Extension and Validation of a 1D Model Applied to the Analysis of a Water Injected Turbocharged Spark Ignited Engine at High Loads and over a WLTP Driving Cycle

The technique of liquid Water Injection (WI) at the intake port of downsized boosted SI engines is a promising solution to improve the knock resistance at high loads. An existing 1D engine model has been extended to improve its ability to simulate the effects of the water injection on the flame propagation speed and knock onset. The 1D model is validated against experimental data collected at different engine speeds and loads for a twin-cylinder turbocharged SI engine. The model predictions are compared with the experimental data, in terms of in-cylinder pressure cycle, burn rate profile and knock propensity. The combustion process is predicted quite well, except for some inaccuracies in the early stage of combustion. Both experimental and numerical data confirm that the WI technology is able to improve significantly the fuel consumption of the tested engine under high-load knock-limited operation. In a second stage, the validated model is used to build-up a complete engine operating map aimed at investigating the potential of WI technique to improve the fuel economy of a segment A vehicle. A reduced impact of WI is observed, since a knock-free operation occurs along most of the WLTP cycle.