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

通过对改善高速柴油机性能的进排气系统数值预测方法的研究，取得了以下成果：1.编制了预测增压复合式发动机性能的模拟程序。该程序可以预测压气机和排气轮机的最优组合，并考虑进排气管系统的动态影响。通过与单级和双级涡轮增压发动机的预测性能比较，验证了程序的有效性。确定了一种简单地根据进气系统与电路的类比来处理进气系统的方法。尝试利用曲轴箱和变截面进气管道，并尝试利用排气歧管两支压差驱动的自由活塞式空压机。数值模拟结果表明，这些装置对提高进气量是有效的。开发了一个实用的计算进气道内三维非定常气体流动的程序。通过对恒定流的计算结果与实验结果的比较，验证了计算的准确性。计算了双进气门螺旋流道结构的变化以及进、排气口压力的时间变化对涡流强度和充气效率的影响。该方法利用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部区域分开分析。因此，在发动机运行条件下，可以估计出气道结构对流动特性的影响。

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.