In an engine working on an ideal Otto cycle, the temperature at the beginning and at the end of the compression are 27°C and 327°C. What will be the compression ratio? (Assume constant specific heat and its ratio γ = 1.4)

Concept:

Otto Cycle:

• It is an air standard cycle idealized for spark ignition engines.
• It consists of 2 isochoric (constant volume) heat transfer processes and 2 adiabatic work transfer processes.
• The compression Ratio (r) of otto cycle is defined as the ratio of volume before compression to the volume after compression.

Mathematically compression ratio can be formulated as 

where Vc = Clearance Volume, Vs = Swept Volume, V1 = Volume before Compression, V2 = Volume after Compression

Since, Process 1-2 is Isentropic Process in Otto Cycle.

So relation between Volume and Temperature for the isentropic process is given by

   ..................................................... (i)

where T1 = Temperature at the beginning of compression and T2 = Temperature at the end of the compression

Calculation:

Given:

T1 = 27°C = 300 K, T2 = 327°C = 600 K

From equation (i), we have

Compression Ratio, r = 22.5