The GM Volt series plug-in hybrid should be able to drive about 40 miles in all-electric mode before a gasoline engine kicks in to recharge the batteries and produce electricity to move the car. Originally, that generator was supposed to be a 1-liter turbocharged 3-cylinder, but the man in charge of the development of the Volt drivetrain, Larry Nitz, has confirmed the switch to a 1.4-liter non-turbo 4-cylinder that will be E85 capable.
Why Make the Change?
Mr Nitz has explained that the four cylinder is less expensive and lighter because it lacks the turbocharging of the three cylinder. It also has better "better brake-specific fuel consumption than the 1.0L turbo when used in steady state mode, as it will be in the Volt application."
How will the Gas Engine be Used?
The gasoline engine in the Volt won't be used to move the wheels directly like in parallel hybrid (like the Toyota Prius, for example). When the battery gets down to about 30% charge (which should be after about 40 miles), the gasoline engine will turn on and generate electricity to charge the batteries.
It will try to meet the demand of the electric motors so that the battery pack stays around 30% charge. The goal is not to try to charge the battery back to "full", but rather to keep the car moving until it can be plugged back in, giving the maximum benefits from charging the batteries from the grid.