S

sc_acro2

Member
KOSH Report, G3ignition systems were over whelmed at Airventure 2008 with interest of the new G3ignition, an interfaced-based electronic ignition control system. The reported fuel economy out of the group was 12% better in the RV-6 over the RV-4 that was equipped with standard slick magnetos. Both aircraft were running the same engine configuration. Also in the group of 4, there was a 2% better fuel economy over the other electronic ignition system that was in another RV-4. I had a blast meeting all of you that stop by and would like to thank everyone once again.

Sincerely,

Thomas S.
www.g3ignition.com
 
I still get 15% better fuel economy from my single LSE plasma III with a Bendix mag, than with dual Bendix mags.

Bob
 
Lightspeed uses a mapped profile though right? As I understand it the G3 system is fixed timing?
 
osxuser said:
Lightspeed uses a mapped profile though right? As I understand it the G3 system is fixed timing?
Click to expand...

LSE FAQ says...
"The Plasma II series is a single spark system which has a fixed spark duration at all rpm.
The Plasma III has a dual output stage which provides a continuous spark for about 20 degrees of crankshaft rotation at all rpm."

G3i product page says...
"The G3i interfaces aircraft magnetos with (MSD) ignition systems. In turn compliments the synchronized firing event in all naturally aspirated and supercharged Lycoming & Continental engines. MSD ignition uses multiple sparking technology, which last for 20° of the crankshaft rotation."

So yeah, LSE Plasma III looks comparable to G3i in regard to spark duration, although LSE appears to have control over the timing (via mapping MAP and RPM, and start retard) while the G3i looks to be triggered by the mag timing (also with optional start retard). After reading their sites and manuals, the implementations look waaay different though...
 
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Osxuser,
Yep, the G3ignition timing is fixed for naturally aspirated engines and it works very efficient. It is the multiple discharges that completes the burn effectively. The benefits obtain from the mapped advance curve in aircraft application is not that critical. With most electronic aircraft applications, when the power settings are above 70%, there is no advance from the base timing.
Thomas S.
 
What is nice about this set up is cost, and if it fails you still are running on the Slicks. The MSD ignition module works well on Lycomings. I had one on my -3 and removed it due to the age of the Bendix mag it operated. I'm looking at this set up closely as it fires BOTH mags with the hotter spark.
 
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Hmmm

So once the charge is lit...its lit..Why does this "continuous spark" make any difference?..I don't see why it makes any difference how long the spark is

Seems from thinking about it you want vairable timing so the max cylinder pressure always occurs at the ideal point (30 deg after TDC I believe)...The higher you go the thinner the air and the slower the flame front...

Sooo in theory you need to advance timing with reduced MP.

Can someone explain this??

Frank
 
frankh said:
So once the charge is lit...its lit..Why does this "continuous spark" make any difference?..I don't see why it makes any difference how long the spark is

Seems from thinking about it you want vairable timing so the max cylinder pressure always occurs at the ideal point (30 deg after TDC I believe)...The higher you go the thinner the air and the slower the flame front...

Sooo in theory you need to advance timing with reduced MP.

Can someone explain this??

Frank
Click to expand...

I can't but perhaps this statement from the Electorair web site will do it. The peak pressure point is 11 degrees after TDC according to EIS.

On a traditional dual magneto system, both magnetos are timed to fire at 25 degrees before Top Dead Center (TDC). When starting the engine, the ignition switch grounds the ?P? lead to the right magneto, stopping it from firing. Meanwhile, the left magneto with the impulse coupling can still fire. The impulse coupling causes the magneto to fire at TDC, and will continue to fire at TDC until the engine reaches about 200 RPM. At this time, the impulse coupling disengages and the magneto falls back to firing at 25 degrees before TDC. Once the ignition switch is released from the start position, the right magneto also begins to fire. From now on, no matter what the RPM, power setting, or altitude the engine spark timing will remain at 25 degrees before TDC.

At any altitudes, a cylinder on the intake stroke draws in fuel and air. At lower altitudes, on the compression stroke (as the piston moves up) at 25 degrees before the piston reaches the top of the cylinder (TDC), the spark plug fires lighting the air/fuel mixture. The objective is to reach the peak pressure point (as a result of igniting the air/fuel mixture) by the time the piston reaches 11 degrees past TDC.

As altitude increases, thinner air reduces the oxygen available for the proper fuel-air mixture creating more space between the air/fuel molecules. When the spark plug fires at 25 degrees before TDC, the thinner air/fuel mixture will burn slower. Therefore, the peak pressure point occurs much later than 11 degrees past TDC, and hence there is a loss in power. By advancing the timing based on RPM and atmospherics, the peak pressure point can be maintained much closer to 11 degrees after TDC. This can only be done with an electronic ignition system and is best done with an Electroair Ignition System (EIS)!



 
Hi Frank,

Here is a good link to MSD that gives a description of Multiple Spark Discharge.
http://www.msdignition.com/page.aspx?id=3356
Simple question, your engine runs better on 2 mags than 1 correct? 2 sparks are better than 1 spark, ok, lets multiple discharge.each plugs now get 2 to 3 sparks per firing event. That a total of 4 to 6 sparks. With the primitive/poor fuel atomization we have in these low RPM engines after the first fuel/air ignition spark take place, there is plenty of air/fuel mixture still not ignited. As it passes by the spark plug during the combustion cycle, the multiple sparks ignites it. A more complete burn = more power = better fuel economy.
Advancing the timing is not a bad thing unless it is a run away and stuck @ full advance or under starting conditions. Under testing and comparing various systems with advance features we just didn’t see a whole bunch of benefits for the complications and possibly detonation failures to follow.

Hope this helps,
Thomas S.
www.g3ignition.com

 
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Hmmm

But running on just one mag effectively retards the timing.I.e the peak pressure occurs later..Hence it does not make as much power..with two plugs your lighting the fire from both sides.so the peak pressure will occur sooner than if you only light it from one side...I.e with a single plug.

The plugs are in a fixed position..in the cylinder head..This does not seem logical to me..But if you have data then its hard to argue with.

Sometimes i hate being an engineer!...:)

Frank
 
frankh said:
Sometimes i hate being an engineer!...:)

Frank
Click to expand...

I too have wrestled with this theory. Seems to me once a fuse it lit, it is lit. I think one thing overlooked in this conversation is the the size of the spark. The MSD produces a much larger, hotter spark. This always help in combustion.

All I know is the MSD ingition module has proven performance gains on the race track, and in the air, so the multiple / hotter spark theory must work.

It must be the gennie in the little red box! ;)
 
frankh said:
But running on just one mag effectively retards the timing.I.e the peak pressure occurs later..Hence it does not make as much power..with two plugs your lighting the fire from both sides.so the peak pressure will occur sooner than if you only light it from one side...I.e with a single plug.
Click to expand...

On the dual LSE system, a cross-connect between the two units will cause an advance in one of the units when the other is turned off to recover the power lost to just firing one plug.
C.F. Taylor, Vol. 2, Revised edition, p.27, says that the spark should keep the peak pressure at the optimum crank angle of 15 deg. to 20 deg. ATC.
 
One of the problems with multiple sparks including from multiple plugs is that you can have two flame fronts moving through the chamber, when these flame fronts collide they often produce detonation. MSD ignitions generally turn off the multiple spark feature at high RPM, above what aircraft engines run at to avoid this problem. The transistor ignitions that first appeared in cars had very long spark duration to insure that the fuel charge burned. This had the effect of retarding the timing which changed the emissions of the engine. Modern control systems have very tight control of these variables and these systems will very likely end up in the piston aircraft engine eventually.

The extremely large bore of the Lycoming engine makes keeping the flame front moving difficult and this is made worse if the mixture is lean. I have often wondered about the very large bore and short stroke that is used in most aircraft engines. It would seem that a longer stroke and smaller bore for a given displacement would provide better combustion and torque characteristics for aircraft engines.

On our test engines here as the manifold pressure reduces and or the mixture leans out the point of maximum torque requires significant increases in spark timing.

We have a system here that allows us to view the combustion as it occurs. It is photographed at up to 4500 frames/second and you can see that pockets of fuel at the sides of the chamber do not burn. The system currently is static, that means that only one combustion event can be studied but we are building and engine where we will be able to watch the combustion happen as the engine runs, very cool stuff.

Bob Parry
 
robpar said:
One of the problems with multiple sparks including from multiple plugs is that you can have two flame fronts moving through the chamber, when these flame fronts collide they often produce detonation. MSD ignitions generally turn off the multiple spark feature at high RPM, above what aircraft engines run at to avoid this problem. Bob Parry
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As far as multiple sparks are concerned, in the LSE Plasma I & III, the sparks are about 80 useconds apart. With a flame-front propagating at 100 fps, the flame would have moved only about 0.1" from one spark to the next. From my experiments with the MSD system, I think the reason the number of sparks vs. rpm drops off is the ability of the HV power supply to recharge the output capacitor for additional sparks in time enough to be useful. I think you will find that the number of sparks multiplied by the rpm is close to a constant in the MSD system, which would be constant input power. The LSE, on the other hand, puts out several sparks at all rpm, so its input power increases with rpm!
 
0.1" between sparks will not cause multiple flame fronts I agree.
MSD makes an ignition for drag racing that does increase power with RPM. It is not recommended for continuous use as the power is very high. I can not remember the number MSD 8 maybe? How much does the power consumption rise on the LSI system?

It would be interesting to see the effect of two plugs and the flame fronts that would be produced. The large bore of the Lycoming engine should cause two flame fronts. Too bad we don't have a system that could look at that.

Bob Parry
 
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