Nitro Engine

The rc nitro car engine has evolved over the years into a very robust and reliable little power unit and modern engines are much more reliable and powerful than they ever were. Incidentally nitro is just another name for glow plug power which is actually the correct name.

Such engines vary in size but the most popular and widely used engines are the small-block ones. These generally range between the .10cu.in. and .28cu.in. capacity (cu.in. stands for cubic inch) although larger ones are of course available.
It's common for nitro car engines, and indeed all model glow plug engines, to be referred to by this size i.e. a '10' size engine or a '28' engine etc.
The engines can have different features such as rear or side mounted exhaust, barrel or sliding carburettor, pull start or non-pull start and can be modified by replacing certain parts to increase performance. But the average rc car or truck owner who isn't in to competition racing will almost certainly just keep their nitro engine exactly as it was when it came out the factory, as the performance of the engine will be more than adequate for the car or truck that it's in.

Two fairly typical rc model car nitro engines are shown below; a pull start one (left) and non-pull start (right):

The basic parts of a nitro RC car engine

A model nitro car engine consists of just the fundamental parts of any internal combustion engine.
The cylinder head sits on top of the crankcase and has extended or additional cooling fins to greatly increase the surface area of the head, to catch more air for cooling. This is because, unlike a glow plug engine in a radio control plane, a rc car engine doesn't get a huge amount of airflow over it so the surface area of the head needs to be increased to compensate.
Inside the cylinder head is the piston which is the drum-shaped component that moves up and down many times a minute (hundreds or thousands) as the fuel/air mixture is ignited in the combustion chamber, which is the area inside the cylinder head above the piston.
The piston is connected to the crankshaft by a connecting rod, or 'con rod'; this crankshaft runs perpendicular to the con rod through the crankcase and is connected to the clutch of the car.
Sitting at the front of the engine on top of the crankcase is the carburettor, which is the part of the engine that introduces the fuel and air into the crankcase. The fuel / air mixture inside the combustion chamber is ignited by a glow plug, screwed into the top of the cylinder head.
The basic parts and features are shown in the diagram below:

How a nitro engine operates

RC nitro car engines are mainly 2 stroke whereas engines for rc planes can be two or four stroke.
Two stroke means that the piston just needs to complete one up-stroke and one down-stroke to complete the whole internal combustion process of drawing the fuel/air mixture in and up to the combustion chamber, compressing the mixture just before it ignites and then expelling the exhaust gases after the explosion. A 4 stroke engine needs two complete revolutions to do the same job.
The piston will keep on moving up and down (hopefully!) so long as the fuel/air mixture is being ignited, but how does the whole process start?
Well, the fuel/air mixture needs to be introduced into the crankcase before anything can happen. This is done by 'priming' the engine which is done by repeatedly pressing a special valve on the fuel tank to force fuel in to the carb, or by removing the air filter and squirting fuel in to the carb from a plastic squeezy bottle.
Now that fuel is in the crankcase and has mixed with air, the glow plug in the top of the cylinder head needs to be heated up and the piston needs to start moving up and down for the whole internal combustion process to get going. So to start, the nitro engine needs to be turned over manually which is either done with the pull cord if it has one, or by an electrical engine starter temporarily attached to the clutch.
At the same time, the plug is made to glow red hot by connecting a glow plug igniter to it for a few seconds; the filament of the plug heats up immediately.
With the fuel/air mixture sitting in the crankcase, it needs to be moved up to the combustion chamber and ignited in order for the engine to start running under its own power. This is done during the piston down-stroke; as the piston moves downwards so it creates a near-vacuum (very low pressure) in the combustion chamber; atmospheric pressure then forces the fuel/air mixture up the transfer ports which run up the outside of the piston chamber and in to the combustion chamber.
The fuel/air mixture is then compressed by the upward returning piston, this compression increases the pressure and temperature of the mixture which greatly aids ignition by the red hot glow plug filament.
When the piston is at the point just before the mixture ignites, it is covering the exhaust ports which run from the sides of the combustion chamber through to the muffler. When the fuel/air mixture does ignite, the resulting explosion forces the piston back down and on its way down the exhaust ports are uncovered and the burnt gas mixture leaves the chamber via the ports.
The momentum of the spinning crankshaft makes the piston move upwards again and the whole process starts over.

Although the glow plug was made to glow red hot initially by the glow plug igniter connected to a 1.5v battery, once the engine is running then the high temperature inside the combustion chamber keeps the plug filament glowing unaided. If the plug fails, then the fuel/air mix will not get ignited and the engine will stop.

A failed glow plug (burned out or broken filament) is a common cause of nitro car engine starting trouble and you should always carry a selection with you. Glow plugs for rc cars and trucks carry different heat ratings, so check your engine requirements according to the manufacturer recommendations. (rc-airplane-world)


Here are some diagrams  engine 

A 2-Cycle engine