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In an engine, carburetion combines the proper ratio of oxygen with a gaseous form of a fossil fuel, like natural gas or gasoline, so it can combust. Internal combustion engines run by igniting fuel that has been sprayed into a fine vapor and mixed with air. This mixture, called an emulsion, will burn with the right amount of energy to fuel the engine. Carburetion usually involves all these stages, from vaporizing the gasoline to letting in the air and finally moving the mixture to where it can be combusted.
Carburetion is responsible for allowing an engine to perform at an optimal level whether it is starting, running at full throttle, or idling. Any combustion engine, such as on a lawnmower, chainsaw, or automobile, must utilize some form of carburetion. If there is too much fuel or too little oxygen, the engine runs "rich" and wastes fuel, produces smoke, creates too much heat, or ruins parts of the engine. If there is too little fuel or too much air, the engine runs "lean" and might sputter, stop, or cause engine damage.
The process of carburetion usually takes place inside a carburetor, but it can even be demonstrated with a home chemistry set. In a carburetor, there must be a central mixing chamber where the air will meet the fuel. One opening, a needle valve, pushes fuel through such a tiny hole that it sprays into that chamber in fine droplets. The other opening, a vacuum or suction valve, uses air pressure to control how much air enters the chamber, called metering. The atomized gasoline, suspended in the full volume of air, exits through a wide tube to another chamber where a spark will ignite it.
The exact amounts of air and fuel depend upon surrounding air pressure, the type of fuel, the fineness of the gaseous particles, and if the engine has settings for faster, slower, or idle. On older models of cars that use a traditional carburetor, that ratio is around 15 parts air to one part fuel. Other engines, such as those for a gas-powered leaf blower, don't have varying speeds; therefore they require simpler carburetion that doesn't account for slightly more or less fuel.