it makes a big difference if you're running on the edge of knocking when it's cold outside. knocking is when the fuel burns before it is supposed to, it sounds like a knock in your engine, it's bad, kinda like taking a sledge hammer the the top of your engine.
Vaporizing the fuel helps fuel economy because it burns more completely, this gives you more power with the fuel you have so you don't need as much to do the same ammount of work. injectors already do this to a point, they have a high pressure pump pushing the fuel through a small nozzle, this makes the fuel into a mist. other things help like ethanol, it helps the fuel vaporize, and apparently acetone (paint thinner).
As for your original question, look on howstuffworks.com for how diesels work, this will give you an idea of the differences between a gasoline engine and a diesel engine. trying to apply a principle from a diesel to a gasoline is usually impossible without completely redesining the engine.