what is detonation in an aircraft reciprocating engine

by Miss Julianne Toy Published 3 years ago Updated 2 years ago

An explosion, or uncontrolled burning of the fuel-air mixture inside the cylinder of a reciprocating engine. Detonation occurs when the pressure and the temperature inside the cylinder become higher than the critical pressure and temperature of the fuel. Detonation is often confused with preignition.

Detonation is the abrupt combustion or explosion of the fuel charge inside the cylinder. During normal combustion, the spark plugs ignite the fuel charge and the fuel has a consistent and even burn as the piston moves through the power stroke and chemical energy is efficiently converted to mechanical.

Full Answer

What is detonation in a car engine?

This is exactly how fuel must burn within a piston engine to develop power without doing damage. Detonation refers to the condition where remote pockets within the fuel air mixture explode violently due to rising pressure following regular ignition.

What is detonation and pre-ignition?

Detonation and Pre-Ignition are two unique conditions that can severely damage an aircraft engine. Forces and severe heat that result from the occurrence of either will usually require the complete teardown and repair of the engine.

What determines the detonation margin of a reciprocating airplane engine?

The detonation margin of reciprocating airplane engines at various power settings is related primarily to induction air inlet temperature and pressure, cylinder head temperature, engine exhaust back pressure, ignition timing, fuel grade, fuel flow, carburetor or injector metering characteristics, compression ratio, and cooling margins.

What are the effects of detonation on an aircraft?

Light detonation may not show any indication in the cabin of the aircraft. Moderate to severe detonation could be noticed as engine roughness, vibration or loss of power and eventually engine damage.

What is a detonation in an airplane?

Detonation refers to the condition where remote pockets within the fuel air mixture explode violently due to rising pressure following regular ignition.

What is meant by engine detonation?

Engine detonation refers to spontaneous combustion of the remaining fuel/air mixture in the chamber after normal spark-initiated combustion. July 21, 2021. The terms “pre-ignition” and “engine detonation” are often thrown around interchangeably to describe the phenomenon that causes engine knock.

What happens during detonation?

Detonation occurs when excessive heat and pressure in the combustion chamber causes the air/fuel mixture to ignite on its own. Instead of a typical single flame kernel within the chamber, this creates multiple flames which collide with explosive force.

What are the three causes of detonation?

What Causes Detonation Engine Knock?Bad Knock Sensor. Your engine has a sensor that is designed to detect when there is a detonation knock. ... Air-Heavy Mixture. Air and fuel combust together to create detonation in the cylinders. ... Low-Octane Fuel. ... Poor Engine Timing. ... Bonus Cause.

How can aircraft detonation be prevented?

What causes detonation and how can it be prevented?Increase the engine mixture.Reduce power to a lower setting.Reduce or stop climb and increase forward speed for greater cooling.

What is the difference between knocking and detonation?

Knocking vs Detonation Knocking is the making sharp sounds due to uneven combustion of fuel in the cylinder of a vehicle engine. Detonation is the process of pre-ignition or auto-ignition of a fuel in an engine's combustion chamber.

How do you control detonation?

Investigations indicate that detonation may be controlled by retarding the rate of combustion by chemicals added to the mixture, which serve to increase its specific heat and prevent excessive temperature, and by reducing the temperature of the walls of the combustion-chamber, so that the temperature of the charge ...

What factors could affect detonation in an engine?

Factors affecting Detonation or Knocking in SI engine:Compression ratio: The pressure and temperature at the end of compression increases with increase in compression ratio. ... Supercharging: ... Increasing inlet temperature: ... Increase in load: ... Advancing the spark: ... Flame travel distance: ... Spark plug location: ... Engine size:More items...

How do you know if your engine is detonating?

What Are the Symptoms of Detonation? Detonation—sometimes called knock or pre-ignition—is a pinging sound that can sometimes be heard during acceleration and throttle tip-in. Unlike normal exhaust noise, detonation is a higher-pitched, raspy note that emanates from the engine compartment.

How do you know if your engine is detonated?

How is it indicated?Knocking or pinging sound.Drop in Exhaust Gas Temperature (EGT)Broken piston rings and/or spark plugs.Damage to the piston and/or valves.

What is difference between detonation and knocking?

Detonation is an uncontrolled combustion event which occurs after the spark event. Pre-ignition is an uncontrolled combustion event which occurs before the spark event. Knock (pinging) is the actual noise that can be audibly heard if detonation is bad enough.

What is the difference between detonation and combustion?

Detonation differs from normal combustion in its ignition mechanism and in the supersonic velocity of 2–5 kilometres per second for gases and 8–9 kilometres per second for solid and liquid explosives. Detonation is impossible when the energy loss from the reaction zone exceeds a certain limit.

What is the frequency of detonation?

Frequency and severity of detonation is defined as follows: 5-9 flashes/minute= incipient detonation; 10-20 flashes/minute= limiting detonation.

How to test for detonation?

The detonation test should be specified to cover power settings throughout the entire operating envelope using fuel of minimum specified octane. The usual method of doing this is to take successive power readings with the mixture leaned out progressively to the point of incipient detonation or where the engine cuts out. Intake air temperatures for detonation testing should account for the heat rise requirements for induction system icing protection. During the tests the engine should be operated with intake air at a temperature which complies with the intended class of aircraft preheated regulator requirements. For fuel injected engines, the intake air temperature should be commensurate

What is a detonation survey?

detonation survey must be performed for the approval of a turbocharged engine installed in an airframe to verify that the detonation margins are still within acceptable limits and that the installation has not caused any detrimental effect related to detonation. e.

What are the changes to the combustion chamber design?

Changes to design features for purpose of meeting the detonation margin, such as compression ratio, ignition timing, and fuel metering and endurance characteristics may require re-certification of an engine. b. The addition of a turbocharger to an engine not certified with it or a change in the engine turbocharger of a certified combination may affect detonation margin. If the original margin is small, unsatisfactory detonation characteristics may result. Turbocharging can also be expected to have an effect on induction system distribution. c. For

Why is induction air temperature critical at altitude?

turbocharged engine, induction air temperature may become critical at altitude because of the increased compression of air required. The turbocharger speed

What is a turbocharger?

The uncontrolled ignition of a charge prior to the occurrence of normal ignition. c. Turbocharger. Any exhaust gas-driven device that is added to or part of a reciprocating engine. This definition applies to: (1) Engines turbonormalized having a turbocharger that maintains approximately sea level manifold pressure to a critical altitude. (2) Engines turbosupercharged having a turbocharger that provides a manifold pressure greater than that of a normally aspirated engine at sea level conditions and maintains this pressure to

What is the difference between detonation and pre ignition?

Detonation refers to the condition where remote pockets within the fuel air mixture explode violently due to rising pressure following regular ignition. Pre-Ignition refers to the condition where either a mistimed spark or another source of ignition exists within the combustion chamber, allowing the burn to start well in advance ...

How does detonation affect pistons?

It occurs at the far reaches of the combustion chamber and usually causes the most damage at the edges of the pistons as a result. It causes rapidly rising temperatures at the piston edges, which can allow subsequent detonation to damage ring lands. It can also trigger pre-ignition due to the hot spots. Once this occurs the damaged piston edge is exposed to severe heat and pressure which can cause a hole to be burned through the corner of the piston. Leaking combustion gasses pushing through broken ring lands also causes torching at the pistons edge which quickly progress to failure of the seal between the combustion chamber and the crankcase.

Why does a combustion chamber detonate?

As the burn starts cylinder pressure quickly rises. If combustion chamber parts are hotter than usual this can cause remote pockets within the cylinder to spontaneously detonate. This can also occur when fuel octane is below the requirements of the engine. Causes of detonation are limited to excessive heat and low octane.

What happens if you break the seal between the piston and the crankcase?

Once the seal between the piston and the crankcase is breached pressurization of the crankcase can push crankcase oil overboard causing additional damage from oil starvation. Engine contamination and the severe stress imposed will require the engine to be completely disassembled.

Why does my car detonate?

Causes of detonation are limited to excessive heat and low octane. Excessive heat can come from improper cooling, high compression from excessive combustion chamber deposits, lean mixture, advanced timing and more. When it is limited to one cylinder the very likely culprit is a partially clogged fuel injector.

Why does my fuel injector glow?

Hot spots from detonation, improper heat range spark plugs and glowing carbon deposits from lean mixtures are common causes of pre-ignition. Carbon deposits do not usually accumulate when the lean mixture is chronic but normal deposits can be quickly heated to glowing temperature when a fuel injector suddenly becomes partially clogged.

What are the two conditions that can severely damage an aircraft engine?

Detonation and Pre-Ignition are two unique conditions that can severely damage an aircraft engine. Forces and severe heat that result from the occurrence of either will usually require the complete teardown and repair of the engine.

What is the process of detonation?

Detonation, as the name suggests, is an explosion of the fuel-air mixture inside the cylinder. Under normal operation, the spark plugs each ignite a point in the fuel/air charge, which then propagate through the cylinder and provides a consistent, regulated burn in a process called deflagration. This extends the time that the burning fuel pushes on the cylinder, providing a gentle power stroke.

What is the detonation of a car called?

However, severe detonation can cause engine failure in minutes. Because of the noise that it makes, detonation is called "engine knock" or "pinging" in cars.

What is the instaneous combustion that occurs due to unburnt gases left in the combustion chamber resulting in?

Detonation is the instaneous combustion that occur due to unburnt gases left in the combustion chamber resulting in high temperature, sufficient for self-ignition

Why is it called engine knock?

Because of the noise that it makes, deton ation is called "engine knock" or "pinging" in cars. Detonation can be caused by a number of factors, but generally they relate to a situation outside of the engine's design.

What happens to the fuel in a detonator?

This extends the time that the burning fuel pushes on the cylinder, providing a gentle power stroke. During detonation, the fuel/air charge (or pockets within the charge) explodes rather than burning smoothly. Because of this explosion, the charge exerts a much higher force on the piston and cylinder, leading to increased noise, vibration, ...

Can a fuel mixture cause detonation?

Using the wrong fuel can cause detonation: the octane rating of a fuel is basically the amount of pressure it can take before it detonates. Similarly, high cylinder temperatures can cause detonation (1). This is why mixture is set very rich when at high power levels: the excess fuel cools the cylinders, preventing detonation.

Can a detonating engine cause a pre-ignition?

Notably, detonation and pre-ignition often cause each other, as a detonating engine will have a very high CHT (potentially enough to cause pre-ignition), and if the charge pre-ignites as the cylinder is still rising, the continued compression may cause the charge to detonate. Share.

What is the detonation of a cylinder?

What is Detonation? Detonation is the abrupt combustion or explosion of the fuel charge inside the cy linder. During normal combustion, the spark plugs ignite the fuel charge and the fuel has a consistent and even burn as the piston moves through the power stroke and chemical energy is efficiently converted to mechanical.

What happens when a plane detonates?

In simplified terms, when detonation occurs, the fuel charge ignites quickly in an uncontrolled explosion, causing a pounding or hammering force on the piston rather than a steady push. Light detonation may not show any indication in the cabin of the aircraft.

What happens if you detonate a car?

Detonation has negative effects throughout the engine. Light detonation may cause premature wear on bearings and bushings. Severe or prolonged detonation can cause damage to the cylinder head and pistons. In some extreme cases, the connecting rod can be bent or broken, the cylinder head may crack or fail, or the piston ring lands may break.

What is the frequency of detonation?from faa.gov