Page 114 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

88 3 Basics of Gas Combustion

3. Propane is burned in dry air at an equivalence ratio of 0.85. Determine,
a. air/fuel mass ratio
b. product gas composition

4. Ethane is burned with 50 % excess air. Determine
a. air/fuel molar ratio
b. equivalence ratio of the mixture
5. Octane (C 8 H 18 ) is burned with 25 % excess air. Determine

a. stoichiometric and actual air/fuel ratio, both on a mole and mass basis
b. equivalence ratio of the mixture
6. Ethylene (C 2 H 4 ) is burned in air at an equivalence ratio of 0.75. Determine
constant pressure AFT. Both fuel and air are initially at temperature of 298 K.
7. Acetylene (C 2 H 2 ) is burned in air at an equivalence ratio of 0.91. Determine
constant pressure AFT by assuming that both fuel and air are initially at tem-
perature of 298 K.
8. Determine which is a better fuel methanol (CH 3 OH) or methane by comparing
their constant pressure AFTs. Assume that fuel and air are initially at 298 K and
equivalence ratio is 1 in both cases. Given that enthalpy of formation of liquid
methanol at 298 K is –239,000 J/mole.
9. A fuel oil contains 88 % carbon and 12 % hydrogen by weight. Its HHV is
6
46.4 × 10 J/kg. Determine the effective chemical formula and enthalpy of
formation for this fuel.
10. Determine the stoichiometric air to fuel ratio for a fuel containing 50 % by
weight octane (C 8 H 18 ), 25 % by weight methanol (CH 3 OH), and 25% by
weight ethanol (C 2 H 5 OH), in kg of air per kg of fuel.
11. Consider a fuel having formula C 5 H 5 N is burned completely to CO 2 ,H 2 O, and
NO. Assume that there is no formation of thermal NO. Calculate the stoichi-
ometric amount of air required in kg of air per kg of fuel and only NO in
products.
12. Calculate the stoichiometric amount of air required (in kg of air per kg of fuel)
when one mole of C 5 H 10 S is burned completely and SO 2 in products.
13. Consider the reaction N 2 +O 2 ↔ 2NO. Calculate the equilibrium concentration
of NO (in ppmv) for a flue gas. The flue gas composition is 79 % N 2 ,6%O 2 ,
7%CO 2 and 8 % H 2 O at temperature of 1,500 K and pressure of 1 atm. Given
−5
K p = 1.1 × 10 .
14. NO and NO 2 formation in flames can be represented by the following two
reactions:

N 2 þ O 2 $ 2NO ð R 1 Þ

NO þ 1=2O 2 $ NO 2 ð R 2 Þ