to increase the output

to increase the efficiency

to save fuel

to reduce the exit temperature

10:1

15:1

20:1

60:1

2-stroke engine

4-stroke petrol engine

4-stroke diesef engine

gas turbine.

varies as square root of the speed

Varies linearly to the speed

varies as square of the speed

varies as cube of the speed

increase first at fast rate and then slow

increase first at slow rate and then fast

decrease continuously

first increase, reach maximum and then decrease