$1\mathrm{.}26$ A certain engine with a bore of $250$ mm has an indicated thermal effi$-$

ciency of $30\%.$ The bsfc and specific power output are $0\mathrm{.}35k\frac{g}{k}Wh$

and $90k\frac{W}{m^2}.$ Find the mechanical efficiency and brake thermal effi$-$

ciency of the engine. Take the calorific value of the fuel as $42M\frac{J}{k}g.$

Ans:

$($i$)81\mathrm{.}7\%($ii$)24\mathrm{.}5\%$