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Calculate flywheel torque

  1. Jan 6, 2016 #1
    I am doing a small project on improving the performance of a flywheel in a single cylinder diesel engine. I am stuck at a point where I have to calculate torque on the flywheel. Information that I have is power of the engine is 5bhp, and rpm of the engine is 2600, I do not have any other information. Can anybody please help
  2. jcsd
  3. Jan 7, 2016 #2


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    Try looking up the formula to calculate horsepower. There are 3 three terms in it (and a constant); RPM, Torque, Horsepower. Given any two, the third can be found.
  4. Jan 7, 2016 #3
    My doubt, is it OK to use the power of the engine directly to calculate the torque on flywheel. Actually I am supposed to do an FEA analysis of that flywheel.
  5. Jan 7, 2016 #4


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    Well, an FEA analysis of the flywheel will not give you the torque produced by the motor.
  6. Jan 7, 2016 #5
    Since I want to do FEA analysis I need to put in the load conditions. Tats y I need the torque
  7. Jan 7, 2016 #6


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    (1) When the flywheel is running at steady speed it will only have centrifugal loading . This loading is only dependent on the speed of rotation .
    Flywheel will experience hoop and radial stresses which can be analysed by standard means .

    (2) Flywheel experiences additional loads when speed is changing as a result of :

    (a) cyclic variation within one rotation of engine or load .
    (b) more general load variation .
    (c) scheduled changes under user control .

    (3) During periods of speed change the flywheel experiences angular acceleration . Consider the flywheel as a notional nest of concentric rings with each ring driving the next outer (or inner dependent on +/- acceleration ) . This gives rise to shear stresses between the notional rings . Not too difficult to evaluate stresses analytically for constant value accelerations but needs a numerical procedure for non constant acceleration and in particular for in cycle accelerations which are commonly rapidly varying .

    The basic hoop and radial stresses will additionally change as speed changes

    (4) When speeding up or slowing down the flywheel is effectively either storing energy or giving it back to the crankshaft .

    (5) The torque between crankshaft and flywheel always acts in such a way as to oppose speed variations . Thus the flywheel acts effectively to make a smoother running engine .

    (6) Single cylinder slow running engines need the flywheel also to maintain running speed during the dead parts of the engine cycle .
  8. Jan 7, 2016 #7
    Thanks for the elaborate explanation nidum... Clearly in my case the flywheel will not be rotating in steady speed, depending on the stroke the speed may vary and hence there will be angular speed variations. But I am curious to know how much of this stress due to speed variations can affect the flywheel. I mean can I not just assume an average speed for stress calculations.
  9. Jan 7, 2016 #8


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    Depends on the application . For your present purpose stresses calculated from average running speed will be probably be perfectly adequate .
  10. Jan 7, 2016 #9


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    Just note that some flywheels have things like shaft couplings , clutch faces and drive gears built in . If you have any of these then further analysis is needed .
  11. Jan 7, 2016 #10
    But then I am not changing anything in those. My motto is to analyze the present flywheel then change its dimensions and again analyze it for improved inertia.
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