The ongoing trend of downsizing and boosting of gasoline engines has already achieved impressive results however leads to an increased tendency of combustion knock at higher engine loads. Varying the compression ratio during engine operation is one measure to avoid this limitation and to enable the demand for increased torque and power with an improved fuel consumption in the entire engine map.
Varying the compression ratio on diesel engines results in reduced peak firing pressures and temperatures, beneficial for lowered thermo-mechanical stress and reduced engine-out pollutant emissions. This enables two different opportunities for VCR application. First option is to extend the power output on an already PFP limited base engine. Alternatively: Rightsizing the bearing dimension according the reduced peak firing pressure enables friction reduction and finally an improved fuel consumption. On top of these mechanical advantages, VCR provides potential to lower engine-out NOx under higher operating loads, important for optimal compliance of future RDE demands.
Dual fuel engines suffer from the compromise for the compression ratio. E.g. marine engines require a low compression ratio for the gas application while running most of the time on heavy fuel oil (HFO) where the high compression ratio would enable fuel consumption and operator cost reduction.
Varying the compression ratio during engine operation is one measure to
optimize efficiency for the different fuels.