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The aim of this study is to analyze the emission improvement in the oil-cooled engine by use of internal cylinder gas pressure measurement and 3D simulation of thermal flow and combustion. In the previous study, two test engines were designed to evaluate the benefits of the oil-cooled engine. One was an oil-cooled, and the other was a water-cooled engine. Both engines were single cylinder engines with SOHC valve-train systems. The hardware specifications of both engines were exactly the same except for their cooling systems in order to clarify how the difference in engine cooling system affects their cooling performance, warm-up performance and emission performance.

Improvement of warming performance is required for engine cooling system, because such improvement has an important role for lower emissions. However, the cooling performance and the warming performance of engine are related to the transactions. To improve such trade-off relation between the two performances, oil-cooled system was developed which components are simpler than conventional water-cooled system with a single cylinder, 339cc engine. The oil-cooled system has an “oil jacket” that closely encircles the combustion chamber to cool the cylinder head and cylinder sufficiently. This system adopts the engine lubrication oil to cool combustion chamber, thus the average temperature of the combustion chamber is higher than usual water-cooled engine that enables better warming performance.

To measure the stresses acting on the crankshaft of an engine, signals must be taken out from the rapidly spinning shaft. This paper discusses the measurement of stress signals from the crankshaft using a slip ring, which is the conventional method. By developing a special fixture that allowed us to measure rotations up to 14,000 rpm and using the four-gauge method, we succeeded in accurately measuring stress waves. We confirmed that, during the motoring operation, stresses due to the secondary component of the inertia forces of the reciprocating parts are dominant and that, during the firing operation, deformation occurs at various frequency bands. As the engine speed increased, the stress amplitude increased and reached a maximum around the highest engine speed. The results of a static analysis predicted values close to actual measurements.

Reduction of flow resistance in an intake system is essential for increasing the output of a four-stroke engine. Evaluation method regardless engine displacement or number of valves or cylinder must be required in intake system design. This study proposes intake loss coefficient as total evaluation method from flow in an intake port to charging flow into a cylinder. A three-dimensional, general-purpose Computational Fluid Dynamics (CFD) code was used to calculate an intake loss coefficient. A correlation was confirmed between an intake loss coefficient and the engine power output. Intake loss coefficients and the CFD technique may be used for efficient optimization of the shape of an intake system.