Numerical Assessment of Port Water Injection Capabilities to Reduce CO2 Emissions of a Lambda 1 Turbocharged Spark Ignition Engine

The continuous tightening of CO2 emission targets along with the introduction of Real Driving Emissions (RDE) tests make Water Injection (WI) one of the most promising solutions to improve efficiency, enhance performance and reduce emissions of turbocharged high-performance Spark Ignition engines. This technology, by reducing local in-cylinder mixture temperature, enables higher compression ratios, optimal spark timing and stoichiometric combustion over the entire engine operating range. This research activity, therefore, aims to assess the benefits in terms of CO2 emission reduction of a Port Water Injection (PWI) system integrated in a Downsized Turbocharged Direct Injection Spark Ignition (T-DISI) Engine. In this regard, a 1D-CFD model of the engine capable to predict the impact of the water content on both the combustion process and the knock likelihood was firstly developed. After its validation against a huge set of experimental data collected over the entire operating map in wet and dry conditions, the engine model was embedded in a virtual test rig of a B-segment Sport Utility Vehicle. The fuel economy potential of several calibrations of the PWI system was then evaluated for different type approval and RDE driving cycles. The proposed results give a clear outlook of the capabilities of Port Water Injection which, in conjunction with high compression ratio and Miller strategy, enables a potential improvement of CO2 emission abatement in the range of 4-8% – depending on the driving conditions – with a still acceptable water consumption (lower than 1.1 l/100km).