Right now, there is a truck. A big truck. Rolling down the road.
That truck has an engine that drives the gears that makes the wheels go round. The wheels grind their rubber against the pavement or blacktop or dirt or gravel, and scrape by to nudge the truck on it’s way.
While the engine is metering a tiny bit of fuel, a measure of air into each cylinder, waiting for the time to come that the fuel and air combine under pressure and heat, and explosively drive the piston part of the cylinder chamber away, to push a crankshaft, to twist a gear, to turn a wheel – the aftermath of the explosion in the cylinder is cleaned up.
After the fuel and the air have been burned, their exhaust products, water vapor, unburned fuel, any impurities in the air, will be vented through various mechanisms to limit the impact of the aftermath on the environment around the truck.
A bit of heat will remain.
When the air and fuel burn, they will heat the cylinder, the piston, the valves. The heat will be conducted to the outside of the engine, and will warm the air around the engine. This big truck engine is water cooled – water treated to manage boiling and impurities, is pumped into the engine to absorb heat. The heated water is sent to a radiator that uses a driven fan to draw massive amounts of air through the coils of the radiator. The radiator is designed to convey heat from the water to the air efficiently, and the cooled water is circulated back to the engine. The heat carried from the engine is important. Keeping the engine from overheating prevents overheating related breakdowns. Too much heat can warp bolts and cylinders and pistons and gaskets and seals and .. The potential for overheating damage runs from minor to quite major component failures.
So – why is the extra heat thrown away? Instead of a radiator to heat the air around the vehicle, can’t that heat be transformed into stored energy, in the form of heat, or of ice (an ammonia-cycle freezer?), or of electricity, or compressed air, or ..?
We burn the fuel. Why are we wasting the heat?