Al Gietzen wrote:
There is an interesting anomaly in the EGT data from the dyno run that
I can't explain; maybe someone has an idea. For the most part the EGTs
of the three rotor were relatively close and consistent. Some variation
in spread with rpm that I would expect from different air/fuel flow
characteristics. The thing I can't figure is this:
Most of the operating was done rich of peak, and at 5000 rpm EGTs were
within about 50 degree range with rotors 1 (the lowest) and 2 very
close, and 3 the highest. Maintaining rpm at 5000 by reducing load as
mixture was leaned (EC2), the EGTs crossed and spread out, so that by
about 150 lean of peak rotor 3 was the lowest (1510), and rotor 1 was
the highest (1595. MAP was constant at about 24", rpm constant, so air
flow didn't change. ). I assume that the injector pulse width was
reduced by the same amount on all three rotors. What gives? It seems
it might be important to know. Tracy?
Al
Sounds exactly likewhat I would expect Al.
At the rich of peak condition, #3 was the leanest of the three and
therefore, the hottest. (injector variation, pressure distribution, or
whatever)
At lean of peak, #3 was still the leanest and therefore the coolest.
At the extream lean condition a very small change in mixture can make a big
difference in EGT.
I use the differential mixture adjustments on the EC2 (modes 4 & 5) to
equalize EGT at the cruise condition and ignore minor variations at other
throttle settings.
Some time ago you had asked me another question via email but I think my
server borked my reply so here it is again.
BTW; Tracy, what EGTs were you showing at that point (during race). What
do you get at best power?
Al
EGT during race was around 1650 (LOP). Best
power is around 1750.
Tracy
Hum-m-m; based on my results, these EGTs seem a bit on the high side. I
found best power EGTs (WOT) about as follows: 5000 rpm - 1560, 6000 rpm -
1630. What does it mean?
Al
Good question Al, here's my best guess(es).
Ignition advance affects EGT more than expected so that could be a factor.
Note that EGT continues to fall when advancing the ignition timing past the
point of best power but this probably is not the case here. EGT probe
placement could also account for some difference. My CR is slightly higher
but this causes lower EGT, not higher. Maybe its my tuned intake manifold
giving higher effective manifold pressures. EGT does go up at higher
manifold pressure, all else being equal. My readings were at WOT near SL.
Another factor may be my stinginess with the mixture control. I think you
are correct that *absolute best* power is ~ 150 deg F rich of peak. I don't
usually push it that far because the power increase past about 50 deg is
very small and unless it is a war emergency situation, the increase in power
is not worth the additional fuel burn. The figures I gave reflect this.
Looking back over my notes I see that 1750 is only about 20 - 25 degrees
below peak.
Thanks for passing along the other dyno data. It is amazingly close to the
figures I calculated. My economy cruise BSFC number was .46 - .47.
Tracy
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