Announcement

Collapse
No announcement yet.

Question for the steam experts among us.

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Question for the steam experts among us.

    Given two steam engines, one with a 2.00" bore x 4.5" stroke, the other with a 2.25" bore x 4.5" stroke, but otherwise identical in every respect, how would they differ in performance? Thanks.

  • #2
    The 2" bore has 3.14 square inches of piston surface area, the 2.25" bore has 3.98 square inches of piston area. For a given brake mean effective pressure, say 100 psi, the former would have 314 pounds of pressure acting on the piston, the later would have 398. Given a 4.5 inch stroke The 2" bore engine would produce 117.75 lb.ft of torque, the 2.25 bore engine would produce 149.25 lb ft.
    Sorry, I need to revise these figures, I calculated for a 4.5 inch lever arm rather than 4.5 inch stroke which is a 2.25 inch lever arm giving 58.875 lb ft for the 2" bore, and 74.625 lb ft for the 2.25" bore. Those are theoretical figures that would be reduced by factors such as friction and thermal efficiency.


    [This message has been edited by Carl (edited 02-26-2004).]
    THAT OLD GANG 'O MINE

    Comment


    • #3
      Carl is exactly right,but also another consideration of performance is operating speed,the smaller piston could operate at a higher speed at least in theory and develop similar horse power with lighter wieght like in a traction engine or automobile as compared to things like ships and locomotives where wieght is not as much of a factor.
      I just need one more tool,just one!

      Comment


      • #4
        Thank you both for your replies. Wow, that extra 1/4" of diameter makes a significant difference.

        Comment


        • #5
          They both should operate at the same speeds as it is piston speed that is the limiting factor. The heavier piston will need more balace weighting. Wear for the bigger piston could be a limiting factor if the bearing journals are not increased in size accordingly.

          ------------------
          Neil Peters
          Neil Peters

          When on the hunt, a broken part is better than no part at all.

          Comment


          • #6
            <font face="Verdana, Arial" size="2">Originally posted by wierdscience:
            ...another consideration of performance is operating speed,the smaller piston could operate at a higher speed at least in theory and develop similar horse power with lighter wieght like in a traction engine or automobile as compared to things like ships and locomotives where weight is not as much of a factor.</font>
            Interestingly, the design decision is in the opposite direction in aircraft piston engines. One would initially assume aircraft enginess should be light and horsepower should be delivered through high rpm. Actually, aircraft piston engines are slow running - 2700rpm is often max - and cylinders tend to be huge - coffee can size. This is because the determining factor is propeller tip speed, which must be kept below the speed of sound for best overall efficiency. Gears are avoided because of weight. Propellers are therefore usually driven directly, at the same slow speed as the crankshaft.


            [This message has been edited by NAIT (edited 02-25-2004).]

            Comment


            • #7
              x39,
              I can't help with your question, but you may be interested in this photo posted recently on a Stationary Engine forum, it compares two steam engines, both developing 250hp.

              The photo is titled "Two Engines of Equal Power".
              I found the size difference quite astounding.
              Apparently, the photo originally appeared in 'Power' magazine, 1903 and then as a frontispiece in a book "Modern Engines & Power Generators".

              "Made by Yarrow of Poplar, the large one was built for the East London Water Works, triple expansion, 20, 32 & 53 inch cylinders with a 42 inch stroke, 16 rpm @ 150 psi, 80 ton. Small engine was for torpedo boat: triple expansion, 8, 12 & 17 inch cylinders with 9 inch stroke, 550 rpm @ 250 psi., 2 ton. Both rated at 250 hp."



              For your interest, I found a photo of what I believe is the same engine, in a new book I just purchased, photographed by George Watkins in 1954 at Wanstead Pumping Station.

              Here is what he says - "Yarrow & Co., Poplar, 1903.
              Cylinders 20in, 32in and 53in x 3ft 6in stroke, Corliss valves.
              "This was completely different from any thing in Yarrow's usual practice, which was lightweight steamboats and high speed marine engines and boilers. Being so completely in contrast to stock work, the contract could have brought little profit, but was possibly given to provide work at the Thames yard which was then being transferred to the Clyde. As a pumping station, it was indifferent as the estimated water supply could not be secured, and the engine could only run part time, or unloaded."


              Comment


              • #8
                Wow Peter ..nice photos !
                As another point to make, unlike other engines, steam engines are not really "Horsepower" rated. The Boilers that provide the steam to them are really the limiting factor. Without a governor, the steam engine will go to destruction as long as you can provide more steam to it.
                You may recall that the Stanley Steamer with a souped up boiler ( I think it was over 1000 PSI ?) set a land speed record of 125 MPH in 1904 or there abouts and I also believe the engine was "considered to be a 10 HP engine ".
                This was the same time as the Wright bros were doing their stuff with a 15 HP aircraft engine

                Comment


                • #9
                  Rich,

                  That's right. The expansion of steam is limited by the speed of sound, and that is pretty high piston speed.
                  Free software for calculating bolt circles and similar: Click Here

                  Comment


                  • #10
                    The C&O Allegheny type steam locomotive produced 7500 draw bar horsepower measured with a dynamometer car at approximately 40 miles per hour.
                    THAT OLD GANG 'O MINE

                    Comment


                    • #11
                      Speaking of aircraft engines, one of my favorites is the Pratt & Whitney R2800 Double Wasp, 18 cylinder radial engine displacing 2800 cubic inches, two stage supercharging, 2000+ horsepower, used in several WWII planes including the F4U Corsair which had a 13 foot diameter propeller!
                      THAT OLD GANG 'O MINE

                      Comment


                      • #12
                        Wow! Some real interesting posts and some great images. PeterS, that's quite a contrast between those two engines. Rich Carlstedt- I have seen the engine from the Stanley that set the speed record at Daytona. It is in storage at the Smithsonian's Silver Hill, MD facility. The engine featured roller bearings throughout. If I'm not mistaken, ten replicas of that engine were recently built at a shop in Quebec. Glen Curtiss of aircraft fame ran a V-8 powered motorcycle of his own construction the same day the Stanley ran. Pretty advanced stuff for the time.

                        Comment


                        • #13
                          <font face="Verdana, Arial" size="2">Originally posted by NAIT:
                          Interestingly, the design decision is in the opposite direction in aircraft piston engines. One would initially assume aircraft enginess should be light and horsepower should be delivered through high rpm. Actually, aircraft piston engines are slow running - 2700rpm is often max - and cylinders tend to be huge - coffee can size. This is because the determining factor is propeller tip speed, which must be kept below the speed of sound for best overall efficiency. Gears are avoided because of weight. Propellers are therefore usually driven directly, at the same slow speed as the crankshaft.

                          [This message has been edited by NAIT (edited 02-25-2004).]
                          </font>
                          Yes,that is quite true for radial engines,but not most v-types like the Liberty 12,they ran reduction gears,as I remeber from what I have read the Liberty routinely ran up to 3900+,or at least thats what figures were given in a article on Lindberg's contribution to the flight proceedure on the P-38.



                          [This message has been edited by wierdscience (edited 02-26-2004).]
                          I just need one more tool,just one!

                          Comment


                          • #14
                            Sounds like we're getting the Liberty and Allison 1710 mixed up. The Liberty [V-12 version most common] was a quickee WW1 design than, due to funding constraints hung around for years, spawning all sorts of mods. It never reached anywhere near that RPM range, neither the P-38's Allison or the famous Rolls Merlin never did either. 3000RPM max. With a 6" stroke that is 3000FPM piston speed which is considered high for a continuous duty engine.

                            A distant derivitive of the Liberty, Hyper #2 was designed for RPM in this range, although it wasn't part of any mass produced engine in the end, being a victim of gas turbines.

                            For high max RPM's see Napier's Sabre, an H-24 sleeve valve. The stillborn last generation of engines were short stroke, high RPM ones such as Wright's r-2160.

                            While most Liberty's and other WW1 era engines were not geared, all WW2 tactical and strategic allied engines, inline or radial were geared.They swung some pretty large props and the speed of sound was reached at fairly low revs. Ballpark gear reduction was somewhere around 0.5 to 1 but it varied a lot.

                            Comment


                            • #15
                              X39, here's a couple of steam engine related forums:

                              http://www.stanleysteamers.com/phorum-3.3/list.php4?f=1

                              http://www.steamautomobile.com/ForuM/list.php?f=1

                              The membership of both forums tend to overlap, but the folks there have been helpful in answering the questions I and others have had.

                              Comment

                              Working...
                              X