Supersession of carburetors

Throughout the 1950s and 1960s, various federal, state and local governments conducted studies into the numerous sources of air pollution. These studies ultimately attributed a significant portion of air pollution to the automobile, and concluded air pollution is not bounded by local political boundaries. At that time, such minimal emission control regulations as existed were promulgated at the municipal or, occasionally, the state level. The ineffective local regulations were gradually supplanted by more comprehensive state and federal regulations. By 1967 the state of California (Governor Reagan), created the California Air Resources Board, and in 1970, the U.S. Environmental Protection Agency was formed. Both agencies now create and enforce emission regulations for automobiles, as well as for many other sources. Similar agencies and regulations were contemporaneously developed and implemented in Europe, Australia, and Japan.

Car carburetor

The ultimate combustion goal is to match each molecule of fuel with a corresponding number of molecules of oxygen so that neither has any molecules remaining after combustion in the engine and catalytic converter. Such a balanced condition is known as stoichiometry. Extensive carburetor modifications and complexities were needed to approach stoichiometric engine operation in order to comply with increasingly-strict US exhaust emission regulations of the 1970s and 1980s. This increase in complexity gradually eroded and then reversed the simplicity, cost, and packaging advantages carburetors had traditionally offered.

Fuel injection appeared first as novelty equipment on American-made cars in the late 1950s, such as the 1958 Chrysler products equipped with Bendix' ElectroJector, and 1957–1965 Rochester fuel injected Chevrolet Corvettes. About a decade later, more practical fuel injection systems were introduced in European-made cars. As emission regulations progressively tightened worldwide, generally led by the US state of California's especially stringent rules, automakers had to improve the precision and accuracy with which fuel was metered to the engine. Catalytic converters also became practically universal equipment.

There are three primary types of toxic emissions from an internal combustion engine: Carbon Monoxide (CO), unburnt hydrocarbons (HC), and oxides of nitrogen (NOx). CO and HC result from incomplete combustion of fuel due to insufficient oxygen in the combustion chamber. NOx, in contrast, results from excessive Oxygen in the combustion chamber. The opposite causes of these pollutants makes it difficult to control all three simultaneously. Once the permissible emission levels dropped below a certain point, catalytic treatment of these three main pollutants became necessary. This required a particularly large increase in fuel metering accuracy and precision, for simultaneous catalysis of all three pollutants requires that the fuel/air ratio be held within a very narrow range of stoichiometry. The open loop fuel injection systems had already improved cylinder-to-cylinder fuel distribution and engine operation over a wide temperature range, but did not offer sufficient fuel/air ratio control to enable effective exhaust catalysis. Closed loop fuel injection systems improved the air/fuel ratio control with an exhaust gas oxygen sensor. The O₂ sensor is mounted in the exhaust system upstream of the catalytic converter, and enables the engine management computer to determine and adjust the air/fuel ratio precisely and quickly.

Fuel injection was phased in through the latter '70s and '80s at an accelerating rate, with the US and German markets leading and the UK and Commonwealth markets lagging somewhat, and since the early 1990s, almost all gasoline passenger cars sold in first world markets like the United States, Europe, Japan, and Australia have come equipped with electronic fuel injection (EFI). Many motorcycles still utilize carbureted engines, though all current high-performance designs have switched to EFI.

Fuel injection systems have evolved significantly since the mid 1980s. Current systems provide an accurate, reliable and cost-effective method of metering fuel and providing maximum engine efficiency with clean exhaust emissions, which is why EFI systems have replaced carburetors in the marketplace. EFI is becoming more reliable and less expensive through widespread usage. At the same time, carburetors are becoming less available, and more expensive. Even marine applications are adopting EFI as reliability improves. Virtually all internal combustion engines, including motorcycles, off-road vehicles, and outdoor power equipment, may eventually use some form of fuel injection.

It should be noted that carburetion remains a less costly alternative where strict emission regulations and advanced vehicle diagnostic and repair infrastructure do not exist, as in developing countries. Fuel injection is gradually replacing carburetors in these nations too as they adopt emission regulations conceptually similar to those in force in Europe, Japan, Australia and North America.

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