2nd Semester Faculty of Engineering- Mataria
Mechanical Power Engineering Dept.
2024-2025
Course Code: MPE 305
Course Level: 3
Sheet (1): Course Title: Combustion
Fuels and Combustion Course Max. Grades: 150 marks
Course Offered By
UNV ENG MPE AUT MDE CIV ARC ENE SEP ADT AMP
Answer the following Questions:
1- What are the main characteristics of a good fuel? Name and explain the properties of liquid
fuel.
2- What are the Conditions necessary for combustion?
3- With the aid of a sketch, classify the different types of combustion.
4- What are the causes of incomplete combustion?
5- Which is more likely to be found in the products of an incomplete combustion of a
hydrocarbon fuel, CO or OH? Why?
6- What does 100 percent theoretical air represent?
7- Are complete combustion and theoretical combustion identical? If not, how do they
differ?
8- Consider a fuel that is burned with (a) 130 percent theoretical air and (b) 70 percent
excess air. In which case is the fuel burned with more air?
9- One kmol of octane (C8H18) is burned with air that
contains 20 kmol of O2, as shown in Fig. 1.
Assuming the products contain only CO2, H2O, O2,
and N2, determine the mole number of each gas in
the products and the air-fuel ratio for this
combustion process. The molar mass of air is Mair =28.97 kg/kmol = 29.0 kg/kmol (Table
A–1).
10- Ethane (C2H6) is burned with 20 percent excess air
during a combustion process, as shown in Fig. 2.
Assuming complete combustion and a total pressure
of 100 kPa, determine (a) the air-fuel ratio and (b)
the dew-point temperature of the products. Use table
(Table A–5).
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Ahmed Emara
11- A certain natural gas has the following volumetric
analysis: 72 percent CH4, 9 percent H2, 14 percent
N2, 2 percent O2, and 3 percent CO2. This gas is now
burned with the stoichiometric amount of air that
enters the combustion chamber at 20°C, 1 atm, and
80 percent relative humidity, as shown in Fig. 3. Assuming complete combustion and a
total pressure of 1 atm, determine the dew-point temperature of the products.
12- Octane (C8H18) is burned with dry air. The volumetric analysis of the products on a dry
basis is (Fig. 4): CO2: 10.02 percent, O2: 5.62 percent, CO: 0.88 percent, N2: 83.48
percent. Determine (a) the air-fuel ratio, (b) the percentage of theoretical air used, and (c)
the amount of H2O that condenses as the products are cooled to 25°C at 100 kPa.
13- Calculate the stoichiometric A/F ratio for the combustion of a sample of dry anthracite of
the following composition by mass: carbon 90%; Hydrogen 3%; Oxygen 2.5%; Nitrogen
1%; Sulfur 0.5%; ash 3%. Determine the A/F ratio and the dry and wet analysis of the
products of combustion by volume when 20% excess air is supplied.
14- The analysis of a supply of coal gas is: H2 49.4%; CO 18%; CH4 20%; C4H8 2%; O2
0.4%; N2 6.2%; CO2 4%. Calculate:
(a) The stoichiometric A/F ratio
(b) The wet and dry analysis of the products of combustion if the actual mixture is 20%
Weak.
15- For the combustion of ethyl alcohol (C2H6O) in a petrol engine, Find out:
(a) The stoichiometric A/F ratio.
(b)The A/F ratios for the extreme equivalence ratios of 0.9 and 1.2
(c) The wet and dry analysis by volume of the exhaust gas for each equivalence ratio.
(d)For the stoichiometric mixture, calculate the volume of the mixture per kg of fuel at a
temperature of 65 oC and a pressure of 1.013 bar.
(e) The volume of the products of combustion per kg of fuel after cooling it to a
temperature of 120 oC at a pressure of 1 bar.
(f) If the products are cooled to 15 oC at constant pressure, calculate the amount of water
that will condense per kg of fuel
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Ahmed Emara
16- The gravimetric analysis of a sample of coal is given as 80% carbon, 12% hydrogen, and
8% ash
Calculate:
(a) The stoichiometric A/F ratio.
(b) The analysis of the products by volume.
17- Heptane (C7H16) is burnt in an engine, and the rich mixture gave an analysis of the
products, by volume as 8.8% CO2, 9.2% CO, 7.8 % H2,0.4 % CH4, and 73.8%N2
Calculate the air-fuel ratio & the excess air used.
18- The analysis of fuel by mass is 60.6% H2; 2% CO; 25% CH4; 3% C4H8; 0.4% O2; 1%
CO2; and 8% NO2. If the air-fuel ratio is 6.5/1 by volume. Calculate the analysis of the
dry products of combustion. It can be assumed that the stoichiometric A/F ratio is less
than 6.5/1.
19- For the combustion of ethyl alcohol C2H6O in a petrol engine, find out:
A) The stoichiometric A/F ratio
B) The A/F ratios for extreme equivalence ratio 0.9
C) The wet and dry analysis by volume of the exhaust gas equivalence ratio
D) For the stoichiometric mixture, calculate the volume of the mixture per kg of fuel at
a temperature of 65oC and a pressure of 1.013 bar
E) The volume of the product of combustion per kg of fuel after cooling it to a
temperature of 120oC at a pressure of 1 bar
20- A gaseous fuel has an analysis, by volume, of 91% CH4, 3% C2H6, 2% C3H8, 2% N2, and
2% CO2. Calculate the stoichiometric air/fuel ratio, volume of wet products; theoretical
dew point; and %CO2 in the dry stoichiometric products. The total pressure of products
=1 bar
21- The fuel analysis, by volume, is 50% hydrogen, 40% carbon monoxide, 6 % carbon
dioxide, and 4% nitrogen. The fuel is burnt in air, and the dry combustion products
contain by volume of 9.2 % CO2, and no CO. Calculate:
A) The stoichiometric A/F ratio.
B) The actual A/F ratio.
C) The % oxygen in the dry products.
D) The theoretical dew points.
E) The HCV of fuel if it burns with 25% excess air.
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Ahmed Emara
22- Methane (CH4) is burned with a stoichiometric amount of air during a combustion
process. Assuming complete combustion, determine the air-fuel and fuel-air ratios.
23- Propane (C3H8) is burned with 75 percent excess air during a combustion process.
Assuming complete combustion, determine the air-fuel ratio.
24- Acetylene (C2H2) is burned with a stoichiometric amount of air during combustion.
Assuming complete combustion, determine the air-fuel ratio on a mass and a mole basis.
25- 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 theoretical air used during this process.
26- 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.
27- 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.
28- Propal alcohol (C3H7OH) is burned with 50 percent excess air. Write the balanced
reaction equation for complete combustion and determine the air-to-fuel ratio.
With my best wishes
Assoc. Prof. Dr. Ahmed Emara
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Ahmed Emara
