DIESEL POWER PLANT 261Example 7. From the data given below, calculate indicated power, brake power and drawn heat
balance sheet for a two stroke diesel engine run for 20 minutes at full load:
r.p.m. = 350
m.e.p. = 3.1 bar
Net brake load = 640N
Fuel consumption = 1.52 kg
Cooling water = 162 kg
Water inlet temperature = 30°C
Water outlet temperature = 55°C
Air used/hg of fuel = 32 kg
Room temperature = 25°C
Exhaust temperature = 305°C
Cylinder bore = 200 mm
Cylinder stroke = 280 mm
Brake diameter = 1 metre
Calorific value of fuel = 43900 kJ/kg
Steam formed per kg of fuel in the exhaust = 1.4 kg
Specific heat of steam in exhaust = 2.09 kJ/ kg K
Specific heat of dry exhaust gases = 1.0 kJ/kg K
Solution. N = 350 r.p.m., pmi = 3.1 bar, (W – S) = 640N, mf = 1.52 kg, mw = 162 kg, tw 1 = 30°C,
tw 2 = 55°C, ma = 32 kg/kg of fuel, tr = 25°C, tg = 305°C, D = 0.2 m, L = 0.28 m, Db = 1 m, C = 43900 kJ/
kg, cps = 2.09, cPg = 1.0,
k = 1 for two stroke cycle engine.
(1) Indicated power, I.P. =?
I.P. = npmiLANk ×10
6=1 3.1 0.28 0.2^2 350 1 10
4
6π
×× × × × ××
= 15.9 kW.(2) Brake power, B.P. =?B.P. =[(W S) D N]
(60 1000)−Πb
×=(640 1 350)
60 1000×Π× ×
×= 11.73 kWHeat supplied in 20 minutes = 1.52 × 43900 = 66728 kJ
(i) Heat equivalent of I.P. in 20 minutes
= I.P. × 60 × 20 = 15.9 × 60 × 20 = 19080 kJ
(ii) Heat carried away by cooling water
= mw × Cpw × (tw 2 – twl) = 162 × 4.18 × (55 – 30) = 16929 kJ