Farm Power · Farm Power · 2 marks · Multiple choice
A three-cylinder, four-stroke diesel engine has bore73 mm, stroke78 mm, speed 2200 rpm, brake torque55 N·m and indicated mean effective pressure1050 kPa. Find mechanical efficiency in percent.
Brake power is $P_b=2\pi NT/60=2\pi(2200)(55)/60=12671.09$ W. Total displacement is $V_d=3\pi(.073)^2(.078)/4$. For a four-stroke engine,$P_i=p_mV_dN/120\approx18853.1$ W. Therefore $\eta_m=P_b/P_i=.6720968$,or **67.21%,C**.
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