 (Contributed
by Dave Pound)
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 plugs coil
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
glow 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 of platinum will be required to generate
the required catalytic reaction.
Correspondingly a lesser oil content can
mean more available methanol and lesser surface area of platinum would
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 at 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 coil 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 very long time |
