Accurate Prediction of Charging Characteristics of a Four-Stroke Cycle Engine with High EGR Rate

废气再循环(EGR)技术可用于降低汽柴油发动机的NOx排放。研究的目的是对废气再循环率进行数值预测，并估算气缸间废气再循环率的差异。主要研究结果如下：1.采用特征线法对一台四缸四冲程汽油机的高EGR系统的一维气体流动进行了非定常分析。通过计算结果与实验数据的对比，验证了该方法是研究气缸间EGR率差异的常用方法。通过对废气再循环系统中气体流动的研究发现，气缸间废气再循环率的差异不仅与管路系统的几何形状有关，还与进排气系统中的气体动力学有关。用特征线法模拟了进排气系统的排气浓度和气体流动行为，采用了两种不同的网格划分，数值扩散小得多。通过将预测的EGR率与实验值进行比较，得到了较小的数值扩散误差。为了提高进排气系统中非定常气体流动的模拟精度，将激波格式引入到管道系统中的气体流动计算程序中具有重要意义。但由于程序的复杂性，激波格式的计算程序尚未编制完成。完成该计划的努力将持续到明年。

The technique of exhaust gas recirculation (EGR) is available for NOx reduction of gasoline and Diesel engines. The objects of research are to predict numerically EGR rate and also to estimate the differences in EGR rate between cylinders. The results obtained are as follows :1. The EGR rate has been predicted in a 4-cylinder four-stroke cycle gasoline engine with high EGR system, using the characteristic method to analyze one-dimensional gas flow unsteadily. It has been validated from the comparison between the predicted results and the experimental data that this method is usual to investigate the differences in EGR rate between cylinders. It has been founded from the investigation of the gas flow in EGR systems that the differences in EGR rate between cylinders are produced not noly owing to the geometry of pipe system but also owing to the gas dynamics in intake and exhaust systems.2. The behaviors of exhaust gas content and gas flow in intake and exhaust systems have been simulated with much less numerical diffusion by the characteristic method, in which two kinds of meshes are prepared. Much less numerical diffusion error is confiumed through the comparison between the predicted EGR rate and the experimental one. In order to improve the simulation accuracy of the unsteady gas flow in intake and exhaust system, it is important to incorporate shock wave schemes into the calculation program of gas flow in pipe systems. However, the calculation program with shock wave schemes has not yet completed owing to the complexity of program. Effort to complete the program is continued to the next year.