A four$-$cylinder, four$-$stroke petrol engine has a compression ratio of $6$ to $1.$ A test of this engine

gave the following results: net brake load $=20$ kg$,$ effective brake arm length $=0\mathrm{.}5$ m$,$ indicated

mean effective pressure $=6$ bar, engine speed $=2400$ rpm$,$ fuel consumption $=10$ kg$/$h$,$ calorific

value of fuel $=44$ MJ$/$kg$,$ cylinder bore $=86$ mm$,$ stroke $=100$ mm$.$ Calculate $($a$)$ the mechanical

efficiency, $($b$)$ the brake thermal efficiency, $($c$)$ the relative efficiency, assuming the engine

works on a constant volume cycle and that $\backslash$gamma $=1\mathrm{.}4$ for air and $($d$)$ the brake mean effective

pressure.Ans: $($a$)88\mathrm{.}4\%($b$)20\mathrm{.}2\%($c$)44\mathrm{.}58\%($d$)5\mathrm{.}3$ bar