Question

The engine has the flywheel of mass 7 tons and the radius of gyration is 1.7 m. The fluctuation of energy is 55 kN-m. The mean speed of the engine is 150 rpm. What is the coefficient of fluctuation of speed?

(a) 0.021

(b) 0.011

(c) 0.031

(d) 0.041

I got this question in an interview.

Enquiry is from Flywheel in division Internal Combustion Engines of Automobile Engineering

Answer 1

Right choice is (b) 0.011

Explanation: The fluctuation of energy = ΔE, the mass of the flywheel = m, the radius of gyration = k, the mean speed of the flywheel = N.  ΔE = \(\frac{π^2}{900}\)*m*k^2*N*(N1-N2) = \(\frac{π^2}{900}\)*7000*1.7^2*150*(N1-N2) = 33277*(N1-N2) ⇒ 55000 = 33277*(N1-N2) ⇒ (N1-N2)=  \(\frac{55000}{33277}\) = 1.652 rpm. Coefficient of fluctuation of speed = Cs = \(\frac{N_1-N_2}{N}\) = \(\frac{1.652}{150}\) = 0.011.