Aerothermal Propulsion

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Aerothermal Propulsion

• Lecture 4
• Chemical Reactions of Combustion

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Agenda

• Combusting Flows
• Heats of Formation
• Equilibrium Reaction Rates

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Combustion
Combustion is a chemical reaction that releases
energy
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Combustion in Flows
Energy release in a flow means propulsion
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Steady Flow Combustion
Q?H Hproduct H reactants
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Steady Flow Combustion
Q?H Hproduct H reactants C(solid) ½ O2
(gas) -110,530kJ/kmole CO 28kg/kmole , ?HCO2
-3.94MJ/kg
?HCO defined for given temperature (25C) and
final state (gas)
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Steady Flow Combustion
Q?H Hproduct H reactants C(solid) O2 (gas)
-393,522 kJ/kmole CO2 44kg/kmole , ?HCO2
-8.94MJ/kg
?HCO2 defined for given (25C) and final state
(gas) CO2 formation better than CO
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Steady Flow Combustion
Q?H Hproduct H reactants H2(gas) ½ O2 (gas)
-241,820 kJ/kmole H2O 18kg/kmole , ?HCO2
-13.4MJ/kg
?HH2O defined for given (25C) and final state
(gas)
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Isothermal Combustion Analysis
Product at Tf
Reactants at Tf
Steady Flow Reaction Chamber
Qf
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Combustion Analysis Cont.
Product at TFinal
Reactants at Treference
Steady Flow Reaction Chamber
Qf
Isothermal reactions at Treference
Reaction products
Elemental reactants
Reactants at Treference
Decomposition Reaction Chamber
Formation Reaction Chamber
Mixing Chamber
Product at TFinal
Q3?HFinal
Q1
Q2
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Chemical Equilibrium
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Chemical Equilibrium
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Chemical Equilibrium
Example H2 ½ O2 ?? H2O
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Chemical Equilibrium
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Stoichiometric Mixtures
2H2 O2 ? H20 Molar ratio of H2O2 of 21
required for reaction to go to completion. O-16,
H-1 molar weight so 2/1 x 1/16 1/8 ratio of
oxygen to hydrogen by mass for complete
combustion
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Stoichiometric Mixtures
CH4 3O2 ? CO2 2H2O MethaneOxygen 13 mole
ratio for complete combustion CH412416amu,
3O26x16amu96 13 1696 ? 16 mass
ratio Oxygen is heavy! Why not get it from the
air?
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Stoichiometric Mixtures Cont.
Make sure to do dimensional analysis!
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Examples of Shifting Composition and Temperature
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Octane C8H18 burned with air Stoichiometric
mixture Tfinal 2000K
High oxygen and high temperature produces CO2 and
water
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Octane C8H18 burned with air at ½ stoichiometric
(fuel rich) Tfinal 2000K
Fuel rich high temperature produces CO and 50/50
hydrogen and water
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Octane C8H18 burned with air ½ stoichiometric
(fuel rich) Tfinal 1000K
Fuel rich, low temperature, produces CO and
hydrogen rich product -carbon grabs all the oxygen