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Scott,
You said:
Remember that magneto systems don't measure any factor yet the engine manufacturer has no problem with LOP or ROP operations with some restrictions (see below). Indeed, there are no timing adjustments for CR while EIs provide fjor such. As I have said, EIs don't provide much timing change from the base timing (dependent on CR) for power settings over 75% as inferred by a combination of RPM and MAP - a typical way of expressing power. At lower power settings there is a benefit of advancing the spark to get more work done by the combustion event occurring in the cylinder. At low power settings it is hard to get bad events to occur, including damaging peak cylinder pressures.
Finally, please stop using ROP settings where the EGT is -50F from peak as that is outside the good operating range of my engine (that's info from both Lyc and GAMI, worst peak pressures) - Of course, if you are running a Continental engine, well, uh, you have to find your own info.
Scott Krueger
Scott,
As a graduate of the AP Seminars, I have drunk the GAMI Koolaid. What they said about Electronic Ignition makes sense to me - the advance curves are proprietary and do not take into account the effect of mixture on timing.
Several quick comments:
- Does your abbreviation "CR" mean compression ratio? My engine has a 10:1 compression and the timing has been retarded to account for this.
- "please stop using ROP settings where the EGT is -50F from peak" I do not use this setting although I think it is acceptable to use this power setting at low enough power settings - <70%. If I am at a low power setting I am typically LOP.
- You say: "EIs don't provide much timing change from the base timing (dependent on CR) for power settings over 75%" What is the timing change that EI uses? Do you have data on this that you can share?
I think we would all like an electronic ignition system that provides a hot consistent spark, easy starting and does not have the maintenance and arcing problems of magnetos. We would also like one that kept the effective timing at 16 deg ATDC. The problem with current electronic ignition systems is that since they don't take mixture into account, they can't maintain the same effective timing with different mixtures.
I would actually like to be able to advance my spark during certain flight regimes (LOP at less than 70% power) in which I am fairly certain nothing bad will happen and advanced timing will give better power/economy. It is the rest of the flight regime (like takeoff at 2700 RPM, 30" MAP and 10:1 compression) that I am worried about
-----Original Message-----
From: Sky2high@aol.com
Sent: Nov 18, 2010 7:52 PM
To: lml@lancaironline.net
Subject: [LML] Re: Electronic Ignition
Doug,
You said:
===My
point was that electronic ignition systems measure only 2 of the 3 factors that
influence timing. Mixture can have a significant effect on when Peak
Intracylinder Pressure (= effective timing) occurs. Hence the effective
timing at a best power mixture (50 to 100 deg ROP) would be significantly
advanced compared to the effective timing at best economy mixture (approx 50
LOP). This is not accounted for by electronic ignition systems and could
lead to excessive spark advance.
===
Remember that magneto systems don't measure any factor yet the engine
manufacturer has no problem with LOP or ROP operations with some
restrictions (see below). Indeed, there are no timing adjustments for
CR while EIs provide fjor such. As I have said, EIs don't provide much
timing change from the base timing (dependent on CR) for power settings
over 75% as inferred by a combination of RPM and MAP - a typical way of
expressing power. At lower power settings there is a benefit of advancing
the spark to get more work done by the combustion event occurring in the
cylinder. At low power settings it is hard to get bad events to occur,
including damaging peak cylinder pressures.
Finally, please stop using ROP settings where the EGT is -50F from
peak as that is outside the good operating range of my engine (that's info from
both Lyc and GAMI, worst peak pressures) - Of course, if you are running a
Continental engine, well, uh, you have to find your own info.
Scott Krueger
PS If you are talking about supercharged/turbocharged engines always
running at high power then the benefits of EIs are simply a better, more
reliable spark without worrying about esoteric things such as that the
magneto is properly pressurized so no sparking occurs in the mag.
In a message dated 11/16/2010 6:11:46 P.M. Central Standard Time,
douglasbrunner@earthlink.net writes:
Scott,
I
will concede your point about the hotter, longer and more consistent spark,
although in most flight regimes (no extreme of F/A mixture) it probably
doesn’t make much difference.
With
respect to your comment:
“your
argument of moving timing by messing with the mixture is, uh, not good
operational practice”
I
think you misunderstood my point. I certainly do not advocate “messing
with the mixture” – especially at power levels above 70%.
My
point was that electronic ignition systems measure only 2 of the 3 factors
that influence timing. Mixture can have a significant effect on when
Peak Intracylinder Pressure (= effective timing) occurs. Hence the
effective timing at a best power mixture (50 to 100 deg ROP) would be
significantly advanced compared to the effective timing at best economy
mixture (approx 50 LOP). This is not accounted for by electronic
ignition systems and could lead to excessive spark
advance.
D.
Brunner
From: Lancair Mailing
List [mailto:lml@lancaironline.net] On Behalf Of
Sky2high@aol.com
Sent: Tuesday, November 16, 2010 9:25
AM
To: lml@lancaironline.net
Subject: [LML] Re: Electronic
Ignition
I
have a problem with your argument. It seems to be upside down. In
reference I refer you to my 11/2/2010 email entitled "NA Injected Engine
Performance LOP". In any event, for any given proper fuel/air ratio
(mixture), there is a narrow timing range that produces efficient
cylinder pressures at the correct crank angle range. The Lycoming
engine manual (for my 320) displays the acceptable range for the EGT
for best power as 100F to 180F ROP, and best economy as 0F to 80F
LOP. Running 50F ROP is very bad for cylinder pressures as stated by
GAMI - thus your argument of moving timing by messing with the mixture is, uh,
not good operational practice.
Secondly,
you imply that the only function of an electronic ignition is to advance the
timing. Au contraire mon ami! An electronic ignition provides for
a hotter, longer, more consistent spark over a greater plug gap that
better insures the reliable and timely ignition of the combustible
mixture even though the F/A may be at some extreme. This results in
greater efficiency/HP depending on the way one looks at it. See the
pamphlet on the benefits of the LASAR electronic ignition that shows speed
increases for the same fuel burn or reduced fuel burn at the same speed of a
magneto driven engine.
The
fixed timing of a magneto (i.e. 25 DBTDC) is a compromise.
Generally speaking, EIs advance the base spark timing minimally
until the power, as measured by RPM and MAP, is reduced below
75%. Bad events, such as pre-ignition, detonation and incorrectly timed
cyl pressure, are less likely in this regime (that is why the GAMI lean test
is done at less than 75% power). Furthermore, EGTs (representing F/A
ratios) are still maintained in the engine
manufacturer's recommended ranges and the timing is a better match for
the combustion event pressures.
Note
that during my best power cruises at middle altitudes (2500 RPM, MAP >
22", EGT > 120F ROP), the EI timing is about 25 DBTDC plus or minus a
degree.
Yes,
more HP. Better speed for the same fuel burn holding other conditions
equal.
Yes,
in all the modes you mentioned.
I
haven't reached TBO yet, I go too fast to accumulate that much
time.
IO
320 Dual Lightspeed Plasma III EI
In a
message dated 11/15/2010 8:21:27 P.M. Central Standard Time,
douglasbrunner@earthlink.net writes:
At
the risk of starting a “theological” controversy, I would like to raise some
reservations about electronic ignition systems (other than reliability and
loss of electrical power)
Peak
intracylinder pressure (the point in the combustion cycle at which pressure
in the cylinder is highest = effective timing) is related to 3 things; spark
timing, rpm and MIXTURE.
Why
mixture? Because air and fuel mixtures burn at different rates depending on
how rich or lean they are. So at a given RPM, MAP and spark advance
you can vary your effective timing by changing the mixture.
·
Want
to advance your timing? Change your mixture to a 50 deg ROP mixture – which
is the fastest burning.
·
Want
to retard your timing? Make your mixture richer or leaner from 50 deg
ROP.
And
since optimal power is achieved at an effective timing of 16 deg ATDC,
advancing the spark timing may or MAY NOT increase horsepower
depending on the mixture. But advancing the timing will likely
increase the magnitude of peak intracylinder pressure leading to higher
intracylinder pressures, higher cylinder head temperatures and greater
stress = shorter enging life.
For
those of you who are using electronic ignition (I am
not):
·
Are
you sure you are getting more horsepower? How do you
know?
·
If
you are getting more horsepower, are you getting it during all modes of
engine operation? Rich of peak, lean of peak, high MAP, low MAP,
etc
·
What
is happening to your TBO?
D.
Brunner
The biggest
advantage of any of the electronic systems (in my opinon) is that they
provide a spark advance that is a function of at least manifold pressure,
giving an advantage any time the manifold pressure is much lower than maybe
25 inches. But there is very little combustion taking place in the
exhaust system regardless. The reason the exhaust temperature rises is
that more of the combustion occurs after TDC and that means less of the
energy is being converted to work. The down side of advancing the
spark is that since more combustion occurs at the highest cylinder pressure,
more heat is transferred to the cylinder head and piston.
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