My Idea is to modify a hybrid car in order to use the heat of the engine that goes in to the environment without any use. 60% of the energy on the fuel is thrown in to the environment without using it.
All this heat from the radiator and the exhaust pipe can be recovered after the catalytic converter in a recovery boiler that can evaporate water or any kind of liquid to move a turbine in a closed circuit. This turbine can propel an electric generator and help the engine to propel the car.
By doing this the car engine can be almost half of its actual size without losing power and using half of the fuel it uses actually.