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Petrol to lpg

Discussion in 'Members Lounge' started by Little Ghostman, Feb 12, 2017.

  1. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    How difficult is it to convert a small petrol engine to gas? Small as in around 5hp.

    I know cars can run on both, and I am aware you can get kits for this, but how much work would be involved in converting a small engine? Actually its not propane or LPG, I have another gas in mind.

    The google stuff I found is mostly based on cars, what i am not sure about is single cylinder engines and conversion.
     
  2. spec

    spec Well-Known Member Most Helpful Member

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    Hi LG,

    I assume that the engine is a four stroke. I am not sure about converting two stroke engines to run on gas.

    The number of cylinders has no bearing on the matter.

    In the 1970s there was a whole sub-culture of people who built LPG conversions for their cars so, in answer to you question, it is relatively easy, especially if you are considering a stationary engine rather than a car engine. In essence, all you do is squirt gas into the intake of the engine where the carburetor is. To control the gas you use a modified standard gas regulator.

    At one time, I had all the details and I even collected all the necessary bits, but they got lost in one of the house moves.

    I will see if I can get some information for you though.

    spec

    UPDATE: If the engine is essentially a fixed speed and fixed load, as in say a generator, that would make the gas conversion even simpler.
     
  3. JimB

    JimB Super Moderator Most Helpful Member

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    So which gas is it?
    Methane perhaps?

    JimB
     
  4. dave

    Dave New Member

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  5. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    To date, the simplest conversion I've seen.

    Somewhat dangerous in that the connection to the filter box (or the box itself) might leak, creating the attendant safety issues.

    And it assumes a certain gas pressure availability that, if you'll be using methane (or some other homebrew gas), might be difficult to achieve.
     
  6. JonSea

    JonSea Well-Known Member

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    Backup generators for home use often have kits to convert from gasoline (petrol) to natural gas or propane. Research on what's done to make these conversions should turn up info for similar-sized engines.
     
  7. Les Jones

    Les Jones Well-Known Member

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  8. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    Thanks guys, No idea why google gives me so much non relevant results? Only been the last 6 months or so google just throws up rubbish for me. Yes its fixed to certain extent, obviously if load increases then so do the revs. Yes its another generator, this time pretty much home built from what I could find.

    Gas will be Hydrogen or methane, both because mainly I have access to alot of methane, every few weeks I have Hydrogen. Hydrogen is from a commercial unit that splits water for the Oxygen, the hydrogen is vented off, would be nice to actually use it. No idea what the unit was originally for?? I only got half of it, it runs off a small hydro at the bottom of the hill.

    But I guess we can ignore hydrogen for the main part. I have a couple of engines I could use, the generators are from the wind turbines that were taken down, rated for 6KW each but I also have a 3 phase motor. the plate is worn so I dont know the details, its extremely large and heavy and I doubt any of the engines would turn it without a decent gearbox.
     
  9. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    Constant pressure for Methane has been sorted out, eventually solved by water and an IBC container! A container inside a container with one upside down. The upside down one is weighted.
     
  10. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    Oh and yes 4 stroke engine, me and two strokes dont get on that well.
     
  11. tech master 117

    tech master 117 Member

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    well seein ya after such a long time,
    BTW as per your query the only way i can help is that there are some car modders in my locality who do this kind of job,want me to ask them about it??
     
  12. Les Jones

    Les Jones Well-Known Member

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    Hi LG,
    If you can set your regulator to just below zero (With respect to local atmospheric pressure.) then you would not need the regulator. My understanding is they regulate to about zero pressure so that the gas only flows into the carburetor when the pressure in the carburetor is below zero. (The same way it would suck petrol up from the float chamber.) I would imagine that you would feed the gas pipe into the carburetor at near the smallest diameter point.

    Les.
     
  13. spec

    spec Well-Known Member Most Helpful Member

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    Hi Les,
    That's more or less what I was implying in post #2.

    For safety though you need a master gas cut off valve which automatically shuts the gas off if the engine is not running.

    The modified standard gas regulator that I mentioned controls the gas pressure according to inlet manifold depression, so you need a connection to the engine's inlet manifold down stream of the throttle.

    The regulator then controls the gas pressure, and hence gas flow, inversely proportional to inlet manifold depression (a lightly loaded engine has a high depression and a heavily loaded engine has a low depression). This same principle is used on constant depression carburetors, like SU and Strongberg. You tune the gas system by the size of the gas jet aperture and the tension on the regulator spring.

    Just a few points about running engines on gas:
    Gas does not need to be atomized and and mixed with air- this is one of the major tasks with liquid fuel.
    Gas ignites more easily than liquid fuel
    The engine runs cleaner because there are no condensates on the cylinder walls.
    But, gas has a lower calorific value for a given volume, so the engine will not be so powerful.

    spec

    PS: Rolls Royce run their car engines in using gas.:cool:

    spec
     
  14. shortbus=

    shortbus= Well-Known Member

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    When I was around LG's age, a neighbor had a generator type welder that he tan on natural gas. His natural gas carb was a tin can with both ends cut out between the carb and air cleaner. A copper line and a valve was hooked on one end to the house gas supply and into the side of the tin can, in the air stream from the air cleaner. He would start the engine on gasoline, set his RPM he wanted, the slowly open the natural gas valve. He stopped opening the valve when the RPM's went up a slight amount. Then he shut a valve off in the gasoline supply, and the engine continued to run on natural gas.

    This wouldn't work in an engine that needs to vary it's RPM, but for his home made DC welder it worked perfect. The welder was made from a surplus aircraft generator. In the 1950's you could find them for sale in the back of magazines like Popular Mechanics.
     
  15. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    Is the master valve also known as a anti flash back? I have an inline anti flash contraption to fit to the gas line. Its actually copper pip of wider diameter, stuffed with fine iron wall (I took it apart).
     
  16. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    Completely off topic....................

    We have flounder around the pier at the moment! Apparently not normal for here and not normal for the time of year. I was after Pollock but havnt caught or seen any for months, that is really odd!

    Ok back on topic again :D.
     
  17. Little Ghostman

    Little Ghostman Well-Known Member Most Helpful Member

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    Which member was working on de sulphating batteries? I have 6 12V large car ones, They dont hold a charge well so I was looking to see if I could get them working a bit better.
     
  18. spec

    spec Well-Known Member Most Helpful Member

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    No, an anti flash back device is different to a master cut off valve. They are two separate functions, but they may be combined in one physical unit. It may be possible that a pressure regulator performs the anti flash back function by virtue of the regulator design, but I am not sure of this.

    My advise, based on unfortunate experience, is to pay particular attention to safety when you are messing with gas, especially home made gas.

    spec
     
  19. shortbus=

    shortbus= Well-Known Member

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    An anti flash back valve is basically a check valve. But it is more sensitive than a regular check valve, to reverse pressure, which they block. Oxy/acetylene welding torches should always have them on the hoses. That is also a good place to find them, a welding supply shop.
     
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  20. spec

    spec Well-Known Member Most Helpful Member

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    At one time a gang of us used to get spare parts, including body sections, from scrap yards, to keep our jalopies on the road.

    We were at a scrap yard and one of our gang asked for a wing and flitch plate to be cut off one of the scrap cars.

    The owner of the yard wheeled over his oxyacetylene trolley, adjusted the taps and lit up.

    There was an almighty bang and three-feet section of the rubber pipe split neat the acetylene tank. A huge flame, just like you see from military flame throwers, bellowed from the ruptured pipe.

    The flame hit the guy who wanted the wing in the face and he was badly burnt.

    There was a court case and the guy who got burned was awarded considerable damages. The technical report for the court said that the equipment was badly maintained and was not configured correctly. I wounder if that was a problem with an ani flash valve ( I was young and carefree in those days and didn't pay much attention to the details).

    spec
     
  21. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Put yourself in the US when you do your searches. Maybe the government is trying to protect you?
     

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