Nearly all airplanes are powered by one or more combustion engines. Combustion engines are fuel-burning engines that have an internal chamber. They are designed to burn a mixture of fuel and air in this chamber, which creates hot exhaust gases to propel the airplane forward. Like the combustion engines used in automobiles, however, they may experience ignition problems, such as preignition.
Overview of Preignition
The term “preignition” is used to describe a phenomenon in which the fuel and air mixture ignites prematurely in the engine’s combustion chamber. It typically occurs with piston engines.
As the name suggests, piston engines feature one or more reciprocating rod-like pistons to convert fuel into motion. Normally, the fuel and air combination ignites synchronously with the motion of the pistons. With preignition, however, the fuel and air combination ignites early and out of sync with the pistons.
Effects of Preignition
What are the effects of preignition exactly? While early, out-of-sync ignition may sound harmless enough, it can lead to several problems.
Airplanes that experience preignition may burn an excessive amount of fuel. They will become less efficient, resulting in greater fuel consumption.
A more serious concern for preignition is overheating. Preignition can raise engine temperatures. While most airplane engines have safeguards in place to regulate temperatures, such as cooling fins, it’s not always enough to counter the excess heat of preignition.
If left unchecked, preignition can damage the engine’s pistons and valves. The excess heat can warp these parts to the point where they leak and no longer function as intended.
Spark Plugs and Preignition
While preignition has many potential causes, one of the most common causes of this phenomenon is fouled spark plugs.
Over time, carbon deposits will accumulate on spark plugs. These carbon deposits will retain heat, which can cause preignition. Rather than igniting synchronously with the pistons, the fuel and air combination will ignite early due to the carbon-capped, fouled spark plugs. Preignition can also occur when the piston or cylinder head develops a layer of carbon.
Preignition vs Detonation: What’s the Difference?
Preignition isn’t the same as detonation. Preignition occurs when the fuel and air combination ignites before the piston fully compresses the mixture. Detonation, on the other hand, occurs after the piston has completed the compression stroke.
Preignition and detonation are both considered serious engine problems. Preignition, however, has the potential to cause more damage, and it’s also more difficult to identify.
