Fuel vapourising

To "vaporise" something means to change it from a (usually) a liquid state to a gaseous one.

Vaporised water -> steam

Vaporised gasoline -> gasoline fumes 

 I wrote "usually" because some materials don't go through a liquid state. Dry ice, for example, goes directly from solid to gas.

The temperature surrounding the vapor affects whether you can see the vapor or not.  Given the right temp. you can see the fuel vapor.

When water vapourisers they do not turn in to clouds - they turn in to steam ( the gas form of water ) gasoline vaporous are similar to steam in that that they obey the laws of gas physics. basically the gas molecules are scattered in the air and broken down with time.

http://zebu.uoregon.edu/~soper/Physics/gas.html

Lots of fuels. Gasoline stablizes at about 60 degrees above o but will still lose it's charterisicts over time. Gasoline at higher temps ( like in your car) being used by the engine, moving around in the tank causes vapor to rise from the liquid. Without modern tech devices incorporated in our automobiles all the fumes would be going directly into the atmosphere. So gasoline fumes (unburnt),( vapor from gasoline) go into the air and mixes with oxygen, breaks down and soon becomes useless.

It gets burned in our cars.