LPG powered engine

Discussion in 'Gas Engines' started by Marco1, Jun 19, 2010.

  1. Marco1
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    Marco1 Senior Member

    I was wondering if anyone has had first hand experience in LPG conversion on a boat.

    There seem to be comon in Italy, UK and even Malta where LPG is half the price of petrol.

    http://www.marinegasconversions.co.uk/
     
  2. FAST FRED
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    FAST FRED Senior Member

    The usual problem is range, as there are far fewer BTU per gallon .

    The engine life is greatly extended as the fuel burns cleaner .

    On many motor homes the LPG gen sets outlive similar sized diesels .
     
  3. jonr
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    jonr Senior Member

    On cars, it takes a tank, regulator and new carburetor.
     
  4. CDK
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    CDK retired engineer

    For a short time I converted a Glastron Bayflite to LPG.

    Of course propane/butane is an excellent fuel for your boat engine. A smaller range is only true if you calculate by volume, by weight there is no difference with gasoline.

    What made me terminate the experiment was twofold.
    First there are no fuel stations for LPG near the waterside so you have to use bottles and carry these from the trunk of your car to your boat. That makes boating a lot less fun and is bad for your back.

    The other problem is the flow rate. The biggest bottle you can handle contains 10 kg gas. Before you have used half of that, even on a sunny day the evaporation extracts so much heat that the bottle freezes over and there is no gas pressure anymore. The only way to overcome this is to put the bottle upside down, but without a dedicated construction it doesn't stay upside down very long. And after less than an hour you have to switch bottles already.
     
  5. jonr
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    jonr Senior Member

    Yes, normally the liquid is extracted from the tank and then evaporated with heat from engine coolant. Possibly someone could build a refueling trailer that could be moved to a dock where the boat is.

    I'm in the middle of a partial CNG (compressed natural gas) conversion for a car - the tank (3600 psi) is heavy and doesn't hold that much.
     
  6. Marco1
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    Marco1 Senior Member

    Thank you for sharing your experience.
    I must clarify that in Australia if the experiment has to work I could only use what we call "autogas" a mixture of propane and butane for automotive consumption that is priced below half the cost of gasoline. Propane in bottles used for cooking is priced well over the cost of fuel and therefore makes little sense.
    Like in your case we don't have the LPG stations on the water like in Europe and so it is bottles. The bottles I had in mind are the forklift cylinders and I would have two hooked up to the same fuel line in order to minimise cooling.
    Because I have the boat moored at my own jetty and I can drive right to it, the bottles transport when not fun shouldn't be a problem. Also, this would not work if I indended to go out for several days, and is only OK for day trips. I would keep the petrol tank.
    Accepting the limitations of the exercise, my interest is in the accesories necessary to do this safely and that can not be borrowed from automotive conversion. I can easily find a technician that can install and convert the engine to LPG using all the car gear. What remains is for me to find a way to have positive ventilation and gas detectors with sufficiently high sensitivity.
    How did you do yours ?
     
  7. CDK
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    CDK retired engineer

    In my case I used standard gas bottles because they weigh around 25 kg when full, but I filled them from my own 1200 kg tank. I had (and still have) a 90 liters tank from a large Chevy, but lifting that one exceeds my capability.
    I used a single stage Italian pressure regulator with electric "choke", connected to the cooling circuit between the engine block exit and the manifold input. It was very important to run on gasoline to warm up the engine or on LPG with no more than 1/4 throttle, otherwise the water in the single loop of the regulator immediately froze and the engine stopped.

    To inject the gas I made a 2nd venturi placed on top of the carburetor, with a number of small holes just below the smallest diameter. The flame arrester came on top of that, now 35 mm higher. A single injection pipe is also possible, but this setup mixes better. In the hose from the regulator to the injection piece there was a crude limiter valve, a piece of pipe with a screw and a spring.

    I didn't install any gas detectors, but there was a blower with its suction hose reaching almost to the bilge. I wired that directly to the ignition supply lead so it was always working while the engine was running.
    My gas bottles were in the open.

    In a cabin cruiser with gas bottles below deck I probably would install a gas detector near the floor, wired directly to the battery.
     
  8. powerabout
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    powerabout Senior Member

    using an explosive fuel that is heavier then air in a boat?
     
  9. jonr
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    jonr Senior Member

    That's as crazy as using gasoline/petrol.
     
  10. powerabout
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    powerabout Senior Member

    You would think that yet in the 80's when I was in business in Australia diesel powered boats were the highest risk catagory for insurance companies.
    Hot turbos and fuel/oil under pressure....no boom but instant fire

    Remember the old story of spilling fuel on your hot exhaust as you fill your motorbike and nothing happens..try it with diesel

    The most dramatic demonstration is to put diesel ( rather than test fluid) in to an injector pop tester and hold a cigarette lighter in the injector spray....
     
  11. powerabout
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    powerabout Senior Member

    Explosion proof DC electric motor....that must have cost a few dollars.....
     
  12. CDK
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    CDK retired engineer

    I really wouldn't know.
    U.S. boat builders install such blowers to comply with regulations. Perhaps they use a closed electric motor, I would use an ordinary one because explosion risk at that location is minimal.
     
  13. tom kane
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    tom kane Senior Member

    I do not know why boat builders are so fixed in their ideas about how you build a boat. If you design a boat to run on volatile fuel you design it accordingly. Does it Have to look pretty? Unfortunately the LAW dictates how you shall build a boat which restricts innovation. You can build a safe petrol or gas engined boat if you want to,but no one seemed to think safety important and follow the traditional methods.
     

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  14. Marco1
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    Marco1 Senior Member

    Traditional methods?
    You lost me.
     

  15. tom kane
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    tom kane Senior Member

    The Rules (some) for Building a no-explosive boat.

    Do not have gasoline or LPG tanks under the floorboards or in the motor compartment or inside of the hull of the boat.

    Do not have any parts (carb,pumps,fuel lines) of the fuel reticulation system inside of the hull of the boat.

    Do... have fuel storage and reticulation systems and crank case gases isolated from venting and draining into the hull of the boat.

    Do... have all parts of the fuel system vented and drained outside of the hull.
     
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