All nitro / glow engines which run on methanol-based fuels are ignited with a glow plug. Glow plugs are made of steel and have a platinum wound wire. Positioned at the uppermost part of the combustion chamber, glow pug platinum wires and under the right compression, cause the alcohol to burn in a catalytic reaction. For the initial glow, a 0.5V to 1.2V battery should be attached to the glow plug. The engine then can be started and this is when the catalytic reaction between the alcohol and platinum wire takes place. The battery can then be removed as long as the engine is running and fuel is passing.
Glow plugs can range between cold to hot. The difference in operation can be noticed at idle speed. You can go richer on with the fuel mixture with hotter glow plugs and leaner with a colder one.
The difference between hot and cold glow plugs is the amount of heat they hold. By changing the glow plug from cold to (let’s say) medium, ignition timing will change – will happen faster in the cylinder (given that you don’t modify the needle settings), or will happen at a lower pressure.
A hotter plug will allow for faster acceleration if the engine is retuned after changing it.
It is recommend to use the glow plug supplied with the engine in the beginning, or if one is not supplied, use the one that the manufacturer recommends. After you break in the engine and tune it well, try to increase the heat range just a little bit (from cold to medium cold, from medium cold to medium and so on). See how the engine behaves (torque, heat), make sure you retune the engine after changing the plug.
Assessing the Condition of Your Glow Plug
The way you operate you engine defines the lifetime of the glow plug. Glow plugs on the market today are of good quality and designed to last longer.
When should you change the glow plug?
– When you see a twisted or mangled glow plug element. This usually happens on a compression ratio.
– Small “bumps” are attached to the glow plug element. This will usually occur during the break-in process when tiny pieces of aluminum attach to the glow plug element and hinder its operation.
– The glow plug element is dull and not shiny anymore and almost white powder color. This only comes with age and is caused by the catalytic reaction. The shinier the wire, the better the catalytic reaction can be.
Operating indications that you need to change your glow plug are:
– When there is a physical short or breakage in the element wire which will cause the wire not to glow when connected to a charged igniter.
– If the engine quits when the igniter is removed after starting.
– When the engine starts and at full throttle there is a loss in RPM when the igniter is disconnected. This is a clear indicator that the white powder residue is building up on the platinum wire and the catalytic reaction is not occurring.