Compression ratio of an internal combustion engine is defined as _______.

[V_S = Swept volume, V_C = Clearance volume]

Explanation

Volume Ratio:

• The ratio of larger volume to lesser volume during any process is known as the volume ratio of that process.
• The volume ratio during the compression process is known as the compression ratio and the volume ratio during the expansion process is known as the expansion ratio.
• Thus compression ratio is given by the ratio of volume before compression to volume after compression.

​\(Compression~ratio\left( r \right) = \frac{{{V_1}}}{{{V_2}}} = \frac{{{V_c}\; +\; {V_s}}}{{{V_c}}}\)

• The compression ratio of the petrol engine is approximately 6 to 10. As the compression ratio is low the petrol engine is lighter and cheaper.
• A diesel engine has a compression ratio of approximately 15 to 20. As the compression ratio is high diesel engine is heavier and costlier.