An Innovative Two-Stroke Twin-Cylinder Engine Layout for Range Extending Application

Global trends show an increasing approval of electrified mobility due to advantages like local zero emission and low noise. But range anxiety, missing comprehensive availability and high costs significantly obstruct the acceptance and growth of electro mobility. Extended research on finding innovative solutions focus on the elimination of the disadvantages of pure electric drivetrain systems. Therefore an ICE range extended electric vehicle is a promising approach. Commonly, small-capacity gasoline engines with low cylinder numbers are used for range extending applications. Targets are low emissions, efficient packaging, good NVH behaviour and low costs.

In this paper the layout and design of an innovative two-stroke twin-cylinder engine with a capacity of one litre is presented. Compared to conventional single- or twin-cylinder four-stroke engines a two-stroke engine has better running smoothness due to the ignition sequence of 180 degrees. The use of uniflow scavenging with intake ports and exhaust side valves enables low untreated emissions and the application of a closed loop 3-way catalytic exhaust aftertreatment. The essential scavenging pressure is continuously provided by a mechanical blower. The thermodynamical layout through an extended CFD simulation ensures an optimized scavenging process. Cost and simplicity targets can be met by applying an external mixture preparation. Unique to small two-stroke engines are the pressure lubrication and the use of friction bearings. Additionally, a sophisticated mass balancing system with full compensation could be obtained. The final layout presents an unconventional engine applying well-proven technologies.