next tesla turbine question
science_geek
Posts: 247
http://www.hobbytron.com/NTE/html/2500to2599/NTE2582.html·i have one of the switching transistors from the supplied link, and i need an arc in the combustion chamber in order to ingite the fuel to start the engine, i thought hey, why not use the prop to start the engine since im using it to monitor the engine, as for creating the arc to start it i was thinking about using several(20ish) photo flash caps all charged and then running the duty cycle from the prop to turn the switching transistor on and off fast enough to create an arc and not completely drain the caps, my question is, will the above transistor handle the current the output of the caps can put out, and can it switch fast enough, i know it says 400v, but with a duty cycle i was wondering if it would fry it, also is there any chance of a stray voltage hitting the prop and frying it
Comments
Do you have any idea of the sort of voltage necessary to create an arc (like across a spark plug) in your combustion chamber? Do you have any idea of the amount of current involved? Do you understand how electronic ignition systems work?
With the amount of knowledge you seem to have about this sort of stuff, you are very likely to fry your Propeller. To produce an ignition spark, you probably need about 40KV, generally produced by an ignition coil from a 250-300V pulse that could be switched by a transistor like the one you have, but more commonly by a thyristor. You probably will want an optoisolator to protect the Propeller from the high voltage in the ignition system.
You might read through some of the artlcles on electronic ignition systems and engine control systems on the Wikipedia. There are some links, including to an "open source" capacitor discharge ignition controller that might be useful.
Post Edited (Mike Green) : 11/10/2008 9:02:25 PM GMT
as far as current, when i used the cap bank with a coil of wire to make a small coil gun, i was getting about 330 to 660 amps depending on which coil i used
as far as electronic ignition systems go, in the case of a small internal combustion engine the shaft of the piston is connected to the crank shaft which is connected to a flywheel with a magnet embedded in it, this magnet moves past a coil generating a current, this current is fed into a spark plug, also known as a high voltage tranformer, this applies a small spark across the electrods of the spark plug ingiting the fuel and causing combustion, since im dealing a type of jet engine the explosion of the fuel does not have to be timed with the movement of a piston but instead ignited at a certain rpm so that the engine can start turning on its own,
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As for the 40KV to produce a spark on a spark plug... I'm pretty sure that is more like 4KV, tops.
Anyway, science_geek, that isn't an electronic ignition system at all... That's an "electrical ignition system" if you want to call it that... An Electronic ignition system is computer controlled and uses computerized timing to dictate when to fire the spark.
as for making my own·circuit i thought it would be easier and cheaper (unless i fry the prop) to do with a prop and transistor, i have used a basic stamp and a relay to pulse a 9 volt battery through several transformers and got it to·shoot lightning bolts through a disposable flash camera bulb, i thought that with the ease of use of the prop already being in·the control system i would add just one more function for·it to do
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It might be helpful to review the workings of a small internal combustion ignition system. Your explanation was incorrect and incomplete. No electricity passes the spark plug until the field collapses, the field doesn't collapse until the points open etc...
Rich H
W9GFO, i understand this about jet ignitors, but the jet i was thinking about making has a combution chamber that is about the size of a 2 liter bottle, not as big as the one real jets use, and im using a gas for a fuel, not an atomized liquid so a spark as large as that used in a real jet engine is not needed, it probably wont be mounted to a plane or anything more than my testing station so a flame out is no big deal, im just trying to prove my cousing wrong and that i can build something if i put my mind to it, as far as my explanation about the ignitor in a small ic engine, it was not incomplete, that is the most basic workings of an ignition system without going into great detail about the electro theory·behind it since im not using that type of igniter, i posted that because mike asked if i knew how the ignition system worked
Rich H
If you must use a spark ignition system and the turbine isn't very big, I bet there's an electronic ignition system available for four-stroke model airplane engines that might be adaptable. There are more and more model jet turbines out there these days as well, take a look at how they start those puppies up.
Tell us more about how you're using the propeller in this application... Block diagram and/or pictures? I've seen home-brew Tesla turbines that receive air or other relatively cool fluids to drive them. I seem to remember internal combustion Tesla turbines are difficult to build as the discs at high temperature and high forces require smoothness and uniformity in order to maintain laminar flow. Materials become the issue.
Good Luck, David
Post Edited (pmrobert) : 11/11/2008 12:05:20 PM GMT
Graham
p.s. an arc and a spark are not the same thing
Also most car ignition coils are operated in a flyback mode.
we have tested and confirmed that the tesla turbine will work for the compressor as it can put out a high volume of air at 20,000+ rpm to sustain a super heated flame, we have tested and confirmed the combustion chamber and have found that a combustion chamber the size of a colemen propane tank will get us a flame that can burn 90% alcohol mixture and sustained by a smooth flow of air, it does get a little hot so we are looking at making it either out of titanium or making a cooling system to cool the outside of the combustion chamber, one thing that we did find out during testing was that if we achieved optimal conditions we could get the vortex to pull away from the outside of the combustion chamber about 1/4 of an inch, which we think may be enough to allow the combustion chamber to cool enough to keep from melting, we also found out that the vortex wasnt as broken up as we thought it would be and that by containing the vortex in a sealed container with one output hole would cause the vortext to give a pretty laminar flow out the output,
we havent been able to finish the engine for 2 main reasons and a few other that arnt that hard to overcome, one of the big reasons is that the temperature coming out of the combustion chamber can easily melt the steel discs we are useing, we found this out by holding one over the output of the combustion chamber and it started to flex and melt, the other is that in order to run this engine for a long time we need to have a turbine chamber that can withstand immense amounts of heat, one solution to this we came up with is a titanium aluminum alloy, and we would get heat sink fins milled into the outside and maybe even look at·liquid cooling, some of the minor things is money and the fact that one of my cousins working with me lives about 4 hours away and doesnt come over often,
the reason for the electrical ignition that i have questioned about is that it is minimaly invasive and a central post coming close to the output of the fuel injector would ignite the fuel very quickly and it wouldnt impede the flow of the vortex created
The part about burning the fuel making the vortex stronger sounds tenuous to me.
Graham