@gsuberland @malwaretech
Also the fact that they need to handle wildly variable running speed and load.

One reason the Prius is so efficient despite being a gas only car is that the engine can be designed for a very tight, well defined operating envelope.

@gsuberland @malwaretech yep, using the kinetic energy of expanding gasses is straight up the least efficient way of converting petrol into momentum, it's basically a side effect of combustion, most of the released energy is heat.