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 [at] aol.com
Sent: Nov 18, 2010 7:52 PM

To: lml [at] 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. 

 

/files/LML/56756-02-R/X.MA1.1290103540 [at] aol.com" sandbox="" width="654" height="997" comp_state="quality" datasize="141380">

 

In a message dated 11/16/2010 6:11:46 P.M. Central Standard Time,
douglasbrunner [at] 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 [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf Of
Sky2high [at] aol.com
Sent: Tuesday, November 16, 2010 9:25
AM
To: lml [at] lancaironline.net
Subject: [LML] Re:
Electronic Ignition

 

Doug,

 

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.

 

Scott
Krueger

IO
320 Dual Lightspeed Plasma III EI

 

In
a message dated 11/15/2010 8:21:27 P.M. Central Standard Time,
douglasbrunner [at] 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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