Water Injection: a Technology to Improve Performance and Emissions of Downsized Turbocharged Spark Ignited Engines

Knock occurrence and fuel enrichment are the major obstacles to further increase performance and efficiency of down-sized turbocharged spark ignited engines. A technique that has the potential to overcome these restrictions is the injection of water within the mixture charge. One of the main objectives of this investigation is to demonstrate that water injection (WI) could be a reliable solution to advance the spark timing and make the engine run at leaner mixture ratios with strong benefits on knock tendency and efficiency. Experiments were carried out on a downsized port fuel injection (PFI) twin-cylinder turbocharged spark ignition engine equipped with a variable valve actuation (VVA) system over the speed range from 2500 to 4500 rpm at medium loads. A spark advance sweep was performed up reach incipient knocking conditions. In-cylinder pressure measurements allowed estimating the main combustion parameters such as the rate of heat release and the combustion phasing. The effect of water injection on turbine inlet temperature and combustion efficiency are also presented. Further, combustion noise analysis carried out post-processing the in-cylinder pressure signal. The results coming from such analysis are discussed to determine the capability of water injection to reduce combustion noise level and improve sound quality index.