Numerical Investigation of Water Spray Dynamics and Combustion Characteristics in Gasoline Direct Injection Engines under Variable Injection Pressure and Timing

Water injection is a promising approach for enhancing performance and reducing emissions in gasoline direct injection (GDI) engines. However, its effectiveness is constrained by challenges related to efficient evaporation and uniform in-cylinder distribution. This study explores strategies to improve water evaporation and distribution in a direct water-injected GDI engine, aiming to enhance overall performance and emission characteristics. To analyze spray breakup and droplet evaporation under dynamic in-cylinder conditions, water is injected during the intake and compression strokes at injection pressures ranging from ۲۰ to ۱۰۰ bar. The effects of the start of water injection (SOWI) and water injection pressure (WIP) on water evaporation delay, evaporation rates, film formation, spray impingement, water vapor distribution, velocity fields, volumetric efficiency, and combustion parameters are investigated. The objective is to establish a benchmark for identifying effective injection parameters and to formulate strategies that enhance water evaporation and engine performance, with applicability to other engine configurations. A validated three-dimensional CFD framework with a Lagrangian spray model, KH-RT breakup, and detailed combustion modeling is used to study water spray dynamics and combustion characteristics. Results showed that water injection during the intake stroke caused significant evaporation delay, while higher WIP and delayed SOWI significantly increased water film formation. SOWI has a stronger influence on combustion behaviour than WIP, as it governs both - water evaporation and vapour stratification. Water injection at ۶۰۰ CAD with ۵۰ bar pressure improved indicated mean effective pressure (IMEP) by approximately ۱۰.۲%, while nitric oxide and soot emissions were reduced by about ۴۶% and ۲۳.۵%, respectively, compared to the no-water injection case.

کلیدواژه ها:

Computational fluid dynamics ، Gasoline direct injection engine ، Combustion and emissions ، Water evaporation ، Water injection ، Water injection timing ، Water injection pressure