Nitromethane is a highly combustible substance that is generally only used in very specifically designed engines found in Top Fuel drag racing and in miniature internal combustion engines in radio control, control line and free flight model aircraft.
On the first stroke as the piston travels upward, a mixture of fuel and air is sucked into the crankcase, from the carburettor.
Catalysis from methanol vapor on the heated platinum element keeps it red-hot even after voltage has been removed, which ignites the fuel and keeps the engine running.
Nitro engines typically use a carburetor to mix the fuel and air together, although for some applications where throttling is not required they have a simple venturi with a spraybar and needle valve.
A high speed needle tunes how much fuel is allowed into the carburetor at mid to high RPM, and a low speed needle determines how much fuel is allowed into the carburetor at low to mid range RPM.
If the engine is too rich, it will run poorly, and fuel that has not yet been burnt may start to spit out of the exhaust.
An excessively lean mixture can damage an engine in a short time, as it will run above its design temperature.
Off-road engines are usually used in 1/8 scale buggies where high speeds and bad accelerations are less important.
Monster truck engines generate much of their torque and horsepower at low to mid range RPM.
They are usually used in large and heavy trucks where all that power is needed to get good performance out of the vehicle.
Members of the full scale drag racing industry use much higher concentrations of nitromethane: they are limited by the rules to 90% (at least in the NHRA, the main sanctioning body).