Propane gas (C3H8) enters a steady-flow combustion chamber at 1 atm and 25°C and is burned with air that enters the combustion chamber at the same state. Determine the adiabatic flame temperature for (a) complete combustion with 100 percent theoretical air, (b) complete combustion with 200 percent theoretical air, and (c) incomplete combustion (some CO in the products) with 90 percent theoretical air.
(a)
The adiabatic flame temperature for complete combustion with 100 percent theoretical air.
Answer to Problem 106RP
The adiabatic flame temperature for complete combustion with 100 percent theoretical air is
Explanation of Solution
Express the theoretical combustion equation of propane
Here, propane is
As the combustion process is a steady flow process, thus heat lost is equal to the heat gained.
Here, number of moles of products is
Conclusion:
Refer Equation (I), and write the number of moles of products and reactant.
Here, number of moles of products carbon dioxide, water and nitrogen is
Refer Appendix Table A-18, A-19, A-20, A-21, A-23 and A-26 and write the property table for products and reactants as in Table (1).
Substance |
|
|
0 | 8682 | |
0 | 8669 | |
9904 | ||
8669 | ||
9364 |
Substitute the values from Table (I) into Equation (II) to get,
Perform trial and error method to balance the Equation (III).
Iteration I:
Take
Iteration II:
Take
Perform the interpolation method to obtain the adiabatic flame temperature of the product gases.
Write the formula of interpolation method of two variables.
Here, the variables denote by x and y is enthalpy and adiabatic flame temperature respectively
Show the adiabatic flame temperature corresponding to enthalpy as in Table (1).
Enthalpy |
Adiabatic flame temperature |
2350 | |
2400 |
Substitute
Thus, the adiabatic flame temperature when burning with 100% theoretical air is,
Hence, the adiabatic flame temperature for complete combustion with 100 percent theoretical air is
(b)
The adiabatic flame temperature for complete combustion with 200 percent theoretical air.
Answer to Problem 106RP
The adiabatic flame temperature for complete combustion with 200 percent theoretical air is
Explanation of Solution
Express the balanced combustion equation of propane
As the combustion process is a steady flow process, thus heat lost is equal to the heat gained.
Conclusion:
Refer Equation (V), and write the number of moles of products and reactant.
Here, number of moles of products carbon dioxide, water nitrogen and oxygen is
Substitute the values from Table (I) into Equation (VI) to get,
Perform trial and error method to balance the Equation (VII).
Iteration I:
Take
Iteration II:
Take
Show the adiabatic flame temperature corresponding to enthalpy as in Table (2).
Enthalpy |
Adiabatic flame temperature |
1500 | |
1540 |
Substitute
Thus, the adiabatic flame temperature when burning with 200% theoretical air is,
Hence, the adiabatic flame temperature for complete combustion with 200 percent theoretical air is
(c)
The adiabatic flame temperature for incomplete combustion with 90 percent theoretical air.
Answer to Problem 106RP
The adiabatic flame temperature for incomplete combustion with 90 percent theoretical air is
Explanation of Solution
Express the balanced combustion equation for incomplete combustion with 90% theoretical air.
As the combustion process is a steady flow process, thus heat lost is equal to the heat gained.
Conclusion:
Refer Equation (VIII), and write the number of moles of products and reactant.
Here, number of moles of products carbon monoxide is
Substitute the values from Table (I) into Equation (IX) to get,
Perform trial and error method to balance the Equation (X).
Iteration I:
Take
Iteration II:
Take
Show the adiabatic flame temperature corresponding to enthalpy as in Table (3).
Enthalpy |
Adiabatic flame temperature |
2250 | |
2300 |
Substitute
Thus, the adiabatic flame temperature for incomplete combustion with 90 percent theoretical air,
Hence, the adiabatic flame temperature for incomplete combustion with 90 percent theoretical air is
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Chapter 15 Solutions
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