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OT: propane puzzle

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  • OT: propane puzzle

    I've had my dual fuel (propane/gas) generator running for a couple of months now, so far only to test and exercise it - previous discussion here:

    http://bbs.homeshopmachinist.net/thr...fuel-generator



    One thing puzzles me: when using propane, a cold start requires that the choke be off, while a warm start wants half choke. That's what the manual says, and that's actually the way it works.

    Huh? Can someone explain?

    -js
    There are no stupid questions. But there are lots of stupid answers. This is the internet.

    Location: SF Bay Area

  • #2
    Here is the propane puzzle.

    https://www.jigsawplanet.com/?rc=play&pid=305bf537d79d

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    • #3
      Maybe because the density of propane when cold is much greater than when hot, so you need to restrict the amount of air when hot, to achieve an ideal mix for easy combustion. Propane/air must be between 2.15% and 9.60% to ignite.

      https://www.propanecarbs.com/propane.html

      http://www.propane101.com/aboutpropane.htm
      http://pauleschoen.com/pix/PM08_P76_P54.png
      Paul , P S Technology, Inc. and MrTibbs
      USA Maryland 21030

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      • #4
        I have a propane generator, it's not a duel fuel, strictly propane. I wanted the propane because it does not go bad with age. A couple of things I have learned about starting it is, to open the propane valve at the tank very slowly, don't know why but it works better. Second I always use the choke. I have never had to use it as a backup as yet in the three years I've had it, only a monthly warm up.
        This thing is like the snow blower I bought in my other life in Idaho. We spent a winter with several feet of snow, so I bought a snow blower, it never snowed again for four years. Now that I have two generators, one in the motorhome and this propane one. Never have had to use either one in three years, go figure.
        _____________________________________________

        I would rather have tools that I never use, than not have a tool I need.
        Oregon Coast

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        • #5
          Maybe that is the secret to making it through winter.
          mark costello-Low speed steel

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          • #6
            Think about it, gasoline mixes with air in the carb & turns into a gas. When using propane it arrives as a gas so no enrichment (choke) needed. I own 2 just like that & don't know how they can build, ship to the US & then to me for $250 each. Those great chinese.
            Last edited by flylo; 05-02-2018, 11:41 PM.
            "Let me recommend the best medicine in the
            world: a long journey, at a mild season, through a pleasant
            country, in easy stages."
            ~ James Madison

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            • #7
              Not sure where you're going with that flylo, propane still has to mix with air before it'll combust in the engine. The choke changes that air/fuel ratio regardless whether it's propane or gasoline.

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              • #8
                Here's what puzzles me.

                - no choke when starting cold. OK, I can see that.
                - no choke when running, either when cold or hot. No problem.
                - no choke when running after a hot restart. Check.
                - choke required only during a hot restart - as soon as the engine catches the choke must be opened.

                What's going on there that's different from above?

                -js
                There are no stupid questions. But there are lots of stupid answers. This is the internet.

                Location: SF Bay Area

                Comment


                • #9
                  Originally posted by Jim Stewart View Post
                  Here's what puzzles me.

                  - no choke when starting cold. OK, I can see that.
                  - no choke when running, either when cold or hot. No problem.
                  - no choke when running after a hot restart. Check.
                  - choke required only during a hot restart - as soon as the engine catches the choke must be opened.

                  What's going on there that's different from above?

                  -js
                  The intake manifold temperature probably rises once you shut down the engine. When you try to re-start it, the hot intake manifold might lean out the mixture too much and the choke corrects that until the flow through the intake cools it back down.

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                  • #10
                    Originally posted by 3 Phase Lightbulb View Post
                    The intake manifold temperature probably rises once you shut down the engine. When you try to re-start it, the hot intake manifold might lean out the mixture too much and the choke corrects that until the flow through the intake cools it back down.
                    Hmmm. Sounds plausible...

                    -js
                    There are no stupid questions. But there are lots of stupid answers. This is the internet.

                    Location: SF Bay Area

                    Comment


                    • #11
                      Originally posted by Yondering View Post
                      Not sure where you're going with that flylo, propane still has to mix with air before it'll combust in the engine. The choke changes that air/fuel ratio regardless whether it's propane or gasoline.
                      Usually there's a prime button to give it a shot of propane when it's cold at least on Northern Hyds brand but I have 2 of these & that work this way? I think the chinese write brappy directions.
                      "Let me recommend the best medicine in the
                      world: a long journey, at a mild season, through a pleasant
                      country, in easy stages."
                      ~ James Madison

                      Comment


                      • #12
                        Originally posted by flylo View Post
                        Usually there's a prime button to give it a shot of propane when it's cold at least on Northern Hyds brand but I have 2 of these & that work this way? I think the chinese write brappy directions.
                        Yeah, there's a prime button you're supposed to press three (IIRC) times when first opening the valve on the propane tank. Not to be used on a hot start, or at least they don't say so.

                        Actually, I'm very happy with the manual that comes with this rig. Detailed and written in American English. By a real writer, I'd say.

                        In fact, I'm very happy with the generator too. So nice not to have to worry about old gas.

                        One of these days I should put some gas in the tank to make sure the carb works, I guess...

                        -js
                        There are no stupid questions. But there are lots of stupid answers. This is the internet.

                        Location: SF Bay Area

                        Comment


                        • #13
                          So I have to ask, why would anyone want a portable propane generator. I can't think of a more expensive less accessible fuel. Unless you have a 500 tank in the yard you were going to plumb it into. Is there something I'm missing?

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                          • #14
                            Propane does not go bad the way gas does in a fairly short time.

                            If you DO have it available, it makes a good deal of sense to have just one fuel to deal with. The military runs everything they can on JP-8 for that exact reason.
                            1601

                            Keep eye on ball.
                            Hashim Khan

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                            • #15
                              Originally posted by Jim Stewart View Post
                              Yeah, there's a prime button you're supposed to press three (IIRC) times when first opening the valve on the propane tank. Not to be used on a hot start, or at least they don't say so.

                              Actually, I'm very happy with the manual that comes with this rig. Detailed and written in American English. By a real writer, I'd say.

                              In fact, I'm very happy with the generator too. So nice not to have to worry about old gas.

                              One of these days I should put some gas in the tank to make sure the carb works, I guess...

                              -js
                              Yes you should, I've got a Champion dual fuel and can't get it to start with gasoline but runs like a top on propane.

                              Sent from my SM-G892A using Tapatalk

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