Why the 1200LC is not Twin Spark

[Pullaway]

Seems that the new BMW has lost its spark.

[TheBear]

Seems that the new BMW has lost its spark.

 

[Ou Krokkedil]

Why put to spark plugs, why cant the one just fire 2 times? I am sure with the right computer you can have one spark plug and have 2 sparks from one spark plug.

you will probably have to change the plug every 20k and not 50k but it will be more cost effective

[TheBear]

Why put to spark plugs, why cant the one just fire 2 times? I am sure with the right computer you can have one spark plug and have 2 sparks from one spark plug.

you will probably have to change the plug every 20k and not 50k but it will be more cost effective

If my understanding is correct, it is not so much about the number of sparks but rather the positioning.

[alanB]

Why put to spark plugs, why cant the one just fire 2 times? I am sure with the right computer you can have one spark plug and have 2 sparks from one spark plug.

you will probably have to change the plug every 20k and not 50k but it will be more cost effective

If my understanding is correct, it is not so much about the number of sparks but rather the positioning.

Ja thats right.  Firing the same spark plug twice is useless.  There will be nothing left to burn in the vicinity of the spark at that point.

The problem is that before ignition, the combustion chamber is full of fuel/air mixture - the objective is to burn as much of that mixture as possible during the piston's power stroke, without the mixture all simultaneously self detonating/exploding (which is knock).

Its a complex problem because the mixture ignites at the position of the spark plug and then burns outwards from that in a 3D flame front the spreads throughout the chamber.  That flame front travels at a speed defined by the properties of the fuel used.

Depending on the shape of the chamber, the flame front may or may not reach all the crannies during the piston's power stroke.

The hemispherical head was designed to for this reason, where the spark plug is positioned in the centre of the hemisphere.

Using two spark plugs helps because then the flame front starts in two places simultaneously. and thus the combined flame front can reach further in the same time.

Another thing which makes this quite complex is auto ignition delay.  The unburned mixture in front of the flame front is being compressed by the rapidly expanding  flame front.  All fuel air mixtures have a pressure/temp curve above which the mixture simply all self detonates/explodes which is called knock, and which can destroy an engine.  The mixture in front of the flame front can often be compressed above this self detonating pressure/temp threshold, but there is a delay before it actually explodes, so as long as the flame front reaches all the unburned mixture before then, you will not experience knock even though the auto ignition press/temp was exceeded.  High performance engines all work in this mode and thus are susceptible to knock in some situations.  Twin spark designs are sometimes used to avoid this problem.

[OomD]

Why put to spark plugs, why cant the one just fire 2 times? I am sure with the right computer you can have one spark plug and have 2 sparks from one spark plug.

you will probably have to change the plug every 20k and not 50k but it will be more cost effective

If my understanding is correct, it is not so much about the number of sparks but rather the positioning.

Ja thats right.  Firing the same spark plug twice is useless.  There will be nothing left to burn in the vicinity of the spark at that point.

The problem is that before ignition, the combustion chamber is full of fuel/air mixture - the objective is to burn as much of that mixture as possible during the piston's power stroke, without the mixture all simultaneously self detonating/exploding (which is knock).

Its a complex problem because the mixture ignites at the position of the spark plug and then burns outwards from that in a 3D flame front the spreads throughout the chamber.  That flame front travels at a speed defined by the properties of the fuel used.

Depending on the shape of the chamber, the flame front may or may not reach all the crannies during the piston's power stroke.

The hemispherical head was designed to for this reason, where the spark plug is positioned in the centre of the hemisphere.

Using two spark plugs helps because then the flame front starts in two places simultaneously. and thus the combined flame front can reach further in the same time.

Another thing which makes this quite complex is auto ignition delay.  The unburned mixture in front of the flame front is being compressed by the rapidly expanding  flame front.  All fuel air mixtures have a pressure/temp curve above which the mixture simply all self detonates/explodes which is called knock, and which can destroy an engine.  The mixture in front of the flame front can often be compressed above this self detonating pressure/temp threshold, but there is a delay before it actually explodes, so as long as the flame front reaches all the unburned mixture before then, you will not experience knock even though the auto ignition press/temp was exceeded.  High performance engines all work in this mode and thus are susceptible to knock in some situations.  Twin spark designs are sometimes used to avoid this problem.

Nice and quite informative. Thanks!

[Master Beerkie]

Useless info – twin spark technology was used for the first time in a Alfa Romeo Grand Prix car in 1914

[jaybiker]

That doesn't make the info useless. Many forum readers weren't around in 1914. That even includes me, I didn't learn about ignition and combustion chamber technology until the early 1960's, and it's still new stuff to some who weren't around even then.
But if BMW, or any other manufacturer can revert from twin to single spark through advances in cooling or cylinder head design, or any other research and still achieve efficient engine running, then it's something to be glad about.
Even if their primary concern wasn't easier, less costly maintenance for DIY owners!

[TheBear]

Even if their primary concern wasn't easier, less costly maintenance for DIY owners!

If the cost of two extra spark plugs every 10000 or so km's is a costly problem, that particular owner should perhaps go for another make of vehicle?  Something like this:

 



I have to say, the cost of the two extra plugs does become an issue when you are charged for 4 plugs after a service.  Conversation that followed:

Me:  "I see four plugs on te invoice here?"

Workshop Manager: "That is correct, Sir.  4 plugs"

Me: "But this bike is a 2-cylinder!"

WM (rather condescending): "Yes Sir.  It is because of the twin spark setup of the bike."

Me:  "Really?  This bike is a twin spark?"

WM:  "Yes.  All of these models are twin spark"

Me: "Why did you only replace 2 plugs at the previous service?"

WM: "Uhm ... er .... ahem ... aaah ... impossible!"

Me (rather condescending): "No Sir, this is a DL1000.  It is NOT a twin spark like the DL650.  How are we going to go about the refund?"

WM:  "Uhm ... er ... ahem .... aaah ... hmmm ...."

[2StrokeDan]

Watercooling would have nothing to do with having to have 1 or 2 sparkplugs per cylinder. Cylinder head design and combustion chamber size would.

So, what have changed inside the GS1200 combustion chamber in the evolution from air/oil to watercooling? Where's the Beemer engine boffins?

Either there was a dramatic change, or the twinspark was a sales "foofy".

[TheBear]

Watercooling would have nothing to do with having to have 1 or 2 sparkplugs per cylinder. Cylinder head design and combustion chamber size would.

So, what have changed inside the GS1200 combustion chamber in the evolution from air/oil to watercooling? Where's the Beemer engine boffins?

Either there was a dramatic change, or the twinspark was a sales "foofy".

My guess is that, since they did a complete redesign of the engine, they also did the cylinder heads and combustion chambers.

[jaybiker]

They have actually made a considerable change in the head design, in that the induction/exhaust 'flow' is now 'vertically' across the combustion chamber. Possibly that contributes to more complete and efficient combustion. Also the liquid cooling, may have a bearing on the consistency of combustion chamber cooling even though it doesn't actually circulate through the head.
In any case I doubt whether the engine overall is designed to run any cooler than an air or air/oil design, because the optimum running temperature remains pretty much the same for any gasoline fueled engine. Rather, the objective is to reduce the tendency toward 'localised' hot spots.

Agreed, the additional cost of a couple of extra plugs every 20,000 km isn't such a big issue, although it does seem that the type of plug used in twin spark designs are often a damn sight more costly than the 'cheap, simple ' plugs used in single spark engines. Why should that be? They also tend to be more inaccessible, making access to the plugs a pain in the ass.
But really, my comments are more of a tongue in cheek dig at my perception that bike designers have very little regard to the concerns of the old school home spannerman.


Oh and who was the daft bugger who put the wheels in that bike at the wrong ends? don't they know that for dirt riding the larger wheel goes in front?   

[Pullaway]

The plugs with the resistor in are the more expensive one's. They last much longer and often have to be changed after 60 000km - often less accessible, because you don't need to get to them so often. Good idea to check if you got the plugs with the resistor if you do long intervals between plug changes. With NGK, they got n R before the numbers.

[TheBear]

But really, my comments are more of a tongue in cheek dig at my perception that bike designers have very little regard to the concerns of the old school home spannerman.

No!  Don't be .  I was just taking a tongue-in-cheek dig at your tongue-in-cheek perception. 

[2StrokeDan]

The "R" symbol stands for a spark plug with a certain resistance value, as some ignition designs need to run with resisitor spark plugs.

The expensive ones are 1. the iridium centre/nickel ground electrode ones, which is good for around 80-100 000kms, and 2. the iridium centre/platinum ground electrode
ones, which last considerably longer.

To leave a spark plug in it's thread undisturbed for these amounts of kilometres is potentially asking for trouble, because the threads could "seize' into the cylinder head.
Good to remove them every 30 000kms or so to lubricate the thread.
So, while long life spark plugs are not more expensive over their lifespan than normal ones regarding purchase price, the removal/refitting would add to cost.

[TheBear]

The "R" symbol stands for a spark plug with a certain resistance value, as some ignition designs need to run with resisitor spark plugs.

The expensive ones are 1. the iridium centre/nickel ground electrode ones, which is good for around 80-100 000kms, and 2. the iridium centre/platinum ground electrode
ones, which last considerably longer.

To leave a spark plug in it's thread undisturbed for these amounts of kilometres is potentially asking for trouble, because the threads could "seize' into the cylinder head.
Good to remove them every 30 000kms or so to lubricate the thread.
So, while long life spark plugs are not more expensive over their lifespan than normal ones regarding purchase price, the removal/refitting would add to cost.

+1.