Your "Feeble" mind is right on.
Peak EGTs can get to near 2,000 degrees. Only ceramic apex seals come back from that after more than a few seconds. All of my comments apply to 12 A normally aspirated engines, but in general the data can be applied to other rotaries.
The object of lighting the fuel in the confined space is to have the cylinder pressure to
peak at about 50 degrees after After Top Dead Center (ATDC). Think big piston, short stroke. So it likes high revs to make power.
From too rich to run to too lean to run is a bigger range than a piston engine. The ideal power producing fire happens when the EGTs are just rich of peak. Peak EGT is different on each engine, and is all over the map as you tune the burn with timing changes, fuel type and octane and so-on. So you have to think about what happens with each possible change you can make. First, the EGT probes are in the outside of any bends, 3" from the port face. So the supersonic flow passes over the probes, and delivers accurate combustion data. You may find subsonic flow returning to the port
along the short side radius, thus the need for the probe on the bottom of the pipe or outside of the turn.
Once at speed changing the timing for a specific set of conditions, changes the location of peak pressure. In general you will be moving away from ideal, and watching the revs with a fixed load will tell you this. More revs is better. So, since an airplane is just a big expensive Dyno, you can dial up best revs with timing variations,
and then with that setting recorded, you move mixture up and down until you get best revs again. Then go back to timing and tune again. You are looking for the best combination of settings not just a collection of best settings unrelated to each other.
The low EGTs suggested are for maximum power while staying well rich of peak.
So for take off and fast climb you will be producing close to max power while fuel cooling the engine and apex seals. It uses more fuel and less engine life. To save fuel
you can lean quickly past peak EGT to well lean of peak for low fuel consumption cruise. Again tune for this set of conditions. Since the fuel bits are further apart (Lean) they tend to burn slower, so a bit more ignition advance can be used. Keep leaning to lean miss, then back up rich a bit then add more advance and lean again.
A monster ignition system can get you further into lean. Notice the low EGTs indicate low fuel consumption (and lower power).
Remember the object is peak pressure at 50 degrees ATDC.
Everything affects everything. The OAT, the pressure, humidity. And so-on.
I can trick factory controllers and so can you. Measure the resistance values of the sensors that the controller uses to determine fuel delivery. Then get some Radio Shack pots that cover that range top and bottom. Install two DPDT switches with the controllers wires on the center lugs, the sensor wires on one end and the pot wires on the other end. Now in one switch position the system is as stock. In the other position
the sensor is replaced with the pot, and you can change the value to tune the engine.
Now if you should loose a sensor you have a backup. Once you have this working, replace the Chinese crap with American pieces.
This is not to suggest that people driving "Show Room Stock" racers would ever stoop this low just to go fast. I would never do this. But if you did, you would hide the switch in the heater ducting (they never look in the ducting) and use a magnetic switch, and turn it off on exiting the car with that magnet in the toe of your driving shoe. The idiot light goes out when the switch is off and all is stock again. Like taking candy from a baby.
Lynn E. Hanover
In a message dated 4/20/2011 4:33:35 P.M. Atlantic Daylight Time, ceengland@bellsouth.net writes:
I wouldn't claim to have any hands-on experience with running a rotary
(except in cars), but 'normal' internal combustion engine EGTs would go
up as you lean, to a point, but should then start dropping as you
continue to lean. If your 'lean' setting is too rich, that might explain
both high EGT & high fuel consumption relative to HP. In my rather
feeble mind (based on conventional a/c engine experience), I'd expect
'rich' to yield slightly lower than max EGT for full power operation,
and 'lean' to yield significantly lower than max EGT for cruise power
settings.
Unfortunately, no constructive thoughts on how to remedy the situation
if you're running Mistral's
controller....
Charlie