Things that I learned … thx Hooked-on-RC-Airplanes.com

RC glow plugs control the timing where ignition occurs. The goal is to have the air/fuel mixture ignite just prior to TDC.

Methanol is critical to the ignition process. The chemical reaction between the fuel’s methanol and the plug’s platinum filament with a catalyst of cylinder pressure keeps the filament hot. To control the timing of our engine you must have the correct RC glow plug that corresponds to the methanol content in your fuel. If your fuel has a higher methanol concentration (less oil and nitro) you will want a glow plug that will react “less” to the methane during the catalytic reaction in order to have the coils of the plug to produce the necessary heat to reach ignition temperature at the correct time. Plugs that react “less” to the methane are called “cold” plugs. “Hot” plugs react more with the methane causing the plug to get hotter more quickly. In a nut shell, higher nitro fuels require colder plugs. And vice versa.

Note:

· Higher cylinder pressure will result in a greater reaction between the methanol and platinum and will result in a hotter the plug filament igniting fuel earlier in the cycle.

· Fuel with less methanol (more oil and nitro) will result in later ignition and fuel with more methanol (less oil and nitro) will result in earlier ignition.

· Rich air/fuel mixture will result in later ignition and a lean mixture will result in earlier ignition.

· With everything else equal a “hot” plug will ignite the mixture earlier in the cycle and a “cold” plug will ignite the mixture later.

Big issue is determining when ignition is early or late … If the engine speed decreases significantly when the glow driver is removed you could have a bad glow plug. If you are absolutely sure the glow plug is good, you may want to switch to a hotter plug or switch to a fuel with more nitro (less methanol). If the coils of the glow plug continuously fail or break over and over then you may consider changing to a colder plug. If the engine seems to backfire constantly, you may want to change to a cooler plug or switch to a fuel with less nitro (more methanol). Again, unless you have a legitimate reason, stick with the glow plug that comes with the engine.