Study On The Effects Of Cylinder Flow On Opposed Piston Diesel Engine

As the two stroke engine with novel structure, OPOC(Opposed Piston andOpposed Cylinder)engine has the advantages of compact structure, high efficiency,high power density, good overall balance, flexible layout, with so many advantagesmeans that this engine has a broad prospect in application. As a special two strokeengine, although OPOC engine used DC sweep gas, electronic fuel injection, electricbooster technology, but unavoidably it has the common two stroke engine drawback,such as poor exchange quality, incomplete combustion etc.Based on existing research, this paper analyzed the influence of air exchangeprocess in cylinder and the combustion process of OPOC engine, considering the flowcondition of cylinder under different air outlet structure.Aiming at the situations change of the OPOC engine cylinder volume and theinlet and outlet circulation area, this paper firstly calculated the specific motion law ofinside and outside piston in cylinder. Then, the one-dimensional simulation modeleventually established through setting reasonable parameters of the combustion, byanalysis of the simulation model, parameters under different engine speed wereobtained, such as intake and exhaust pressure, scavenging efficiency, pressure incylinder.Setting boundary conditions base on the piston motion simulation results, andestablishing the three-dimensional simulation model of OPOC engine scavengingprocess, then analyzed the scavenging process on the speed of3600r/min,2500r/minand1600r/min, the differences of transient distribution of flow field, distribution ofresidual gas in scavenging process is compared. The analysis revealed some problemsin the original structure such as in-cylinder flow organizational forms unreasonable,scavenging poor quality at high-speed conditions. On the basis of the original air inlet model5°/15°tangential obliquity, threedifferent modification scheme with tangential obliquity of10°/20°,15°/30°,20°/40°were designed, and then for the three different scavenging scheme, the flow incylinder, exhaust residue on different speed were analyzed. To ensure the engine withhigh sweep gas quality in the whole speed span, scheme15°/30°is choosed as thefinal plan.To further study the impact on the overall performance of the selected15°/30°scheme, the combustion process of15°/30°scheme and original scheme in3600r/minare analyzed separately. To ensure the accuracy of the analysis, the simulation modelof engine is established from the exhaust port open to the end of combustion process.By comparing the combustion process with original scheme,it is found that thecylinder flow with optimized scheme is more reasonable, the optimization scheme caneffectively speed up the evaporation process of fuel and combustion exothermic isfaster, at the same time, combustible gas mixture also more evenly distribute, burnmore rapidly. Finally through the calculation of P-V curve in the whole workingprocess, the improved scheme has bigger engine torque and power, lower fuelconsumption.