Question
1.-Using octane C8H18 as fuel in combustion with an excess of 10% of theoretical air. Calculate the heat released if air enters the combustion process at 25°C and gases exit the combustion chamber at 327°C.
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Answer to a math question 1.-Using octane C8H18 as fuel in combustion with an excess of 10% of theoretical air. Calculate the heat released if air enters the combustion process at 25°C and gases exit the combustion chamber at 327°C.
Birdie
4.5104 Answers
1. **Balanced Combustion Equation with Theoretical Air:**
- Combustion of octane:
C_8H_{18} + 12.5 O_2 \rightarrow 8 CO_2 + 9 H_2O
- With theoretical air:
C_8H_{18} + 12.5 O_2 + 12.5 \left(\frac{79}{21} N_2\right) \rightarrow 8 CO_2 + 9 H_2O + 12.5 \left(\frac{79}{21} N_2\right)
2. **Combustion with 10% Excess Air:**
- Total air with 10% excess:
\text{Total air} = 1.1 \times \text{theoretical air}
- Updated equation:
C_8H_{18} + 1.1 \times 12.5 \left(O_2 + \frac{79}{21} N_2\right) \rightarrow 8 CO_2 + 9 H_2O + 1.1 \times 12.5 \left(\frac{79}{21} N_2\right) + 0.1 \times 12.5 O_2
3. **Calculate the Heat Released:**
- Enthalpy of Combustion:
\text{LHV of octane} = 44,740 \, \text{kJ/kg}
- Molecular weight of octane:
114.23 \, \text{g/mol}
- Heat released per mole:
\text{Heat released per mole} = 44,740 \, \text{kJ/kg} \times \frac{114.23 \, \text{g/mol}}{1000 \, \text{g/kg}} = 5112.7 \, \text{kJ/mol}
4. **Heat Change Due to Exit Temperature:**
- \( Q = \Delta H = H_\text{enter} - H_\text{exit} \)
- Assuming minor variations of heat capacity, results in:
Q = 5112.7 \, \text{kJ/mol}
The heat released from the combustion of octane with 10% excess air, with the given conditions, is approximately **5112.7 kJ per mole** of octane.
- Combustion of octane:
- With theoretical air:
2. **Combustion with 10% Excess Air:**
- Total air with 10% excess:
- Updated equation:
3. **Calculate the Heat Released:**
- Enthalpy of Combustion:
- Molecular weight of octane:
- Heat released per mole:
4. **Heat Change Due to Exit Temperature:**
- \( Q = \Delta H = H_\text{enter} - H_\text{exit} \)
- Assuming minor variations of heat capacity, results in:
The heat released from the combustion of octane with 10% excess air, with the given conditions, is approximately **5112.7 kJ per mole** of octane.
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