Question

A single cylinder petrol engine has $90$% relative efficiency and 75% mechanical efficiency. The brake specific fuel consumption is ____ kg.h-kW. (Correct upto three decimal places) Take $\gamma$ for air 0.4

• A. 0.236

Answer 1

The correct option is A 0.236
Air standard efficiency for petrol engine,
${\eta }_{air}=1-\frac{1}{(r{)}^{\gamma -1}}=1-\frac{1}{(8{)}^{1.4-1}}$

${\eta }_{air}=0.56472$

${\eta }_{indicated}={\eta }_{air}\times n_{relative}$

$=0.56472\times 0.90$

${\eta }_{indicated}=0.50825$

${\eta }_{brake}={\eta }_{indicated}\times {\eta }_{mechanical}$

$=0.50825\times 0.75$

${\eta }_{brake}=0.3819$

Brake specific fuel consumtion

$BSFC=\frac{3600}{{\eta }_{brake}\times CV}=\frac{3600}{0.38119\times 40\times {10}^3}$

$BSFC=0.2361kg/j-kW$