Glowplug Types

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Kar Krazy

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I was just looking on rushrc.com and I was looking at glowplugs and noticed that there are different types. What is the differance between Hot, Cold, and Medium glowplugs? Is it just designed different for different heats or different qualities?
 
For different heats. Larger engines take different plugs then little car engines do.
 
All about GLOW PLUGS

Written by Brian Gardiner, and Central Coast Model Aero Club Inc.
Submitted by Wayne Beasley
_________

How Does A Glow Plug Work?

Contrary to what many have previously been lead to believe the following is an explanation of how a
glow plugfunctions in a motor. The plug is initially heated by applying a voltage (typically 1.5 volts) to it.
This is to cause it to glow so as to ignite the fuel at compression and start the internal combustion cycle.

Once the cycle has started, the power source can be disconnected, as with the heat generated at
combustion the CATALYTIC Reaction generated between the methanol and platinum in the plug coils
becomes sufficient to keep the process going. The catalytic reaction is a reaction whereby platinum will
glow in the presence of methyl alcohol vapour. This will happen without any external power source
being applied.

How do you select the correct PLUG for your application, and why ?

To do this you need to understand a little more of the theory behind the process. In glow fuel the catalytic
reaction is generated between the methanol and platinum only. Castor oil, synthetic oil, nitro methane,
etc do not generate a catalytic reaction with the platinum.

Next you need to understand that a certain surface area of platinum is required to generate a sufficient
catalytic reaction to keep the internal combustion process going. Also it is necessary to allow extra
surface area for the reaction to be great enough when it diminishes with the available methanol dropping
as in the case at motor idle. Simply put, cold plugs are manufactured using a thicker wire to give greater
surface area to facilitate a greater reaction and thus the required catalytic reaction where less methanol
is present in the fuel mixture.

So! More nitro means less methanol which in turn means a greater surface area to platinum will be
required to generate a sufficient catalytic reaction. Suddenly it all makes sense! To work out which
temperature plug to use, you need to know how much methanol is in your fuel, not how much nitro or oil.

As a rough rule of thumb;

80% methanol or above, use a hot plug.

70%-75% use a medium plug.

60%-75% use a cold plug.

65% or less use a very cold plug.

Idle Bars and Other Stuff

Again, contrary to what many believe, the idle bar on a glow plug is not necessarily what its name would
suggest. It is in fact to stop any fuel not vapourised from dousing the platinum coil of the glow plug by
dispersing it away from the coil.

Why are plated coils not as good as platinum alloy coils?

Plated coils suffer from very quick degeneration as the plating breaks down under operating conditions.
As bits of plating come off, the plug is effectively becoming a hotter and hotter unit until in a
comparatively short time it is

no longer able to perform its function. Conversely, a platinum alloy coil will still degenerate, but as it is
platinum alloy throughout, the surface remains as platinum alloy and the plug continues giving much the
same characteristics for quite a long time.

Plated coils are very poor value when compared to platinum alloy coiled glow plugs.



courtesy, Warringah Radio Control Society Incorporated
 
To go along with Neobarts excellent article, general rule of thumb is to use a colder plug the higher the nitro content is.

For example, use a colder plug running 30% or higher fuel.
Medium plug for 25% to 30%.
Hot plug 20% to 25%.

Obviously, there may be instances where you'll run a hotter plug with higher nitro content, for example when it's cold outside, but generally speaking, it's a factor of nitro percentage.
 
i have noticed that the small blocks i have delt with seem to like the hot plugs, where as i run med plugs in the big blocks. seems to work for me, i use 20% nitro white lightning fuel that has 8% oil content.
 

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