By now plenty of people have seen concept vehicles like the Chevy Volt and Ford HySeries Drive Edge. One of the biggest advantage of the series hybrid drivetrains in these machines is the flexibility they provide in choosing an auxiliary power unit. With the battery system providing the primary energy source to the electric motor the transient load demands of acceleration are taken off the range extender. This allows the range extender to operate in a constant mode doing nothing more than driving a generator to keep the battery charged.
When an engine operates in a constant mode like that it can be optimized for those conditions. However while the original Volt showed a fairly conventional three cylinder flex-fuel engine, there is also the possibility of using something radically different. We recently covered work being done on homogeneous charge compression ignition (HCCI) engines that can provide significantly reduced fuel consumption and emissions. Unfortunately getting HCCI works best only under certain light load conditions. However the series hybrid may well provide the perfect application for something like HCCI.
During a conversation with GM Vice President of R&D Larry Burns I brought the idea of HCCI and E-Flex and he agreed that the series layout could be a potential application for the new combustion process. Burns said that GM is investigating many different possibilities for the E-Flex power-train because the constant rpm duty cycle allows many ideas that might not have been feasible before suddenly become a real possibility. A whole new world gets opened up by this setup so thing only thing that's certain right now is change.