Spark and size of explosion???

[Ihorse]

On the subject of spark and the resulting explosion in the cylinder!---if you have spark!! is that enough?? or is a bigger spark-better?? a match will lite a pool of gas! a bigger match don;t make any difference--does a bigger hotter spark make a bigger hotter explosion???
thanks d,j,

[Harvey Teal]

Nope, D.J., all you need is a spark. Of course it has to be healthy enough to start the explosion. On every ingition cycle. Under compression. This is what separates the men from the boys. No room for bad condensers, leaky wire insulation, weak magnets, dead batteries here. Once you have a reliable, strong spark established, the engine won't produce more power if you put more power into the spark. But as we all know, a weak spark will cause the engine to misfire, misbehave, etc.....

[Kelly Tytlandsvik]

We were taught in Technical school that as you excelerate the extra flow of air and fuel into the cylinder caused cylinder pressures to go higher which requires a higher secondary ignition voltage. (this of course is referring to a modern engine but may apply some what to what you are working with) This is why sometimes an engine will miss as you excelerate after turning a corner. The cause is usually a bad wire, poor resistor in a plug or a weak coil basicly high resitance in the secondary circuit.

Kelly T

[Jim McIntyre]

Originally Posted by Ihorse

does a bigger hotter spark make a bigger hotter explosion?
thanks d,j,

I don't think so. Once a certain threshold is exceeded, the spark has enough energy to heat the mixture to the ignition temperature, and the entire charge in the cylinder will burn very quickly. Increasing the spark size does nothing.

I've always lumped 'high energy spark' gizmos in with perpetual motion machines, get rich schemes, and diets claiming you can eat all you want and still lose weight.

[John Newman, Jr.]

I agree that it is far better to have reliable spark than "hotter" spark. Even with the questionable gasoline we have to work with today, it far exceeds the quality of what was available when some of the earliest engines were expected to start and run on when they were new. If the ignition system on your particular engine was adequate then, it should have no trouble today if you maintain your ignition system properly. This of course means having solid connections on all wires; no corrosion; no worn, cracked, oil soaked or burned insulation; good points properly gapped; adequate magnet strength with clearances set where applicable; condenser of correct value securely mounted for good grounding. I'm sure there are more things that could go on this list. Make sure your existing system is working at 100% and you will probably eliminate any problem.

[Neale Behm]

The arguments here all seem reasonable.
What I do know for fact is that an engine with dual ignition (2 spark plugs per cylinder) does have a very noticable effect on performance. Piston aircraft engines will lose about 75-150RPM during a magneto test at 1700 RPM (turning off the mags one at a time). My reasoning for this is that dual ignition is lighting the charge at two different places in the cylinder allowing a bit more even combustion in the cylinder.
Thanks Harry

[Elden DuRand]

Originally Posted by Neale Behm

The arguments here all seem reasonable.
What I do know for fact is that an engine with dual ignition (2 spark plugs per cylinder) does have a very noticable effect on performance. Piston aircraft engines will lose about 75-150RPM during a magneto test at 1700 RPM (turning off the mags one at a time). My reasoning for this is that dual ignition is lighting the charge at two different places in the cylinder allowing a bit more even combustion in the cylinder.
Thanks Harry

Neale:

My theory about that is that with two plugs firing the charge, the pressure builds up faster because the fuel is burned faster (two flame fronts). Because the pressure rises faster, less timing advance is needed.

When you kill one mag, the engine runs like the spark is retarded a bit. That's why it runs slower when the one mag is cut-out.

My two cents' worth!

Take care - Elden

[Forrest A]

It's harder for the spark to jump the gap under compression so a hotter spark (Higher voltage) will tend to jump the gap better under compression. Also, what is ideal is a nice even burn not an explosion.

Forrest A

[Neale Behm]

Elden,
I knew I could count on you to take my simple minded explaination and put it into technical terms everyone else could understand!!

Neale

[Dennis K. Nash]

A hotter spark does increase the ignition and burn rate. Street racers found out there was a noticeable increase in acceleration if all electrical equipment is turned off (lights, radio, heater etc.). The less load on the electrical system, the hotter the spark and more efficient running.
The same as using a magnum primer opposed to a standard primer in a bullet increases the pressure and fps. Hotter spark, increased efficiency.

[JoeFisher]

if two ignition sources both have enough spark to jump the plug gap under all conditions for a particuler engine, the engine will not run any better if one has a much hotter spark. street racers ran better with the lites out because the system voltage without so much load would be higher and the spark,marginal at best, became better when the coil was supplied with higher voltage. most modern ignition systems are much hotter than they need to be to just to run the engines today. Joe Fisher in central Texas

[Andrew Mackey]

Today's fuel is not gasoline as the old timers know it. It is a blend of fuels including: Hexane, Octane ISO-Butane, ISO-Propane ethers, methanol, ehtanes and all that good stuff. If you live out west, you even get 10% ethanol, sometimes called Gasohol This admixture of volatiles needs a hotter sparl, and a wider gap, in order to light off. Your typical ignition system built today puts out a minimum of 75,000 volts (the GM HEI system exceeds 100,000 Volts ) There is a service bullitin from GM telling mechanics not to pull off HEI hi tension wiring by hand - the result of doing so may be fatal! GM HEI can stop your heart! The old gasolines would light off with an .010 spark! In the cae of 2 plugs per cylender, there were several reasons for it. 1) with 2 ignition systems, you had a redundant system to keep the engine running, in case of failure. 2) with 2 points of ignition, combustion was more effecient, leading up to a 15% gain in power, from each cylender. 3) If a plug fouled, the cylender would keep firing. The draw backs: unless you had a Pass Thru Type coil, Timing becomes a critical tune up item..If one spark leads another, it could lead to detonation, if the 2 flame fronts did not meet in the planed space in the combustion chamber. (This is a major cause of piston melt down in the racing circut!) Higher compression requires more voltage to jump the gap, not nescessarily a hotter spark plug. Another misnomer is that 'Hi Test' or high octane gas is hotter. In fact the opposite is true, Hi Test actually burns cooler than regular. The purpose of 'Hi Test' was to lessen or prevent pinging or engine knock. With todays engine technology (lower compression, knock sensers, and multi port fuel injection), There is actually no need for 'super'. If you do use it, you will get a little more power, and slightly better gas milage, but at todays prices, it hardly seems worth it. Most of your high performance engines today are dual ignition. See also my posts in the 2 plugs 1 wire post.
Andrew

[Andrew Mackey]

I guess I missed the reason for the original posting, CRS is a tough desease to live with, and I have more than one reason for it! Any way, you really don't want an explosion inside your combustion chamber The ignition process is a controlled burning of the fuel and air mixture in a confined space. There are many things that alter the way fuel burns in there! If the mixture is too lean, you will probably end up with an explosion! An explosion produces little power, but makes for extreme pressures for short perions of time. This 'explosion' often leads to detonation -a much more destructive phenomenon. Detonation is the uncontrolled ignition of fuel , in the combustion chamber, either by excessive heat or pressure. Detonation is often described as knocking, and in effect it is! The piston is slapped against the cylender wall, and a lot of force is applied to the connecting rod and the crankshaft. The long term effects are bearing destruction, and holed pistons. The new wide gap plugs (.065"+) are needed to light the charge in the new engines, because they run at a much leaner mixture than our old timers! If you were to put an .025 gap plug in a modern auto, it will probably spit and backfire something fierce! The new fuels themselves do not help the situation either. As for the plugs them selves - just because they have a bigger gap, does not mean they run hotter. All they do is expose more fuel and air mixture to the ignition source. The shape of the combustion chamber controls how the fuel produces power. The old style engines usually started combustion on one side of the cylender, usually near the valves. The flame front would then travel thru the chamber, eventually burning itself out, with the piston about 2/3 of the way down the bore. Like a steam engine, expansion does the rest! The newer style engines, especially the 'Hemi' engines, centralized the flame front to start at the center and work toward the edges. This makes the flame front burn more effeciently, and provides more push to the piston and conrod, to provide more power, instead of wasting it on the cylender walls and the combustion chamber itself. A hotter longer spark will light a leaner mixture, but won't have any effect on how effeciently the engine makes power. The internal combustion engine has not changed much in 150 years!
Andrew

[Elden DuRand]

Originally Posted by Dennis K. Nash

A hotter spark does increase the ignition and burn rate. Street racers found out there was a noticeable increase in acceleration if all electrical equipment is turned off (lights, radio, heater etc.). The less load on the electrical system, the hotter the spark and more efficient running.

Dennis:

I wonder if the reason for higher speed with all the accessories turned off is actually caused by less power being drawn from the engine via the alternator.

Just a thought.

Take care - Elden

[Forrest A]

One other reason for the "racers" noticing an increase in power when other electrical items are shut off is the load on the alternator was less. "Racers" also found that removing the alternator would also increase HP to the wheels.

Dual spark allows for a more complete burn of the fuel/air mixture at higher revs not a hotter burn. A hotter burn would be one caused by by a lower octane rated fuel or higher compression ratio.

Airplanes used dual spark, not because of power increases but because it's hard to fix a bad spark plug at 30,000 feet.

Forrest A

[J.B. Castagnos]

The main reason for dual ignition on aircraft was reliabilty. Most aircraft engines were large bore, the flame had a long way to travel, lighting it at both ends helped increase power. Automobile engines with dual ignition usually turn one off above 3000 rpm to prevent spark knock. A bad cap or coil on a Nissan would act like a hit and miss governor, the engine would sit at 3000rpm cycling on and off.