Throttle
From Wikipedia, the free encyclopedia
A throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction. In an engine, the engine's power can be increased or decreased by the restriction of inlet gases i.e. by the use of a throttle. The term throttle has come to refer, informally and incorrectly, to any mechanism by which the power or speed of an engine is regulated.
[edit] Internal combustion engines
In a petrol internal combustion engine, the throttle is a valve that directly regulates the amount of air entering the engine. In a motor vehicle the control used by the driver to regulate power is sometimes called the throttle pedal.
The throttle is typically a butterfly valve. In a fuel-injected engine, the throttle valve is housed in the throttle body. In a carbureted engine, it is found in the carburetor.
When a throttle is wide open, the intake manifold is usually at ambient atmospheric pressure. When the throttle is partially closed, a manifold vacuum develops as the intake drops below ambient pressure.
Usually the throttle valve is mechanically linked with the throttle pedal or lever. In vehicles with electronic throttle control, the throttle valve is electronically controlled, which allows the ECU greater possibilities in reducing air emissions.
Diesel internal combustion engines lack a butterfly valve in the intake tract and instead regulate engine power via direct control of the quantity of fuel injected into the cylinder during the power stroke. I.e. diesel engines do not have a throttle.
[edit] Other engines
Most engines have some kind of throttle control, though the particular way that power is regulated is often different.
Liquid rockets are throttled by controlling the pumps which send liquid fuel and oxidizer to the combustion chamber. Solid rockets are more difficult to throttle, but some may have mechanisms for this.
In a jet engine, engine output is also directly controlled by changing the amount of fuel flowing into the combustion chamber, usually with an autothrottle.
