Parametric Study Of The Tangential Port With Complex Surface In Internal Combustion Engine Based On Multiple Constraints

The flow characteristics of the intake port are critical for intake and combustionprocesses of internal combustion engines, and significantly affect the output power,fuel economy and emissions of engines. The multiple constrains including the flowcharacteristics of air, spatial structure, casting and machining processes of intake port,and so on, result in the irregular and complex shape of the inlet port. Thus, the designand performance evaluation of the intake port have been one of the most difficultiesand focus of engine development. In this study, a series of investigations were carriedout on the method for evaluating the flow characteristics of the intake port, fullyparametric design of the intake port and the sensibility of the intake port.Because of the unreasonable assumption in the conventional methods forevaluating the flow characteristics of the intake port, it is difficult to predict thevolumetric efficiency, swirl ratio and tumble ratio under engine transient operatingcondition on the basis of steady flow test. To solve the problem mentioned above,further study was performed and a new method was proposed according to theoreticalanalysis in this study. The variations of the in-cylinder pressure, flow state of the air,volumetric efficiency, the evolution of the swirl and tumble, residual gas,compression ratio were considered in the new method. Then, the relationship betweentransient operating condition and steady operating condition was established, thus thevolumetric efficiency, swirl ratio and tumble ratio can be accurate predicted underengine transient operating conditions on the basis of steady flow test for the first time.Finally, the method was verified on a4-valve diesel engine, the low deviations (lessthan4%for the volumetric efficiency) confirm the reliability of the new method.Subsequently, a fully parametric design study was carried out. Eighteen structuralparameters were taken into account for establishing the tangential intake port and the3D software Pro/E was employed with secondary development for building the portconstruction system. A three-dimensional model of the tangential intake port can begenerated by inputting those eighteen structural parameters based on the portconstruction system. In order to build the relationship between the key portparameters and port performance, computational fluid dynamics (CFD) numericalsimulation was further conducted in this study. Simulation results show that portparameters have little impact on flow coefficient for a uniform transition from inlet tooutlet of the port. Swirl/tumble intensity, however, are more sensitive to the entranceand exit surface of port. As for diesel engines, the perpendicular and horizontal guiderole of the port outlet surface could result in the variation of swirl ratio up to20%and15%, respectively. For gasoline engines, the guide role of the port inlet surface and outlet surface could result in the variation of tumble ratio up to4%and10%,respectively.In order to optimize the port parameters, artificial neural network (ANN) wasused to predict the port performance based on the key structural parameters. Then, thegenetic algorithm combined with artificial neural network was used to optimize theperformance of intake port, and the performance coefficient of intake port was definedas an objective function during the optimization process. The results show that thepredictions using artificial neural network are similar to those of3D simulation. Thedeviation of flow coefficient and swirl/tumble ration between ANN predictions and3D simulations are less than1%and1.5, respectively. The optimization method wasfurther verified in a gasoline engine. Optimization results show that a new design hasa remarkable increase (about6.12%) in the tumble intensity while flow coefficientremains unchanged. The application of genetic algorithm for the optimization ofintake port has been successfully proved in this study, which overcomes thelimitations of the traditional methods based on experience and database.After finishing the design and optimization of the intake port, the casting andmachining processes of intake port may introduce significant deviations, leading toundesirable variation of intake port flow, and subsequent deterioration in enginecombustion and emissions. Therefore, steady flow tests were carried out on a4-valvediesel engine to investigate how and to what extent the casting and machiningdeviations of the intake port influence the in-cylinder flow characteristics. It is foundthat these deviations have unnoticeable impact on mean flow coefficient, but stronglyaffect swirl ratio. As for the case with inclination defect of1°, the maximumreduction of the swirl ratio can reach as high as9.3%relative to the standard port. Foreccentric defect with the eccentric distances of1.5mm, the maximum variation of theswirl ratio could reach19.6%relative to the standard intake port. For swelling defectwith the swelling thickness of1mm, the maximum variation of the swirl ratio couldreach7.8%compare to the standard intake port.