Flywheel
A flywheel wheel is used in machines to serve as a four reservoir, which stores energy during the period when supply of energy is more than the requirement, and release it during the period when the requirement of energy is more than the supply. Flywheel does not maintain a constant speed, it simply reduces fluctuation of speed. It does not control the speed variations caused by the varying load.
Turning Moment Diagram for a Four Stroke Engine
A turning moment diagram for a four stroke cycle internal combustion engine is shown in figure. We know that in a four stroke internal engine, there is one working stroke after the crank has turned through two revolutions, i.e., 720° (or 4π radians).
Work Done Per Cycle
Word done per cycle = Tmean × θ
Tmean = Mean torque,
θ = angle turned is one cycle
=2π, in case of two stroke engine
=4π, in case of 4 stroke engine
Tmax – Tmean = I.αmax.
Fluctuation of Speed
- The difference between the maximum and minimum speeds during a cycle is called maximum fluctuation of speed.
- The ratio of maximum fluctuation of speed to the mean speed is called coefficient of fluctuation of speed (Cs).
Cs = Nmax-Nmin/Nmean = (Nmax-Nmin)/Nmax+Nmin/2
- Coefficient of Steadiness: The reciprocal of the coefficient of fluctuation of speed.
m= 1/Cs = Nmean/(Nmax-Nmin)
Maximum Fluctuation of Energy
The turning moment diagram for multi-cylinder engine is shown in Figure. The horizontal line AG represents the mean line. Let a1, a3, a5 be area above mean torque line and a2, a4 and a6 be area below mean torque line.
Dimensions of the Flywheel RIM
Let D =Mean diameter of rim in meters,
R =Mean radius of rim in meters,
A =Cross-sectional area of rim in m2,
ρ =Density of rim material in kg/m3
N=Speed of the flywheel in r.p.m.,
ω=Angular velocity of the flywheel in rad/s,
ν =Linear velocity at the mean radius in m/s = ωR
σ =Tensile stress or hoop stress in N/m2 due to the centrifugal force.
∴ Total vertical upward force tending to burst the rim across the diameter XY
=2ρAR2ω2
This vertical upward force will produce tensile stress of hoop stress and it is resisted by 2P,
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