Practical use of MGD

  1. OK, let's try a little "applied physics".

    First, I like to race. Now that the season is over, it's time to use
    the cold winter to find more horsepower. While browsing through my
    large stack of science, engineering and physics books, I stopped with
    a copy of Schaum's Outlines, "Fluid Dynamics, Second Edition".

    Buried in the back of the book was a chapter titled "Compressible Flow -
    MagnetoGasDynamic Channel Flow". Hmmm, that sure sounds like an intake
    port to me! Started reading and fired up my copy of StudyWorks (a small
    version of MathCAD) to see if I could get the equations to work out. The
    theory behind MGD seems to indicate that I'm understanding what's going on,
    at least a little.

    Woe is me! I think that the explanation in the book is incomplete. At
    least to my understanding. Here is what I would like to do. Compute how
    fast the charge in the intake tract would move under how much of a
    magnetic field. I need to see if I can get the flow to accelerate to about
    .6 Mach at less than 4000 RPM and hold that figure up to about 6500 RPM.

    I plotted my current intake speed and I'm about 21% Mach at 4000 RPM (my
    current torque peak). At 3500 - 18%, 3000 - 15.5%, 2500 - 13%.

    I also need to compute how much voltage I need to produce that magnetic
    effect to achieve that .6 Mach.

    I am very sure that at some time in the future, someone will come to visit
    me and find a large crater where my garage used to reside. It will be the
    result of either the failure of one of my "speed experiments" or the success
    of my invention of a space/time warp!

    P.S. I am not above jumping over to the Chemistry forum to see if there is
    a chemical I add to the fuel to increase conductivity (which appears to be one
    of the parameters of MGD). Naturally without decreasing the power produced by
    the fuel. ;-))

    Am I going in a wrong direction? If not, can some one help me?

    P.P.S. I came across this site many years ago but this is the first opportunity I've had to use it so please be patient! ;-))))

  2. jcsd
  3. K^2

    K^2 2,470
    Science Advisor

    Are you trying to accelerate the mixture flow between throttle and intake manifold to increase compression ratio?

    I'm pretty sure that you aren't going to be able to come up with anything that's more efficient than an electric turbine. So a commercial electric supercharger is your best bet.
  4. Bobbywhy

    Bobbywhy 1,908
    Gold Member

    The flow of compressible, electrically conducting gasses of sufficient density will satisfy the continuum assumptions of gasdynamics. That is, the flowing gasses need to be electrically conductive. For example, ionized gas or plasma. Seems to me your fuel-air mixture does not conduct. As far as I can see (not too far) you scheme will not work.

  5. That's why I stated that I would not be adverse to a "chemically induced" increase in conductivity. As long as the chemical does not detract from the combustibility of the fuel. Hmmm, how about if I ionize the air (or gas) prior to mixture? Is that something that could be done relatively easily?

    >>Are you trying to accelerate the mixture flow between throttle and intake manifold to >>increase compression ratio?

    What I'm trying to do is increase Volumetric Efficiency at a lower RPM and maintain the increased VE over a broader RPM band, not really increase the compression ratio. Yes, this would be accelerating the flow between the carb and intake valve, a distance of about 3 1/2 inches. I'm currently at a little over 140 feet per second at 2000 RPM. Even if I could increase that 20%-30% and then maintain that effect up to about 6000-6500 RPM, it would give me a tremendous boost.

    And, truth be told, I'm also trying to be a bit "sneaky" and do something my competitors won't be able to figure out (at least not right away). There's nothing in the rule book to cover something something like this, sooooo, like the old saying goes, "Better to beg forgiveness than ask permission".

  6. K^2

    K^2 2,470
    Science Advisor

    A gas will only be conductive if ionized. I'm not sure if ionizing the air-gasoline mixture is a particularly good idea...
  7. Bobbywhy

    Bobbywhy 1,908
    Gold Member

    As you clearly stated in your opening post, no motive force can be developed unless there is electrical conductivity across the fluid MHD (EGD) channel. Gasoline is a good electrical insulator. Any additives to the fuel to make it conductive may leave a residue after combustion that could interfere with flow through valve openings or otherwise damage the engine. Electrical Conductivity of Fluids was discussed here on PF nearly four years ago:

    In all the below examples the introduction of substances into the liquid was necessary to achieve the desired conductivity to support the MHD effect.

    One of the most cited references in all the literature is a paper by Moffatt called “Field Generation in Electrically Conducting Fluids”

    Electrically Conductive Fluids
    US Patent Number: 5,104,582
    Date of Patent: April 14, 1992
    Magnetic particles dispersed in a carrier fluid by means of a dispersant. The fluid is characterized therein that it also contains an electrolyte, which is held in solution by means of one or more complex-forming substances known as ligands.

    US Patent Number: 5,888,198
    Date of Patent: 30 March 1999
    Isotonic saline (having the same concentration of solutes as the blood)

    In the two cases cited below the sodium and chloride ions in the saltwater act as conductors. When they act as conductors, they also become magnetically charged. This allows the circuit to be completed and the sodium and chloride ions to get pushed out the back therefore creating thrust.

  8. K^2

    K^2 2,470
    Science Advisor

    Bobbywhy, just because fluid is conductive does not make the aerosol or vapors of that fluid conductive. I'm not sure there is a good way to achieve conductivity through air-gasoline mixture without igniting it.
  9. Bobbywhy

    Bobbywhy 1,908
    Gold Member

    Oh, K^2, I certainly agree with you. I can't see any way the proposed scheme could work. Excuse me for not being more clear.

  10. I really appreciate the comments and the thought required behind them. That chapter in the book was only about 2 1/2 pages long and, without some additional background, apparently left a lot to be desired. I was looking for a "edge" and apparently, this is not the way.

    <<Electrical Conductivity of Fluids was discussed here on PF nearly four years ago:

    Yeah, the only info I could find on gasoline was a paper done by Roberts, Roberts and Roberts in 2011. They gave the conductivity for gas at about 25 picoSiemens/meter. Now I know that "pico" is VERY small but not having a point of reference, I couldn't tell if "25" was good or bad.

    <<the two cases cited below the sodium and chloride ions in the saltwater act as <<conductors. When they act as conductors, they also become magnetically charged. <<This allows the circuit to be completed and the sodium and chloride ions to get <<pushed out the back therefore creating thrust.

    One common trick is to add water/alcohol to the mix at higher RPM to cool the mixture so as to avoid detonation from advanced timing or high compression. If I changed that to a SALT water/alcohol mix, do you think that would be sufficient to accelerate the charge flow a bit?

    Like I said, I'm simply looking for an edge. Using a power adder such as a turbo or blower would take me out of "class" and put me where the wallets are bigger. Any other ideas?????

  11. K^2

    K^2 2,470
    Science Advisor

    Again, you are looking for conductivity in the air-gasoline mixture. It's not a liquid state anymore. It's an aerosol in air-vapor mix. Even if your fluid is conductive, that mix will not be. You can't really make it conductive without ionizing it, which would require a spark through the mix, and that will ignite it.
  12. Again, my apologies. I was just curious. I guess I'll just drop the idea. Thanks to you and BobbyWhy for straightening me out. :'-((

  13. I hope you don't mind me bothering you again. I am trying to understand the process here. I looked at all Bobbywhy's links (see above). All I could get from the Moffatt link was a preface to the paper, not much help there. The Evil Mad Scientist link is a hoot! And very informative.

    OK, completely disregard an air/fuel mixture. Let me ask about only salt water (as in the Evil Mad Scientist boat). Now with a 9-volt battery, they say they got the salt water to move, slightly. You seem to be saying that even tho this liquid is conductive, a vapor (steam) composed of the same elements (water and salt) wouldn't be. Would it be a more true statement to say that the vapor/aerosol would be LESS conductive than the liquid? If this statement (or assumption) is incorrect, could you please tell me how the vapor/aerosol LOSES it's conductivity? Would the ionization simply INCREASE the conductivity of the vapor/aerosol or does it ADD conductivity to something that doesn't have any? And, please, in layman's terms. Or is the conductivity a function of the density of the fluid (be it gas or liquid)?

    It's been a LONG time since I've been in school but I am very curious and have nothing against learning. ;-))

    Thanks in advance.

  14. boneh3ad

    boneh3ad 1,609
    Gold Member

    It would lose conductivity because there would be a whole lot of air in between each molecule of salt and water. Air is a good insulator.
  15. K^2

    K^2 2,470
    Science Advisor

    Salt water conducts because ions of salt (Cl- and Na+ if we are talking about table salt) can move around and carry charge. If you have tiny droplets suspended in air, these ions can only move within a droplet. Each droplet is going to be mostly neutral, because positively charged droplets will quickly find negatively charged droplets to merge with. So you end up with nothing that can actually carry charges across air.

    Ionization increases conductivity because you end up with free ions of nitrogen and oxygen actually moving through the air.

    It might be possible to ionize the air a little, as well as have some imbalance in charge on droplets, but the amount of carriers you are going to have is going to be very small, so conductivity is going to be very, very poor. Not quite zero, but small enough to be useless.
  16. boneh3ad

    boneh3ad 1,609
    Gold Member

    Don't forget that the energy required to ionize the air in the first place would likely largely negate any gains in engine energy output from doing what the OP originally intended.

  17. Thank you K^2. That makes it more understandable. So it's really not the density but the form that the density takes. Thank you for clearing this up.

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