Abstract
During initial development of a high performance small single cylinder with SOHC valvetrain system engine, we observed high rate of change in combustion pressure – thru cylinder gas pressure measurement system – and induced harshness in the engine operation. With a conventional approach this could have been resolved with a water-cooled concept, which is costly and requires more space for packaging. To resolve this a novel oil-cooled combustion chamber concept has been proposed and evaluated for benefits. Cooling passage and structural geometry have been optimized by using CAE tools (CFD and FEA). Proto type engines were built to evaluate the benefits of the oil-cooled combustion chamber concept in comparison with conventional engine. Hardware specifications of both engines were kept same except for their cooling features in order to quantify how the difference in oil cooling system affects their cooling performance, warm-up performance, emission performance and NVH performance. The effect of oil-cooling shows improved combustion chamber cooling and NVH behavior of engine without compromising the intended engine performance targets. The temperature measurement at critical locations for the components and oil were measured and found acceptable. This study was done with standard engine oil and without an oil cooler attached to the engine. No significant effect on oil drain period witnessed with this standard engine oil. However, a separate study needs to be done with various demographic engine oils. The unique architecture of the multi-valve (three or four valve) combustion chamber demands efficient cooling performance and NVH performance with compactness. The cylinderhead is designed with an oil-cooled combustion chamber that enables to achieve intended performance levels with effective cooling. This system has improved the engine smoothness due to the oil damping hence improved NVH performance which has been validated using subjective and objective methods. Oil cooled combustion chamber concept is an appropriate and cost effective option with optimal benefits.