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

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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.