carburetor

/kahr"beuh ray'teuhr, -byeuh-/, n.

a device for mixing vaporized fuel with air to produce a combustible or explosive mixture, as for an internal-combustion engine.

Also, carburator, carbureter; esp. Brit., carburettor, carburetter /kahr"byeuh ret'euhr/.

[1860-65; CARBURET + -OR²]

* * *

Device for supplying a spark-ignition engine with a mixture of fuel and air.

Carburetors are used in small gasoline engines, such as lawn mowers and chainsaws. Once an essential component in all gasoline engines, automobile carburetors were displaced by electronic fuel injection systems from the late 1970s through 1990. Carburetors for automobile engines usually contained a storage chamber for liquid fuel, a choke, an idling jet, a main jet, an airflow restriction, and an accelerator pump. The quantity of fuel in the storage chamber was controlled by a valve actuated by a float. The choke, a butterfly valve, reduced the intake of air so that a fuel-rich charge was drawn into the cylinders when a cold engine was started. As the engine warmed up, the choke was gradually opened. Reduced pressure near the partially closed throttle valve caused the fuel to flow from the idling jet into the intake air. Further opening the throttle valve activated the main fuel jet. Then the venturi-shaped airflow restriction created reduced pressure, drawing fuel from the main jet into the airstream at a rate related to the airflow so that a nearly constant fuel-air ratio was obtained. The accelerator pump injected fuel into the inlet air when the throttle was opened suddenly. See also gasoline engine; venturi tube.

* * *

▪ mechanics

also spelled  carburettor  

      device for supplying a spark-ignition engine with a mixture of fuel and air. Components of carburetors usually include a storage chamber for liquid fuel, a choke, an idling (or slow-running) jet, a main jet, a venturi-shaped air-flow restriction, and an accelerator pump. The quantity of fuel (gasoline) in the storage chamber is controlled by a valve actuated by a float. The choke, a butterfly valve, reduces the intake of air and allows a fuel-rich charge to be drawn into the cylinders when a cold engine is started. As the engine warms up, the choke is gradually opened either by hand or automatically by heat- and engine-speed-responsive controllers. The fuel flows out of the idling jet into the intake air as a result of reduced pressure near the partially closed throttle valve. The main fuel jet comes into action when the throttle valve is further open. Then the venturi-shaped (venturi tube) air-flow restriction creates a reduced pressure for drawing fuel from the main jet into the air stream at a rate related to the air flow so that a nearly constant fuel-air ratio is obtained. The accelerator pump injects fuel into the inlet air when the throttle is opened suddenly.

      In the 1970s, new legislation and consumer preferences led automobile manufacturers to improve fuel efficiency and lower pollutant emissions. To accomplish these objectives, engineers developed fuel injection management systems based on new computer technologies. Soon, fuel injection systems replaced carbureted fuel systems in virtually all gasoline engines except for two-cycle and small four-cycle gasoline engines, such as those used in lawn mowers.

* * *