
(a)
The theoretical air fuel ratio required for the combustion reaction.
(a)

Answer to Problem 99RP
The theoretical air fuel ratio required for the combustion reaction is
Explanation of Solution
Write the chemical reaction for the combustion of liquid gas fuel mixture of 90% octane and 10% alcohol with 200% excess theoretical amount of air.
Write the expression to calculate the theoretical air-fuel ratio
Here, mass of the air is
Conclusion:
Balance for the Carbon from Combustion reaction Equation (I).
Balance for the Hydrogen from Combustion reaction Equation (I).
Balance for the excess Oxygen from Combustion reaction Equation (I).
Balance for the Oxygen from Combustion reaction Equation (I).
Substitute
Balance for the Nitrogen from Combustion reaction Equation (I).
Substitute
Rewrite the complete balanced chemical reaction for combustion as follows:
From the table A-2 of “Molar mass, gas constants, and critical-point properties”, select the molar masses of carbon dioxide, water, air, oxygen, nitrogen, octane and alcohol as,
Substitute
Thus, the theoretical air fuel ratio required for the combustion reaction is
(b)
The ratio of products of the combustion to the fuel.
(b)

Answer to Problem 99RP
The ratio of products of the combustion to the fuel is
Explanation of Solution
Write the formula to calculate the molar mass of the product gases
Here, number of moles of carbon dioxide is
Write the formula to calculate the mass of the product gases per unit mass of fuel
Conclusion:
Substitute
Substitute
Thus, the ratio of products of the combustion to the fuel is
(c)
The mass flow rate of the air required for the combustion.
(c)

Answer to Problem 99RP
The mass flow rate of the air required for the combustion is
Explanation of Solution
Write the formula to calculate the actual air-fuel ratio
Write the formula to calculate the mass flow rate of air
Here, mass flow rate of fuel is
Conclusion:
Substitute
Substitute
Thus, the mass flow rate of the air required for the combustion is
(d)
The lower heating value of the fuel mixture.
(d)

Answer to Problem 99RP
The lower heating value of the fuel mixture is
Explanation of Solution
Write the expression to calculate the equation for steady-flow energy balance.
Here, enthalpy of product is
Write the expression to calculate the enthalpy of reactant
Here, enthalpy of vaporization is
Write the expression to calculate the enthalpy of product
Calculate the lower heating value on mass basis
Write the formula to calculate the lower heating value on mass basis
Conclusion:
From the Table A-18 through Table A-26, obtain the enthalpies of vaporization and enthalpies of formation for different substances as in Table 1.
Substance |
Enthalpy of vaporization |
Enthalpy of formation at 298 K |
41,465 | ||
42,340 | ||
0 | 8682 | |
0 | 8669 | |
9364 | ||
9904 |
Substitute
Substitute
Substitute
Substitute
Thus, the lower heating value of the fuel mixture is
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Chapter 15 Solutions
Thermodynamics: An Engineering Approach
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