The engines we use in our hobby are known by a number of names, some of these are, 2 stroke, 4 stroke, Otto Cycle, Internal Combustion Engine, Compression Ignition engine, Diesel Engine, Heat Engine, etc.

All Internal Combustion engines rely on heat as their source of energy. When the piston is near the tip of its stroke (usually just before) the fuel and air mixture is ignited within the combustion chamber releasing a large quantity of heat. This heat expands the gas within the combustion chamber to a very high pressure which forces the piston down towards the bottom of the cylinder. The actual force generated is dependent on the amount of air introduced into the cylinder during the induction process, the compression ratio, the type of fuel used, and the timing of the actual combustion.

Ignition can occur a number of ways. In our cars, spark plugs are generally used. In our models, timing of the ignition is not so easily controlled. In diesel, ignition occurs as a result of the heat generated by the actual compression of the air fuel mixture as the piston rises. As compression temperatures increase, the fuel eventually gets to self ignition temperatures and the whole mixture explodes. Glow plug engines on the other hand, do not rely entirely on the compression process but also take advantage of the heat retained by the glow plug to induce combustion. What we also have to consider is the temperature of the engine itself. If the head and cylinders are too hot, then in both the diesel and the glow plug engines the air/fuel charge will heat up too quickly and not only will ignition occur too early it will also occur too rapidly. Hence the fuel will be burnt before the piston has reached the top of its stroke. The effects of this on engine operation are known as pre-ignition (the ignition of the fuel before the desired moment) and detonation (the instantaneous combustion of the fuel or part there of).

Pre-ignition in model engines can be difficult to detect, as in our petrol engines, it may result in 'running on' (engine doesn't stop when turned off), reduced power, poor fuel economy and overheating. In model engines, most of these effects are difficult to detect. No amount of pre-ignition will result in 'running on' if there is no fuel to run on with. Lack of power will be more easily noticed as so too will overheating.

Fortunately pre-ignition is more commonly caused by another ignition source such as leaking headers, glowing carbon, red hot metal burrs or metal gaskets, etc, so de carbonising of the combustion chamber, etc, will more than likely promote the cure. When pre-ignition occurs, detonation will also occur in most cases. The effect of detonation can be far more serious than pre-ignition. The most obvious signs (especially in cars), is the 'pinking or pinging' noise associated with it. The most damaging, is its ability to gouge or pit the surfaces of the combustion chamber, and burn holes completely through the pistons. Other effects are as for pre-ignition.