Steal from the Military? (50 hp multi-fuel outboards)

Discussion in 'Outboards' started by FAST FRED, Jul 22, 2012.

  1. BMcF
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    BMcF Senior Member

    Good point..they probably would. But I've seen no indication that Merc is going to offer them up for commercial sale as "diesel outpboards".

    That might be due to price too, of course.
     
  2. powerabout
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    powerabout Senior Member

    the BRP ones will run on diesel just like a Merc but due to the amount of carbon in the diesel they run badly
    The Military were more interested in running them on jet fuel which they do quite well
     
  3. gonzo
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    gonzo Senior Member

    If someone is shooting at you and you need to evacuate, any fuel is good. The requirements are different from a average user's. They are satisfied with a few hours running time, even if it carbons up.
     
  4. DStaal
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    DStaal Junior Member

    More importantly, they want to simplify logistics: One fuel for everything. Then it never matters which vehicle is running low on fuel, or which vehicle wasn't just blown up. (And, in the middle of a firefight, your high-school-graduate-barely solider (the dummy in the platoon) won't have to think about what fuel they are using: The can says 'fuel', so it will work.)
     
  5. BMcF
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    BMcF Senior Member

    That is exactly what the military was/is after and they will pay a premium for it. And I'm sure they have. That's why I suspect the Mercury multifuel engine is not going to be sitting in any local showrooms anytime soon. If ever.
     
  6. jonr
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    jonr Senior Member

  7. BMcF
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    BMcF Senior Member

  8. phillnjack
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    phillnjack Junior Member

    any 4 stroke petrol engine can run of parrafin/kerosene.
    it used to be known as petrol/parafin .the engines started on petrol then switched to parafin. the uk name for kerosene is parafin.
    also most jet fuel is just parafin as well,not quite as clean as the stuff used in heaters for the homes etc.
    Most army vehicles in the us i presume are petrol, but in europe and the uk they are mainly dieseld ue to milage being a lot better with the diesel.
    The outboards sold as mulit fuel are mainly petro&parafin and petrol /lpg engines
    its only a touch of timming thats diffeent.
    also if you want to run parrafin in a diesel engine, you add 1 pint of normal 4 stroke engine,oil to every 22 litres of parafin to make diesel or its too dry and will ruin pump seals in a short time...parafin is a very dry fuel compared to petrol.

    in india they run lots of outboards on parafin with a touch of oil in them, some even run 2 strokes on it ,but i dont know if they last very long or their performance.
     
  9. powerabout
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    powerabout Senior Member

    OMC made engines right up to the 80's that would run on kero
    Mainly the old 40 of which all army's/navies in the world used
     

  10. Yellowjacket
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    Yellowjacket Senior Member

    I'm sorry Phil, but you don't know what you are talking about. While any engine could run on it, it won't run well and it won't run for long if you don't make some significant changes, and if you don't have gasoline to start it, you aren't going to start it. The idea is to ELIMINATE the use of petrol, not just minimize it. Running an engine that was originally designed for operation on gasoline and converting it to run on heavy fuel (Jet A specifically) is very difficult.

    There is a lot more to it than just retarding the timing. Obviously, since the anti-knock rating of the fuel is lower some modifications are in order, but they go way beyond just timing.

    Specifically the compression ratio has to be reduced. The trapped compression ratio will go down from over 8:1 down to something on the order of 4.5:1. And then the ignition timing has to be recurved to provide less timing at low rotational speeds and almost the same timing at higher speeds. This changes the squish areas in the head, and changes the antiknock performance. In short, you don't get the squish area that modern engines use to control knock so things get a lot more difficult.

    Then there is the issue of deposits. Running on heavy fuel results in much higher deposit formation on the top of the piston crown and in the piston ring area. This requires a different piston ring design and allowance for more deposits on the top of the piston, which could cause the deposits to build and the piston and head to collide. Spark plug fouling is also a big big issue, engines need to run hundreds of hours without fouling spark plugs and prolonged idle and low speed operation can result in plug fouling issues. Just changing to a higher heat range won't do it because that will make the detonation problem worse, so you need different plugs that may or may not exist that are not as prone to fouling.

    Then there is the issue of starting. Heavy fuels don't atomize as well and require more ignition energy to start. Once the engine is running that is less of an issue, but in the military environment, you can't start on gasoline, and OBTW, you have to be able to start at low temperatures, so cold starting is a big problem with heavy fuel spark ignition engines.

    As you can see there is a lot of work involved in coming up with an engine that is very lightweight and can run on heavy fuel for a long time. Big heavy diesel engines do just fine, but if you need lightweight propulsion, then you need a spark ignited heavy fuel engine and those are few and far between.

    And no, most US Army vehicles don't use gasoline, they already operate on heavy fuel, diesel or JetA. There is an initiative of "one fuel forward" and, aside from the fact that the Navy want's nothing to do with gasoline storage on ships, the logistics of getting light fuel is a big problem for the Army too, now that most all vehicles are already running on heavy fuel. For that reason alone there are big incentives for the military to operate on one fuel for everything.

    Mercury has come up with their heavy fuel outboards based on the Optimax engines. These engines were a lot easier to convert because they used the Orbital fuel injection system. That system injects a premixed shot of air and fuel AFTER the exhaust port is closed. That is important since the fuel consumption of a two stroke with this kind of injection is essentially as efficienct as a 4 stroke engine. In addition, the injection of a fine mist of air and fuel is much easier to start than just dumping heavy fuel into the cylinder, so cold starting is substantially improved. Still Mercury had to do a lot of re-engineering of the engine, including the redesign of pistons, and other aspects to get it to work. It was far from just turning back the timing.

    Because of the lower compression ratio a converted 2 stroke won't be as efficient as a gasoline 4 stroke engine or a diesel, but the power to weight ratio will be far better than a 4 stroke engine and the resulting fuel consumption will be better than a conventional 2 stroke engine.

    In short there's a lot of work that goes into coverting a spark ignition engine to operate reliably and successfully on heavy fuel. I know, because I'm doing it right now under contract to the government for another application. It isn't as easy or as straight forward as you might think.
     
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