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Ernest,
The base timing for the test was set as recommended in Tracy's EC2 manual. TDC was determined using minimum displacement which matched the front pulley mark. The manual states that the timing is adjusted by the controller depending on "many" factors. I did not investigate the controller timing characteristics since I had no desire to second-guess or duplicate Tracy's "years of testing".
Steve
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From: Rotary motors in aircraft [flyrotary@lancaironline.net] on behalf of Ernest Christley [echristley@att.net]
Sent: Friday, May 18, 2012 10:55 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: BSFC and EGT
I think this is going to be useful information, and concurs to what I was taught as a trucker...to save fuel, run slow
and gear high.
The first step for me is going to have to be mapping the EGT to AFR. Has anyone done this, BTW? Is there a direct
and consistent correlation? Once I have that, tuning then becomes a matter of setting the target AFR in a table of RPM
vs [TPS | MAP] and then running the engine through several power cycles across the timespan of a couple minutes. The
computer will then adjust the fuel injector open times as needed to obtain the target AFRs.
One question I have about the data presented is, "What was done with ignition timing?" If the timing was held constant
throughout the test, that explains a lot about the numbers. As the EGT drops off from the AFR increases, the mixture is
taking longer to burn. You could possibly be getting peak pressure well after the 50* ATDC that Lynn has called out.
The same would inform the peak heat transfer to coolant numbers. The heat absorbed by the coolant is going to be as
dependent on how long the fully burned mixture stays in the chamber as it is on the AFR.
I can't speak directly to this experiment, because it doesn't mention timing. An interesting enhancement to the data
generated would be to vary the mixture as before, but to tune the timing for max power at each data point. If that was
done, I'd be interested to see what the graph you shared yesterday would look like with the timing numbers added.
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