Explanation Write the complete balanced reaction for combustion of methyl alcohol with 200% excess theoretical amount of air. CH 3 OH + 3 a th ( O 2 + 3.76 N 2 ) → CO 2 + 2 H 2 O + 2 a th O 2 + ( 3 ) 3.76 a th N 2 (I) Write the energy balance equation for the combustion of octane ( C 3 H 8 ) . − Q out = ∑ N P ( h ¯ f o + h ¯ − h ¯ o ) P − ∑ N R ( h ¯ f o + h ¯ − h ¯ o ) R (II) Here, the amount of heat transfer for the combustion of octane gas is Q out , number of moles of product is N P , number of moles of reactants is N R , enthalpy of vaporization is h ¯ f o , enthalpy of formation at a temperature is h ¯ , and the enthalpy of formation at the standard reference state is h ¯ o . Write the formula to calculate the entropy of an i component ( S i ) . S i = N i s ¯ i ( T , P i ) S i = N i [ s ¯ i o ( T , P o ) − R u ln ( y i P m ) ] (III) Here, number of moles of i component is N i , entropy of the i component is s ¯ i ( T , P i ) , entropy of vaporization is s ¯ i o ( T , P o ) , universal gas constant is R u , mole fraction of i component is y i , and the total pressure is P m . Write the formula to calculate the entropy generation ( S gen ) for the combustion process. S gen = S P − S R + Q out T surr (IV) Here, entropy of the products is S P , entropy of the reactants is S R , and the temperature of the surroundings is T surr . Write the formula to calculate the maximum amount of work generated ( W max ) from the automobile engine. W max = X dest M fuel W max = T o S gen M fuel (V) Here, exergy destroyed is X dest , molar mass of fuel is M fuel , and surrounding temperature is T o . Conclusion: Balance for the oxygen from combustion equation (I). 0.5 + 3 a th = 1 + 1 + 2 a th a th = 1.5 Rewrite the combustion reaction of propane with 95% theoretical amount of air. CH 3 OH + 4.5 ( O 2 + 3.76 N 2 ) → CO 2 + 2 H 2 O + 3 O 2 + 16.92 N 2 (VI) Rewrite the Equation (II) for the heat transfer from combustion. − Q out = { N CO 2 ( h ¯ f ∘ + h ¯ − h ¯ ∘ ) CO 2 + N H 2 O ( h ¯ f ∘ + h ¯ − h ¯ ∘ ) H 2 O + N O 2 ( h ¯ f ∘ + h ¯ − h ¯ ∘ ) O 2 + N N 2 ( h ¯ f ∘ + h ¯ − h ¯ ∘ ) N 2 − N CH 3 OH ( h ¯ f ∘ ) CH 3 OH } (VII) Here, number of moles of product is N P , number of moles of reactants is N R , number of moles of CO 2 is N CO 2 , number of moles of H 2 O is N H 2 O , number of moles of O 2 is N O 2 , number of moles of N 2 is N N 2 , number of moles of CH 3 OH is N CH 3 OH

8th Edition

ISBN: 9780073398174

Author: Yunus A. Cengel Dr., Michael A. Boles

Publisher: McGraw-Hill Education

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Chapter 15.7, Problem 88P

To determine

The maximum amount of work that can be generated from the automobile engine.

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Chapter 15.7, Problem 87P

Chapter 15.7, Problem 89P

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Chapter 15 Solutions

Thermodynamics: An Engineering Approach

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