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1. 04:39 AM - Re: More combustion concepts (Ralph E. Capen)
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| Subject: | Re: More combustion concepts |
Carl - thanks for your insight - prior to the teardown (hangar door blown in to
prop by tornado), I had the cylinders balanced for LOP to within .1gph fuel flow.
I have the instrumentation to record the data you have described and had
already used it to balance the flows. I haven't run the peak test you've described
yet due to fear of toasting my cylinder.
I will be replacing the EGT probe prior to next flight since I have a spare on
hand.
-----Original Message-----
>From: Carl Froehlich <carl.froehlich@verizon.net>
>Sent: Dec 17, 2012 5:55 PM
>To: "lycomingengines-list@matronics.com" <lycomingengines-list@matronics.com>
>Subject: Re: LycomingEngines-List: More combustion concepts
>
>
>Not sure I follow. The actual EGT reading is dependent on many factors, so the
reading itself is of little value other that to demonstrate very abnormal conditions
(a dead cylinder as example).
>
>As you report the CHTs are comparable, and without knowing relationship between
cylinder to cylinder fuel flow at peak EGT, I would guess you don't have a problem.
If on the other hand the cylinder in question is first to peak and there
is a significant fuel flow change to get the next cylinder to peak, then I
would agree with the conclusion that the cylinder in question has a leaner mixture
than the others.
>
>The data run I suggest you do is to establish cruise conditions at 5K-7K feet,
2400 RPM, 23"-24" MP. Lean to get the first cylinder to peak EGT and record
fuel flow. Continue leaning to get to the second cylinder to peak and record
fuel flow and degrees lean of peak on the first cylinder, repeat for the next
two cylinders.
>
>A nicely matched engine will run smooth LOP with all cylinders within 20 to 50
degrees on the lean side of whatever temperature was peak EGT for that cylinder.
>
>Again, as the EGT reading is very sensitive to sensor location and clocking on
the exhaust pipe, the EGT value itself has little meaning. The "Degrees LOP
or ROP" comparison between the cylinders as well as having each cylinder peak
at about the same fuel flow tells you if you have a problem or not.
>
>Carl
>
>On Dec 17, 2012, at 4:49 PM, "Ralph E. Capen" <recapen@earthlink.net> wrote:
>
>>
>> Did some vacuum hunting prior to my most recent flight and rebuilt the MAP sensor
hoses that go to the suspect cylinder. Still have consistently high EGT
on that cylinder only.
>>
>> Cycling the magnetos shows elevated egt regardless of which magneto is running....even
the LASAR electronic ignition. I have verified the base timing for
when in the magneto mode.
>>
>> My conceptual thinking here is that both plugs for that cylinder are firing.
>> Leaving mixture as the culprit...
>>
>> CHT's are within the range for the other three cylinders.
>> My conceptual thinking here is that the ignition is lean and completely igniting.
>>
>> When I returned, I opened everything up again and pulled the intake runner for
that cylinder. The rubber connecting hose looked fine but the top gasket ahad
a couple of spots that looked like they were not forced in to contact with
the head - and could leak. I replaced the gasket and carefully aligned the tube
while putting it back together.
>>
>> I'm also replacing the EGT sensor just in case. I have had a sensor failure
before but it indicated lower than normal readings instead of higher.
>> My conceptual thinking here is that the thermocouple effect would fail low instead
of high - but I don't plan to take that one to the bank....
>>
>> Thoughts?
>>
>>
>>
>>
>>
>>
>
>
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