A short study on ignition timing and combustion

Oh yum Alan. I ain't the chemist you are but have caught my self and lab ware on fire, yet saved the product before my skin. Its all about outer electron orbital shells and photons, as exposed vulnerable or covered shielded by the positions on carbon chain. Deflageration combustion occurs below the speed of sound [in the chamber conditions] and its mechanisms to reach-spread activation energy threshold depends mainly on 2 slow-ish phenomena,
1. heating by shear closeness of bumping molecules and short range photons, 2. stirring-mixing on macro and micro levels. Detonation takes things super sonic. Its mainly spreads activation energy via 1. shock wave compression bump heating, 2. long range photon heating > even out to rim of chamber & 3. plasma plumes, ie: atoms of molecules hit so hard it separates all their electrons from nucleus.

To paraphrase ancient organic text...
TEL has no effect on flame velocity in fuel would not knock w/o lead in it.
TEL, a 4 legged star looking molecule, helps prevent the loss of methyl CH and ethyl CC carbon species under combustion turmoil so they burn later longer like methanol and carbon monoxide. Spectrographs show lead is blasted off its carbon radials so at flame fronts its in the form of pure lead atoms or lead oxide.

I also think the lead like water absorbs some the long range photons that crack the fuel chains down to fast to react too fast. i think that sparks over 20kv are producing UV photons that race ahead of electron kernal like a welder arc can burn retinas or skin at a distance.
http://corescholar.libraries.wright.edu ... s_seminars

comnoz said:

Dances with Shrapnel said:

Getting back on topic - So the Norton intake tract orientation promotes swirl and with the combustion chamber shape this supports less ignition advance required to achive max torque for various engine speeds.

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I think I heard that somewhere before..

Thanks for the more technical explanation. Jim

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That's exactly what happens when you start a response, step away for 90 minutes, come back to complete the response and submit. :lol:

Jim, thinking about the balance required between mixture, comp ratio and ignition advance required for best mid-range torque. From what you've said, for a given combustion chamber configuration and comp. ratio, the critical factor is when the maximum pressure is achieved in the combustion chamber. Even with a programmable advance curve, don't you end up setting where the max pressure occurs towards the end of the event in relation to crank rotation, then jetting to the timing curve you have chosen ? It seems to me that often a slight variation in the ignition timing has the same effect on torque as altering the shape of needle in the carburettor.
I am not up with engine management systems on modern bikes, however I believe the balance of air/fuel and ignition advance and revs, are achieved electronically . So what we do with commando engines is slightly more hampered by lack of fuel injection systems , however the optimum for a given circumstance is still achievable ?

acotrel said:

Jim, thinking about the balance required between mixture, comp ratio and ignition advance required for best mid-range torque. From what you've said, for a given combustion chamber configuration and comp. ratio, the critical factor is when the maximum pressure is achieved in the combustion chamber. Even with a programmable advance curve, don't you end up setting where the max pressure occurs towards the end of the event in relation to crank rotation, then jetting to the timing curve you have chosen ? It seems to me that often a slight variation in the ignition timing has the same effect on torque as altering the shape of needle in the carburettor.
I am not up with engine management systems on modern bikes, however I believe the balance of air/fuel and ignition advance and revs, are achieved electronically . So what we do with commando engines is slightly more hampered by lack of fuel injection systems , however the optimum for a given circumstance is still achievable ?

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I get the fuel mixture right first and then I map the ignition advance looking for minimum timing for best torque at each rpm division. Repeat as needed. Jim

Does that mean the completion of the combustion event is as late as possible while delivering maximum torque ? I'm finding this a bit of a brain teaser. I'd like to talk to you about this a bit later after I've had the argument with my motor mechanic/A grade racer friend, he's spent most of his life tuning Japanese cars.
By 'minimum timing' do you mean minimum ignition advance ? When you say you get the mixture right first, does that mean using fixed advance at certain revs? Or do you tune the carburation right across the usable rev range and throttle openings using fixed advance, then work from there finding max torque with the advance curve ? That would make more sense to me.

acotrel said:

Does that mean the completion of the combustion event is as late as possible while delivering maximum torque ? I'm finding this a bit of a brain teaser. I'd like to talk to you about this a bit later after I've had the argument with my motor mechanic/A grade racer friend, he's spent most of his life tuning Japanese cars.
By 'minimum timing' do you mean minimum ignition advance ? When you say you get the mixture right first, does that mean using fixed advance at certain revs? Or do you tune the carburation right across the usable rev range and throttle openings using fixed advance, then work from there finding max torque with the advance curve ? That would make more sense to me.

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I start with a near stock ignition curve first when setting the fuel mixture.

When I say minimum timing I an referring to the total timing at that particular rpm. The final curve is made up of the timing figures that produced the best torque at each rpm. I normally test at 500 rpm intervals and use no more timing advance than is necessary to produce maximum torque. Jim

Bare with me on this . Combustion ...taking this subject a little deeper.
I hope i can get my question over and understandable....so here it is ...At tick over ,with the throttle valve almost closed .a small amount of air/fuel us drawn into the cylinder ..this mixture is only a fraction of the area inside the available area.. i assume the rest of the area is a void? well there cannot be air in this..otherwise the mixture will be diluted to produce a very weak mixture..so what happens to the fuel droplets that migrate into this none oxygenated area? As we now the size and shape of fuel droplets determine the burn rate plus the speed they pickup oxygen ..so again i ask do these fuel drops just go un-burned?

john robert bould said:

Bare with me on this . Combustion ...taking this subject a little deeper.
I hope i can get my question over and understandable....so here it is ...At tick over ,with the throttle valve almost closed .a small amount of air/fuel us drawn into the cylinder ..this mixture is only a fraction of the area inside the available area.. i assume the rest of the area is a void? well there cannot be air in this..otherwise the mixture will be diluted to produce a very weak mixture..so what happens to the fuel droplets that migrate into this none oxygenated area? As we now the size and shape of fuel droplets determine the burn rate plus the speed they pickup oxygen ..so again i ask do these fuel drops just go un-burned?

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The fuel air mixture expands throughout the space. There is just less density due to the lower pressure. [lower than ambient pressure until compression]
After compression it is still going to be pressurized to 50 or 60 PSI at the point of ignition and the burn will be complete if there is enough time.

That is where a load sensing ignition has an advantage. If there is low manifold pressure under partially closed throttle positions the timing will be advanced to give the low pressure mixture more time to burn. Jim [just like the vacuum advance on an old car]

'That is where a load sensing ignition has an advantage. If there is low manifold pressure under partially closed throttle positions the timing will be advanced to give the low pressure mixture more time to burn. Jim [just like the vacuum advance on an old car] '

Jim I've always thought that the vacuum advance on a car senses when there is vacuum present and that moves the timing forward. If there is less vacuum (leaner mixture ?) the timing retards ? The VOES switch on the Harley Dynatek 2000 ignition closes if there is less vacuum in the ports, and switches the system to a more retarded advance curve. If you earth the purple wire which normally goes to the VOES switch, the system uses the retarded advance curve. I've never had the you-beaut modern racer, however I understand that the curves are usually switchable from the handle bar.
I sometimes look at the MotoGP Workshop videos on Youtube, they never seem to discuss engine management systems or the effects of changing steering geometry (steering on the throttle). The torque characteristics combined with the gearing and steering are the key issues in getting around fast, smooth and safe.

I have the habit when riding the bike hard, that when coming out of corners I always feed the throttle on early in a deliberate controlled firm fashion, keeping the operation as smooth as possible. If you believe that the faster you get on the gas the quicker you go , you are kidding yourself. If you lose vacuum with fixed timing the bike goes slower. If you've ever raced a two stroke, the effect is much more pronounced and dangerous when it comes on song again.

acotrel said:

'That is where a load sensing ignition has an advantage. If there is low manifold pressure under partially closed throttle positions the timing will be advanced to give the low pressure mixture more time to burn. Jim [just like the vacuum advance on an old car] '

Jim I've always thought that the vacuum advance on a car senses when there is vacuum present and that moves the timing forward. If there is less vacuum (leaner mixture ?) the timing retards ? The VOES switch on the Harley Dynatek 2000 ignition closes if there is less vacuum in the ports, and switches the system to a more retarded advance curve. If you earth the purple wire which normally goes to the VOES switch, the system uses the retarded advance curve. I've never had the you-beaut modern racer, however I understand that the curves are usually switchable from the handle bar.
I sometimes look at the MotoGP Workshop videos on Youtube, they never seem to discuss engine management systems or the effects of changing steering geometry (steering on the throttle). The torque characteristics combined with the gearing and steering are the key issues in getting around fast, smooth and safe.

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Correct -the vacuum advance unit senses low pressure in the manifold. [low pressure, ie pressure below ambient = vacuum]
Low manifold pressure indicates low load so the compressed mixture pressure will be at a lower pressure and the mixture will burn slower.
So the ignition is advanced to give the mixture time to burn. Jim

Remember: Low pressure = high vacuum. Easier to understand that way.

Jaydee

That vacuum advance on older cars allowed them to be more economical when cruising, bay advancing the timing and keeping the power on with less fuel in the cylinders . I wonder if it would be possible for the manufacturers of our electronic ignitions to utilise a MAP sensor as well as a Knock sensor to manage the ignition timing better.
We have just benefited from enlightened discussions on what really happens when fuels "burns" in our engines. Thank you
Dereck

kerinorton said:

That vacuum advance on older cars allowed them to be more economical when cruising, bay advancing the timing and keeping the power on with less fuel in the cylinders . I wonder if it would be possible for the manufacturers of our electronic ignitions to utilise a MAP sensor as well as a Knock sensor to manage the ignition timing better.
We have just benefited from enlightened discussions on what really happens when fuels "burns" in our engines. Thank you
Dereck

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The MSD ignition that I have been using will take an input from a map sensor or a throttle position sensor for load.

Knock sensors are a whole different ballgame and would increase the complexity [and price] by a large margin. Jim

Old distributor hot rodder would block the vacuum retard for more spunk on tap. Hi open throttle flow = low vacuum" numbers" = less pressure drop = hi manifold pressure, ie: negative 12 PSI manifold at idle to only negative 2-3 PSI at WOT.

Btw way just having an ignition that can develop 100kv don't mean it gets even half that potential before tension discharged. To get gap enough to develop 100kv jump may hit rising piston. Above 40kv electrons don't behave straight forward simple confined-defined arc across a gap but also explosive plasma balls and jets occur so spark plug design must be adapted to enhance the plasma effects rather than suppress it.

Some Powerarc models have wires to power or unpower functions to change stored curves that sensor switches of various sorts can trigger. Powerarc also has out put switches to turn other things on/off too. Peel gets both an adjustable vacuum and a boost sensor to snick anti-detonation aids on and off, plus a pop off safety valve. Even ole black box bayahs can get a faster rise advance by switching in some short circuiting resistance between the trigger leads. Buy Jim's Schimdt's Race Book on it.

Looked into various versions of pla$$ma ignitions. Plasma jets gets stronger/faster/bigger the higher PSI, heated denser the mixture medium. Jim and others tell me not to bother but bought a bunch of diodes for a system that don't need other power sources as taps into another dimension's whiplashing, which statement I hope to delay others to try it first. All the various plasma demo's like to show the dramatic increase in plasma size when upping humidity such and sprizting water directly on plugs. Peel's Powerarch will switch on water which might irradiate toast me inside out just before engine parts pass though my groin but what a rush to leave on.


https://www.youtube.com/watch?v=Z6QgG7iORgM
https://www.youtube.com/watch?v=d_rJ5LP4y58
https://www.youtube.com/watch?v=DFi0ysZgVJ0

Btw way just having an ignition that can develop 100kv don't mean it gets even half that potential before tension discharged. To get gap enough to develop 100kv jump may hit rising piston

Actually probably not even 1/4 of the voltage potential is ever needed but the ability to charge the primary side of the coil with 600 volts does make for a lot of current flow through the arc and allow a fast charge /discharge cycle for multiple sparks. Jim

Salt damaged stator.



$15.00 worth of wire, $20.00 worth of high temp rosin and one blister from winding 630 turns of 18 guage wire and the big alternator is back in shape. Jim

I'm sorry to see salt wasting and glad you're so handy to recover but more so that we can get more copper in that space, which Peel may need. 38 amps at 12v = 450 watts, nice though more size that I'd need so may actually fit a DIY stator that's thin enough to cover up. I'm sort of up on alternators after lurking the windmill forums which routinely get destroyed by pressing luck on potting, epoxy, conductor heat loads, wind and lightening. Striking Red Hot Tomale primary.

Jim, Are you saying my Pazon unit advances instantly at tick over, to take account of the low fuel/air? Only strobing it there is no advance at tickover, it appears static untill reving high?

comnoz said:

john robert bould said:

Bare with me on this . Combustion ...taking this subject a little deeper.
I hope i can get my question over and understandable....so here it is ...At tick over ,with the throttle valve almost closed .a small amount of air/fuel us drawn into the cylinder ..this mixture is only a fraction of the area inside the available area.. i assume the rest of the area is a void? well there cannot be air in this..otherwise the mixture will be diluted to produce a very weak mixture..so what happens to the fuel droplets that migrate into this none oxygenated area? As we now the size and shape of fuel droplets determine the burn rate plus the speed they pickup oxygen ..so again i ask do these fuel drops just go un-burned?

Click to expand...

The fuel air mixture expands throughout the space. There is just less density due to the lower pressure. [lower than ambient pressure until compression]
After compression it is still going to be pressurized to 50 or 60 PSI at the point of ignition and the burn will be complete if there is enough time.

That is where a load sensing ignition has an advantage. If there is low manifold pressure under partially closed throttle positions the timing will be advanced to give the low pressure mixture more time to burn. Jim [just like the vacuum advance on an old car]

Click to expand...

I've been under the impression that absence of vacuum ( absence of low manifold pressure) at large throttle openings causes lean mixture and if it happens when the ignition system is still advanced you get detonation. So if you have the bike under load and whack the throttle open, you lose vacuum so that is when you get detonation and thus need retard. While you have high air flow through the carburettor you have full atomisation occurring, when you whack the throttle open the air velocity drops so atomisation in the carb body is less. In all cases the balance between comp.ratio, ignition advance and mixture must be kept within fairly close limits, so ideally the combustion event stays with max pressure developed at about the same piston position regardless of the revs, load, throttle opening.
Approx. how long does the combustion event take with petrol to reach max pressure in a commando engine at standard comp ? Or put another way how many degrees crank rotation does it take from spark to max pressure in most cases ? My feeling is that at a fixed comp. ratio it stays fairly constant at all advance settings. I would have thought that it would reach max pressure about ten degrees past TDC, so for a standard commando on petrol using 28 degrees static advance the combustion event would take 38 degrees crank rotation, for the max pressure to be reached at about 3000 RPM. And the time the mechanicals allow for that to happen decreases as the revs rise. Thus the need for the curve ? I think the ideal shape can be calculated, and then the ideal advance at the 500 RPM steps up through the rev range can be set by programming from the theory.
The algorithm is the same one used for converting degrees crank rotation to distance of the piston from TDC with an addition of a bit for the fixed time combustion event. (a sine wave).