GATE 2020 AE – Question 58

Propulsion · Gas turbine combustors: types, combustion and stoichiometric fuel-to-air ratio · 2 marks · Numerical answer

An aircraft combustor receives air total enthalpy at 28.94 MJ/s and discharges at 115.42 MJ/s. Air flow is 32 kg/s, air/fuel mass ratio 15.6, and fuel lower heating value 46 MJ/kg. Find combustor efficiency in percent to 2 decimals.

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Correct answer: 91 to 93

Explanation

Fuel flow is $\dot m_f=32/15.6=2.05128$ kg/s. Fuel chemical-energy rate is $2.05128(46)=94.35897$ MJ/s. The useful total-enthalpy rise is 115.42−28.94 = 86.48 MJ/s. Thus $\eta_b=100(86.48/94.35897)=91.65\%$ in the paper’s stated enthalpy-rate convention.

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