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Powertrain system duplication for hybrid electric vehicles and range-extenders presents serious cost challenges. Cost increase can be mitigated by reducing the number of cylinders but this usually has a negative impact on noise, vibration and harshness (NVH) of the vehicle system. This paper considers a novel form of two-stroke cycle engine offering potential for low emissions, reduced production cost and high potential vehicle efficiency. The engine uses segregated pump charging via the use of stepped pistons offering potential for low emissions. Installation as a power plant for automotive hybrid electric vehicles or as a range-extender for electric vehicles could present a low mass solution addressing the drive for vehicle fleet CO2 reduction. Operation on the two-stroke cycle enables NVH advantages over comparable four-stroke cycle units, however the durability of conventional crankcase scavenged engines can present significant challenges.

In recent years, automotive manufacturers have introduced an increasing array of in-line three cylinder engine solutions with the objective of providing efficient low CO2 emission power train solutions for small vehicles and in some cases to address down-sizing targets. At the same time, three cylinder engines have seen recent introduction in range-extender and hybrid electric vehicles such as the BMW i8. Unfortunately in-line three cylinder units present serious challenge to engineers in terms of noise, vibration and harshness and this often yields criticism from customer perceptions. The in-line three-cylinder arrangement however does offer an attractive packaging solution for vehicles and an effective method of reducing overall vehicle cost.