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Single Stroke Engine with two cranks

  1. Aug 1, 2008 #1
    I got curious about a single stroke engine design that popped into my head and made the attached animation. .
    It does not look to me like it would have any use but curiosity value. In fact it does not appear to have any redeeming features whatsoever - two crankshafts that speed up and slow down so gearing cannot connect them, valving would be horrendous, it just doesn't look like it would be efficient etc etc.
    However it should work, and it can sort of be said to to be One-stroke, "sort of" probably being a very important qualification.
    Note that the animation is with the left hand crank running at a constant rotation and that the right hand crank speeds up and slows down during one rotation.
    I have searched the net looking for anything similar but can't find anything. Has anybody seen similar and what are they called?

    Attached Files:

  2. jcsd
  3. Aug 2, 2008 #2
    looks nice, but what would you have your variable speed shaft do?
  4. Aug 2, 2008 #3
    I do not have a clue.
    I thunk this up on Thursday 31st July, did the calculations in the attached spreadsheet on Friday, and did the conversion to code and graphic in VB on Friday night.
    I thunk it up because I am looking for an engine for a pushbike. I was thinking of options for an engine to fit within the pushbike frame (use part of the tubular pushbike frame as the engine's cylinder) and something that runs much slower than current small engines.
    Small 4-stroke engines have maximum efficiency at 6,000 rpm and gearing down from 6,000 rpm to a pushbike wheel's 300 rpm is particularly inefficient. One gearbox site shows 94% efficiency for a 2:1 reduction gearbox but the efficiency drops down to 70% for 20:1 reduction. The three methods currently used on motorised pushbikes all have pathetic inadequacies.
    I am aiming for a motor assisted pushbike offering 1,000 km/litre, as outlined in the attached pdf file. Efficiency is prime, it is the only consideration.
    Anyway the idea of a two piston, two contra-rotating crank engine slipped into my head. I was wondering about having the cranks well separated and a large slow rotating gear connecting the cranks for the slow rotation power output. I couldn't visualize it too good so I drew it, still couldn't visualize it too good so I did some numbers. It wasn't until I did the numbers that I realized that it also exhausts in the middle of the stroke.
    So what I am saying is that if it is a new design it is a particularly fresh meme. It is a doodle that may be of interest. Whether it has any use I do not know. How it can be used I do not know. Whether it has any redeeming features I do not know. How you would valve it I do not know. How you would spark it I do not know. As you can see, I know very little, but it is probably still more than you??!! (LOL:tongue2:, just had to throw that in, sorry- it is not very becoming for a 50 year old to stick out his tongue and say “so there” is it!).
    Currently (9:35 am Sunday Morning oz time) I am fixing the spreadsheet so I can identify the spacing between the pistons and the angle variance between the first and second cranks. Should be simple – but I decided to write this. I'll tart up the spreadsheet before I lodge this post, hopefully within the hour. Spreadsheet tarted up – lodged at 1:15 pm my time

    Attached Files:

  5. Aug 3, 2008 #4


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    Who knows if it has any actual value but this can be how new and sometimes good ideas come up. I would valve it by having an exhaust and intake port in each end of the cylinder with a valve in each port also. There are lots of variations of this engine I'm sure. A single stroke engine certainly would howl when wound up.
  6. Aug 3, 2008 #5
    A more fundamental question remains firstly though. On Sunday I ascertained that the design has two possible firing cycles, it can either fire at the end of the stroke (as shown in the animation) or during the compression in the middle of the stroke. Firing in the middle of the stroke seems to have an advantage. As the connector length increases the gap between the pistons increases, but it increases differently for the middle compression and the end compression. The gap between the pistons at the end compression seems to be only 50% of the gap for the middle compression.
    In a current ICE there always remains an amount of burnt gases in the head space, the cylinder is never fully evacuated. This head space is the combustion chamber, so with a compression ration of 10:1, 10% of the gasses in the chamber at ignition have already been burnt.
    With this design if the middle compression is set to a 10:1 compression the exhaust stroke at the end of the cylinder will leave only half of the burnt gases. In the spreadsheet this is with a connector length set to 1.58. Curious
  7. Aug 3, 2008 #6


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    I was looking at the animation again and it seems to me that this would be a fairly noisy and quite possibly short lived engine. Look at the amount of sideways pressure that is put on each piston during the cycle. The piston seems to come to a rest and start back up again quite suddenly. Experimenting with the connecting rod and connector lengths I am sure would yield some interesting results.
  8. Apr 26, 2009 #7
    Intrigued by the title, we picked up the Idea of a single stroke engine. thanks for the input>

    I am building one now and will then try to put some info here. Not sure yet what fuel to use.

    I am contemplating on a more exotic fuel such as HHO but guess the gas generation will be too low.

  9. Mar 11, 2010 #8
    can you tell me the working principle and the basic cocept of single stroke engine.....?????
    it will very very useful to me.......my mail address is ishak460@gmail.com
  10. Mar 11, 2010 #9
    Hello ishak460
    The thumbnail in the original post is an animated gif file that displays the engine functioning.
  11. Mar 11, 2010 #10


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    It isn't actually a "single stroke" engine in the first place, it has the standard strokes of a 4-stroke engine (intake, compression, combustion, exhaust). It's basically a single cylinder engine.

    The gif file shows a moving animation, but the path followed by the piston and "connecting rods" would be impossible to fabricate, and wouldn't make any useful torque or power.
  12. Mar 11, 2010 #11
    So it undertakes the four functions of intake, compression, combustion and exhaust. A two-stroke engine undertakes two of the four functions in one stroke, a four stroke engine undertakes one function in one stroke. The single stroke undertakes the four functions in one stroke.
    I do not believe it is impossible to fabricate, it is a simple 2D drawing that shows the functionality and shows it can be fabricated.
    I have no idea whether useful torque would be produced, some torque would be produced, whether it is sufficient to keep the engine going I have no idea.
  13. Mar 12, 2010 #12
    I dont think this engine would run any cycles at all. It will just settle in the middle and start violently shaking.
  14. Mar 12, 2010 #13
    As does any engine without a fly-wheel
  15. Mar 12, 2010 #14
    No there is a fundamental difference here. The only reaction force to the piston expansion is the inertia of the piston itself.Unless you make it super heavy, you cant use the power cycle effectively. If its that big, its useless anyway. It will tend to quickly settle in the middle and try to expand towards both sides and collapse back.
  16. Oct 14, 2011 #15
    That was a impressive design....it may work..but each engine has a specification.like in here we have two crank shafts. which definitely adds up to the weight ..but it plays good in other areas where weight is not a factor
  17. Oct 14, 2011 #16
    Have you considered mounting your engine as one of your wheels? A few early radial engines rotated along with the prop. Instead of having the pistons towards the outside, however, you might have them towards the center, with an off-set hub. A simple diesel would do.

    Getting fuel to it might be difficult.
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