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mechanical engineering

Thermodynamics An Engineering Approach 8th edition Yunus A. Cengel, Michael A. Boles - Solutions

What is the air–fuel ratio? How is it related to the fuel–air ratio?
What are the causes of incomplete combustion?
Which is more likely to be found in the products of an incomplete combustion of a hydrocarbon fuel, CO or OH? Why?
What does 100 percent theoretical air represent?
Are complete combustion and theoretical combustion identical? If not, how do they differ?
Methane (CH4) is burned with stoichiometric amount of air during a combustion process. Assuming complete combustion, determine the air–fuel and fuel–air ratios.
Propane (C3H8) is burned with 75 percent excess air during a combustion process. Assuming complete combustion, determine the air–fuel ratio.
Acetylene (C2H2) is burned with stoichiometric amount of air during a combustion process. Assuming complete combustion, determine the air–fuel ratio on a mass and on a mole basis.
One kmol of ethane (C2H6) is burned with an unknown amount of air during a combustion process. An analysis of the combustion products reveals that the combustion is complete, and there are 3 kmol of free O2 in the products. Determine (a) The air–fuel ratio and (b) The percentage of
Ethylene (C2H4) is burned with 200 percent theoretical air during a combustion process. Assuming complete combustion and a total pressure of 14.5 psia, determine (a) The air–fuel ratio and (b) The dew-point temperature of the products.
Propylene (C3H6) is burned with 50 percent excess air during a combustion process. Assuming complete combustion and a total pressure of 105 kPa, determine (a) The air–fuel ratio and (b) The temperature at which the water vapor in the products will start condensing.
Propel alcohol (C3H7OH) is burned with 50 percent excess air. Write the balanced reaction equation for complete combustion and determine the air-to-fuel ratio.
Butane (C4H10) is burned in 200 percent theoretical air. For complete combustion, how many kmol of water must be sprayed into the combustion chamber per kmol of fuel if the products of combustion are to have a dew-point temperature of 60°C when the product pressure is 100 kPa?
A fuel mixture of 20 percent by mass methane (CH4) and 80 percent by mass ethanol (C2H6O) is burned completely with theoretical air. If the total flow rate of the fuel is 31 kg/s, determine the required flow rate of air.
Octane (C8H18) is burned with 250 percent theoretical air, which enters the combustion chamber at 25°C. Assuming complete combustion and a total pressure of 1 atm, determine(a) The air€“fuel ratio and(b) The dew-point temperature of the products.
Gasoline (assumed C8H18) is burned steadily with air in a jet engine. If the air–fuel ratio is 18 kg air/kg fuel, determine the percentage of theoretical air used during this process.
In a combustion chamber, ethane (C2H6) is burned at a rate of 8 kg/h with air that enters the combustion chamber at a rate of 176 kg/h. Determine the percentage of excess air used during this process.
One kilogram of butane (C4H10) is burned with 25 kg of air that is at 30°C and 90 kPa. Assuming that the combustion is complete and the pressure of the products is 90 kPa, determine (a) The percentage of theoretical air used and (b) The dew-point temperature of the products.
One lbm of butane (C4H10) is burned with 25 lbm of air that is at 90°F and 14.7 psia. Assuming that the combustion is complete and the pressure of the products is 14.7 psia, determine (a) The percentage of theoretical air used and (b) The dew-point temperature of the products.
A certain natural gas has the following volumetric analysis: 65 percent CH4, 8 percent H2, 18 percent N2, 3 percent O2, and 6 percent CO2. This gas is now burned completely with the stoichiometric amount of dry air. What is the air–fuel ratio for this combustion process?
Repeat Prob. 15–27 by replacing the dry air by moist air that enters the combustion chamber at 25°C, 1 atm, and 85 percent relative humidity.
A gaseous fuel with a volumetric analysis of 60 percent CH4, 30 percent H2, and 10 percent N2 is burned to completion with 130 percent theoretical air. Determine (a) The air–fuel ratio and (b) The fraction of water vapor that would condense if the product gases were cooled to 20°C at 1 atm.
Reconsider Prob. 15–29. Using EES (or other) software, study the effects of varying the percentages of CH4, H2, and N2 making up the fuel and the product gas temperature in the range 5 to 150°C.
A certain coal has the following analysis on a mass basis: 82 percent C, 5 percent H2O, 2 percent H2, 1 percent O2, and 10 percent ash. The coal is burned with 50 percent excess air. Determine the air–fuel ratio.
Octane (C8H18) is burned with dry air. The volumetric analysis of the products on a dry basis is 9.21 percent CO2, 0.61 percent CO, 7.06 percent O2, and 83.12 percent N2. Determine (a) The air–fuel ratio and (b) The percentage of theoretical air used.
Carbon (C) is burned with dry air. The volumetric analysis of the products is 10.06 percent CO2, 0.42 percent CO, 10.69 percent O2, and 78.83 percent N2. Determine (a) The air–fuel ratio and (b) The percentage of theoretical air used.
Methane (CH4) is burned with dry air. The volumetric analysis of the products on a dry basis is 5.20 percent CO2, 0.33 percent CO, 11.24 percent O2, and 83.23 percent N2. Determine (a) The air–fuel ratio and (b) The percentage of theoretical air used.
What is enthalpy of combustion? How does it differ from the enthalpy of reaction?
What is enthalpy of formation? How does it differ from the enthalpy of combustion?
What are the higher and the lower heating values of a fuel? How do they differ? How is the heating value of a fuel related to the enthalpy of combustion of that fuel?
When are the enthalpy of formation and the enthalpy of combustion identical?
The hf of N2 is listed as zero. Does this mean that N2 contains no chemical energy at the standard reference state?
Which contains more chemical energy, 1 kmol of H2 or 1 kmol of H2O?
Determine the enthalpy of combustion of methane (CH4) at 25°C and 1 atm, using the enthalpy of formation data from Table A–26. Assume that the water in the products is in the liquid form. Compare your result to the value listed in Table A–27.
Reconsider Prob. 15–42. Using EES (or other) software, study the effect of temperature on the enthalpy of combustion. Plot the enthalpy of combustion as a function of temperature over the range 25 to 600°C.
Repeat Prob. 15–42 for gaseous ethane (C2H6).
Repeat Prob. 15–42 for liquid octane (C8H18).
Derive an energy balance relation for a reacting closed system undergoing a quasi-equilibrium constant pressure expansion or compression process.
Consider a complete combustion process during which both the reactants and the products are maintained at the same state. Combustion is achieved with (a) 100 percent theoretical air, (b) 200 percent theoretical air, and (c) The chemically correct amount of pure oxygen. For which case will the
Consider a complete combustion process during which the reactants enter the combustion chamber at 20°C and the products leave at 700°C. Combustion is achieved with (a) 100 percent theoretical air, (b) 200 percent theoretical air, and (c) The chemically correct amount of pure oxygen. For
Methane (CH4) is burned completely with the stoichiometric amount of air during a steady-flow combustion process. If both the reactants and the products are maintained at 25°C and 1 atm and the water in the products exists in the liquid form, determine the heat transfer from the combustion chamber
Hydrogen (H2) is burned completely with the stoichiometric amount of air during a steady-flow combustion process. If both the reactants and the products are maintained at 25°C and 1 atm and the water in the products exists in the liquid form, determine the heat transfer from the combustion chamber
Liquid propane (C3H8) enters a combustion chamber at 25°C at a rate of 1.2 kg/min where it is mixed and burned with 150 percent excess air that enters the combustion chamber at 12°C. If the combustion is complete and the exit temperature of the combustion gases is 1200 K, determine(a) The
Liquid propane (C3H8) enters a combustion chamber at 77°F at a rate of 0.75 lbm/min where it is mixed and burned with 150 percent excess air that enters the combustion chamber at 40°, if the combustion is complete and the exit temperature of the combustion gases is 1800 R, determine (a) The
Acetylene gas (C2H2) is burned completely with 20 percent excess air during a steady-flow combustion process. The fuel and air enter the combustion chamber at 25°C, and the products leave at 1500 K. Determine (a) the air–fuel ratio and (b) the heat transfer for this process.
Liquid octane (C8H18) at 77°F is burned completely during a steady-flow combustion process with 180 percent theoretical air that enters the combustion chamber at 77°F. If the products leave at 2500 R, determine (a) The air–fuel ratio and (b) The heat transfer from the combustion chamber
Benzene gas (C6H6) at 25°C is burned during a steady-flow combustion process with 95 percent theoretical air that enters the combustion chamber at 25°C. All the hydrogen in the fuel burns to H2O, but part of the carbon burns to CO, if the products leave at 1000 K, determine (a) The mole
Diesel fuel (C12H26) at 25°C is burned in a steady flow combustion chamber with 20 percent excess air that also enters at 25°C. The products leave the combustion chamber at 500 K. Assuming combustion is complete determine the required mass flow rate of the diesel fuel to supply heat at a rate of
Diesel fuel (C12H26) at 77°F is burned in a steady flow combustion chamber with 20 percent excess air that also enters at 77°F. The products leave the combustion chamber at 800 R. Assuming combustion is complete determine the required mass flow rate of the diesel fuel to supply heat at a rate of
Octane gas (C8H18) at 25°C is burned steadily with 30 percent excess air at 25°C, 1 atm, and 60 percent relative humidity. Assuming combustion is complete and the products leave the combustion chamber at 600 K, determine the heat transfer for this process per unit mass of octane.
Reconsider Prob. 15–58. Using EES (or other) software, investigate the effect of the amount of excess air on the heat transfer for the combustion process. Let the excess air vary from 0 to 200 percent. Plot the heat transfer against excess air, and discuss the results.
Ethane gas (C2H6) at 25°C is burned in a steady-flow combustion chamber at a rate of 5 kg/h with the stoichiometric amount of air, which is preheated to 500 K before entering the combustion chamber. An analysis of the combustion gases reveals that all the hydrogen in the fuel burns to H2O but
A constant-volume tank contains a mixture of 120 g of methane (CH4) gas and 600 g of O2 at 25°C and 200 kPa. The contents of the tank are now ignited, and the methane gas burns completely. If the final temperature is 1200 K, determine (a) The final pressure in the tank and (b) The heat
Reconsider Prob. 15–61. Using EES (or other) software, investigate the effect of the final temperature on the final pressure and the heat transfer for the combustion process. Let the final temperature vary from 500 to 1500 K. Plot the final pressure and heat transfer against the final
A closed combustion chamber is designed so that it maintains a constant pressure of 300 kPa during a combustion process. The combustion chamber has an initial volume of 0.5 m3 and contains a stoichiometric mixture of octane (C8H18) gas and air at 25°C. The mixture is now ignited, and the product
A constant-volume tank contains a mixture of 1 kmol of benzene (C6H6) gas and 30 percent excess air at 25°C and 1 atm. The contents of the tank are now ignited, and all the hydrogen in the fuel burns to H2O but only 92 percent of the carbon burns to CO2, the remaining 8 percent forming CO. If the
A constant-volume tank contains a mixture of 1 lb mol of benzene (C6H6) gas and 30 percent excess air at 77°F and 1 atm. The contents of the tank are now ignited, and all the hydrogen in the fuel burns to H2O but only 92 percent of the carbon burns to CO2, the remaining 8 percent forming CO. If
To supply heated air to a house, a high-efficiency gas furnace burns gaseous propane (C3H8) with a combustion efficiency of 96 percent. Both the fuel and 140 percent theoretical air are supplied to the combustion chamber at 25°C and 100 kPa, and the combustion is complete. Because this is a
Liquid ethyl alcohol (C2H5OH( )) at 25°C is burned in a steady-flow combustion chamber with 40 percent excess air that also enters at 25°C. The products leave the combustion chamber at 600 K. Assuming combustion is complete determine the required volume flow rate of the liquid ethyl alcohol, to
A fuel is completely burned first with the stoichiometric amount of air and then with the stoichiometric amount of pure oxygen. For which case will the adiabatic flame temperature be higher?
Hydrogen (H2) at 7°C is burned with 20 percent excess air that is also at 7°C during an adiabatic steady-flow combustion process. Assuming complete combustion, determine the exit temperature of the product gases.
Reconsider Prob. 15–70. Using EES (or other) software, modify this problem to include the fuels butane, ethane, methane, and propane as well as H2; to include the effects of inlet air and fuel temperatures; and the percent theoretical air supplied. Select a range of input parameters and discuss
Hydrogen (H2) at 40°F is burned with 20 percent excess air that is also at 40°F during an adiabatic steady-flow combustion process. Assuming complete combustion, find the exit temperature of the product gases.
Acetylene gas (C2H2) at 25°C is burned during a steady-flow combustion process with 30 percent excess air at 27°C. It is observed that 75,000 kJ of heat is being lost from the combustion chamber to the surroundings per kmol of acetylene. Assuming combustion is complete determine the exit
An adiabatic constant-volume tank contains a mixture of 1 kmol of hydrogen (H2) gas and the stoichiometric amount of air at 25°C and 1 atm. The contents of the tank are now ignited. Assuming complete combustion, determine the final temperature in the tank.
Octane gas (C8H18) at 25°C is burned steadily with 30 percent excess air at 25°C, 1 atm, and 60 percent relative humidity. Assuming combustion is complete and adiabatic calculate the exit temperature of the product gases.
Reconsider Prob. 15–75. Using EES (or other) software, investigate the effect of the relative humidity on the exit temperature of the product gases. Plot the exit temperature of the product gases as a function of relative humidity for 0 < 0 < 100 percent.
Express the increase of entropy principle for chemically reacting systems.
How are the absolute entropy values of ideal gases at pressures different from 1 atm determined?
One kmol of H2 at 25°C and 1 atm is burned steadily with 0.5 kmol of O2 at the same state. The H2O formed during the process is then brought to 25°C and 1 atm, the conditions of the surroundings. Assuming combustion is complete determine the reversible work and energy destruction for this process.
Ethylene (C2H4) gas enters an adiabatic combustion chamber at 25°C and 1 atm and is burned with 20 percent excess air that enters at 25°C and 1 atm. The combustion is complete, and the products leave the combustion chamber at 1 atm pressure. Assuming T0 = 25°C, determine (a) The temperature of
Liquid octane (C8H18) enters a steady-flow combustion chamber at 25°C and 1 atm at a rate of 0.25 kg/min. It is burned with 50 percent excess air that also enters at 25°C and 1 atm. After combustion, the products are allowed to cool to 25°C. Assuming complete combustion and that all the H2O in
Acetylene gas (C2H2) is burned completely with 20 percent excess air during a steady-flow combustion process. The fuel and the air enter the combustion chamber separately at 25°C and 1 atm, and heat is being lost from the combustion chamber to the surroundings at 25°C at a rate of 300,000 kJ/kmol
A steady-flow combustion chamber is supplied with CO gas at 37°C and 110 kPa at a rate of 0.4 m3/min and air at 25°C and 110 kPa at a rate of 1.5 kg/min. Heat is transferred to a medium at 800 K, and the combustion products leave the combustion chamber at 900 K. Assuming the combustion is
Benzene gas (C6H6) at 1 atm and 77°F is burned during a steady-flow combustion process with 95 percent theoretical air that enters the combustion chamber at 77°F and 1 atm. All the hydrogen in the fuel burns to H2O, but part of the carbon burns to CO. Heat is lost to the surroundings at 77°F,
Liquid propane (C3H8) enters a steady-flow combustion chamber at 25°C and 1 atm at a rate of 0.4 kg/min where it is mixed and burned with 150 percent excess air that enters the combustion chamber at 12°C. If the combustion products leave at 1200 K and 1 atm, determine (a) the mass flow rate of
Reconsider Prob. 15–86. Using EES (or other) software study the effect of varying the surroundings temperature from 0 to 38°C on the rate of energy destruction, and plot it as a function of surroundings temperature
A 1-g sample of a certain fuel is burned in a bomb calorimeter that contains 2 kg of water in the presence of 100 g of air in the reaction chamber. If the water temperature rises by 2.5°C when equilibrium is established, determine the heating value of the fuel, in kJ/kg.
Hydrogen (H2) is burned with 100 percent excess air that enters the combustion chamber at 90°F, 14.5 psia, and 60 percent relative humidity. Assuming complete combustion, determine (a) The air–fuel ratio and (b) The volume flow rate of air required to burn the hydrogen at a rate of 25 lbm/h.
A gaseous fuel with 80 percent CH4, 15 percent N2, and 5 percent O2 (on a mole basis) is burned to completion with 120 percent theoretical air that enters the combustion chamber at 30°C, 100 kPa, and 60 percent relative humidity. Determine (a) The air–fuel ratio and (b) The volume flow rate
A gaseous fuel with 80 percent CH4, 15 percent N2, and 5 percent O2 (on a mole basis) is burned with dry air that enters the combustion chamber at 25°C and 100 kPa. The volumetric analysis of the products on a dry basis is 3.36 percent CO2, 0.09 percent CO, 14.91 percent O2, and 81.64 percent
A steady-flow combustion chamber is supplied with CO gas at 37°C and 110 kPa at a rate of 0.4 m3/min and air at 25°C and 110 kPa at a rate of 1.5 kg/min. The combustion products leave the combustion chamber at 900 K. Assuming combustion is complete determine the rate of heat transfer from the
Methane gas (CH4) at 25°C is burned steadily with dry air that enters the combustion chamber at 17°C. The volumetric analysis of the products on a dry basis is 5.20 percent CO2, 0.33 percent CO, 11.24 percent O2, and 83.23 percent N2. Determine (a) The percentage of theoretical air used and (b)
A 6-m3 rigid tank initially contains a mixture of 1 kmol of hydrogen (H2) gas and the stoichiometric amount of air at 25°C. The contents of the tank are ignited, and all the hydrogen in the fuel burns to H2O. If the combustion products are cooled to 25°C, determine (a) The fraction of the H2O
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 300 percent
Determine the highest possible temperature that can be obtained when liquid gasoline (assumed C8H18) at 25°C is burned steadily with air at 25°C and 1 atm. What would your answer be if pure oxygen at 25°C were used to burn the fuel instead of air?
Determine the work potential of 1 lb mol of diesel fuel (C12H26) at 77°F and 1 atm in an environment at the same state.
Liquid octane (C8H18) enters a steady-flow combustion chamber at 25°C and 8 atm at a rate of 0.8 kg/min. It is burned with 200 percent excess air that is compressed and preheated to 500 K and 8 atm before entering the combustion chamber. After combustion, the products enter an adiabatic turbine at
The combustion of a fuel usually results in an increase in pressure when the volume is held constant, or an increase in volume when the pressure is held constant, because of the increase in the number of moles and the temperature. The increase in pressure or volume will be maximum when the
Reconsider Prob. 15–99. Using EES (or other) software, investigate the effect of the initial volume of the combustion chamber over the range 0.1 to 2.0 liters on the results. Plot the maximum pressure of the chamber for constant volume combustion or the maximum volume of the chamber for constant
Repeat Prob. 15–99 using methane (CH4 (g)) as the fuel instead of methyl alcohol.
A mixture of 40 percent by volume methane (CH4), and 60 percent by volume propane (C3H8), is burned completely with theoretical air and leaves the combustion chamber at 100°C. The products have a pressure of 100 kPa and are cooled at constant pressure to 39°C. Sketch the T-s diagram for the water
Liquid propane (C3H8(ℓ)) enters a combustion chamber at 25°C and 1 atm at a rate of 0.4 kg/min where it is mixed and burned with 150 percent excess air that enters the combustion chamber at 25°C. The heat transfer from the combustion process is 53 kW. Write the balanced combustion equation
A gaseous fuel mixture of 30 percent propane (C3H8), and 70 percent butane (C4H10), on a volume basis is burned in air such that the air–fuel ratio is 20 kg air/kg fuel when the combustion process is complete. Determine (a) the moles of nitrogen in the air supplied to the combustion process, in
A liquid–gas fuel mixture consists of 90 percent octane (C8H18), and 10 percent alcohol (C2H5OH), by moles. This fuel is burned with 200 percent theoretical dry air. Write the balanced reaction equation for complete combustion of this fuel mixture. Determine (a) the theoretical air–fuel ratio
The furnace of a particular power plant can be considered to consist of two chambers: an adiabatic combustion chamber where the fuel is burned completely and adiabatically and a heat exchanger where heat is transferred to a Carnot heat engine isothermally. The combustion gases in the heat exchanger
A consist of two chambers: an adiabatic combustion chamber where the fuel is burned completely and adiabatically and a counter flow heat exchanger where heat is transferredto a reversible heat engine. The mass flow rate of the working fluid of the heat engine is such that the working fluid is
Using EES (or other) software, determine the effect of the amount of air on the adiabatic flame temperature of liquid octane (C8H18). Assume both the air and the octane is initially at 25°C. Determine the adiabatic flame temperature for 75, 90, 100, 120, 150, 200, 300, 500, and 800 percent
Using EES (or other) software, write a general program to determine the heat transfer during the complete combustion of a hydrocarbon fuel (CnHm) at 25°C in a steady-flow combustion chamber when the percent of excess air and the temperatures of air and the products are specified. As a sample case,
Using EES (or other) software, write a general program to determine the adiabatic flame temperature during the complete combustion of a hydrocarbon fuel (CnHm) at 25°C in a steady-flow combustion chamber when the percent of excess air and its temperature are specified. As a sample case, determine

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