In a message dated 11/16/2010 6:11:46 P.M. Central Standard Time,=20 douglasbrunner@earthlink.net writes:

Scott,

I=20 will concede your point about the hotter, longer and more consistent spar= k,=20 although in most flight regimes (no extreme of F/A mixture) it probably= =20 doesn=E2=80=99t make much difference.

With=20 respect to your comment:

=E2=80=9Cyour=20 argument of moving timing by messing with the mixture is, uh, not good=20 operational practice=E2=80=9D

I=20 think you misunderstood my point. I certainly do not advocate =E2= =80=9Cmessing=20 with the mixture=E2=80=9D =E2=80=93 especially at power levels above 70%.= =20

My=20 point was that electronic ignition systems measure only 2 of the 3 factor= s=20 that influence timing. Mixture can have a significant effect on whe= n=20 Peak Intracylinder Pressure (=3D effective timing) occurs. Hence th= e=20 effective timing at a best power mixture (50 to 100 deg ROP) would be=20 significantly advanced compared to the effective timing at best economy= =20 mixture (approx 50 LOP). This is not accounted for by electronic=20 ignition systems and could lead to excessive spark=20 advance.

D.=20 Brunner

From: Lancair Mailing=20 List [mailto:lml@lancaironline.net] On Behalf Of=20 Sky2high@aol.com
Sent: Tuesday, November 16, 2010 9:25=20 AM
To: lml@lancaironline.net
Subject: [LML] Re: Elect= ronic=20 Ignition

Doug,

I=20 have a problem with your argument. It seems to be upside down. = ; In=20 reference I refer you to my 11/2/2010 email entitled "NA Injected Engine= =20 Performance LOP". In any event, for any given proper fuel/air = ratio=20 (mixture), there is a narrow timing range that produces efficient=20 cylinder pressures at the correct crank angle range. The Lycom= ing=20 engine manual (for my 320) displays the acceptable range for the E= GT=20 for best power as 100F to 180F ROP, and best economy as 0F to 80F=20 LOP. Running 50F ROP is very bad for cylinder pressures as stated b= y=20 GAMI - thus your argument of moving timing by messing with the mixture is= , uh,=20 not good operational practice.

Secondly,=20 you imply that the only function of an electronic ignition is to advance = the=20 timing. Au contraire mon ami! An electronic ignition provides= for=20 a hotter, longer, more consistent spark over a greater plug gap that= =20 better insures the reliable and timely ignition of the combustible= =20 mixture even though the F/A may be at some extreme. This results in= =20 greater efficiency/HP depending on the way one looks at it. See the= =20 pamphlet on the benefits of the LASAR electronic ignition that shows spee= d=20 increases for the same fuel burn or reduced fuel burn at the same speed o= f a=20 magneto driven engine.

The=20 fixed timing of a magneto (i.e. 25 DBTDC) is a compromise. =20 Generally speaking, EIs advance the base spark timing minimally= =20 until the power, as measured by RPM and MAP, is reduced below= =20 75%. Bad events, such as pre-ignition, detonation and incorrectly t= imed=20 cyl pressure, are less likely in this regime (that is why the GAMI lean t= est=20 is done at less than 75% power). Furthermore, EGTs (representing F/= A=20 ratios) are still maintained in the engine=20 manufacturer's recommended ranges and the timing is a better match f= or=20 the combustion event pressures.

Note=20 that during my best power cruises at middle altitudes (2500 RPM, MAP= >=20 22", EGT > 120F ROP), the EI timing is about 25 DBTDC plus or min= us a=20 degree.

Yes,=20 more HP. Better speed for the same fuel burn holding other conditio= ns=20 equal.

Yes,=20 in all the modes you mentioned.

I=20 haven't reached TBO yet, I go too fast to accumulate that much=20 time.

Scott=20 Krueger

IO=20 320 Dual Lightspeed Plasma III EI

In a=20 message dated 11/15/2010 8:21:27 P.M. Central Standard Time,=20 douglasbrunner@earthlink.net writes:

At=20 the risk of starting a =E2=80=9Ctheological=E2=80=9D controversy, I wou= ld like to raise some=20 reservations about electronic ignition systems (other than reliability = and=20 loss of electrical power)

=

Peak=20 intracylinder pressure (the point in the combustion cycle at which pres= sure=20 in the cylinder is highest =3D effective timing) is related to 3 things= ; spark=20 timing, rpm and MIXTURE.

=

Why=20 mixture? Because air and fuel mixtures burn at different rates dependin= g on=20 how rich or lean they are. So at a given RPM, MAP and spark advan= ce=20 you can vary your effective timing by changing the mixture. =20

=

=C2= =B7 &n= bsp;      =20 Want=20 to advance your timing? Change your mixture to a 50 deg ROP mixture =E2= =80=93 which=20 is the fastest burning.

=C2= =B7 &n= bsp;      =20 Want=20 to retard your timing? Make your mixture richer or leaner from 50= deg=20 ROP.

=

And=20 since optimal power is achieved at an effective timing of 16 deg ATDC,= =20 advancing the spark timing may or MAY NOT increase horsep= ower=20 depending on the mixture. But advancing the timing will likely=20 increase the magnitude of peak intracylinder pressure leading to higher= =20 intracylinder pressures, higher cylinder head temperatures and greater= =20 stress =3D shorter enging life.

=

For=20 those of you who are using electronic ignition (I am=20 not):

=C2= =B7 &n= bsp;      =20 Are=20 you sure you are getting more horsepower? How do you=20 know?

=C2= =B7 &n= bsp;      =20 If=20 you are getting more horsepower, are you getting it during all modes of= =20 engine operation? Rich of peak, lean of peak, high MAP, low MAP,= =20 etc

=C2= =B7 &n= bsp;      =20 What=20 is happening to your TBO?

=

D.=20 Brunner

The biggest=20 advantage of any of the electronic systems (in my opinon) is that they= =20 provide a spark advance that is a function of at least manifold pressur= e,=20 giving an advantage any time the manifold pressure is much lower than m= aybe=20 25 inches. But there is very little combustion taking place in th= e=20 exhaust system regardless. The reason the exhaust temperature ris= es is=20 that more of the combustion occurs after TDC and that means less of the= =20 energy is being converted to work. The down side of advancing the= =20 spark is that since more combustion occurs at the highest cylinder pres= sure,=20 more heat is transferred to the cylinder head and piston. =20

&n= bsp;