Water Injection Contribution to Enabling Stoichiometric Air-to-Fuel Ratio Operation at Rated Power Conditions of a High-Performance DISI Single Cylinder Engine 2019-24-0173

The next generation of gasoline turbo-charged engines will have to deal with the continuous tightening of emissions regulations. In fact, to better represent real-world emission figures, WLTP and RDE cycles focus on stricter criteria; spanning higher speeds and loads potentially covering the whole engine operating map. It is common practice at present to use overfueling to avoid catastrophic failure of turbine and aftertreatment systems at very high engine speeds and loads due to excessive temperatures.

A past technology, which is presently enjoying a resurgence of interest, is water injection. In particular, for high-specific-power applications, this could be used as replacement strategy for overfueling, potentially enabling full operating range stoichiometric operation with no compromise in terms of maximum performance with respect to today.

In order to validate this scenario, an experimental campaign on a single cylinder engine has been carried out to highlight port water injection benefits and possible limitations at high engine speed and loads. A dedicated port injector has been characterized in a spray bomb and 3D-CFD simulations have been performed with the goal of better understanding and illustrating the air cooling effect along the water pathway from the injector tip to the cylinder charge. Detailed chemical thermo-kinetics modelling of gasoline/water gaseous mixtures was used to help separate thermal from chemical effects arising from use of a water injection system. A number of injector types, locations, water flow rates and inlet valve timings have been included in the study in order to fully explore the potential benefits of this technology.