2.16 Abnormal Combustion Flashcards

Questions and Answers

Detonation occurs in a reciprocating aircraft engine when:

Hot spots in the combustion chamber ignite the fuel/air mixture in advance of normal ignition

The spark plugs are fouled or shorted out or the wiring is defective

The unburned charge in the cylinders explodes instead of burning normally (correct)

Detonation may occur at high-power settings when:

The fuel mixture ignites instantaneously instead of burning progressively and evenly (correct)

The fuel mixture is ignited too early by hot carbon deposits in the cylinder

An excessively rich fuel mixture causes an explosive gain in power

If a pilot suspects that the engine (with a fixed-pitch propeller) is detonating during climb-out after takeoff, the initial corrective action to take would be to:

Lean the mixture

Apply carburetor heat

Lower the nose slightly to increase airspeed (correct)

If the grade of fuel used in an aircraft engine is lower than specified for the engine, it will mostly likely cause:

<p>Detonation</p> Signup and view all the answers

The uncontrolled firing of the fuel/air charge in advance of normal spark ignition is known as:

<p>Pre-ignition</p> Signup and view all the answers

Study Notes

Detonation in Aircraft Engines

Detonation is defined as the explosion of the fuel/air mixture in the cylinders rather than a normal burn, causing a rapid downward force on the piston.
Common causes include fouled spark plugs, defective wiring, or hot spots within the combustion chamber triggering premature ignition.

Detonation Under High-Power Settings

Detonation can occur when the fuel mixture ignites instantaneously, leading to a lack of progressive burning.
An excessively rich fuel mixture can also lead to explosive power gains, increasing the risk of detonation.
Early ignition by hot carbon deposits in cylinders is a contributing factor.

Corrective Actions During Detonation

During climb-out after takeoff, if engine detonation is suspected, the initial step is to lower the nose slightly to boost airspeed and reduce engine load.
Engine detonation typically results from using poor quality fuel or excessive temperatures.

Impact of Fuel Grade on Engine Performance

Utilizing a lower grade of fuel than specified for an engine is likely to induce detonation, as lower grades ignite at lower temperatures.
Higher temperature engines that require a higher grade fuel may cause lower grade fuels to detonate.

Pre-Ignition Defined

Pre-ignition occurs when the fuel ignites before normal spark ignition, often triggered by excessively hot components, such as exhaust valves or carbon particles.
It is characterized by ignition in only a few cylinders, differentiating it from detonation, which affects all cylinders under similar conditions.

Description

Test your knowledge on abnormal combustion in aircraft engines with these flashcards. Focus on concepts like detonation and the effects of ignition failure. Ideal for aviation mechanics and engineering students.