Mass Moment of Inertia of Flywheel for an IC Engine:

The function of the flywheel is to store up excess energy throughout period of harvestation and it supplies energy throughout period of starvation. Thus, it drops of fluctuation in the speed in the cycle. Consider ω₁ be the maximum angular speed and ω₂ be the minimum angular speed.

Consider I be the mass moment of inertia of the flywheel.

By neglecting mass moment of inertia of the other rotating parts that are negligible in comparison of mass moment of inertia of the flywheel.

Maximum kinetic energy of flywheel

Minimum kinetic energy of flywheel

Change in K.E., that means

Δ K.E. = fluctuation in energy, that means Δ E

here 'w' is average speed given by following formula

 Equation (11.12) may also be written as:

here k is the radius of gyration.

Consider V₁ be the maximum tangential velocity at the radius of gyration and V₂ be the minimum tangential velocity at the radius of gyration

∴ V₁  = k ω₁      and        V₂  = k ω₂

and

                                  . . . (11.14)

It may be observed from equation. (11.13) that

(a) The flywheel shall be heavy and of big size if Δ E is large. The value of k_s is restricted by the practical considerations. Thus, single cylinder 4-stroke engine will needs larger flywheel as compared to the multi-cylinder engine.

(b) Also for slow speed engine the flywheel needed is larger in size due to high value of I required.

(c) For high speed engines, the size of flywheel shall be considerably smaller because of lower value of I needed.

(d) If system may tolerate considerably higher speed fluctuations, the size of flywheel shall also be smaller for similar value of Δ E.