Diesel Engine Runaway
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Diesel engine runaway is an occurrence in
diesel engine The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to Mechanics, mechanical Compr ...
s, in which the engine draws excessive fuel from an unintended source and overspeeds at higher
RPM Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or r⋅min−1) is a unit of rotational speed (or rotational frequency) for rotating machines. One revolution per minute is equivalent to hertz. Standards ISO 80000-3:2019 def ...
s, producing up to ten times the engine's rated output resulting in a catastrophic
mechanical failure Structural integrity and failure is an aspect of engineering that deals with the ability of a structure to support a designed structural load (weight, force, etc.) without breaking and includes the study of past structural failures in order to ...
due to a lack of lubrication.
Hot-bulb engine The hot-bulb engine, also known as a semi-diesel or Akroyd engine, is a type of internal combustion engine in which fuel ignites by coming in contact with a red-hot metal surface inside a bulb, followed by the introduction of air (oxygen) compr ...
s and
jet engine A jet engine is a type of reaction engine, discharging a fast-moving jet (fluid), jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition may include Rocket engine, rocket, Pump-jet, water jet, and ...
s can also run away and fail via the same process.


Causes

In a diesel engine, the torque and the rotational speed are controlled by means of ''quality torque manipulation''. This means that, with each intake stroke, the engine draws in air which is not mixed with fuel; the fuel is injected into the cylinder ''after'' its contents have been compressed during the compression stroke. The high air temperature near the end of the compression stroke causes spontaneous combustion of the mixture as the fuel is injected. The output torque is controlled by adjusting the mass of injected fuel; the more fuel injected, the higher the torque produced. Adjusting the amount of fuel received per stroke alters the quality of the air-fuel-mixture, and adjusting the amount of the mixture itself is not required, negating the need for a
throttle valve A throttle is a mechanism by which fluid flow is managed by construction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle'' ha ...
. Diesel engines can combust a large variety of fuels, including many sorts of oil, petrol, and combustible gases. This means that if there is any type of leak or malfunction that increases the amount of oil or fuel unintentionally entering the combustion chamber, the quality of the air-fuel-mixture will increase, causing torque and rotational speed to increase. Fuel and oil leaks causing engine runaways can have both internal and external causes. Broken seals or a broken turbocharger may cause large amounts of oil mist to enter the inlet manifold, whereas defective injection pumps may cause an unintentionally large amount of fuel to be injected directly into the combustion chamber. If a diesel engine is operated in an environment where combustible gases are used, a gas leak may result in an engine runaway if the gas can enter the engine's inlet manifold.


Stopping a runaway engine

Several ways to stop a runaway diesel engine are to block off the air intake, either physically using a cover or plug, or alternatively by directing a
fire extinguisher A fire extinguisher is a handheld active fire protection device usually filled with a dry or wet chemical used to extinguish or control small fires, often in emergencies. It is not intended for use on an out-of-control fire, such as one which ha ...
into the air intake to smother the engine. Engines fitted with a decompressor can also be stopped by operating the decompressor, and in a vehicle with a manual transmission it is sometimes possible to stop the engine by engaging a high gear (i.e. 4th, 5th, 6th etc.), with foot brake and parking brake fully applied, and quickly letting out the clutch to slow the engine RPM to a stop, without moving the vehicle. This should be the last option because it can result in catastrophic damage to the whole transmission, mainly the gearbox, but this operation can save the engine.


Notable incidents involving diesel engine runaway

In the 2005
Texas City refinery explosion On March 23, 2005, a hydrocarbon vapor cloud ignited and violently exploded at the isomerization process unit of the BP-owned oil refinery in Texas City, Texas. It resulted in the killing of 15 workers, 180 injuries and severe damage to the re ...
, an instance of diesel engine runaway is thought to have provided the ignition source that triggered the massive explosion. After the refinery's
blowdown stack A blowdown stack is an elevated vent or vertical stack that is used to vent the pressure of components of a chemical, refinery or other plant if there is a process problem or emergency. A blowdown stack can be used to complement a flare stack or a ...
malfunctioned and started releasing a cloud of
raffinate In chemical separation terminology, the raffinate (from French ''raffiner'', to refine) is a product which has had a component or components removed. The product having the removed materials is referred to as the extract. For example, in solvent e ...
vapor into the air, a pickup truck that had been parked near the stack with its engine idling was engulfed by the vapor cloud released and the engine began to race. As staff at the refinery attempted to stop the truck's now-overheating engine, it
backfired "Backfired" is the debut solo single from American singer and Blondie vocalist Debbie Harry. Released in 1981, it was taken from her debut solo studio album, ''KooKoo''. Background "Backfired" peaked at number 32 in the UK, and number 43 on the ...
, igniting the vapor cloud and triggering the disaster.U.S. Chemical Safety and Hazard Investigation Board. Investigation Report - Refinery Fire and Explosion and Fire. BP Texas City March 23, 2005, para 2.5.13 Ignition Source, p66


References


Bibliography

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See also

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Rev limiter A rev limiter is a device fitted in modern vehicles that have internal combustion engines. They are intended to protect an engine by restricting its maximum rotational speed, measured in revolutions per minute (RPM). Rev limiters are Engine contr ...


External links


A General Electric ES44AC locomotive in the process of a runaway

Norfolk Southern diesel locomotive in runaway
{{DEFAULTSORT:Diesel Engine Runaway Engine problems Diesel engines