Wasted Spark Vrs. Direct Fire

[petert 550]

Coil-wise i have and everyone seems to use an Xu10 wasted spark type affair.

 

I picked this up from the XU section. Not everyone runs wasted spark. Certainly not myself or DrSarty. Wasted spark fires two plugs at once. This means the current flows from one plug to the other. Thus only one has optimum spark. I run four individual coils fired by a four channel CDI. Richard runs four LS1 coils, which while they fire in pairs, have individual internal ignitiors.

[welshpug 1,622]

Intriguing, is it always one that is stronger?

 

You don't need a cam phase sensor for this? (works off the missing tooth on the TDC timing ring I think?)

 

but you do for sequential injection right?

Edited June 9, 2009 by welshpug

[Tom Fenton 1,525]

In practise though, is there any noticeable difference??

[DrSarty 90 1 Cars]

Intriguing, is it always one that is stronger?

 

You don't need a cam phase sensor for this? (works off the missing tooth on the TDC timing ring I think?)

 

but you do for sequential injection right?

 

You need a cam phase sensor to get anything sequential, as the signal rate required is twice that of the crank.

 

Is it noticable? Hmmmmm. I would approach it the Tesco way: 'Every little helps'. Anything which is less than optimum must combine with other things that are less than optimum too. We know internal combustion engines (especially otto cycle) are inherently inefficient, so surely everything you can do to claw this back must help; in isolation, perhaps not in terms of performance. But maybe fuel economy or throttle response or emissions benefit.

 

And it surely was invented for a reason (?). Wasted spark has double the coils and no dizzy, which I guess means better spark and less moving parts to go wrong (cheaper construction too). Sequential spark involves more parts, but must've been invetned for a reason.

 

Discuss.

 

P.S. Yes WP I only have a CAS/CPS, sending a signal to the ECU from the flywheel teeth. But I have 4 separate coils (LS1s) each with ignitors that fire in pairs but the sparks are equally strong (and huge). I could adapt mine to use a cam sensor and run sequential, but I've heard it really only effects emissions/economy, and I CBA if that's the case.

Edited June 9, 2009 by DrSarty

[petert 550]

Discuss.

 

It took a while to find it:

 

"the current reaching the spark plug is direct and thus the center electrode can be positive or negative depending on the circuit; ideally, the center electrode should be negative when igniting the fuel charge--a positive electrode requires 40% higher voltage to make it spark; hence it will erode faster and have an increased chance of misfiring."

 

http://www.wastedspark.com/stories/mechanics5.html

 

 

Also here:

 

http://www.auto-solve.com/back_to_basics/b2b_part_5.pdf

 

Thus the centre electrode of one plug will be positive, the other negative. At least that's how I see it. Anyone else?

 

 

So the LS1 solution gives all the advantages of wasted spark and direct fire without any of the disadvantages. My solution of running a four channel CDI is better again, but at additional cost and an additional trigger.

Edited June 10, 2009 by petert

[Rob Turbo 3]

So could you run wasted spark with the standard gti6 coils rather than say a 2.0 8v turbo coil pack?

[Cameron 16]

If you connected 2 coils together (so they are fired together) then yeah, you could. Might take some fiddling to get the rev counter signal.

[jackherer 543]

So could you run wasted spark with the standard gti6 coils rather than say a 2.0 8v turbo coil pack?

 

The previous owner of my GTI6 engine was doing precisely that with an Emerald.

[ifcho 0]

indeed you are correct in your assumptions. It is much better to use COPs in a wasted spark mode, than the double coil setup.

The current in a wasted spark systems rungs as on the diagram in the first post, and one of the sparks is always getting a worse spark.

Edited June 13, 2009 by ifcho

[wracing 19]

i've just posted this on another topic and thought it might be relevant while i know that testing on the bench is different from igniting compressed mixtures, i hope to retest on a running engine by running 4 current loops per sparking pair i need another 100mhz oscilloscope first though!

 

tbh it depends on your system comp ratios boost pressures mixtures... not as simple as a hotter spark is better. for instance i pulled a wasted spark system ran it on a bench under the watch of current loops and a high speed camera, i couldn't measure a stable difference it spark energy luminosity or current while true if one plug fails both do but running on 3 is just as bad as 2

 

sorry to be controversial

 

 

james

[taffycrook 2]

The wasted spark system does indeed have one spark weaker than the other, but the weaker spark is always the wasted one.

When 2 cylinders are at TDC one is on compression/power stroke the other exhaust/inlet, so one cylinder has a compressed wall of mixture to pass the spark through the other doesn't. The amount of energy available to jump the gap is shared, but not equal so the wasted spark is weaker, but on the next cycle it will be stronger, and so on.

Modern ign systems have plenty of spark energy to do this, but problems can arise with high boost turbo engines as the spark energy required increases as the pressures in the cylinder increase.

Wasted spark systems can reduce emissions by burning any fuel left in the cylinder on the exhaust stroke, have less output channels (cheaper) and less wiring. This makes them attractive to OEM's.

Edited June 15, 2009 by taffycrook

[petert 550]

but the weaker spark is always the wasted one.

 

So little monkeys swap the leads around between cylinder cycles?

[snillet 1]

So little monkeys swap the leads around between cylinder cycles?

 

I was also thinking about that, the coil is always charged in one direction electrically, therefor the coil core is always charged magnetically in ONE direction before it uncharged in...the other direction.

 

That means that the uncharge direction will always be the same unless there´s a "little monkey" that swithces the cables around every other spark, or switches the charge polarity every other spark. To my knowledge these very basic and simple systems, always has the same polarity on the charge.

 

If i´m wrong, please correct me....

[DrSarty 90 1 Cars]

If i´m wrong, please correct me....

 

Yes, you are wrong. And so is Pete.

 

Do you mean to tell me you don't have monkeys under your bonnet doing this for you? I thought they were OE.

 

[tom_m 0]

Do you mean to tell me you don't have monkeys under your bonnet doing this for you? I thought they were OE.

 

 

my monkees escaped a long time ago, something about the last train to clarksville...

[wracing 19]

haha good stuff guys

 

snillet is right that the secondary coils polarity is of reference to the primary and i dont know any oe monkey systems

 

for some reason something tells me that because this is a very dynamic system with lots of changing variables its not as simple as one is stronger than the other.

 

think about it an ignition coil is an isolated coil, yes you do have a positive leg of the coil and a negative with reference to the exciting coil, positive and negative under measurement what are you referencing it to ground, the negative side of the coil?!?!

 

referencing from the system ground you would see 40kv or whatever sum on both side of the coil

 

referencing from the negative side of the coil your going to see 0v on the negative and any sum between 40kv-80kv depending on where the ground whats to float

 

moving on an ignition coil is more of a dc than ac transformer, a dc coil doesnt have a polarity!!

 

now tell me electrically speaking which is stronger?

 

please correct me if im wrong....

 

james

Edited June 15, 2009 by wracing

[wracing 19]

just another thought,

 

assume that the secondary winding is a inductor (which it is, one that is magnetically coupled with another winding). when the inductor is charged with 'electricity' and connected to ground current will flow out of the inductor equally through each connection (in an ideal world).

 

lets connect a resistor in series with one of the inductor connections on discharge the resistor will resist the flow of electrons thus more energy will pass down the unresisted connection

 

assume that the resistor was a high pressure environment. this would mean that the more energetic spark would always be on the exhaust side?!? or the atmosphere with the least resistance, as i don't know the resistance of the exhaust gases to spark.

 

just a thought

 

james

[snillet 1]

Your right about the "easiest path" always being on the exhaust spark, couldn´t be any other way really since it takes a lot to "spark" in the compressed A/F mixture. But that only makes the plug in the exhaust cylinder a very easy path to just pass through so it doesn´t rellay do much to weaken the spark ini the compression cylinder, some yes, of course....., but not a whole lot. Unless you´re running a overcharged engine on ehtanol or something like that , that takes SERIOUS spark-energy to work good.

 

And i´m not either shure of what path is the best for a spark to travel, as mentioned before in this thread there ARE some references in the "spark buisness" on this, but i´m not all convinced that the total energy of the spark is of any significant difference, the coil as, as mentioned an inductor, and the plugs are just a path to unload the charge that´s being built up in the inductor core, so the amount of energy really is the same, i don´t see how the uncharge could be very much different between the plugs if they were both in the same environment really.

 

But, for REALLY high-spec systems on high compression or overcharged engines, it´s not really wise to have a longer path for the spark, although wasted spark systems are generally very powerful

[Cameron 16]

Surely though, as the plugs are wired in series, you would see the same voltage at both of them? When you have two resistors in series, the voltage across them is the same, right?

 

Also, coil per plug was invented so you could have longer dwell and therefore a stronger spark at high revs (where dwell time is reduced).

[Cameron 16]

Ok, so if one plug has the weaker spark by default, regardless of cylinder conditions.. say in this case its plug 1, and plug 4 has to be the weaker spark since it is after plug 1 in the circuit. How can you then have one spark stronger due to the cylinder conditions!? What you're saying is if cylinder 1 is the wasted spark then it is weaker, right? That can't happen, surely, since energy can't be created or destroyed.

What I mean is, if plug 1 is the stronger plug by default, then plug 4 HAS to be weaker. It can't get stronger than plug number 1, since it is after it in the circuit.

 

Make sense?

 

There's a lot of contradictory information going on here.

[James_R 3]

Well twin coil wasted spark set ups on bikes manage (my YZF750 for example) 11.5:1 compression and a max revs of 12.5krpm with no ignitions issues so I can't see how a car only managing 7-8krpm would be any problems.

 

They work who cares!

[wracing 19]

conservation of energy is at the heart of every theory

 

i have presented two theories to clarify

one is that the coils have polarity but there is an unmeasurable difference between the potential energies available to each plug. this leading me to the idea that the coils are actually dc transformers with no polarity

 

secondly

 

i have commented on the atmospheric conditions within the spark environment adding a resistance to one of the inductor legs thus shunting energy away from one plug through another, therefore creating a more energetic spark on the least 'resistive atmosphere', which i assume to me the exhaust side

 

really these theories compound not contradict

 

Cameron i dont mean to be an arse but your not understanding the system assume the coils are the energy source (this is the case as the transformer is operating in discontinuous mode ) and the plug tips are ground therefore the energy flow is equally split between to plugs, if you introduce a resistance (atmospheric conditions ) the energy will flow toward the path of least resistance.

 

imho wasted is good enough for 95% of applications cop is only necessary on very high compression engines or charged engines the cost and complexity dosent not warrant fitting to a 'road' engine

 

 

 

james

[petert 550]

We are starting to get somewhere now, but I'm still not sure if monkeys are needed or not. The coil is indeed a transformer, and as such, could polarise the secondary winding either way if fed from an AC source. However, given that the primary winding is always energised the same way, wouldn't the secondary current always flow in the same direction? Also keep in mind, that unlike a normal transformer where the primary and secondary windings are totally separate, the secondary and primary windings in a coil share a common connection (which is ground?).

[snillet 1]

We are starting to get somewhere now, but I'm still not sure if monkeys are needed or not. The coil is indeed a transformer, and as such, could polarise the secondary winding either way if fed from an AC source. However, given that the primary winding is always energised the same way, wouldn't the secondary current always flow in the same direction? Also keep in mind, that unlike a normal transformer where the primary and secondary windings are totally separate, the secondary and primary windings in a coil share a common connection (which is ground?).

 

About the polarisation, see my posts further up in this thread, i belive you´re right there.

But you´ve missed the fundamental function of wasted spark coils, and that is that the secondary is not connected to anything but 2 sparkplugs, at each end of the coil, there at least WAS a figure of this in the top of the thread.