Shock cooling

Last updated

Shock cooling refers to the theory that damage to engines (particularly air-cooled aviation piston engines) may occur because of an excessively rapid decrease in temperature.


The situation where rapid cooling arises is on descent from altitude. In this condition, less power is demanded of the engine (it is throttled back) so it is developing much less heat. In a descent, the plane's airspeed increases, simultaneously increasing the cooling rate of the engine. As metals expand and contract under temperature changes, dimensional changes in the engine may exceed tolerance limits.


Damage from shock cooling is most commonly believed to manifest itself as stuck valves, [1] cracked pistons and cracked cylinders.


While the subject is very controversial, some believe shock cooling, as commonly explained, is nothing but a myth. This position is supported by the fact twin engine planes commonly experience ideal conditions for shock cooling during simulated, single engine failures, yet statistically show no difference in wear or damage probability distribution between engines. Equally, it has been pointed out the rate cylinder head temperatures drop off after a normal engine shutdown is often much faster than the usual rates deemed to present a shock cooling risk. Furthermore, others believe[ citation needed ] damage usually associated with shock cooling is actually caused by rapid throttle changes where fuel, which has been supercooled during high-altitude flight, is introduced into a very hot engine cylinder during descent, where rich of peak (as opposed to lean of peak [2] ) operation is considered the norm, thus causing higher operating temperatures. It is well established[ citation needed ], high operating temperatures in of themselves, can contribute to excessive component wear and damage, which is typically associated with "shock cooling". Given the available data, it strongly suggests "shock cooling" is nothing but a myth, at least in the context as commonly explained.

Detection and prevention

A single cylinder head temperature (CHT) sensor, or in more sophisticated installations, an array of sensors, one for each cylinder, may be employed to monitor the temperature and cooling rate of the engine. Usually a simple analog gauge or a more advanced graphical bar-graph display [3] (see external links below for an image) is used to present information to pilots. Spoilers on the wings or thrust reversal may also be deployed to lose lift without having to reduce engine power substantially, slowing the rate of engine cooling.

Notes and references

  1. "Shock Cooling: Myth or Reality?". 19 February 1997.
  2. "General Aviation Modifications, Inc".
  3. "Archived copy". Archived from the original on 2011-07-08. Retrieved 2008-11-12.{{cite web}}: CS1 maint: archived copy as title (link)

Related Research Articles

<span class="mw-page-title-main">Carburetor</span> Component of internal combustion engines which mixes air and fuel in a controlled ratio

A carburetor or carburettor is a device that mixes air and fuel for internal combustion engines in an appropriate air–fuel ratio for combustion. The term is sometimes colloquially shortened to carb in the UK and North America or to carby in Australia.

<span class="mw-page-title-main">Exhaust gas recirculation</span> NOx reduction technique used in gasoline and diesel engines

In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. The exhaust gas displaces atmospheric air and reduces O2 in the combustion chamber. Reducing the amount of oxygen reduces the amount of fuel that can burn in the cylinder thereby reducing peak in-cylinder temperatures. The actual amount of recirculated exhaust gas varies with the engine operating parameters.

In spark ignition internal combustion engines, knocking occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.

<span class="mw-page-title-main">Aircraft engine controls</span>

Aircraft engine controls provide a means for the pilot to control and monitor the operation of the aircraft's powerplant. This article describes controls used with a basic internal-combustion engine driving a propeller. Some optional or more advanced configurations are described at the end of the article. Jet turbine engines use different operating principles and have their own sets of controls and sensors.

Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. For small or special purpose engines, cooling using air from the atmosphere makes for a lightweight and relatively simple system. Watercraft can use water directly from the surrounding environment to cool their engines. For water-cooled engines on aircraft and surface vehicles, waste heat is transferred from a closed loop of water pumped through the engine to the surrounding atmosphere by a radiator.

<span class="mw-page-title-main">Spoiler (aeronautics)</span> Device for reducing lift and increasing drag on aircraft wings

In aeronautics, a spoiler is a device which intentionally reduces the lift component of an airfoil in a controlled way. Most often, spoilers are plates on the top surface of a wing that can be extended upward into the airflow to spoil the streamline flow. By so doing, the spoiler creates a controlled stall over the portion of the wing behind it, greatly reducing the lift of that wing section. Spoilers differ from airbrakes in that airbrakes are designed to increase drag without disrupting the lift distribution across the wing span, while spoilers disrupt the lift distribution as well as increasing drag.

Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere.

<span class="mw-page-title-main">Engine control unit</span> Computer that adjusts electronics in an internal combustion propulsion system

An engine control unit (ECU), also commonly called an engine control module (ECM), is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure optimal engine performance. It does this by reading values from a multitude of sensors within the engine bay, interpreting the data using multidimensional performance maps, and adjusting the engine actuators. Before ECUs, air–fuel mixture, ignition timing, and idle speed were mechanically set and dynamically controlled by mechanical and pneumatic means.

Carburetor, carburettor, carburator, carburettor heat is a system used in automobile and piston-powered light aircraft engines to prevent or clear carburetor icing. It consists of a moveable flap which draws hot air into the engine intake. The air is drawn from the heat stove, a metal plate around the exhaust manifold.

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 pre-set by the engine manufacturer. There are also aftermarket units where a separate controller is installed using a custom RPM setting. A limiter prevents a vehicle's engine from being pushed beyond the manufacturer's limit known as the redline. At some point beyond the redline, engine damage may occur.

A throttle is the mechanism by which fluid flow is managed by constriction or obstruction.

<span class="mw-page-title-main">Ignition timing</span>

In a spark ignition internal combustion engine, Ignition timing refers to the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke.

<span class="mw-page-title-main">Supercharger</span> Air compressor for an internal combustion engine

In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement.

Oil cooling is the use of engine oil as a coolant, typically to remove surplus heat from an internal combustion engine. The hot engine transfers heat to the oil which then usually passes through a heat-exchanger, typically a type of radiator known as an oil cooler. The cooled oil flows back into the hot object to cool it continuously.

An exhaust gas temperature gauge is a meter used to monitor the exhaust gas temperature of an internal combustion engine in conjunction with a thermocouple-type pyrometer. EGT gauges are found in certain cars and aeroplanes. By monitoring EGT, the driver or pilot can get an idea of the vehicle's air-fuel ratio (AFR).

A pressure carburetor is a type of fuel metering system manufactured by the Bendix Corporation for piston aircraft engines, starting in the 1940s. It is recognized as an early type of throttle-body fuel injection and was developed to prevent fuel starvation during inverted flight.

<span class="mw-page-title-main">Radiator (engine cooling)</span> Heat exchangers used for cooling internal combustion engines

Radiators are heat exchangers used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plant or any similar use of such an engine.

Internal combustion engines come in a wide variety of types, but have certain family resemblances, and thus share many common types of components.

<span class="mw-page-title-main">Internal combustion engine</span> Engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber

An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to. This replaced the external combustion engine for applications where the weight or size of an engine was more important.

<span class="mw-page-title-main">1972 Puerto Rico DC-7 crash</span> Aviation accident

The 1972 Puerto Rico DC-7 crash was an aviation accident that occurred on December 31, 1972, in Carolina, Puerto Rico. As a result of inadequate maintenance, the aircraft's No. 2 engine failed after takeoff. After initiating a turn to return to the airport, the aircraft eventually descended into, or attempted to ditch into, the ocean a mile offshore. All five people on board died, including baseball legend Roberto Clemente. The crash site was listed on the US National Register of Historic Places in 2022.