The turning moment diagram for a petrol engine is drawn to the following scales

Question

The turning moment diagram for a petrol engine is drawn to the following
scales : Turning moment, 1 mm = 5 N-m ; crank angle, 1 mm = 1°. The turning moment diagram
repeats itself at every half revolution of the engine and the areas above and below the mean turning
moment line taken in order are 295, 685, 40, 340, 960, 270 mm2. The rotating parts are equivalent
to a mass of 36 kg at a radius of gyration of 150 mm. Determine the coefficient of fluctuation of
speed when the engine runs at 1800 r.p.m.

Explanation / Answer

We know that maximum fluctuation of energy, ? E = Maximum energy – Minimum energy = (E + 295) – (E – 690) = 985 mm2 985 86 N-m 86 J 36 = × p = = Let CS = Coefficient of fluctuation of speed. We know that maximum fluctuation of energy (? E), 86 = m.k2 ?2.CS = 36 × (0.15)2 × (188.52)2 CS = 28 787 CS ? CS = 86 / 28 787 = 0.003 or 0.3% Ans

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