Model engine

Most model engines run on a blend of methanol, nitromethane, and lubricant (either castor or synthetic oil).

While the methanol and nitromethane blended "glow fuel" engines are the most common, many larger (especially above 15 cc/0.90 ci displacement) model engines, both two-stroke and a growing number of four-stroke examples are spark ignition, and are primarily fueled with gasoline — with some examples of both two and four-stroke glow plug-designed methanol aeromodeling engines capable, with aftermarket upgrades, to having battery-powered, electronically controlled spark ignition systems replacing the glow plugs normally used.

The valve reed, cross shaped above its retainer spring, is still beryllium copper alloy, in this old engine.

Large production volume makes it possible to use a machined cylinder and an extruded crank case (cut away by hand in the example shown).

These Cox Bee reed valve engines are notable for their low cost and ability to survive crashes.

The burning of the fuel/air mixture in a glow-plug model engine, which requires methanol for the glow plug to work in the first place, and sometimes with the use of nitromethane for greater power output and steadier idle, occurs due to the catalytic reaction of the methanol vapor to the presence of the platinum in the filament, thus causing the ignition.

Since the ignition timing is not controlled electrically, as in a spark ignition engine or by fuel injection, as in an ordinary diesel, it must be adjusted by the richness of the mixture, the ratio of nitromethane to methanol, the compression ratio, the cooling of the cylinder head, the type of glow plug, etc.

After starting the engine can easily be leaned (by adjusting a needle valve in the spraybar) to obtain maximum power.

Nitro engines require a 1.5 volt ignitor to light the glow plug in the heat sink.

Apart from sharing the diesel's use of compression ignition, their construction has more in common with a small two-stroke motorcycle or lawnmower engine.