# Flywheel

The wheel on the end of the crankshaft that gives the crankshaft momentum to carry the pistons through the compression stroke.

Normally constructed from a heavy steel or iron disc.

A flywheel has two main functions:

- Moderating speed fluctuations in an engine through its inertia. Any sudden increase due to fuelling changes or load on the system will be evened out.
- Energy storage medium, as an alternative to the chemical battery.

### Angular Acceleration

The angular acceleration of a flywheel is:

where

α = angular acceleration in [rad s^{-2}]

ω_{1,2} = angular velocity at time 1 and 2 [rad s^{-1}]

t = time between 1 and 2 [s]

### Angular Velocity

The angular velocity of a flywheel is:

where

ω = angular velocity [rad s^{-1}]

N_{rpm} = rotational speed of the flywheel [revolutions per minute]

### Coefficient of Fluctuation of Energy

This is defined as the maximum fluctuation of energy to the work done per cycle.

Six Cylinder 4-stroke gas engine | 0.031 |

Four cylinder 4-stroke gas engine | 0.066 |

Cross-compound steam engine | 0.096 |

Single cylinder double acting steam engine | 0.21 |

Single cylinder 4-stroke gas engine | 1.93 |

### Coefficient of Fluctuation of Speed

The ratio of the maximum fluctuation of speed (maximum speed - minimum speed) to the mean speed.

Hammering machines | 0.2 |

Spinning machinery | 0.1 to 0.02 |

Pumping machines | 0.03 to 0.05 |

Direct drive electric machines | 0.002 |

### Energy Stored

The energy stored in a flywheel is:

where

E = energy stored [J]

I = moment of inertia of the flywheel [kgm^{2}]

ω = angular velocity of the flywheel [rad s^{-1}]

If the flywheel is attached to an engine then the **energy from the engine per revolution** is given as:

where

E_{engine} = energy from engine per revolution [J]

P = engine power [W]

N_{rpm} = engine rotational speed [revolutions per minute]

### Maximum Fluctuation of Speed

Difference between maximum and minimum speeds during a cycle.

### Reference

"Theory and Design of Automotive Engines", B Dinesh Prabhu, Assistant Professor, P E S College of Engineering, Mandya, KARNATAKA

**See also: **Energy Storage, Engine Excitation Mechanisms, Flywheel Battery, Internal Combustion Engine, Piston, Stored Mechanical Energy.

**Subjects: ** Automotive Mechanical Engineering