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Inquiring minds want to know....

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  • Inquiring minds want to know....

    I was reading in my Strictly I.C. magazine the other day and was surprised to read that a "diesel" model airplane engine is technically a Compression engine rather than a true diesel....wish he'd said why.

    While in this neighborhood I have a couple of more things I'd like to bring up, have any of you read about the "DUX diesel" from the fellow in Holland?

    Ironically I overlooked it right on the cover because it looked like a dogs breakfast....he was interested in the technical aspects not the he needed to say that . At any rate I was quite interested but his information was pretty thin. I'm hoping he's still interested and still alive (you never quite know with this hobby) it was almost a decade ago. I'd be interested in emailing him if by some strange stretch one of you has been in touch with him.

    I'm interested in building a diesel (real or compression?) I want to make it compact, light (for a diesel), slow with lots of torque, and very durable. I have about a half dozen or so slightly off the wall ideas that might help me achieve some of those goals. I really consider this a longer term project with a goal of completion several years out because frankly I just need to improve some of my skills and increase my knowledge significantly before I can take a reasonable crack at it.

    Those interested: apply here.
    Allans Rule: Anything worth doing is going to be a pain in the butt.

  • #2
    Try not to get caught up in an argument about semantics, it will only drive you wonky.

    Reciprocating engines 101 - there are two common types of recip engines, spark ignited and compression ignition. Speaking about a "diesel" engine is rather vague, as it could imply an engine that is 100% diesel fueled, or 0.5% diesel fueled. It also could imply 2, 4, 6, or more strokes. It could also imply a specific type of valvetrain, even though multiple types exist and have been successfully used in "diesel" engines.

    I would like to build a miniature version of one of these someday, as I work with our proprietary versions in the lab rather often.
    "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."


    • #3
      A few years ago there was a lively discussion on the PM site about just this thing, is a model airplane engine a true diesel. The model airplane diesel is a compression diesel and not a true diesel in that the fuel is not injected into the combustion chamber.

      However me and a lot of others still like to call it a diesel engine. This may get interesting.

      Clevelander, just how big of a diesel engine do you propose to build? I have plans for a small model airplane diesel.
      It's only ink and paper


      • #4
        Dunno..... most all of what would be known as "diesels" inject the fuel, because the compression ratios are large enough that fuel would pre-ignite badly if already present before compression.

        Model diesels are compression ignition, but are carbureted.... the key being that the compression ratio is adjustable so that ignition takes place when you want it..... probably wouldn't work well, if at all, otherwise....

        You typically start them and then tune the running with the compression screw for best performance, which will be optimum ignition..
        CNC machines only go through the motions


        • #5
          I have a question. Does anyone happen to know what old Otto had in mind
          or said or wrote in his note book. It seem the public has taken it upon
          themselves to re-define almost all the inventors terms or ideas.

          Or as a somewhat famous person once said : "A rose by any other
          name will smell as sweet". (or something very close) :-)


          • #6
            Lew, were you one of the discussion group on PM when we discussed this issue? I and many others did searches and posted links to sites about Otto and I even got a few books about him from the library. It was interesting in that what Otto proposed in his patent never worked and in fact had to be modified by others to make his "Diesel" engine finally run.

            It can get real complicated with charts and texts but it all boils down to firing by compression whether you inject or use a carburetor. However this will have everyone taking sides on what a diesel really is.

            The purists will say by injection only, others will say either will work and it's still a "Diesel".

            I don't go to PM anymore and told Don I would never visit the site again so I will not go looking for a link to the old thread.
            Last edited by Carld; 03-04-2012, 10:41 PM.
            It's only ink and paper


            • #7
              Then there are 'semi-Diesels' too, the fuel is injected but injected some time before ignition. It is injected into a small space and does not ignite until the rising piston forces air/oxygene in to create an explosive mixture. IIRC


              • #8
                Guys, please don't confuse Nicolaus Otto (four stroke gas engine 1876) with Rudolf Diesel (Diesel engine first demonstrated in 1897 after years of testing). Both men hugely important.

                And yes it is abhorent to equate a Diesel engine with a compression ignition model engine. A true diesel compresses pure air only and then injects fuel, whereas ingesting a fuel/air mixture and then compressing it until it ignites is utterly foreign to Rudolf's engine.


                • #9
                  There are & have been full size diesel aircraft engines. As I understand the glitch comes in at higher altitudes. I saw one run at Oshkosh a few years ago & the company had them flying & ran out of capitol before production as I understand it. I believe it was a German company. Maybe Black Forest has more details.


                  • #10
                    Originally posted by flylo
                    There are & have been full size diesel aircraft engines. As I understand the glitch comes in at higher altitudes. I saw one run at Oshkosh a few years ago & the company had them flying & ran out of capitol before production as I understand it. I believe it was a German company. Maybe Black Forest has more details.
                    The German was Michael Zoche.
                    He designed three radial aero engines, a twin-, a four- and an eight-cylinder. They were supercharged AND turbocharged two-strokes, producing 75, 150 and 300HP respectively. The twin was a vee (i.e., half a four), and the eight was two banks of four, one behind the other.
                    Zoche had some brilliant ideas. I particularly liked the starting sequence, whereby compressed air from a soccer-ball-sized receiver was blasted in to the air inlet, compressing a small piston on the way which instantly pressurised the oil system. The air then passed through the supercharger, which, being geared to the crank, started turning over the engine. It then passed through whichever cylinders were open to it, and began spinning the turbo. There was a video on his website of the 300HP version going from zero to full revs (2,400 IIRC) in one second flat.
                    Unlike a four-stroke radial, there was no need for a master con-rod and a set of slaves. All the conrods apparently bore on the crank (don't ask me how).
                    As for a glitch at higher altitudes, Zoche claimed that being both super- and turbo-charged his engines would keep producing full power all the way up.
                    They were always going to be on the market "next year" or the one after. He did apply for certification, but I lost interest in following his long-drawn-out saga years ago, and I've no idea if the project still exists.
                    Last edited by Mike Burch; 03-05-2012, 01:45 AM.


                    • #11
                      The Germans made thousands(?) of diesel aircraft engines including the Junkers Jumo 205. That was an inline with six cylinders, twelve pistons and two crankshafts. Two stroke but I do not know if they were supercharged or just had a blower for starting purposes. If I recall correctly they were started with a cartridge which produced hot gas to start the engine.

                      I have seen one in the flesh and they were a remarkable engine and no doubt well worth a Google..


                      • #12
                        One of the big differences between a typical model airplane engine and a diesel is the glow plug. Where in a diesel engine the glow plug is just need for starting a model airplane engine can not run without it. The glow plug stays incandescent even without external power when the engine is running. It needs this to ignite the fuel.

                        There are true diesel model airplane engines though. They have an adjustable displacement piston in place of the glow plug.

                        And there are fuel injected model airplane glow engines as well. With roots blowers too.

                        Last edited by macona; 03-05-2012, 03:40 AM.


                        • #13
                          Macona, I have heard 'hot bulb' and other engines that have an incadescent zone in the combustion chamber referred to as 'semi-diesels'. They are variations on the Hornsby-Ackroyd engine.


                          • #14
                            Model airplanes run on diesel fuel? I thought the engines in my RC cars back in the day were the same engines they put in the planes and my car engines ran on methanol.

                            "Model engine "glow" fuel is made up of three key elements: methanol, oil and nitro methane. Many fuel manufacturers include other additives that are designed to solve any number of common problems that may occur with our fuel. But for now, let's only address the most common elements of the fuel and how you can care for your fuel to keep it fresh and stop it from going "bad." These steps will ultimately make your model engine operations easier."


                            • #15
                              Model airplane diesel engines use a mixture of kerosene, oil and ether and sometimes other ingredients to aid ignition.

                              Sorry about using Otto in reference to Dr. Diesels patents.
                              It's only ink and paper