As I wrote in another thread, the main function of the fuel needles in a
glow engine, is to control the ignition advance, since a lean mixture will flash
earlier and burn faster than a richer mixture
This is incorrect. A lean mixture will not flash any sooner than a correct mix.
The richness of the fuel charge does nothing for the ignition timing....the start
of the burn. A greater amount of fuel takes longer to burn, (richening the mixture)
which allows it to get over the hump....into the ATDC where the force can be
applied to the downward motion of the piston. A normal burn, with too much
compression causes the cylinder pressure to reach maximun before the piston
reaches TDC, which causes the detonation....or "ping"....because the burn was
started too early.
This is the same as having too much spark advance in a spark plug engine. It
has nothing to do with the carb mixture, asuming that the mixture is near normal.
Keep in mind these engines are like a compression ignition type, similar to a diesel.
We do of course have the glow (or spark) on all the time. When the compression
and heat of the air/fuel charge builds up to the point of explosion, it does just that...
set off by the glow plug.
The correct way to retard the timing is to lower the compression, or....to a lesser
degree....use a colder plug. Keep in mind also that the heat range of a glow plug in
completely different from a spark plug.
...the richness of the fuel mixture is used to control ignition timing...
If this statement were true, there would be no such thing as detonation....richening
the mixture would be the cure-all. Trust me....this is not the case. Richening the
mixture can mask the detonation some what, but it does not alter the actual timing
(firing) of the fuel charge.
FBD.
