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Carburetor

A carburetor (North American spelling) or carburettor (Commonwealth spelling), is a device that blends air and fuel for an internal combustion engine. It was invented by Karl Benz before 1885 and patented in 1886. It is colloquially called a carb (in North America and the United Kingdom) or carby (chiefly in Australia).

The word carburetor comes from the French carbure, meaning ‘carbide’. To carburete means to combine with carbon. In fuel chemistry, the term has the more specific meaning of increasing the carbon (and therefore energy) content of a fuel by mixing it with a volatile hydrocarbon.

History and Development

The carburetor was invented by the Hungarian engineer Donát Bánki in 1893. Frederick William Lanchester of Birmingham, England experimented early on with the wick carburetor in cars. In 1896 Frederick and his brother built the first petrol driven car in England, a single cylinder 5 hp (4 kW) internal combustion engine with chain drive. Unhappy with the performance and power, they re-built the engine the next year into a two cylinder horizontally opposed version using his new wick carburetor design. This version completed a 1,000 mile (1600 km) tour in 1900 successfully incorporating the carburetor as an important step forward in automotive engineering.

Carburetors were the usual fuel delivery method for almost all engines up until the mid-1980s, when fuel injection became the preferred method of automotive fuel delivery. In the US market, the last carbureted car was the 1991 Ford Crown Victoria Police Interceptor equipped with the 351 in³ (5.8 L) engine, and the last carbureted light truck was the 1994 Isuzu.[3] Elsewhere, Lada cars used carburetors until 1996. A majority of motorcycles still utilize carburetors due to lower cost and throttle response problems with early injection set ups, but as of 2005, many new models are now being introduced with fuel injection. Carburetors are still found in small engines and in older or specialized automobiles, such as those designed for stock car racing.

Principles

The carburetor works on Bernoulli’s principle: the faster air moves, the lower its static pressure, and the higher its dynamic pressure. The throttle (accelerator) linkage does not directly control the flow of liquid fuel. Instead, it actuates carburetor mechanisms which meter the flow of air being pulled into the engine. The speed of this flow, and therefore its pressure, determines the amount of fuel drawn into the airstream.

When carburetors are used in aircraft with piston engines, special designs and features are needed to prevent fuel starvation during inverted flight. Later engines used an early form of fuel injection known as a pressure carburetor.

Most carbureted (as opposed to fuel-injected) engines have a single carburetor, though some engines use multiple carburetors. Older engines used updraft carburetors, where the air enters from below the carburetor and exits through the top. This had the advantage of never “flooding” the engine, as any liquid fuel droplets would fall out of the carburetor instead of into the intake manifold; it also lent itself to use of an oil bath air cleaner, where a pool of oil below a mesh element below the carburetor is sucked up into the mesh and the air is drawn through the oil covered mesh; this was an effective system in a time when paper air filters did not exist.

Beginning in the late 1930s, downdraft carburetors were the most popular type for automotive use in the United States. In Europe, the sidedraft carburetors replaced downdraft as free space in the engine bay decreased and the use of the SU-type carburetor (and similar units from other manufacturers) increased. Some small propeller-driven aircraft engines still use the updraft carburetor design, however many use more modern designs such as the Constant Velocity (CV) Bing(TM) carburetor.