In SI engines for higher thermal efficiency

Explanation:

The thermal efficiency of the Otto Cycle:

\({\eta _{otto}} = 1 - \frac{1}{{{r^{\gamma - 1}}}}\)

Compression ratio: r = v₁/v₂

Conclusion:

\(\eta = f\left( {r,\gamma } \right)\)

From the above equation, it can be observed that the efficiency of the Otto cycle is mainly the function of compression ratio for the given ratio of Cp and Cv i.e. ratio of specific heats.

The thermal efficiency of the theoretical Otto cycle increases with an increase in compression ratio and specific heat ratio but is independent of the heat added (independent of load).

The efficiency of the Otto cycle is given by

\({\eta _{Otto}} = 1 - \frac{1}{{{r^{\gamma - 1}}}}\)

As \(r \uparrow ,\left( {\frac{1}{{{r^{\gamma - 1}}}}} \right) \downarrow \) and Hence \({\eta _{Otto}} \uparrow\).