Some of the current Hybrid cars, do in fact use regenerative braking systems (i.e. when you brake some of the power is converted into electricity and stored back in the batteries.)

There are other engine designs as well (outside of piston engines). GM (I belieive it was) created a coal dust powered Turbine engine vehicle. Definitely a different sound.

On Tuesday, November 01, 2005, at 11:42AM, Marc Sayer <marcsayer@COMCAST.NET> wrote:

>We store kinetic energy in the car itself when it is moving, then we
>convert that energy to waste heat when we use the brakes. Why not make
>that energy do some work instead? And why rely solely on atomization to
>facilitate combustion? Why not take Smokey's idea of a hot vapor engine
>and and supply hot gasoline vapor rather than liquid gasoline to the
>engine? We could use some of that waste heat to make that happen and
>achieve 100% fuel combustion, a goal we are still no where near, even
>with the best FI systems. That would reduce emissions, and increase
>efficiency.
>