A Numerical Study On Optimization Of The Design Parameters Of An Automotive Diesel Engine Helical Intake Port

With the increase of the global car ownership, diesel engines as a main powersource of cars are used more and more widely. However, as the shortage of petroleumresources and environment worsening, it is more and more important to develop highefficiency and low emission diesel engines for the passenger cars. Since diesel enginesfeature diffusion combustion, improving the in-cylinder swirl ratio at the injectiontiming can accelerate fuel-air mixing and hence improve the combustion, which is oneof the keys to realize the high efficiency and low emission operation.This work was on a four-cylinder intercooled turbocharged diesel engine forautomotive applications. The intake port and combustion chamber of one cylinder weremodeled by3D CAD models. In order to achieve numerical optimization of the helicalintake port structure parameters, a state-of-the-art computational fluid dynamicssoftware Converge was used to carry out numerical analysis.This paper firstly analyzed the helical intake port structure parameters of thediesel engine. By using the numerical simulation, the effects of a single structureparameter variation on the in-cylinder swirl ratio were analyzed. It showed that singlestructure parameter variation has important effects on the in-cylinder swirl ratio. Smallchanges of the structure parameters will course great influence on the in-cylinder swirlratio, however its effects on the air charging were negligible. The effects of thevariations of multiple structure parameters on the in-cylinder swirl ratio were thenanalyzed. The results showed that their effects were not simple additions of theinfluence caused by a single structure parameter, rather they were the outcomes of theinteractions. There will be a nonlinear relationship between the structure parametersand the in-cylinder swirl ratio.Secondly, in order to establish the Computational Fluid Dynamics (CFD) methodfor optimizing the helical intake port design, the uniform design technique was adoptedto develop a numerical experiment with5factors and11levels for the five keystructure parameters which have important effects on the performance of the dieselhelical intake port. Then the regression analyzing method was used and the regressionequation for the structure parameters and in-cylinder swirl ratio was obtained from theexperimental data. By analyzing the regression equation, the optimized values of thevarious structure parameters were obtained to get the optimal in-cylinder swirl ratio. The maximum value and the minimum value of the in-cylinder swirl ratio werepredicted.Finally, the structure parameters in the numerical model were varied to theoptimized values, and the in-cylinder flow was analyzed. The results showed that theobtained regression equation for structure parameters and in-cylinder swirl ratio whichwas obtained by design of experiment and regression analyzing method can predict thevalue of in-cylinder swirl ratio well. By analyzing the regression equation, theoptimized values of the structure parameters were obtained for the expected value ofin-cylinder swirl ratio.The innovative contributions of this thesis include the followings: Theoptimization of multiple structure parameters were realized by using a state-of-the-artCFD tools. The development of the in-cylinder swirl ratio at the compression strokeand near TDC was dynamically analyzed. Meanwhile, a systematic method wasutilized to realize the optimization of the design parameters of diesel helical intakeport. These are important to practical design of diesel helical intake ports.