Water Injection Benefits in a 3-cylinder Downsized SI Engine
With progressing electrification of automotive powertrain and the demand to meet increasingly stringent emission regulations, a combination of electric motor and downsized turbocharged Spark Ignited Engines has been recognized a viable solution. Maximum Power and reduction of tailpipe CO2 need to come from optimizing the IC Engine. However, the increased BMEP (Brake Mean Effective Pressure) and drive for higher compression ratio/thermal efficiency increases the propensity of knocking in Downsized Engines. Engine knock occurs when the unburnt charge auto-ignites before the propagation flame reaches the unburnt charge. Currently, knock is mitigated by retarding the ignition timing. Under high power demand, ignition retard is limited by the exhaust components temperature limit. This is compensated by mixture enrichment – injecting more fuel – which in turn reduces combustion temperature at the cost of increased fuel consumption and Carbon Monoxide (CO) emissions.