Effect of Water Injection Timing on the Combustion and Emissions of a Direct Injection Gasoline Engine

Abstract

Knock is the main limiting factor of performance improvement when downsizing spark ignition (SI) engines. Direct water injection in the cylinder can effectively suppress knock. Moreover, water can absorb the heat generated by combustion and reduce the maximum temperature, which can also reduce NOX emissions. The water injection timing will change the distribution of water in the cylinder and affect the combustion and emissions of the gasoline engine. Herein, the effects of different water injection timings on the combustion and emissions of a direct injection gasoline (GDI) engine are examined with numerical simulation. For the combustion performance, the cumulative heat release in the cylinder at different timings of water injection is about 2900 J. However, the instantaneous heat release rate and the combustion duration are different. Compared with other water injection timings, when the water injection time is −80 °CA, the distribution of water in the cylinder is the most even, the potential for reducing knock is the highest, and the NOX emission is the lowest, but the cycle work is also the least. When the water injection time is −20 °CA, the results are opposite.