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Calculating Power from Cylinder

Hi all,

I'm wanting to calculate the instantaneous power of a piston. I know that usually P = Fv, where F is the force applied and v is the velocity. In this case, I'm pretty sure I need to use P = Fomega, where F is the force applied to the piston multiplied by the pressure and omega is the rotational velocity.

My question is

1) Is this formula correct?
2) How do I calculate the force?

I'm not a mechanical engineer, so please excuse my ignorance (my Google-fu hasn't really turned up anything of interest). I can provide more details about the piston if needed.

Thanks.

Replies

  • Zaraphrax
    Zaraphrax
    Since nobody has replied, I thought I'd post this up here. I've done a bit of work with it and gotten some sort of procedure that I need to work backwards from.

    I'm given:

    -Crank angle at all times in the cycle
    - Internal pressure at corresponding times
    - Bore of the cylinder
    - Stroke length
    - Engine RPM

    From this, I've tried to work out a way that I can calculate the power at any given time.

    Working backwards, Pressure = Force x Area (where area is based on the bore), solving this for the Force.
    Using the piston motion equation 0.5*stroke(1-cos theta), where theta is the corresponding crank angle, solve for the distance from top-dead-centre. Now multiply this by the force found previously, giving Torque.
    Now that we have torque, multiply this by the angular velocity in radians per second (2*pi*rpm/60) giving power.

    Sound reasonable?

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