Study On Parametric Analysis Of Combustion Process And Optimization Of System Parameters In High Power D.I. Diesel Engine

The combustion process of diesel engine is mainly restricted by parameters of induction, fuel injection system and chamber profile. Parameters optimize matching for combustion system with CFD technology can result cost saving and design cycle shorten, but the key problem is to ensure the simulations creditability. So, model Validation and Verification (V&V) has been researched. Then, muti-dimensional simulation has been carried out based on a high power D.I. diesel engine, attempting to parameterize and analyze one or two combustion system parameters' influences on mixture formation process and combustion behavior. Meanwhile, matching of much more parameters has been researched by involving optimization theory, and aquires better effect.Firstly, the spray characteristic simulation has been validated, and optimal grid precision, time step have been aquired, then, mesh of high power D.I. diesel engine has been built. Performance of engine actual motion has been predicted in terms of analyzing parametric sensitivity of break-up model and combustion model, also, the weak point of the engine has been deeply analyzed.Secondly, characteristic parameters reflecting air-fuel mixing and combustion behavior have been constructed based on qualitative investigation of swirl ratio, number of nozzle holes (nozzle diameter), injection pressure, spray angle and calibre ratio etc. influencing in-cylinder process, such as turbulent mixing intensity, concentration variance of air-fuel mixture, contribution rate of different equivalence ratio interval to combustion and average chemical reaction rate. Combustion system parameters effecting characteristic parameters have been developed, and mechanism of action of parameters impacting on combustion performance has been revealed. On the other hand, owing to coupling effect, parameters influencing combustion process are not independent. The matches of six pairs of parameters have been achieved via lots of simulations. Based on the two matched parameters' influences on characteristic parameters, the matching mechanisms have been analyzed.Finally, much more parameters of combustion system have been matched by involving orthogonal design method and genetic algorithm method. The weight coefficients of parameters and interactions to the power have been obtained by orthogonal design method, and optimal combination of combustion system parameters to the engine power has been acquired through difFirent analytical methods. Overall optimization has been developed based on genetic algorithm method, and a further optimized result has been obtained. Optimizations and prototype engine have been compared and analyzed based on the characteristic parameters.