Q24. A 6 cylinder 2-stroke diesel engine runs at 200 rev/min. The cylinder bore diameter is 800 mm and the stroke length is 1000 mm. The indicated mean effective pressure is 7.6 bar. The mechanical efficiency is 88%. The fuel consumption is 1.44 tonne/h, the calorific value of the fuel is 42000 kJ/kg and the fuel contains 15% hydrogen by mass. The air/fuel ratio by mass is 25/1. The exhaust gases leave at a temperature of 300°C, and a pressure of 1.05 bar and the dew point temperature of the exhaust is 41.5°C. The temperature of the surroundings is 30°C. The temperature rise of the cooling water is 14 K and the mass flow rate of cooling water is 80 kg/s.
Determine EACH of the following:
(a) the brake thermal efficiency
(b) the rate of heat loss to the cooling water
(c) the rate at which heat could be recovered from the exhaust gases if they were cooled at constant total pressure to a temperature of 30°C, estimating that in this process 50% of the water vapour condenses
(d) the rate of stray heat loss (not accounted for above).
Note: For water, Cp = 4.2 kJ/kg K.
For Dry exhaust gases, Cp = 1.1 kJ/kg K and R = 0.287 kJ/kg K.
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