The GATE Grind

GATE 2024 AE – Question 17

Propulsion · Gas turbine combustors: types, combustion and stoichiometric fuel-to-air ratio · 1 mark · Multiple choice

A surrogate liquid hydrocarbon fuel, approximated as C$_{10}$H$_{12}$, is being burned in a land-based gas turbine combustor with dry air (79% N$_2$ and 21% O$_2$ by volume). How many moles of dry air are required for the stoichiometric combustion of the surrogate fuel with dry air at atmospheric temperature and pressure?

  1. 61.9
  2. 30.95
  3. 13
  4. 10

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Correct answer: (A) 61.9

Explanation

$C_{10}H_{12} + a\,O_2 \rightarrow 10\,CO_2 + 6\,H_2O$ needs $a = 10 + \frac{12}{4} = 13$ moles of oxygen. Air is 21% oxygen, so the air needed is $\frac{13}{0.21} = 61.9$ moles.