Question

What is compression ratio of an Otto cycle? How does it affect the thermal efficiency of the cycle?

Answer 1

Answer:

$r= \dfrac{V_1}{V_2}$

$\eta =1-\dfrac{1}{r^{\gamma-1}}$

Explanation:

Compression ratio:

   Compression ratio is the ratio of volume in the cylinder.Generally it is denoted by r.

The compression ratio for Otto cycle is about 8 to 12.But the compression ratio of diesel engine is about 14 to 25.

So from the Otto cycle compression ratio can be define as

$r= \dfrac{V_1}{V_2}$

As we know that efficiency defines as the ratio of work out to the heat input.In the Otto cycle the efficiency is given as in terms of compression ratio r as

$\eta =1-\dfrac{1}{r^{\gamma-1}}$

Where γ is the heat capacity ratio.