Engine Knock Toughness Improvement Through Water Jacket Optimization

Improvement of engine cycle thermal efficiency is an effective way to increase engine torque and to reduce fuel consumption simultaneously. However, the extent of the improvement is limited by engine knock, which is more evident at low engine speeds when combustion flame propagation is relatively slow. To prevent engine damage due to knock, the spark ignition timing of a gasoline engine is usually controlled by a knock sensor. Therefore, an engine's ignition timing cannot be set freely to achieve best engine performance and fuel economy. Whether ignition timings for a multi-cylinder engine are the same or can be set differently for each cylinder, it is not desirable for each cylinder has big deviation from the median with respect to knock tendency. It is apparent that effective measures to improve engine knock toughness should address both uniformity of all cylinders of a multi-cylinder engine and improvement of median knock toughness. In the present work, CFD analysis was applied to evaluate the necessity of improving engine water jacket design in order to further improve performance and fuel economy of Honda engines. Subsequently, a series of design parameter combinations involving engine block, head gasket and cylinder head were optimized on computer, and an optimized design package with the least modifications to the current production process was chosen for prototyping and testing. The measurement results show that predicted surface heat transfer coefficient correlates well with measured surface temperature reduction on combustion chamber surfaces. The optimized water jacket significantly improved the uniformity of cylinders in terms of knock limited ignition timings. The bench test results confirmed that new water jacket design results in about 2.3% increase of engine WOT torque and 2.2% reduction of fuel consumption.