Anyone thought about a diesel bike?

Discussion in 'Motorized Bicycle General Discussion' started by LongboardMalinois, Sep 9, 2015.

  1. LongboardMalinois

    LongboardMalinois New Member

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    Lately i have been researching the laws surrounding MBs, and i started noticing that all the laws clearly state that they are regarding any bicycle with an attached gasoline engine. I have been thinking that if i could build a diesel MB it might be a loophole through a lot of those laws. So, i decided that i am going to buy a cheap ebay china girl and attempt to convert it to diesel. The first step would be hugely increasing the compression, so maybe a custom machined head with a very small chamber volume would be a start, and then i will have to change the ignition system to a glow plug type ignition, and then there is the carburetor. If anyone here has experience with diesel carburetors i would appreciate any ideas on how to convert a gasoline carb to work on diesel, and if it could even be done.
    Thanks everyone!
     
  2. 2door

    2door Moderator
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  3. LongboardMalinois

    LongboardMalinois New Member

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    Thanks! I will read that article!
     
  4. Agreen

    Agreen Member

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    Diesel carburetors...

    Glow plug ignition...

    I don't like being a nay-sayer, but it's not going to work. Converting a china girl to diesel is not impossible, but extremely impractical. It's like converting a cat to a dog.

    But let me explain a couple things first. (I'm really not trying to be a jerk here, I genuinely want to help!)

    Diesel engines don't have a carburetor. They can't. Diesel engines control the speed of the engine by fuel flow, not air flow. As a matter of fact, diesels don't even have a throttle plate! That's why cars and trucks with diesel engines have to use power steering assist brakes. Gasoline engines create vacuum when the throttle isn't fully open, so the brake booster uses vacuum to assist the brake force. Diesels don't have a throttle, so at any speed the manifold pressure is always zero.

    So how do you control speed with fuel flow? Diesel engines use a very special high pressure fuel pump called an injection pump. It pressurized the fuel to somewhere between 3000 to 15,000 psi (depending on the engine or manufacturers) and a port gets uncovered at the right time to deliver the high pressure fuel to a poppet valve, known as an injector. The injector is positioned directly in the combustion chamber. Fuel flow is throttled through a valve, and engine speed is directly related to fuel.

    At idle, there is very little fuel flow. There's a lot of air, and not a lot of fuel. That's why they're so loud at idle. That clackety clackety noise is detonation! But don't worry, the engine is designed to handle it! They have BEEFY components. Cast iron cylinder blocks, huge cooling channels, cast iron heads, mega-beef conrod, etc. They're beasts. That's why they last forever! Plus, the fuel is an awesome lubricant, so it gets lubricated from both sides of the piston as well.

    As far as ignition is concerned, it's as easy as it gets. The compression ratio is in the neighborhood of 25:1. So when the air is drawn in, it fills the chamber with ONLY fresh air. No fuel. The piston starts heading up and compresses the bejeezus out of the air, which superheats the air. So hot. The injection pump sends fuel to the poppet, and a blast of atomized diesel comes rushing in to the hot air. Boom. And the rest of the cycle is the same for gas 4 strokes.

    Glow plugs are used to preheat the air coming in so it makes the engine easier to start cold. It does not sit in the combustion chamber. It's in the intake.

    Now, you may ask "but aren't there 2 stroke diesels?"

    Of course there are. But they utilize a "scavenging air blower", which is effectively a supercharger. It blows exhaust gasses out the exhaust ports so that the piston only has to compress fresh air.

    So there. MAJOR differences, and not too practical to try and figure out on a bicycle.

    I hope this has been educational for everyone reading.

    I like your way of thinking, though, longboard. If you can find a small diesel (they're out there) then you may be on to something...
     
  5. Davezilla

    Davezilla New Member

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    Very well said...

    About all I could add would be on the 2 stroke diesels, you could look more into how small model glow fuel engines work and try to up scale it, but glow fuel engines also tend to have a size limit where they can't perform as well, this is mainly because these use glow heads, not glow plugs, there's a wire coil heating element in the combustion chamber and it needs some electrical current to heat up the glow head then the engine can be started, and once the engine is running, the glow is maintained by the super heating of the air in the combustion stroke from the previous compression stroke.... this is why they are size limited as it takes some really high rpm to maintain this glow, we're talking in the 25000 to 35000 rpm range so this means a really short stroke to keep piston speed in check, so these engines are rarely larger than 1/2 cubic inch. Glow fuel is basically methanol and castor oil blended together so it's not exactly cheap which also makes a 49 or 66cc glow engine even more impractical...
    This would be the closest thing to a true diesel 2 stroke as the engines are typically piston port or they use a hollow crank with the opening at just the right moment similar to a rotary valve, they burn their fuel by compression heat except this heat also keeps a wire red hot inside the combustion chamber and the other exception is that the fuel is metered in thru a needle valve making throttling a different story as well.

    If I was to build a diesel bicycle, I would look for a 4 to 6 hp 4 stroke diesel engine and take it from there as a 4hp diesel will have an output similar to a 6 or 7hp 4 stroke gas engine, the reason for this is because of the diesel's superior torque and that they make most their power at a much lower rpm, but with the right gearing to take advantage of this torque, you could still make a very fast bike that could both out accelerate and out run a gasoline powered bike of similar horsepower.
    This doesn't come without its disadvantages tho... diesel engines are heavy, bulky, and messy, not to mention more expensive in most cases. They typically have a narrow rpm range and a narrow powerband. A small diesel engine can usually rev to about 4500 rpm and make peak power at 2500 to 3500 rpm depending on displacement...
     
  6. LongboardMalinois

    LongboardMalinois New Member

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    Thanks, Agreen for all the information about diesels and how they work! I guess i revealed how completely ignorant i am about diesel engines haha. But now i have my mind set that i will build a diesel MB and see how many laws it circumvents. So if anyone knows of a small diesel that will fit into a bike somehow let me know! Another good possibility would be any fuel other than gasoline that one of these engines can burn without modifications. I think that alternative fuels are a loophole through the laws that hasn't yet been used. I wonder if one of these engines could burn nitro racing fuel? It would be expensive, but it would also be fast! I will keep everyone posted on how the diesel MB build is going once i get the engine.
     
  7. TheEwaffle

    TheEwaffle New Member

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  8. LongboardMalinois

    LongboardMalinois New Member

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  9. Tony01

    Tony01 Active Member

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    I suggest you look into Diesel engines converted from nitro glow engines in rc airplanes. I used to have a Norvel .061ci/1cc BigMig engine I converted to diesel by changing the head to one with only a compression ratio adjustment. The ignition happened by the rapid compression of the diesel fuel. The fuel itself was very expensive however, having a special mix for small 2-strokes with lots of ether, designed for ignition by compression. The same carburetor and exhaust were used and the engine proved far torquier. IIRC on nitro it liked a 5.5x3 prop, with the diesel conversion I was able to swing a 7" diameter prop.

    The conversion head and fuel were manufactured by Davis Diesel.
     
  10. Scol

    Scol Member

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    Over the side of the pond we use different colours of Diesel.
    Green for farm macherery and it's 2/3 the price of white dur to the
    Tax rate been different.

    What about trying to mod a small diesel motor first ??? and then I
    could get to work on the green stuff !!!
     
  11. Ludwig II

    Ludwig II Well-Known Member

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  12. TheNecromancer13

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    My uncle once showed me a really old model airplane with a tiny 2 stroke diesel engine on it, might look to those for inspiration.
     
  13. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    To clear up a few things.
    Glow engines, (model plane) are semi diesel, and the glow head or plug is only used to start them. They can be 2 or 4 strokes. They stay running because the combination of compression and catalytic reaction between the platinum of the glow element and the alcohol in the fuel keeps the element lit- not from being 'super heated'. They can be run as low as 2000 rpm, some idle lower.

    Model engines that are full diesel start and run using compression only, most with an adjustable combustion chamber, which helps with starting. These run on a combination of ether, oil, and sometimes some other additives.

    Once r/c guys get to a certain size (usually) they go to guess what? Small ignition engines like those in weedwackers/chain saws, ect .

    Just thought I'd clear that up....now back to your regularly schedualed thread.
     
    #13 Bikeguy Joe, Nov 7, 2015
    Last edited: Nov 7, 2015
  14. WECSOG

    WECSOG Member

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    I've thought about it, but there aren't many diesel engines available that would fit in a bicycle frame. And as mentioned, a China Girl would be too difficult to convert and would never stand up to the stress. If I were gonna try to convert something, I would start with the 79cc Predator 4 stroke.
    But here's another idea: convert a China Girl to distillate/kerosene. All you have to do to convert a gasoline engine is reduce the compression ratio to around 4.5 or 5:1 and preheat the intake tract. The China Girl might already have low enough compression, but if not you could just add a second head gasket.
    Route the exhaust so that it preheats the intake.
    You will still need to start on gasoline, or use something like naphtha with premix oil. Just put it in a small can like a metal brake fluid can or whatever, and connect it to the fuel line via a two-way fuel petcock.
    In some areas of the world (Sierra Leone comes to mind) the same utility engines we get as 2 and 4 stroke gasoline engines are sold in modified form as kerosene engines. The 2 strokes usually use straight kerosene (no premix) because kerosene has lubricity without adding oil. I would probably still add a bit of oil though, just to be on the safe side. Or better yet, use diesel fuel with added oil. That way they can't charge you with running untaxed fuel.

    Btw, the engine will make less power running this way. If it makes 3 hp in standard trim, it will probably only make 2 hp converted to kerosene.
     
  15. Ryoskate

    Ryoskate New Member

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    There is a guy in NZ that builds drome racers that did this. He's over on Rat Rod Bikes forum.
     
  16. LongboardMalinois

    LongboardMalinois New Member

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    WECSOG, thank you for your input on converting to kerosene! I will look into that idea further! I have been wondering if there is an alternative fuel which can be used without modifications to the engine, and nitromethane and ethanol come to mind. What does everyone think about trying to run a china girl on nitromethane or ethanol? I might try some E85 ethanol/gas mixture fuel just to see if the china girl will run it.
     
    #16 LongboardMalinois, Dec 2, 2015
    Last edited: Dec 2, 2015
  17. Ludwig II

    Ludwig II Well-Known Member

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    How many of you know about the hot bulb or hot tube engine? The earliest i/c engines had a chamber leading off the cylinder head, preheated and then kept hot by combustion itself. This sort of engine had the advantage of being able to burn most flammable liquids.

    It's most commonly known as an industrial or farm engine but it was used on tractors and the like as well.

    https://www.youtube.com/watch?v=z2hd2sHAPvs

    In Britain, the mixed petrol and diesel from wrongly fueled cars is bought by canal boat owners with vintage Bolinder and suchlike engines, so you could reasonably find a source of fuel from your local breakdown contractors who have to find a legal and safe way of disposing of the mixture.
     
    #17 Ludwig II, Dec 2, 2015
    Last edited: Dec 2, 2015
  18. WECSOG

    WECSOG Member

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    I wouldn't do that. Certainly not without majorly drilling out the jets to double fuel flow; and even then I predict you will stick the piston in the bore.
     
  19. Greg58

    Greg58 Well-Known Member

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    The thread below was started by a member that did a diesel bike, his 2 stroke build was nice also.
    WOW ! I thought I was on my own... By member Dougy
     
    #19 Greg58, Dec 2, 2015
    Last edited: Dec 2, 2015
  20. WECSOG

    WECSOG Member

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    Link? dnut
     

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