Potential of Direct Water Injection to Reduce Knocking and Increase the Efficiency of Gasoline Engines

Abstract

Given the need to further reduce CO₂ s from passenger cars powered by internal combustion engines and in the light of future tighter exhaust emission regulations, further improvements are necessary to enhance the efficiency and emission behavior of gasoline engines. One major constraint encountered in the gasoline engine is knocking combustion. Its negative effects on efficiency and emission behavior can be counteracted by reducing knock tendency.

One approach to reducing knocking tendency lies in injecting water. This is capable of extracting heat from the cylinder charge and, on this basis, reduce final compression temperature. It also increases charge mass in the cylinder and ultimately improves efficiency as a result of the lower tendency to knock.

With a view to implementing water injection, attention initially turns to the thermodynamic aspects of water injection in the gasoline engine and to comparing and evaluating the water manifold and direct water injection concepts. With the aim of conducting fundamental studies on a test engine with direct water injection, discourse then presents the design-related aspects involved in the implementation of such. The engine tests conducted focus on identifying the main water injection parameters influencing the gasoline engine’s working cycle. Selected test results provide the basis for illustrating them and presenting the key underlying mechanisms. The potential for increasing the compression ratio can be determined in relation to the effect of water injection on reducing knock. The resultant higher level of efficiency makes it possible to reduce the emission of CO₂.

Finally, consideration is given to the challenges involved in injecting water, with further concept approaches being presented for water injection.