Experimental investigation of Miller cycle combustion technology with water injection

The future RDE legislation as well as the associated fleet consumption targets require a high efficiency of the gasoline engine under real driving conditions. Throttled operation is increasingly losing in significance for RDE in downsized gasoline engines. Conversely, engine operating points are increasingly being shifted toward high brake mean effective pressures in the boosted range. The knock limit frequently results in late centers of combustion, which are not optimal in terms of efficiency. Consequently, a high knock resistance of the gasoline engine is crucial for low fuel consumption under real driving conditions. In consideration of this, the Miller combustion cycle with early intake closing offers advantages with regard to efficiency. The additional use of water injection leads to a reduction of the cylinder charge temperature, which further increases the knock resistance. The combination of these two technologies in the interests of improved efficiency represents an attractive approach for future powertrain configurations.This article evaluates port water injection in comparison with direct water injection with regard to the potential for efficiency improvements. The article also demonstrates the thermodynamic effect of water injection on combustion and analyzes the emissions behavior. The experimental investigations are conducted on a newly developed singlecylinder engine based on the downsizing concept and with a high geometrical compression ratio.