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Water Injection Benefits in a 3-Cylinder Downsized SI-Engine
Abstract:
With progressing electrification of automotive powertrains and demands to meet increasingly stringent emission regulations, a combination of an electric motor and downsized turbocharged spark-ignited engine has been recognized as a viable solution. The SI engine must be optimized, and preferentially downsized, to reduce tailpipe CO2 and other emissions. However, drives to increase BMEP (Brake Mean Effective Pressure) and compression ratio/thermal efficiency increase propensities of knocking (auto-ignition of residual unburnt charge before the propagating flame reaches it) in downsized engines.
Currently, knock is mitigated by retarding the ignition timing, but this has several limitations. Another option identified in the last decade (following trials of similar technology in aircraft combustion engines) is water injection, which suppresses knocking largely by reducing local in-cylinder mixture temperatures due to its latent heat of vaporization. Addition of adequate water can lead to stoichiometric air/fuel ratio engine operation, and hence both reduction in fuel consumption and full utilization of a three-way catalytic converter (TWC).
Further information about effects of various water injection parameters is required. Thus, in this study, a 4-stroke, 1.5 liter, 3-cylinder turbocharged engine with direct fuel injection and port water injection was operated on 91, 95 and 98 RON gasoline fuel to assess effects of water injection on knock mitigation, combustion phasing, required air:fuel ratios and exhaust gas temperature control. Full- and part-load curves obtained with different fuels and water injection strategies are presented and discussed.