Detonation occurs in a reciprocating aircraft engine when

a) the spark plugs are fouled or shorted out or the wiring is defective
b) hot spots in the combustion chamber ignite the fuel/air mixture in advance of normal ignition
c) the unburned charge in the cylinders explodes instead of burning normally

C : Detonation occurs when the fuel/air mixture in the cylinders explodes instead of burning normally. This more rapid force slams the piston down instead of pushing it.

Detonation may occur at high-power settings when

a) the fuel mixture ignites instantaneously instead of burning progressively and evenly
b) an excessively rich fuel mixture causes an explosive gain in power
c) the fuel mixture is ignited too early by hot carbon deposits in the cylinder

A : Detonation occurs when the fuel/air mixture in the cylinders explodes instead of burning progressively and evenly. This more rapid force slams the piston down instead of pushing it.

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

a) lean the mixture
b) lower the nose slightly to increase airspeed
c) apply carburetor heat

B : If you suspect engine detonation during climb-out after takeoff, you would normally decrease the load on the engine. Detonation is usually caused by poor grade fuel or an excessive engine temperature.

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

a) a mixture of fuel and air that is not uniform in all cylinders
b) lower cylinder head temperatures
c) detonation

C : If the grade of fuel used in an airplane engine is lower than specified for the engine, it will probably cause detonation. Lower grades of fuel ignite at lower temperatures. A higher temperature engine (which should use a higher grade of fuel) may cause lower grade fuel to explode (detonate) rather than burn evenly.

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

a) combustion
b) pre-igniton
c) detonation

B : Pre-ignition is the ignition of the fuel prior to normal ignition or ignition before the electrical arcing occurs at the spark plug. Pre-ignition may be caused by excessively hot exhaust valves, carbon particles, or spark plugs and electrodes heated to an incandescent, or glowing, state. These hot spots are usually caused by high temperatures encountered during detonation. A significant difference between pre-ignition and detonation is that, if the conditions for detonation exist in one, they usually exist in all cylinders, but pre-ignition often takes place in only one or two cylinders.