I've been thinking about this for years, but as of yet have not tried it. Less chance now because if I had the right vehicle to use the engine from then I'd probably be using it to save gas. (Provided the rest of the car wasn't totaled.)
You might think that all of the energy used by burning gasoline in your car goes to making power to run it. That is far from being the case. The way it works is only about 1/3 of the energy is used for that. 1/3 is lost through heat which is removed by the radiator and 1/3 is lost through exhaust and goes out the tailpipe without doing anything other than polluting. Also while you are driving there are several other things that can cut down on efficiency. Like the weight of the vehicle and the engine having to work to keep it moving and buck the resistance from the wind it pushed in front of it.
This works the same for any internal combustion engine (car engine, generator, lawnmower and so on) EXCEPT for a diesel engine which is about 1/3 more efficient than a gasoline engine. That is because the diesel engine produces far less heat than a gasoline engine does and that savings goes toward making power. Therefore I'm leaving diesel engines out f this equation. However, burning propane in an internal combustion engine is much better for several reasons. (the first being that it is far less polluting and the second is that the engine stays much cleaner and requires less maintenance because the oil doesn't need to be changed as often because of the cleaner burning fuel.) Propane also has pretty near the same energy per gallon as gasoline so no big lost there.
Now with that behind us here is my idea and what I some day hope to start working on.
My idea is to route the antifreeze water mixture through an inside coil / fan unit to provide some of the heating inside during the winter and possibly a heat exchanger in the summer to run an absorption (refrigeration system) for cooling the inside of a cabin or what ever. At the same time use a heat exchanger on the exhaust system for heating water for various uses. It could also probably be routedthrough a boiler to provide steam for a small steam turbine for extra power to run other stuff. (Generate extra power, or run a refrigeration device for cooling.)
The actual output of the engine could be used to run a generator, refrigeration system and alternators to charge battery banks from when the engine isn't running. To get the most out of this I'd need a very efficient small car engine converted to run on propane. Not only would the engine not have to over come the drag from pushing a vehicle down the highway and wouldn't have to be pushing all of the wind a vehicle has to push while moving.
This is not something a person would want to use all the time UNLESS they run a generator all the time, but it could have its uses quiet often when you need a lot of power, heat and so on at the same time and should make it economically with a minimum of pollution.
A very cold day - It is days like today that I am glad I am not working. It has been cold! Lucky for me we do not have any appointments until later on this week. I really ...
10 minutes ago