Mass Benefit Analysis of 4-Stroke and Wankel Range Extenders in an Electric Vehicle over a Defined Drive Cycle with Respect to Vehicle Range and Fuel Consumption

The gradual push towards electric vehicles (EV) as a
primary mode of transport has resulted in an increased
focus on electric and hybrid powertrain research. One
answer to the consumers’ concern over EV range is the implementation
of small combustion engines as generators to
supplement the energy stored in the vehicle battery. Since
these range extender generators have the opportunity to run
in a small operating window, some engine types that have
historically struggled in an automotive setting have the potential
to be competitive.
The relative merits of two different engine options for
range extended electric vehicles are simulated in vehicle across
the WLTP drive cycle. The baseline electric vehicle chosen
was the BMW i3 owing to its availability as an EV with and
without a range extender gasoline engine.
Two different range extenders were considered; a single
rotor Wankel rotary and a 4-stroke reciprocating engine, with
the baseline vehicle electric glider mass fixed for all options.
Fuel tank capacity was fixed at 9 litres. Baseline EV performance
was evaluated on simulated European drive cycles with
mass sensitivity conducted before the implementation of each
range extender.
Potential options for the optimisation of the range
extender operation were considered with respect to their
impact on vehicle performance. Total combined fuel efficiency
was compared and an assessment of maximum range and
vehicle performance was also conducted.