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We all know bio diesel works

  1. Feb 10, 2006 #1
    hey all, so we all know bio diesel works, and im guessing that most of us know what it is and even how to (basicly) make it. you obviously have to use it in diesel engines, thus the name. This must mean that it has a low octane, high cetane make up. my question is, is it possible to just mix the bio diesel with some octane booster from the corner auto parts store and use it as a regular gasoline? if not, can somone explain why, and is there any way to convert a bio diesl to be used in a regular gasoline engine?
  2. jcsd
  3. Feb 10, 2006 #2


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    The octane equivalent rating isn't really the issue, the proper atomization of the fuel for proper combustion would be. A typical diesel injection system would be a thousand psi or higher, a typical gasoline would be fifty psi.

    Also, with the lower compression ratio of a gasoline engine, the efficiency would be low as well in comparison, although the higher energy density may offset that to a certain extent.

    While E85 is being used in FFV gasoline engines, some people in the midwest are reporting success with E95 in diesels. So should one bio-derived fuel be desired to assist in supplanting oil, ethanol has a little better compatibility.
  4. Feb 10, 2006 #3
    so that means that diesel fuel requires the higher psi for atomization? and this just sprung into my head, any ideas about converting a wankel engine into a diesel wankel by adding a turbo or supercharger? im sure other mods would have to be made but, could it be done? (reasonably i mean; of couse anything could be done)
  5. Feb 10, 2006 #4


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    Yes, Diesel engines need high injection pressures for successful atomisation, - Diesel fuel won't burn as a liquid. As an aside, Octane and Cetane numbers aren't telling you anyhing about the content of the fuel, just how knock resistant, or knock prone they are. (You don't want autoignition in a petrol engine, you do in a Diesel engine, as you know!).

    I don't see that there would be an inherent problem in making a Wankel style Diesel engine, but imagine that the ever-present problem of sealing would be excarbated, and it might prove quite an engineering challenge to find a way of getting sufficient trapped mass to get the compression ratio high, but I suppose it could be done! Anyone else?
  6. Feb 10, 2006 #5


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    Well turbos make short work of filling up a wankel, the RX7 proved that well enough. Too bad the quench area made for so many emission problems. Obviously they got it sorted out in the RX8 and its even turbo free, but I'd guess its just begging for one. :smile:

    I think it'd be really tricky to get the engine management software written correctly though for a diesel wankel, at low RPM that could be difficult to get the AR of the turbo to be high enough to pack in enough air to get it to CI. Now one of those european diesel turbos with an interated electric motor to spin up the turbine at low RPMs would be warranted, and I'd think the extra work seems to be of little utility.

    Most diesels are designed for like 300,000 miles of service with iron inserts in the pistons and so on. Much easier to leverage the existing tech, and with the TDI diesels and such making their way over in VWs and MBs they're making the reciprocating engine work very well.
  7. Feb 11, 2006 #6
    hmm ya I read about that somewhere... it was interesting, the reciprocating engine i mean. Just as a passing by question, anyone know why the design for the wankel is a triangle? i mean, i suppose it is simplest and a strong shape, but with like a hexagon couldnt you have 2 times the power with almost the same engine? just drill some more intake and exhaust holes and change the timeing around etc. i havnt like sat down to draw anything so not much thought into this, but it just seems like such a logical step forward to me, just like going from one cylinder to two, etc.
  8. Feb 11, 2006 #7


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    Ayrity - you would need a new shape for the hexagon to rotate around inside of because the way the triangle rotor moves is very odd to begin with. Also, I don't see how you'd get a real effective compression ratio with a hexagonal shape because the difference in length from the points to the middle of the flat areas isn't much.

    Mazda simply increased the number of rotors, the RX7 had 2 and racing versions had as many as 4 rotors. Since the crank makes 3 revolutions for each revolution of the triangle rotor, the 4 rotor was like a 12 cylinder.
  9. Feb 11, 2006 #8
    very true, i didnt think of the compression ratio, i guess to fix that with a different shape, the engine would have to get alot more complex
  10. Feb 16, 2006 #9
    What about using bio-diesel to power a steam engine? Maybe for Large vechiles?
  11. Feb 16, 2006 #10


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    What sort of steam engine? For most vehicles, power density and efficiency are the issues, particularly if you're after a reciprocating engine.
  12. Mar 4, 2006 #11
    nbo10: Depending on the design of the boiler you can use just about any heat source to make steam. So your vehicle must be large enough to carry the boiler, the engine, water and fuel. Do a search on triple expansion engines, both land and marine. Some interesting history there.

    Ayrity: I believe the Wankel is actually a rouleux(sp?). Similar to a triangle but not one. An odd shape that resembles a circle in that all points on the circumference are equidistant from the center.
  13. Mar 14, 2006 #12


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    Diesel cycle in a wankel motor

    Is is possible to create a diesel cycle in a wankel motor without using injectors? I am a student at the University of Pennsylvania and for my senior design project I am attempting to reverse engineer a wankel motor(one designed to run on gasoline) and get it to run on alcohol and in a diesel cycle. I'm sure using injectors is the optimal idea but I don't have the resources to create the necessary injection system. Can I go without the injectors?

    If anyone knows somebody who would like to sponsor me that would be great too
  14. Mar 15, 2006 #13


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    Sounds like a tall project! I'm sure it can be made to work, but I imagine it to be a tad crude. I don't know a great deal about the rotary engine, but control of timing would be my first worry, followed by governing.
  15. Mar 15, 2006 #14


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    rym - can you even achieve the necessary compression ratio to achieve ignition without using a compressor like a turbo/supercharger ahead of the motor?

    Also, alcohol has a higher ignition temperature than gasoline, meaning that you would have a lot of problems without the correct CR to achieve CI, and a glowplug or some other solution would be necessary.

    But as brewnog pointed out, since a CI engine is in effect operating in a detonation condition, the introduction of the fuel becomes the timing for the combustion process. And with the relatively slow rotor speed in a wankel, the timing would be quite important (although seemingly appropriate for a diesel burn).

    Sounds like a project with fundamental problems. Something like a cleaner burning/higher efficiency direct-injection engine running on ethanol/gasoline sounds like a more future ready project where research is warranted.
  16. Apr 24, 2006 #15


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    One problem that I see is pre-ignition, you have to inject the fuel with an injector AFTER you have compressed, otherwise you get pre-ignition (a similar problem is seen in high-compression and/or forced induction gasoline engines called ping). If your fuel ignites before your engine is at the right stage of the cycle bad things will happen.

    Also, for a diesel to work well, it needs to have a compression ratio of about 20:1, so either some heavy duty forced induction or a re-design on the combustion chamber geometry. Also, that kind of compression ratio requires stronger components, which is why reliable diesel engines are so dang heavy.

    Are you going to make your own engine, or try to modify an existing one?

    I think the only way to get an engine to work with compression-ignition and not use injectors is a 2-stroke design, which would be quite a feat in a rotary...
  17. Apr 29, 2006 #16
    A small digression; wouldn't a wankel be splendid for a hydrogen-fueled engine? I was browsing around for a few pages on small submersibles. For prolonged submersion with the infeasibility of very small nuclear reactors a stochiometric mixture of hydrogen and oxygen could be fed (from separate tanks) at the desired manifold pressure.

    The exhaust can be condensed by the cold seawater and fed straight to the sub's ballast tanks, so it doesn't upset bouyancy. Any exhaust that remains gaseous after that can be safely fed back to the engine. Sounds better to me than using a conventional diesel with a CO2 scrubber.

    I think it would have several benefits in the simplicity of the wankel and the safety of no CO poisoning. But unburned H2 must obiously be kept out of the cabin at all costs due to its flammability.
  18. Apr 29, 2006 #17


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    Since the wankel generally has low compression (note that Mazda simply spins their RX8 to 9000RPM and put a turbo on the RX7 to increase power) it will have one drawback to using H2 - it will loose efficiency because of H2s lower energy density, so there's 15% loss compared to gasoline. In a piston engine though, the higher resistance to self-ignition of H2 means that a higher compression ratio can be used and thus a 25% improvement can be had. So for a H2 only engine, a piston engine offers a 50%+ advantage over a wankel.

    That means 50% more range on the same fuel storage, with H2 in a metal hydride approaching the storage-to-range ratio that diesel fuel offers assuming the O2 storage is also included.

    Definitely keep H2 out of the cabin, its ignition range starts at like a 3% mixture!!
  19. May 3, 2006 #18
    What is the calorific value of the bio diesel.
    Can it be altered?
  20. May 10, 2006 #19
    Diesel Wankels

    I have come across several websites that puport to have created diesel wankels. I searched on diesel wankel in Google and came up with several:

    SmartPlugs - Rotary on Diesel


    Quasiturbine> Theory> Wankel Differences

    Hope you find this useful and practical
    William Stewart
    E Z Let Ltd.

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