Can anyone provide a link to data supporting a claim of
hotter spark with an EI? I'm speaking of "hotter" in a strict sense, specifically "higher temperature". To be fair, let's stick with cruise RPM. (Note; I fly two EI's.)
BTW, this thing uses magnetos and constant flow injection to make 10,000 HP. I'm just sayin...
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That is a great question. NO DATA FOR YOU. NEXT. Ha ha. My short answer is they are all good enough.
You can review a old EAA Cafe Foundation test of EI's on a Mooney. It mostly was EI (original Jeff Rose design) and Mags. Most of the current crop of EI's did not exist at the time. However it is interesting and shows improved fuel economy. Did they measure spark energy or temperature? Don't recall, but proof is in the pudding, measurable performance. It's not a quantum leap from Mag to EI. From memory one EI + one Mag was 4%. A second EI, dual EI's only added 1% or 2%. So 6% better than Mag in low power. High power all EI's use fixed timing, same as Mags, and the advantage is not as great.
My opinion head up difference between different EI's will be small. No one has ever tested this. The issue is not temperature but size of spark (gap) and duration.
As far as spark energy you need enough to jump a larger gap of an automotive plug. That makes a bigger spark for better more complete combustion. That is why EI's don't use aircraft massive electrodes. Gap is smaller in AC plugs, and reduces advantages of the higher energy EI over Mag. I don't have qualitative numbers. Mags are no slouch to be sure in "temperature" but size of spark smaller. Mags woukd struggle to spark larger gaps under compression. Duration I don't know. Mags were not about squeezing every ounce of power and efficiency out of the engine, but reliability. Ei did not exist in late 1800's when Magnetos were invented.
All EI's use inductive coils from off the shelf automotive applications. Physical size, windings, number of number of coils per plug will clue you into spark energy. P-Mags have 2 coils for 4 plugs. This is called wasted spark method. The coil is from a Fird EI system.
Somw EI manufacture will make claims about volts or energy they make. Others do not and recognize it's not important as long as you have energy for a strong spark across gap. One claims to have the most spark energy of any EI. My question how much energy do you need. All inductive ignotion coils are engineered for this. At some point it's diminished returns. Bigger the coil the more room and weight.
I can tell you Mags use small spark plug gaps because of limited energy. However it is more than adequate to fire the gas air mixture at 2700 rpm and 9 5 to 1 CR with 100LL @ 25 BTDC. It is pretty mild compared to an automobile race engne intentionally. Reliability is more important.
These aircraft EI's are all based on car inductive discharge except Lightspeed II, which is CDI. They all are going to provide adequate spark, just as Mags do.
As important or more is EI's do their best work at lower power by advancing timing. Mags are fixed at 25 degrees BTDC. That is fine at 75% to 100% power. At 55% power; say flying at 12,000 feet you need way more advanced timing. The flame front is so slow you have to kick it off sooner. If timing is too advanced at high power you will damage engine. 25 degrees is the base line compromise timing for Mags on Lycoming typically. So spark energy is not everything, timing is key as well.
Some EI's give you a little more flexibility in messing with the timing advance. That is great but can get you in trouble. P-Mag gives you a choice of fixed and base Adv curve. They really do not want customization. It can be changed but not easily. Some EI's put a controller on your panel to mess with in flight. P-Mags design philosophy is not about tinkering in flight, but flying. P-MAG does have a fairly aggressive stock Advance curve and total advance to safely get great performance with out risking detonation on a STOCK ENGINE. If you have a hot high CR Lyc you will want to time the P-Mag back to limit total Adv. These race applications I would say is where other EI systems may be better, with more controls.
CDI however can provide not only high energy can provide longer duration multi sparks. CDI recovers faster and suitable for high revving engines and two stokes, which sparks every Rev verses every other crank rotation in 4-srrokes. I don't think CDI's claim to fame is hotter spark, but longer duration spark and faster recovery for higher Rev'g engines. Most cars are Inductive discharge ignitions, which is most common and works well, even if it's a single spark. If it's a big gap and timing is right all is good with one spark.
Some EI's use wasted spark as I said, meaning one coil works for two plugs on two cylinder pairs, 360 degrees out of phase, saving complexity. The dwell time of coil is shorter. In theory this could reduce spark energy. I did the math. Lycoming apication it's no issue. The coil saturation is Bueno. RPMs are low l, so dwell is not an issue by wide margins Remember old V8's had one coil and a distributor for 8 cylinders? That is a spark every 90 degrees of crank rotation. On a Lyc with wasted spark we have 369 degree rotation per spark and low RPM compared to an automobile engine.
We are not talking 19,000 RPM formula 1 race car. I am pretty sure they use CDI. High performance street cars use inductive ignition, but use separate coils for each cylinder and plug. My two cylinder BMW motorcycle has 4 plugs and 4 coils.
How much energy or plug Temperature do you need? Plug temperature is controlled by heat range of the plug, not ignition.
Lycoming low compression normally aperated engine, timing advance is the big gain over fixed timing Mags at low power. However to use this Adv timing requires lower power. Advanced timing on a Lycoming at high power will cause detonation.
LIGHTSPEED CDI capacitive discharge promises to be in theory the best design? Again we are talking fairly low RPM and low compression aircraft engines. However if racing may be this is better. Can you measure the difference? My opinion may be and it would be small for normal Lycoming operations. A high revving race car or 2-stroke (which fires every crank revolution) would benifit from CDI ignition. Another benifit of CDI which would benifit any engine including a Lycoming is longer duration. It does this by spitting our multiple sparks making longer duration. Inductive ignition is one spark.
Most important is customer service. Second reliability, cost, form, fit and function. All EI's spark is more than adequate to fire a wide gap automotive spark plug in Lycomings. I think the other factors are as important or more important. P-Mag may not be sexy but is better than a Mag performance wise and is still self powered, the only EI to be self powered.
However back to Mags. They are also self powered and adequate for general local flying at 75% power or greater. Even if you fly at high altitudes and lower power 6% loss in efficiency may not be enough to pay for EI, if you already have Mags. If starting from scratch and given a choice EI is good. If up grading you only need one EI to get most bang for buck (pun intended).