While hybrid electric powertrains are the standard for passenger cars, the application to motorcycles is almost nil. The reason is the increase in weight, cost and overall dimensions, which can compromise the layout and dynamics of the motorcycle. A viable path is to replace the standard internal combustion engine with a much smaller and lighter unit, which leaves room for the installation of the electric components. The 2-Stroke (2S) cycle technology, thanks to the double cycle frequency and inherent simplicity, can be the key to reduce engine dimensions, weight and cost, while keeping high power outputs.
The HybridTec project, discussed in this paper, aims to develop a compact and lightweight V-90° two-cylinder 2S engine, coupled to an electric motor installed downstream of the gearbox (P3 configuration). The total installed power should be about 110 kW.
The engine features loop-scavenging, actuated by a crankshaft-driven supercharger, while an exhaust rotary valve and electronic fuel injection minimize fuel short-circuit over a broad operating range. Moreover, the control of air and residuals trapped within the cylinder is made by a by-pass valve downstream of the supercharger. A 4-Stroke like pressure-lubrication system is also adopted.
Another advantage of this engine design is the possibility to dilute the fresh charge with exhaust gas, at any operating condition: a high percentage of residuals helps to cut NOx emissions without the need for complex and expensive after-treatment systems.
A single cylinder prototype of the engine was preliminarily built and tested, the initial design being carried out with the support of a 1D-CFD model, which was then calibrated based on a preliminary configuration of the engine.
According to the 1D-CFD simulation results, the engine is able to meet the performance targets and shows good potential at part-load operation, but engine injection system and control strategy needs further optimization, which will be supported by future detailed 3D-CFD analysis.