Generating stations 26

 Question = A diesel power station has the following data : • fuel consumption per day = 1000 kg , • unit generated per day = 4000 kwh , • calorific value of fuel = 10,000 kcal/kg ,  • alternator efficiency= 96% , • engine mechanical efficiency = 95% , estimate (1) specific fuel consumption , (2)  η overall , (3) thermal efficiency of engine ? 

Solution = (1)  specific fuel consumption = fuel consumption per day ÷ unit generated per day , = 1000 ÷ 4000 , = 0.25 kg/kWh , answer ✓ 

(2) η overall = electrical output in heat unit per day ÷ heat produced by fuel per day , 

• So first. 

» heat produced by fuel per day = coal consumption/day × calorific value , = 1000 × 10,000 = 10⁷ kcal , 

» electrical output in heat unit per day = 4000 × 860 = 344 ×10⁴ kcal , 

»  η overall = ( 344 ×10⁴ kcal ÷ 10⁷ kcal ) × 100 , = 34.4 % , answer ✓ 

(3) η engine =  η overall ÷ η alternator ,= 34.4 ÷ 0.96 , = 35.83 % , 

So. Thermal efficiency of engine = efficiency engine ÷ mechanical efficiency of engine  , = 35.83 ÷ 0.95 = 37.71 % , answer ✓