Improvement of the Performances of High-Speed Diesel Engines by Tuning the Intake and Exhaust Systems

通过对提高高速柴油机进排气系统性能的数值预测方法的研究，得到了以下结果：完成了涡轮增压复合发动机性能预测的仿真程序。该程序可以在考虑进气管和排气管系统动态影响的情况下，预测压气机和排气机的最佳组合。通过将该复合发动机的预测性能与一级和二级涡轮增压发动机的性能进行比较，证实了该程序的有效性。在将进气系统与电路类比的基础上，提出了一种简单处理进气系统的方法。尝试利用曲轴箱和变截面积进气管，并尝试利用排气歧管两支间的压差驱动的自由活塞式空压机。数值模拟结果表明，这些装置对增加进气量是有效的。开发了一个实用的进气道三维非定常气流计算程序。通过将定常流动计算结果与实验结果进行比较，验证了计算的准确性。对于双气门进气道，可以计算出由于螺旋气道结构的变化和进气道进出口压力的时间变化所引起的旋流强度和容积效率的变化。该方法以气体交换过程的一维计算结果作为进出口边界条件，将进气道内的非定常三维流动与外区分开进行分析。因此，在发动机工作条件下，可以估计出气道构型对流动特性的影响。

By studying the methods for numerically predicting the intake and exhaust systems which can improve the performances of high-speed diesel engines, the following results were obtained:1. A simulation program for predicting the performances of turbocharged compound engines was completed. This program can predict the optimum combination of the compressor and the exhaust turbine, considering the dynamic effect of the intake and exhaust pipe systems. The usefulness of the program was confirmed through the comparison of the predicted performance of the compound engine with those of one- and two-stage turbocharged engines.2. A method which treated the intake systems simply on the basis of the analogy between the intake systems and the electrical circuits was determined. It was attempted to utilize the crankcase and the intake pipe with variable sectional area, and also attempted to utilize the free-piston type air-compressor actuated by the pressure difference between two branches of exhaust manifold. Numerical simulation showed that these devices were effective for increasing the amount of intake air.3. A practical program for calculating the three-dimensional unsteady gas flows in intake ports was developed. The calculation accuracy was examined by comparing the calculated results of steady flow with experimental ones. It was possible to calculate the changes of the swirl intensity and volumetric efficiency due to the changes of the configurations of helical ports and the temporal variation of the pressure at the inlet and outlets of an intake port with two valves. In this method, the unsteady threedimensional flow in the intake port is analyzed separately form outer regions by using the results of the one-dimensional calculation of gas-exchanging process as the inlet and outlet boundary conditions. Therefor, the effect of the port configuration on the flow characteristics can be estimated under the engine operating conditions.