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Scott, let me take the most important
part (your footnote) of your response to Walter, first:
>>PS: BTW, For my Lyc I/O 320,
electronic spark advance does not occur above 26" MAP (generally below 4500-5000
Palt), and then gingerly so thereafter with little power effect, even with the
reduced fuel flows. For my case this is yet awaiting further
study. Still, above 26" I see reduced EGTs.
PPS: How accurate should the timing be? + or - 2 degrees? + or - ?
degrees?<<
If your LASAR system does NOT change the
timing from stock above 26" MAP - - (ie, full or near full power) -
- AND - - you are seeing lower EGTs, :
THEN - -
There is ONLY one explanation that is consistent with all of the data that
I have seen. The EFFECTIVE timing, as measured by the location
of the peak of combustion pressure after TDC *IS* changing
significantly.
The change in the location of the peak
of the combustion event will be measured closer to TDC and the peak pressures
observed will be substantially higher than the OEM intended them to be when they
set the original stock timing on the magnetos.
Notice... I said the
"effective" timing. The effective timing includes all aspects of the
spark issue involved in initiating combustion, including "better"
sparks through higher technology, as well as "when" the sparks actually fire
measured in relation to TDC
Frankly, at high power and rpm,
properly maintained magnetos do a pretty good job in terms of the
"quality" of the spark, and most electronic ignition systems don't
do much better in terms of the quality of the spark.
*********************************
As to the other issues you
raise:
>> Pleeeeeeease. I know
that the sky is falling and my engine is headed for doomsday 'cause I haven't
been to an advanced pilot seminar - but, at least try to help us understand why
our observations, experience and understanding of ignition events at altitude
are not just the product of hypoxia induced lightheadedness. <<
Ok, Scott, Walter was a little
cryptic.
Let me try to be a bit more
elaborate:
>> 1. You
mean the PRISM system doesn't use modern electronic ignition components
and controls, including timing? <<
I am a bit confused by this comment,
and I don't know what the reference was to this.
The issue is NOT how the spark is
generated - - it can be a big box of quick matches set off by
Santa's little helpers, for all I care - - but the issue is
what is the effect of the nature and timing of the event that initiates
combustion on the resulting important stuff that happens in the combustion
chamber after the combustion event is started.
>> 2. Do you mean
that fixed timing, developed via compromise, is the best for all operating
conditions? <<
No. But that doesn't mean that
electronic timing & sparks - - done without the benefit of extremely
thorough understandings of the combustion events is going to make it
better - - without creating other problems - - either.
However, it is remarkable how the combination of the right fuel flow
(which greatly influences the "effective" timing) and fixed timing magnetos
can do a fairly effective job.
>> 3. Do you mean
that the spark energy, shape, duration and consistency is of the same
quality for electronic ignitions and magnetos? <<
No. In some cases, it is worse
for electronic ignitions !!
But, properly done, electronic
ignitions can improve on the important aspects of the initiating sparks that
start the combustion events. It just requires that the electronic
stuff be originally designed with a really thorough understanding of what
is important about the combustion events. From what I have
observed, this is not always the case.
>> 4. Are you
telling me that our excess fuel delivery systems are so good that no
combustion is occurring in the exhaust pipe near the EGT probe? <<
No. Not sure how that plays into
this discussion. Later effective combustion ignition
events will result in higher EGTs. Earlier effective combustion
ignition events will result in lower EGTS, assuming nobody has changed
the camshaft in the mean time! <g>
>> 5. Do you mean
that magnetos deliver a consistent spark (time, duration and strength) 100% of
the time when one manufacturer states that there can be magneto spark
impairments of up to 10% of the time? And, that this deficient
combustion in the cylinder might lead to some combustion completion in the
pipe?
<<
No. However,
consider, the following: I have logged the details
(as in 0.1 to 0.4 degree crank resolution) of the spark and combustion
events over several thousands of combustion events over several years,
and studied them - - manually. I have developed software that
can study them automatically, and summarize the results with
coefficients of variability for almost every conceivable spark and resulting
combustion event parameter. And we have done this for millions of spark
events.
We have done this for both magnetos
and electronic ignitions. There is some variability in the magneto
spark events and the electronic spark events.
However, on properly maintained magnetos, it does not
result in anything like the kinds of changes in EGTs that you are
reporting.
Regards, George
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