Fun with spark plugs

Originally posted by Bill Hahn Jr. No...I was more working along the concept of current path to the spark plug and beyond.  How is this current path completed?  What principle is at work...as the electrical energy passes to the grounded portion of plug / pressure chamber, where is the energy finally dissipated?  What completes the circuit?

Bill, the simple answer of what happens beyond is heat.   Not sure if this is what you are asking.  The return path is the other side of the transformer.   So, for an in-line 4 with wasted spark two plugs will fire together.   Notice that each of the 2 plugs is tied to a common transformer.   Even if you held the two plugs in air, away from the motor, they will spark. 

This may be a little hard to understand as I know it seems like the return path is to the motor to the ignition/battery.   

So for the sake of science lets have some fun.  I start with the chamber isolated.  I am holding the braided wire  that goes to the power supply return.    I have a plug laying on top of the chamber so you can see the effects on the spark.   With the MC-4 running, I slowly move my finger towards the plug.  Watch the tip of my finger.   Next I move the braid near the plug.   Does this seem like the main path?  If so, watch what happens next.....

http://www.youtube.com/watch?v=ww0bw5vel7Q

I tied one more set of another type lot code MSD boots and interesting enough, I can not tell a difference now. 

The wire I was using was MSD 8.5MM Super Conductor and Accel 300+ Ferro-Spriral. 

I then placed each pair of wires next to one another.   I increased the pressure even higher and noticed both pairs of wires started to break down at about the same pressure.  There is a nice corona discharge running the length of the wires.  Using some wire spacers prevents this.   The if the wires are too close they will breakdown before the boots so the spacers can't hurt.  

Next I wanted to see what effect the gap would have.   I adjusted one set of plugs from 0.028 to 0.020 but kept the other two at the 0.028 as a reference.   While the plugs gapped at 0.028 would start to break down the two with  with the tighter gap were working fine.   I took the air pressure to about 270PSI before the coils started to break down under my silicone.   This seems like a very good gain. 

I do not seem to be having any major problems with my bike using a 0.028 gap, but can see where setting it tighter may help with higher boost levels.

It's an interesting video.   I like his gap.   Notice in the video he has another gap with two balls.  More caveman looking. 

Right off I noticed the Pearson transformer.    When he collects and shows the scope, he talks about the secondary current being the yellow.  He goes on to talk about the glitches being cables and setup.   If he set the scope to peak detect, he may actually see the real current.      Notice, he is all the way out at 1mS/division.   This is 0.001 sec/ div.     He needs to be in the nS/division to see it and then the Pearson would fall on it's face.    It's just not a simple problem.  

Towards the end of the video he does a little sweep of the RPM.  You can hear the system alias.   My guess is he makes a comment about a 5mS dwell.  I am guessing he is holding this constant and this is the cause of the problem.    If you listened to that video I made of the MC-4 playing the music you can hear the difference in the sound as I sweep up and down.

Originally posted by turbovmax   Your electronic knowledge is amazing to me. I'm still struggling with trying to catch a signal on a scope properly. My abilities are more mechanical and I just seem to get myself in trouble when trying to figure out electronics. The experiment was very interesting for me because of the gap jump and seemingly strong spark with the LS 2's.   As I mentioned, I'll be using a Haltech ECU and was looking to see what the dwell setting should be with the unit and GM coil combo. There are some turbo 4 cylinder car guys making in excess of 1000 Hp using the setup.      Here's a good link with some useful info about the sparky stuff.    http://www.megamanual.com/seq/coils.htm    Gary

One comment to that breakdown voltage calculator. Compression ratio in this case is how much air/fuel mixture is compressed at the moment of ignition (30 before TDC). That is less than usual compression ratio. Ex. with 1:11 comp ratio "ignition compression ratio" is around 1:7. 

Interesting paper:
Jeonghoon Song and Dae Hee Lee (2003), "Experimental Study of Ignition of a Gasoline-Air Mixture in a Constant-Volume Combustion Chamber", Combustion, Explosion, and Shock Waves, Vol. 39, No. 5, pp. 513-524


Edited by shmot - 23 October 2009 at 12:12pm

I ran a few more tests using industrial grade nitrogen.   For the first test, I set all four plugs to 0.022.   I had two plugs inside the chamber and two outside.     I used the Accel and MSD wires with the blaster coils.     I put the chamber under a vacuum for a few minutes to try and remove any water  best I could.     Boots and plugs were cleaned and boots were coated with the GE.      The wires were all seperated by at leat a 1/4 inch and also kept away from copper by at least this same amount. 

I slowly increased the gas pressure until I noticed that the MSD boots (straight style) started to breakdown again to the plug at about 150 PSI.     Pressure was about 50 PSI higher before the Accel boot would start to  break down.    I continued to increase the pressure to 300 PSI which is where the towers on both coils would breakdown once in a while.   Note that the boots on the two outside plugs never broke down.      I held this pressure for about 5 minutes and there was a noticeable change in the sound.  At this time the MSD boot was arcing so bad that I could see the plug was missing frequently.     While the Accel boot was also arcing, there was a major difference between the two boots. 

One thing with the nitrogen, its dry so the sight window stays clear during the tests.

Streight MSD boots were swapped for the 90 degree ones with the MSD logo.  These boots once again seemed to work about as well as the Accel straight boots until I got to higher pressures and it appeared that they would arc a little worse. 

I took the pressure again at 300 PSI, I never saw the 90 degree MSD boots breakdown like their straight ones, even after the 5 minutes.  I continued to let the system run and after about 8 minutes, the Accel boot started to arc like the MSD straight boot had.   Keep in mind, this is the same set of Accel wires used in the previous test so they had more time on them. 

At least with my testing with the wires I have, I would rank the Accel wires better than the MSD if your going to run the straight boots.    




Edited by geek - 31 October 2009 at 2:46pm

If you don't have one, you may be able to rent a nitrogen tank for a few dollars.    If you want to stay with air, you could buy a cheap bicycle pump.  These things can put out near 300 PSI.    I think the nitrogen is much better.  You don't have to consider effects of humidity and pressure is no problem.   Gas is stored around 3000 PSI.  Number of charges will be volume / pressure ratio between the tanks.  Cost to fill the 40 lb bottle is about $18 US. 

It's a little hard to answer that question.  I need a better way to look for breakdown than just turning off the lights and watching with my eyes.  I have a decent HV probe and may be able to detect it on the primary side.   Hum, need to  think about it.

Agree, it would be great to have some sort of correlation with some sort of known gases against  different fuels, mixes and pressure.   Your last paper talks about some standard pressures and temperatures at the point of ignition.    Dynatek may have sorted all this out.  Doubt they pulled the 200 PSI nitrogen number out of the air.

Let me know what you get for a breakdown and how you measured it.  I would like to know the plug type, gap and pressure as well.    If I could buy a single Nology wire local, I would consider doing a side-by-side with it. 

Post some pictures of your new setup. 

So Mark, do I need to put some silicone orings on my plugs? Could this break down you are showing casue the bike to lose tnat cylinder while it is arcing?

Originally posted by geek I do not know to be honest if it would help.  It's just an experiment.  Have you ever seen anyone, car or bike, putting O-rings on their plugs??  Let me ask it another way.  Does MSD, Dynatek or Schnitz sell O-rings for spark plugs?

Maybe you are first one how did saw this. It happens. O-ring is good idea. Maybe it is reasonable to put some silicone grease to plug insulator and o-rings before installing.

When air is compressed that will heat it and increasing temperature will drop breakdown voltage. Also in high rev engine short compression time also increases temp. If megamanual equations are correct then gas temp is at time of ignition 400 C (750 F). Probably if it works at 300 psi in your test system is good more pressure in realilty. I need to test if temp has an effect to the glow or arc.

Originally posted by Roland Tamaccio ... You guys are giving me a whole another perspective on the dropping of cylinders in a nitro engine. For a decade or two I've been thinking it is the plug becoming wet and the voltage bleeding down without an arc, or the entire fuel air charge too wet and or cold for complete ignition, now I have diluted my ignorance and added a third possibility.