Question

A motor car gas turbine unit has two centrifugal compressors in series giving an overall pressure ratio of 6/1. The air leaving the HP compressor passes through a heat exchanger before entering the combustion chamber. The expansion is in two turbine stages, the first stage driving the compressors and the second stage driving the car through gearing. The gases leaving the LP turbine pass through the heat exchanger before exhausting to the atmosphere. The HP turbine inlet temperature is 800 ?C and the air inlet temperature to the unit is 15 ?C. The isentropic efficiency of the compression is 0.8, and that of each turbine is 0.85; the mechanical efficiency of each shaft is 98 %. The heat exchanger thermal ratio may be assumed to be 0.65. Neglecting pressure losses and changes in kinetic energy,

calculate: (i) the overall cycle efficiency;

(ii) the power developed when the air mass flow is 0.7 kg/s;

(iii) the specific fuel consumption when the calorific value of the fuel used is 42 600 kJ/kg, and the combustion efficiency is 97 %.

ANSWERS(29.4 %, 94.7 kW; 0.302 kg/kWh)

Answer 1

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