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In an automotive application, the accelerator is typically the pedal that a driver uses to increase the engine speed. The accelerator may be commonly known as a gas pedal, though it usually directly affects the air intake rather than the gas. In most vehicles the accelerator is connected to a butterfly valve via mechanical linkage, and depressing it allows more air to enter the engine. This will typically also increase the amount of gas being combusted, as the carburetor or fuel injection will tend to equalize the fuel/air ratio as the volume of air increases.
In carbureted vehicles, the accelerator is typically connected via a cable or other mechanical means to a butterfly valve inside the carburetor. Depressing the gas pedal in these applications will cause the butterfly valve to open, allowing more air to enter the engine. Most fuel injected vehicles operate in a similar way, though the valve that the accelerator controls is typically in a throttle body. This valve generally performs the same function as one inside a carburetor, allowing the gas pedal to directly affect the volume of air that enters the plenum.
Some vehicles use a type of electronic throttle control. These cars typically have a sensor located on the accelerator in the place of mechanical linkage. The sensor will typically send a different signal, depending on how far the gas pedal is depressed. The engine control module (ECM) can then use this signal to determine how much air the throttle body should allow into the plenum, indirectly allowing the driver to control engine speed.
Many other applications also use a some type of accelerator. Airplanes typically use a thrust lever to control engine output. In multi-engine aircraft, each engine may have its own thrust lever. These levers can usually be adjusted individually to achieve the desired amount of thrust from each engine. Some aircraft will also include thrust reversers, in which case each thrust lever will typically be accompanied by a reverser.
Jet engine aircraft will often include an accelerator system known as an autothrottle. Rather than setting each thrust lever manually, these systems may allow the pilot to choose the desired speed or thrust. The system can then automatically adjust the power of each engine to achieve the desired characteristics, resulting in better fuel economy and less work for the pilot. An autothrottle may be automatically set for optimum takeoff, cruising, or a number of other different conditions.