Comparison of Different Downsizing Strategies for 2- and 3-Cylinder Engines by the Use of 1D-CFD Simulation

The internal combustion engine is still the most important propulsion system for individual mobility. Especially for the application of motorcycles and recreation vehicles the extraordinary high power density is crucial. Today, these engines are mainly 4-stroke naturally aspirated MPFI engines. The main difference to the automotive sector is the abandonment of all cost intensive technologies, like variable valve timing, intake air charging or gasoline direct injection. The need for further investigations and implementation of new technologies is given due to the very high share of total road transport emissions of motorcycles and the introduction of the emission limits of EURO5 in 2020. One possibility to reach the future emission limits is the downsizing strategy. For this, the potential for emission and fuel consumption reduction is well known. The question remains if this technology is applicable for high revolution engines without any variability in the valve train, an extraordinary high demand on drivability and a low number of cylinders. The research work in this sector tends up to now to a power increase with relative low importance on fuel consumption and emissions. The here presented investigations deal with the possibility of downsizing two- and three-cylinder engines within the power sport application to combine both investigation targets, power respectively torque increase and fuel consumption improvements. Therefore, two different engines with different charging concepts are compared and analyzed regarding stationary and transient behavior. The analysis implies the interaction of the charging concepts with the engines, the impact on power and torque characteristics, influence regarding fuel consumption as well as the effects on the IMEP and torque build-up after a load step. The challenge hereby is the trade-off between the very wide engine speed range, the high demands regarding response and the very unsteady mass flow distribution.