Glow plug (model engine)
From Wikipedia, the free encyclopedia
For the glow plugs used in automotive diesel engines, see Glowplug
 |
This article relies largely or entirely upon a single source. Please help improve this article by introducing appropriate citations of additional sources. |
A glow plug (alternatively spelled glowplug or glow-plug) is a device, something like a spark plug, used to ignite the fuel in the very small internal combustion engines used in model aircraft, model cars and similar applications. The ignition is accomplished by a durable, mostly platinum, helical wire filament recessed into the plug's tip. When an electric current runs through the plug, or when exposed to the heat of the combustion chamber, the filament glows, enabling it to ignite the special fuel used by these engines.
Glow fuel (usually methanol, sometimes with nitromethane for greater power) burns due to the catalytic reaction of the methanol vapor to the presence of the platinum in the glow plug's filament. Glow fuel also contains a small amount of oil for lubrication and heat-control.
To start a glow plug engine, a direct current (around 3 Amps) is applied to the glow plug, initially heating the filament. The engine is then spun from the outside to introduce fuel to the chamber. Once the fuel has ignited and the engine is running, the electrical connection is removed. Each combustion keeps the plug's filament glowing hot, allowing it to ignite the next charge, thus sustaining the power cycle.
Technically a glow plug engine is similar to a diesel engine in that it uses internal heat to ignite the fuel, but since the ignition timing is not controlled by fuel injection (as in an ordinary diesel), or electrically (as in a spark ignition engine), it must be adjusted by changing fuel/air mixture and plug/coil design. A richer mixture will tend to cool the filament and so retard ignition, slowing the engine. This "configuration" can also be adjusted by using varying plug designs for a more exact thermal control.
Glow plug engines can be designed for two-cycle operation (ignition every rotation) or four-cycle operation (ignition every two rotations). The two-cycle (or two-stroke) version produces more power, but the four-cycle engines have more low-end torque, are less noisy and have a lower-pitched, more realistic sound.[1]
Considerations for choosing the right glow plug: [2] [3]
High-nitro fuels produce more power than low-nitro fuels, but also produce more heat. The higher the nitro content, the colder the plug, also due to the lower methanol content.
Depending on engine type, usage of a turbo plug may be required. For turbo engines use turbo plugs. Never install a turbo plug in a standard engine or vice versa.
Big engines have more mass and retain heat better. Smaller, lighter engines don't, and need the help a hotter plug can offer.
The "right" plug for an engine can change with the temperature. The hotter the day, the colder the plug.
Hot plugs promote better idling and acceleration. If your engine runs rough or accelerates sluggishly, a hotter plug will help.
Cold plugs produce more power and may improve performance if your engine runs hot. The downside is rougher idling and more difficulty in tuning.
For cars: If the track/course has a lot of twists and turns, a hot plug is fine. If the track/course has long straights where you'll reach maximum rpm, a colder plug is best.
Over-leaning an engine can harm it, by raising operating temperatures; "burn up" a plug before its time.
High Nitro = Hot Fuel: needs colder plugs, and vice versa
If engine sags when the battery is disconnected, the plug is too cold or more nitro is needed
If the engine bites back or backfires when hand cranking, the plug is too hot or less nitro is needed
