ORIGINAL: NikolayTT
But what makes you think that downturn RPM-increase is increasing the temperature on the glow-plug ?
The temperature will increase if you pump more fuel proportionally to the RPM increase and that is what
happen if you are dependent on the pressure in the exhaust pipe.
On contrary, if you are not dependent on that pressure, the glow plug temperature should go even lower
beside the RPM increase, because of the increased amount of air in the mixture. I.e. that would lean the
engine without (!) overheating it.
In other words that pipe pressure makes sure that the engine does not go lean in downtuns and burns
more fuel so you have to throtle back, which most of the pilots.
Thus, the Microcontroller inside of the onboard driver might do better job and you do not have to throtle
back; the RPMs will go high but the engine will stay as cool as on normal RPM even more cool maybe.
This should be measured indeed.
strange--
the increase of fuel to air DECREASES temps and cools the plug
downlines cool the engine --as it is working less relative to rpm. When you throttle up -increaseing fuel and air - you are asking the engine to do more work -which is the real reason temps want to climb. and why I used the closed loop setup of tank pressure .
also -as a glow engine is throttled back -in a downline the carbs typically deliver a richer mixture - which is primary reason for th classic flameout at bottom of a split S (as an example
The carbs do this simply because if there was NOT a slightly rich mix at of idle -the engine would go too lean and kill as work load increases. in the case of the good old four strokers they would /will backfire and/or toss the prop
when you start looking at what pipes do/do not do --remember the work being done ,determines the temperature --in any IC engine glow engines are great, simple devices but they change timing as temp pressure changes - they have no choice in the matter. by adding fuel you can always reduce the temp tho the pipe is increasing the pressure .
this is required as work is increased ( pulling uphill) but on a down line, things cool off rapidly and the naughty carbs tend to drop temps such that a flameout can easily happen.
the old OS pumped setups from the late 80's early 90's were horrible in this respect .