Half a croissant, on a plate, with a sign in front of it saying '50c'
h a l f b a k e r y
Get half a life.

idea: add, search, annotate, link, view, overview, recent, by name, random

meta: news, help, about, links, report a problem

account: browse anonymously, or get an account and write.

user:
pass:
register,


                                 

Thunderheads

High-voltage ignition
  (+4, -2)
(+4, -2)
  [vote for,
against]

In a normal gasoline engine, the fuel is ignited by the use of an electric spark generating device, which you probably all recognize as the spark plug. The problem with the spark plug is that, generally speaking, the spark generated is very small and localized (in a poor location no less), which tends to promote uneven and incomplete combustion of the fuel, draining effeciency and causing pollution.

The obvious solution is to make a larger spark--something the spark plug manufacturers know and already promote when selling their products, but they are still limited by the need to have both electrodes on the same plug.

The automotive branch of 5E Inc. has found a solution. By locating the positive side on the cylinder head and the ground on the piston, an enormous spark can be generated, which spans the entire height of the combustion chamber. The result is combustion that is faster, more complete, and more uniform than possible with any spark plug.

Locating one electrode on the piston is not an easy task on the surface, but since it is the ground end, we need only ensure that the pistons and crankshaft are conductive (usually being made of steel or aluminum this is a non-issue), and ground the entire crankshaft by placing a simple brush-type contact at a convinient location. Furthermore, the insides of the cylinders are given a thin ceramic or other insulative coating to ensure the spark does not inadvertently ground to the engine block.

The positive electrode, on the cylinder head, is a simple modification of the conventional spark plug, except that due to its decreased complexity it can be made much smaller, allowing much more room for valves on the cylinder head and further improving power.

The difficulty of course is that a larger spark requires greater voltage to be generated. However, since the auto industry is quickly moving towards a 42-volt electrical standard (rather than the current 12), this should present little problem.

5th Earth, Jun 24 2005

42-volt standard http://www.caraudio...res/0307cae_42volt/
article extolling the other virtues therof [5th Earth, Jun 24 2005]

Saab Engine Closup http://us1.webpubli...les/i7/0766_7mg.jpg
[jhomrighaus, Aug 07 2006]

Whole Article on Saab SCC http://autospeed.dr...A_0766/article.html
[jhomrighaus, Aug 07 2006]

[link]






       The fuel economy would probably go way down. A large spark would, I imagine, need a larger amount of gas to ignite in order to actually make the larger spark be more efficient. Also, the gas doesn't just swim through the chamber, haveing gas throughout the chamber would cause problems. It needs to be below the pistons so that the explosion moves them. Having the charge go throughout would be unnecessary. Also, a larger alternator would be needed to keep up the charge of the larger battery and that would also bog down the motor.   

       Then again, I could be wrong on all of this. My finite knowledge on automobiles is somewhat limited. This is all speculation.   

       A larger spark does not require more fuel to be more efficient--if anything, it requires less, because with more of the fuel being burned (that's the theory anyway), less is needed for the same power output.   

       "Also, the gas doesn't just swim through the chamber, haveing gas throughout the chamber would cause problems. It needs to be below the pistons so that the explosion moves them." --I don't understand what you mean. Could you clarify this? Fuel injection is unaltered--gas is sprayed into the cylinder forming an (ideally) uniform air-fuel mixture, which is then compressed and ignited, just like a normal motor. The only difference is the spark.   

       The larger alternator and battery shouldn't be necessary. At least, not any larger than already required--IF larger is required--than the standard 42 volt system already being implement by automakers, which general consensus seems to be are a significant improvement. Since you only need voltage and not amperage to create a longer spark, the actual drain on the battery does not increase (capacity is only related to amperage). To quote my link: "As voltage levels rise, however, the higher voltage can more readily jump the air gap between electrical conductors and 'arc.' Arcing in a 42-volt environment is a much bigger headache than 12/14-volt systems --the energy in the arcs is much higher." In their context it's supposed to be a bad thing, but for my purposes it's good.
5th Earth, Jun 24 2005
  

       The gasses in a cylinder create a lot of resistance compared to air. One rule of thumb is that each centimeter the spark jumps represents 10,000 volts (in air). You would probably need about 30,000 volts or more in this system, compared with the relatively short spark gap of a regular spark plug. Also, a certain ammount of current would be needed to make a significantly hot spark to ignite the air/fuel.   

       It would probably be best for the spark to begin around the edge of the chamber, not the center. One idea would be to jump the spark between the head and the block, with an extra thick gasket in between.
discontinuuity, Jun 24 2005
  

       Get rid of the spark altogether and raise the compression ratio way, way up to, like, 22:1, and just have the heat of compression ignite the fuel at just the right point. You might need to use a bit less volatile fuel than gasoline, though, to prevent premature or unsynchronized combustion. Maybe kerosene can work. When running, it might sound like thunder or, at least, like marbles thundering about in the engine.
bristolz, Jun 24 2005
  

       I stand corrected   

       As for the "Also, the gas doesn't just swim through the chamber, haveing gas throughout the chamber would cause problems. It needs to be below the pistons so that the explosion moves them." part- I had misread your description. I had interpreted the description to mean that the grounding aspect would allow current to go from two places. I was thinking your idea was to, basically, have two small combustions on each side of the piston which seemed very problematic as the crankshaft would be affected. Clearly, that is really not what you meant at all. I was envisioning two whole sets of wiring systems two run two sets of sparkplugs, one on each side of the piston. As I said, it is clearly not what you meant.   

       Since most of what I said was based in that false mindset then it dosen't really have any relevence. I apologize if it insulted or offended you. I didn't understand what you said and that is my error.   

       However, I do believe you would still need a bigger battery. and alternator. The amperage would likely stay the same but the alternator would need to keep up with the 36 volt battery to maintain the charge in the system. This might be trivial though because the extra power generated by the engine in your system might make up for the increased alternator activity.   

       Hey, [bz], is your last name Diesel?
angel, Jun 24 2005
  

       [Rasberry]--point taken. Actually, I just looked up some numbers and apparently normal spark plugs already run anywhere from 50kV to 100kV, so I may need even more than that.   

       Jumping the spark at the edge might work better, but it isn't as conceptually cool ;)   

       [Bristolz], I think I may have heard of something like that before--started with a "D"... "dee-zul" or somthing like that... ;)   

       [Acrimonious], no worries, I'm no offended at all--I don't post here expecting to have no criticism. I was merely confused, and wanted to be able to address your concerns.   

       As for the alternator, well, you may be right. I've no argument for that other than to say "I disagree", which is no argument at all.
5th Earth, Jun 24 2005
  

       I don't think the power required for the spark is anything to worry about, but the reliability would be.   

       The spark in your scheme would go through the piston, and across the gudgeon pin and big end bearing. I don't know if this would gradually cause a problem.   

       An alternative idea might be to spark from a spark plug to the piston head, and return back to another spark plug. Then there are two separate sparks, and the bearing surfaces aren't damaged.
Ling, Jun 24 2005
  

       [Ling], that might work, but you'd have to design it very cleverly--otherwise the spark would just shoot straight from one plug to the other without bothering to go through the piston first.
5th Earth, Jun 25 2005
  

       [5th Earth], the design need not be so clever; just make sure that the total path of the two sparks from plug to piston and back is shorter than plug to plug.
Ling, Jun 25 2005
  

       sorry, this post is long, but i feel it must be said: first off all, people were talking about detonating a homogeneous charge using compression?! diesel engines do NOT do this. in a diesel engine, the squirting of gas into the chamber takes the place of the spark plug igninting a premixture (a homogeneous charge). the injectors squirt around TDC, about the same time spark plugs fire. it is very dificult to shot in a premix of air and fuel and detonate it from compression alone. at least without getting ping/knock. detonating a premix using compression alone would only work if the compression ratio was perfectly set so that the mixture would reach flash point at TDC. this wont work because: 1) engines start cool, then warm up (PV=nRT!!!) and second, you need the bulk of ignition to come AFTER TDC, when your compression ratio is PAST its peak. if your charge ignited at TDC in a normal piston-conrod-crankshaft engine, then bad things would happen. there are ways to avoid this (complicated ones) but it would never be worth it. HOWEVER, the problem i have with the ORIGINAL IDEA here, is that while a big spark arcing from the head to the piston would more uniformly detonate the air, the pressure shock would mainly be forced out radially from the center of the combustion chamber toward the (stationaly) sleeves. i know most of the pressure energy would bounce around untill the net movement of molecules forced a (mobile) piston downward to create mechanical energy, but you would loose a LOT of thermal efficiency in the process (the cyliner sleeves would absorb a lot more heat instead of that heat going to good use). think about a piston going through a power stroke in SUPER slo motion... when a regular spark plug fires a few degrees PAST TDC, a hemisphere of flame starts to propigate from that location. this expanding gas has not touched the piston yet, but the piston feels its effects from the non-yet-flaming gasses transfering the pressure. the piston begins to move down as the flame front continues to advance. one of the most inneficient areas in a combustion chamber is in the top corners where the flame from this expanding ball of fire simply smacks into the cylinder liner (sleeve) the most energy comes from the column of space in the middle of the cylinder, where the molecules have the greatest impact of mechanical advantage on the piston (felt macrospopically as pressure). also, the molecules toward the middle latitude of this hemisphere (think about the south 45th parallel on a globe) ricochet off the sleeve and then collide with the piston in a smaller, but still usefull net force. the particles on the "equator" of this hemisphere of flame dont do much work on the piston at all. this big lightning bolt idea would create an infinite column of "equators" that wouldent be very thermomechanically efficient. when piston heads are designed they make use of geometry that tries to direct an expanding sphere or air to an ELONGATING cylinder of air. some would call this the opposite of a RADIALLY expanding cylinder or air.
auricom_mech, Aug 02 2006
  

       So the original idea is to basically make a larger spark th ignite the air/fuel charge more efficiently? Wht not have the spark plug gap increased to allow for a physically larger spark, increase the voltage (which is already done on every car by the ignition coil, you would only need a coil built for and even higher voltage), and fire the spark more than opnce in a combustion cycle?   

       All of those are easily achived with aftermarket parts already built. MSD boxes fire up to 6 times a cycle and deliver higher voltage than stock systems. They start at about $200 and work on almost any car (4 cyl, even fire 6's, 8 cyl, and 10 cyl). And a larger alternator isn't needed. most factory ignition systems are fused at 7 Amps, and the MSD system uses about 7 Amps at 7000 or 8000 RPM, so the most you should do is replace your fuse with a 10 Amp.
Hunter79764, Aug 03 2006
  

       There are many misconceptions flying about, about how spark plugs work and what makes them better or worse.   

       Having a longer arc does not improve combustion(well it helps but it can hinder performance) You will read about hotter plugs and colder plugs ands changes in gap. The over all goal is to generate as much pressure in the shortest amount of time, AT THE CORRECT MOMENT IN TIME.   

       hotter plugs will lead to premature ignition and cause damage, cold plugs will lead to delayed combustion and loss of power. All of this is dependent on timing, engine compression, RPMS and about a dozen other variables.   

       My overall point is that an ICE is a very complex system and everyone seems to want to pull out single items and claim an improvement, though many of the improvements discussed will harm other parts of the system or will net no increased performance over the orginal design.   

       Oh and see links for Saabs version of this which is Baked.
jhomrighaus, Aug 07 2006
  
      
[annotate]
  


 

back: main index

business  computer  culture  fashion  food  halfbakery  home  other  product  public  science  sport  vehicle