Overspeed (engine)

Overspeed is a condition in which an engine is allowed or forced to turn beyond its design limit. The consequences of running an engine too fast vary by engine type and model and depend upon several factors, chief amongst them the duration of the overspeed and by the speed attained. With some engines even a momentary overspeed can result in greatly reduced engine life or even catastrophic failure. The speed of an engine is ordinarily measured in revolutions per minute (RPM).

Examples of overspeed

• In aircraft an engine overspeed will occur if the propeller - ordinarily connected directly to the engine - is forced to turn too fast by high speed airflow while the aircraft is in a dive.

• In jet aircraft an overspeed results when the axial compressor exceeds its maximum operating RPM - this often leads to the mechanical failure of turbine blades, flameout and complete destruction of the engine.

• In vehicles an engine can be forced to turn too quickly by changing to an inappropriately low gear.

• Most unregulated engines will overspeed should there be no or little load while power is applied.

Overspeed protection

Sometimes a regulator or governor is fitted to make engine overspeed impossible or less likely. For example:

• Many steam engines use a centrifugal governor which centrifugally close a throttle to restrict steam flow as engine speed increases.
• In motor vehicles automatic gearboxes will change gear to prevent the engine from turning too quickly.
• Some aircraft have constant speed units which automatically change propeller pitch to keep the engine running at the optimum speed.

Large diesel engines are sometimes fitted with a secondary protection device ^[1] which operates if the governor fails. This consists of a flap valve in the air intake. If the engine overspeeds, the air flow through the intake will rise to an abnormal level. This causes the flap valve to snap shut, starving the engine of air and shutting it down.

See also

• Rev limiter
• Diesel engine runaway

References

1. ^ AirTek Systems

This article about a mechanical engineering topic is a stub. You can help Wikipedia by expanding it.v · Categories: Engines Engine problems Mechanical engineering Mechanisms Mechanical engineering stubs Wikimedia Foundation. 2010. Игры ⚽ Нужно сделать НИР? George Rose (rugby league) The Grinch Grinches the Cat in the Hat Look at other dictionaries: Overspeed (aircraft) — Not to be confused with overspeed (engine) or critical Mach number. For structural failure resulting from overspeed, see Loss of structural integrity on an aircraft. Main article: V speeds Overspeed is the aircraft flight condition when the… …   Wikipedia overspeed — i. A condition in which an engine has produced speed greater than its design speed. ii. The condition in which the actual engine speed is higher than the designed engine RPM as set on the propeller control by the pilot. This condition is… …   Aviation dictionary overspeed — I. ˈ ̷ ̷ ̷ ̷ˌ ̷ ̷ noun Etymology: over (III) + speed, n. : speed greater than normal or rated speed subjected to overspeeds Time II. | ̷ ̷ ̷ ̷| ̷ ̷ verb Etymology …   Useful english dictionary overspeed governor — A device to protect the engine against overspeeding. The servofuel is bled off when the governed engine speed is reached. The two types of governors are centrifugal and hydromechanical. The illustration shows the propeller governor for an oil… …   Aviation dictionary overspeed condition — The condition in which an engine is turning at a speed higher than that selected by the governor. This is avoided by the use of governors …   Aviation dictionary Diesel engine runaway — is a rare condition affecting diesel engines, where the engine goes out of control, consuming its own lubrication oil and running at higher and higher RPM until it overspeeds to a point where it destroys itself either due to mechanical failure or …   Wikipedia Diesel engine — Diesel engines in a museum Diesel generator on an oil tanker …   Wikipedia electronic engine control — An electronic fuel control for gas turbine engines. It sends out metered fuel to the engine for all flight conditions by sensing various parameters, such as the throttle position, engine RPM, atmospheric conditions, speed, and height. EEC… …   Aviation dictionary Tachometer — A tachometer is an instrument that measures the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute (RPM) on a calibrated analog dial, but digital displays are increasingly… …   Wikipedia Rev limiter — A Rev limiter is a device fitted to an internal combustion engine to restrict its maximum rotational speed. This is usually carried out to prevent damage to the engine, however sometimes these devices are fitted to prevent an engine reaching the… …   Wikipedia 18+ © Academic, 2000-2024 Contact us: Technical Support, Advertising Dictionaries export, created on PHP, Joomla, Drupal, WordPress, MODx. Mark and share Search through all dictionaries Translate… Search Internet Share the article and excerpts Direct link … Do a right-click on the link above and select “Copy Link”