A spark plug generates a tiny spark inside the plug itself and the heat of this discharge ignites the fuel. The flame travels through the fuel air charge until most of it is ignited. On modern engines multiple plugs are used to burn as much fuel as possible.
The spark piston simply grounds the electrode of the spark plug through the crankshaft so that the electrode can be exposed in the cylinder. The electricity arcs from the electrode through the fuel air mixture to the top of the piston. This will require a much higher voltage to be carried through the plug but has 3 main advantages: 1. The fuel is ignited from the center and burns evenly 2. The cylinder will always ignite at exactly top-dead-center if the voltage is correct 3. It should last longer because of the lower tolerances. Normally as an electrode sublimates (?) the gap between the electrode and housing gets too large and the plug stops firing. In this system even if the electrode does decay some the huge spark will allow it to keep firing until the electrode is completely gone in 200,000 miles or so.
Obviously the whole thing will be powered by magnetos because magnetos are just better.-- DIYMatt, Oct 22 2012 Dual Ignition http://en.wikipedia.../wiki/Dual_ignitionNot really a new thing ... [8th of 7, Oct 22 2012] Crackle, crackle, OW! http://i1-news.soft...s-Tasers-Buzz-2.jpg [DIYMatt, Oct 23 2012] Zeus tag For more info on volts and amps [ytk, Oct 23 2012] // The cylinder will always ignite at exactly top- dead-center if the voltage is correct//
If you mean that, with the right voltage, a spark will always happen only when the piston is a given distance from the top, I would disagree. The breakdown of an insulating medium (like air, or an air/fuel mixture) depends to a considerable extent on things such as humidity and on the precise arrangement of particles (eg droplets or dust) in it.
Thus, at a given fixed voltage, a spark may happen when the gap is 1cm, or it may not happen until the gap is 0.8cm.
Also, do you always want ignition at TDC? I thought a lot of effort went into modifying the timing according to the speed and load on the engine?
That's not to say, though, that a long spark as you suggest isn't a good idea.-- MaxwellBuchanan, Oct 22 2012 You'll need to jack the amperage through the roof, since the piston head, rod, crankshaft, engine block, etc. is all one big conductive medium. The grounding element on a conventional spark plug is tiny, so it doesn't take much juice to build up the resistance needed for a snappy little spark. Your proposed method would require components and energy levels more akin to a small arc welder.-- Alterother, Oct 22 2012 //A spark plug generates a tiny spark inside the plug itself and the heat of this discharge ignites the fuel.//
No, it doesn't. It lights the fuel/air mixture directly by means of an electric spark.
//The spark piston simply grounds the electrode of the spark plug through the crankshaft//
This is already the case. Take a look at a picture of a spark plug. Notice how one of the electrodes comes down from the part that screws into the cylinder? That's a ground connection right there.
//so that the electrode can be exposed in the cylinder//
Again, it already is.
//The electricity arcs from the electrode through the fuel air mixture to the top of the piston.//
No, it follows the shortest possible path. Every single part of the cylinder is grounded, so it'll simply jump to the nearest part of the cylinder—assuming there's enough voltage to create any spark at all given the increased resistance.
I think you're greatly confused about how an ignition system works here.-- ytk, Oct 22 2012 // On modern engines multiple plugs are used to burn as much fuel as possible //
"modern" ?
Errr .. dual-plug (magneto) ignition in aero engines have been around for a very long time ... like about a hundred of your Earth years ...
// magnetos are just better//
Immediate bun.-- 8th of 7, Oct 22 2012 ^nothing about that statement was wrong though, was it?-- DIYMatt, Oct 23 2012 What, about magnetos just being better? Yes, quite a lot, but it seemed a bit unsporting to go there.
But since you asked… Magnetos have mostly disadvantages compared to electronic ignition. The only real advantage they have is reliability (although all told, you're probably still better off using a dual ignition system, even with a single spark plug). That's great for aviation. If your primary concern does /not/ happen to be keeping yourself from falling out of the sky, however, you're probably better off using something a bit less… crude.-- ytk, Oct 23 2012 As someone who's had an alternator fail on the highway in my car (in the middle of effing nowhere), I would much prefer dual magnetos to electronic ignition, disadvantages by damned! My last comment was actually about the "modern" part though. Just because aviation engines have had dual ignition for decades doesn't mean that it isn't just now making a comeback in cars.-- DIYMatt, Oct 23 2012 I also have to add that a taser manages to arc electricity over a long distance by using tens of thousands of volts, at very low amperage.-- DIYMatt, Oct 23 2012 //As someone who's had an alternator fail on the highway in my car (in the middle of effing nowhere), I would much prefer dual magnetos to electronic ignition, disadvantages by damned!//
The “disadvantages” here are a vast reduction in power and fuel economy, and a significant increase in pollution output. Is driving a slow, smoggy gas guzzler really worth the added convenience of not having to call for a tow in the unlikely event of one specific type of failure, among the many that could happen regardless?
Incidentally, I gather that you made it back from your mishap. If you had been flying, you might not have been so lucky. /That/ is a justification for using magnetos. Not having to carry a AAA card, on the other hand…
//I also have to add that a taser manages to arc electricity over a long distance by using tens of thousands of volts, at very low amperage.//
I've explained this here before, but suffice it to say that you can't actually adjust volts and amps independently of each other for a fixed resistance. What you're saying doesn't make any sense. Regardless, a taser does not “arc electricity over a long distance”. It actually shoots out a pair of electrical leads, both of which must make physical contact with the target for it to have any effect.
The bottom line is this: Electricity always follows the shortest path to ground. Apart from removing the ground on the cylinders (good luck) or insulating the inside of the cylinder (theoretically possible, but hardly worth the massive added cost), you can do nothing about the fact that current will flow between the electrode and the nearest path to ground, i.e., the nearest cylinder wall or the piston itself. You simply can't get electricity to flow where it wouldn't otherwise want to go.-- ytk, Oct 23 2012 Since the distance from the center of the piston to the cylinder wall will typically be larger than the distance between the spark plug and the top of the piston at tdc, the electricity should arc to the piston first, correct? The only thing that needs to be insulated is the cylinder head right beside the plug. See my taser link for an example of what I was talking about.-- DIYMatt, Oct 23 2012 You'd still need a massively high voltage in order to do so. And it's not even clear that there'd be any advantage to it. Spark plugs work best when the gap is of a very specific size. Any larger or smaller and they become less efficient. Making the effective gap larger is going to create a /less/ controlled burn, because you're not going to know exactly how the spark will travel through the air/fuel mixture for any given spark. Regularity and repeatability are the keys to engine performance, not just making things bigger.
I'm still not sure what problem you're trying to solve. It seems from your original post you were simply describing some nonexistent problems stemming from your misunderstanding of ignition systems, and then attempting to “solve” them by proposing an existing technology, i.e., a spark plug.
//See my taser link for an example of what I was talking about.//
It's just a very high voltage. Higher voltage necessarily equals higher amperage. You can't adjust those two variables independently of each other. Saying “increase the voltage but decrease the amperage” is illogical (assuming a fixed resistance).
Tasers work (or don't work, depending on your point of view) by reducing the duty cycle significantly. The voltage (and thus the amperage) is very high, but only for a brief enough period of time that (hopefully) it won't prove fatal.-- ytk, Oct 23 2012 obscene voltages [+]-- Voice, Oct 23 2012 So you'd have stalactites coming down from the cylinder head (and possibly the other ones up from the piston crown). Each spike would have to be insulated where it perforated the cylinder head, be insulated on the inside from same and, unless you want all your spark going through just one spike, be individually addressed by the ignition system. I'm not sure how it would be simpler than the current system, though perhaps you might have less wear and tear on 5-6 spikes than you would on 1 spark-plug electrode.
//Saying “increase the voltage but decrease the amperage” is illogical //
<Spock> Hey, don't pin that one on me dude</S>-- FlyingToaster, Oct 23 2012 // Higher voltage necessarily equals higher amperage.//Explain, please.-- AbsintheWithoutLeave, Oct 23 2012 // // Higher voltage necessarily equals higher amperage.// Explain, please.//
Ohm's law: amperage = voltage / resistance
So, for example, doubling voltage without changing resistance doubles amperage. Doubling resistance without changing voltage halves amperage.-- CraigD, Oct 23 2012 //Explain, please.//
I've linked to an idea where I've explained this in greater depth (just look for the really long anno about halfway down the page), but it boils down to what [CraigD] said: Ohm's Law. This is the fundamental law that governs electricity, and it's written as V=IR, or voltage equals current times resistance.
Since it's an equation with three variables, only two of those can be independent, and the third would be calculated from the other two. In the case where the resistance is not adjustable, such as in this idea, it means that only voltage or amperage can be adjusted independently. So increasing the voltage will lead to an increase in amperage, and vice versa.
The main point is that voltage is actually a calculation rather than a specific property, that indicates how much current will flow if a specific material with given electrochemical properties is connected to a specified resistance. So, it can't really be adjusted independently of current, because it both defines and is defined by the rate of current flow.
//Tesla coil//
The Tesla coil, like the Van de Graaff generator, is a constant current device that is capable of generating a high voltage. This means that the voltage is determined by the resistance, unlike most other devices which are constant voltage, such that the current is determined by the resistance. Increase the resistance to a Tesla coil and the output voltage will go up to keep the current at the same level, until the maximum voltage of the coil is reached, at which point current flow would begin to decrease.-- ytk, Oct 23 2012 This is an idea I toyed with a lot a few years ago. The problems that really stuck it for me were:
1) The variations in ignition timing would dramatically change the spark plug gap. Like millimeters change.
2) To keep the gap clean would require it to be "swept" by inlet or exhaust gas, not happening in this scenario.
3) Oil is a good enough insulator that an additional conductor would need to be added somewhere on the piston/con rod/crank. or maybe you would like the spark to find a nice place to arc to the bore. No Bueno.
4) Gap fouls/erodes, a bitch if it cant be easily replaced.-- WcW, Oct 23 2012 Interesting idea.
On the plus side, the spark involved would be huge, many times greater than the improvement in present day multi-point sparkplugs and increased voltage ignitions.
Several previous notes have called out major minus. I think it may not have occurred to the poster how challenging it would be to make only points on the cylinder and piston head, not its walls, be electrodes. You’d have to electrically insulate the cylinders from the rest of the engine, or all of the engine from the electric ground, including from the piston, which in every large engine I’ve ever seen, is sealed with conductive piston rings. The only approach that comes to mind as possibly feasible is to line the cylinder walls and heads with some durable, heat-tolerant non-conductor, likely a ceramic, and insulate the cylinder head from the rest of the engine Since electrical insulators are generally good thermal insulators, this would necessitate nearly all conductive cooling be done via head (and possibly the piston).
Then there’d be the problem of how to get the sparks to spark across their huge gap some sort of well-timed way, which other already notes.
All in all, this sounds like a huge engine redesign challenge, though not beyond the means of a dedicated tinkerer. Would it be worth it, for a huge spark? Could it be made to work at all? Tinkering seems the only practical way to find out.-- CraigD, Oct 23 2012 // Would it be worth it, for a huge spark? //
Not really, since you don't need a huge spark. You're not trying to set off a daisy-cutter here, just ignite a tiny bit of fuel in aerosol form. High-tech spark plugs are actually centered around the concept of delivering smaller, faster sparks.-- Alterother, Oct 23 2012 But again, the question remains—why bother? An engine in good condition emits maybe 1-2% of its input fuel as unburnt hydrocarbons. You're talking about an unnecessarily complicated design that may or may not improve fuel burn (and would likely decrease it, if anything), all for a marginal improvement at best—and it turns out that it's not really an improvement anyway.
You can achieve essentially the same improvement simply by running the engine a bit lean. The key reason for not doing this is it greatly increases temperatures in the combustion chamber, as the extra fuel helps to carry out heat. So there's really no benefit to more complete burning after all. Incomplete burning is actually a feature, not a design flaw.-- ytk, Oct 24 2012 //Ohm's law: amperage = voltage / resistance//
Fine, except that an electrical discharge through gas does not remotely follow Ohm's law. The voltage depends strongly on the length of the spark, but is not directly proportional to current. In fact, for some regions, voltage strongly decreases as current increases.-- spidermother, Oct 27 2012 //Fine, except that an electrical discharge through gas does not remotely follow Ohm's law.//
Of course it does. It's a mathematical relationship. Volts only exist as an abstraction to describe the relationship between current and resistive load.
//The voltage depends strongly on the length of the spark, but is not directly proportional to current. In fact, for some regions, voltage strongly decreases as current increases.//
The only way that could be the case is if the resistance is dropping as well. It is possible that as the gas burns or electricity passes through it, its resistance changes, and modeling that can prove tricky, but at any given instant the properties of the circuit obey Ohm's law. To say otherwise is equivalent to saying 2x2=5.-- ytk, Oct 27 2012 ^this is, in fact, a fundamental operating principle of arc welding. Without a known composition of flux gases, the current of the arc fluctuates too wildly to control the puddle. (Flux gases serve several other purposes as well, including preventing oxygen from getting into the molten metal and spoiling everyone's day.)-- Alterother, Oct 27 2012 Sorry, I should have said that an electrical discharge in a gas does not remotely resemble an ohmic resistance. The voltage of an arc *decreases* with current - which is why arc welders and discharge lights need ballasts - but yes, V = I * R at any instant.-- spidermother, Oct 27 2012 gotta love how me mixing up transformer law with Ohm's law produces 4 pages of annotations.-- FlyingToaster, Oct 27 2012 random, halfbakery