Question

If the compression ratio of an engine working on Otto cycle is increases from 5 to 7, the % age increase in efficiency will be

• A. 2 %
• B. 4 %
• C. 8 %
• D. 14 %

Answer 1

The correct option is D 14 %

$\gamma =1.5$

$r^{\gamma -1}=\frac{7}{5}$

$r=\sqrt{\frac{7}{5}}\approx 1.18$

$\frac{1}{r^{\gamma -1}}=\frac{1}{1.18}\approx 0.845$

$1-\frac{1}{r^{\gamma -1}}=1-0.845\approx 0.14=\frac{14}{100}=14$%

Thus,if the compression ratio of an engine working on Otto cycle increases from 5 to 7, the % increases in the efficiency ,$\eta =14$%