Effects of Water Injector Spray Angle and Injector Orientation on Emission and Performance of a GDI Engine-A CFD Analysis

摘要

Higher water evaporation and proper water vapor distribution in the cylinder are very vital for improving emission and performance characteristics of water-injected engines. The concentration of water vapor should be higher and uniform near the walls of the combustion chamber and nil at the spark plug location. In direct water-injected engines, water evaporation, vapor distribution, and spray impingement are highly dependent on injector parameters, viz., water injector orientation (WIO), location, and spray angle. Therefore, in this article, a computational fluid dynamics (CFD) investigation is conducted to study the effects of water injector spray angle (WISA), and WIO on the water evaporation, emission, and performance characteristics of a four-stroke, wall-guided gasoline direct injection (GDI) engine. The WISA is varied from 10° to 35°, whereas the WIO is varied from 15° to 35° in steps of 5°. The water is injected in the compression stroke with an optimum injection pressure of 50 bar. Water-to-fuel (W/F) ratio and spark timing are fixed at their optimum values with a compression ratio (CR) of 13.5. The engine is operated at the engine speed of 2000 rpm, with stoichiometric and naturally aspirated conditions. The CFD models used in this study are validated with the available data from the literature. Results showed that the WISA of 20° in combination with the WIO of 25° produced the maximum charge cooling, highest water evaporation, and proper water vapor distribution in the cylinder, because of which the indicated mean effective pressure (IMEP) is about 9.3% higher, whereas nitrogen oxides (NO_x) and soot emissions are about 48% and 20.7% lower than that of the no_water case. This research suggests that the WISA and WIO should be chosen in such a manner that most water injection occurs around the piston periphery, without any impingement on the cylinder liner surface to achieve better water vapor distribution and evaporation characteristics.