S engine.Uniflow two stroke engines power satisfying and fuel consumption matching methods are concluded.By ultilizing fuzzy control theory,fuzzy contrl models which built by Matlab/Simulink are couply simulated with GT-Power software and automotive optimizing with the goal of optimizing fuel consumption can be carried out.4)The influences of length and width of intake ports and exhaust ports to engine power and fuel consumption are investigated.The ports length variation has more obviously regulating effects to engine performance than the ports width varation through orthogonal experiment and range analysis.A set of ports length adjustable structure is designed to ultilize the intake and exhaust ports length contiounsly adjustment.For different ports length,the influences of ports length variation to engine fuel consumption are reached under the condition of designed engine power satisfied.Because of the non-linear variation rules,with the goal of optimizing fuel consumption,GA-SVM(Genetic Algorithm-Support Vector Machine)is introduced to predict reasonable intake ports and exhaust ports combination based on machine learning theory and optimized intake ports and exhaust ports combinations for different engine speed are calculated.5)Relying on the aerial piston engine development project which applied by research group,OP2 S diesel virtual engine for aerial application are developed.Based on the design requirements and with the goal of optimizing fuel consumption,intake and exhaust pressure and intake ports and exhaust ports combination are predicted by applying the ports length adjustment structure,intake and exhaust pressure optimizing methods,intake ports and exhaust ports combination optimizing methods which are found in the former chapters.To validate the project feasibility,CFD model is built,and the results are compared with 1D simulation results.