The Effect of Unconventional Piston Movement on SI Engine Combustion and Emissions

A major trend in current automotive research is hybridization of the power supply. This combination of electrical machine and combustion engine results, in some hybridization topologies, in a total decoupling of the combustion engine from the transmission. When the engine is decoupled from the transmission a new degree of freedom arises in engine design. The piston movement does not have to follow an evenly rotating shaft any more. It can be altered by the generator to achieve a movement found to be better from the point of efficiency or environmental concerns.

Modelling work showed a potential of lowered NO emissions if the expansion could be delayed. The experimental study, conducted in a two piston Alvar engine, showed that the state of the art electrical machine (EM) propelling one of the crankshafts was too weak to change the crankshaft speed in an extent to give the fast volume changes required to change the emissions of the internal combustion engine (ICE). By running the EM at four times the speed of the dynamometer coupled to the other piston, more unorthodox volume traces were generated and differences in the emissions of the engine were found. None of the possible changed volume traces generated pressure traces showing major changes in the 10-90% heat release rate of the engine. The experiments were conducted at the limit of what the EM was able to achieve at all times.