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Combustion

This document discusses combustion and thermodynamics concepts. It defines combustion as the burning of fuel with oxygen or air, and describes how chemical reaction equations relate components before and after combustion. It also discusses theoretical air, excess air, and calculating percent excess air. Sample combustion calculations are provided for butane burned with dry air at different air-fuel ratios and oxygen levels.

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7 views18 pages

Combustion

This document discusses combustion and thermodynamics concepts. It defines combustion as the burning of fuel with oxygen or air, and describes how chemical reaction equations relate components before and after combustion. It also discusses theoretical air, excess air, and calculating percent excess air. Sample combustion calculations are provided for butane burned with dry air at different air-fuel ratios and oxygen levels.

Uploaded by

wishvagithdeneth22
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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CSME 2041- Thermodynamics

Dr. Asiri Indrajith

Asiri.Kulathunga@gmail.com

0702077365

Saturday, 16 October 2021


Introduction

Combustion
Introduction

Fuel
Introduction

Combustion
Introduction

Combustion
Introduction

Combustion
Introduction

Combustion
Introduction

Combustion
Introduction

Combustion
Introduction

Combustion
Combustion

Combustion involves the burning of a fuel with oxygen or a substance containing


oxygen such as air. A chemical-reaction equation relates the components before and
after the chemical process takes place. Considering the combustion of propane in a
pure oxygen environment. The chemical reaction is represented by

the number of moles of the elements on the left-hand side may not equal
the number of moles on the right-hand side. However, the number of atoms of an
element must remain the same before, after, and during a chemical reaction; this
demands that the mass of each element be conserved during combustion.

11
Introduction

Combustion
In writing the equation, we have demonstrated some knowledge of the products
of the reaction. Unless otherwise stated we will assume complete combustion: the
products of the combustion of a hydrocarbon fuel will include H2O and CO2 but no
CO, OH, C, or H2. Incomplete combustion results in products that contain H2, CO,
C, and/or OH.
For more complex reactions the following systematic steps prove useful:

1. Set the number of moles of fuel equal to 1.


2. Balance CO2 with number of C from the fuel.
3. Balance H2O with H from the fuel.
4. Balance O2 from CO2and H2O.
Combustion

13
Combustion

The minimum amount of air that supplies sufficient O2 for complete combustion of
the fuel is called theoretical air or stoichiometric air. When complete combustion
is achieved with theoretical air, the products contain no CO or O2. In practice, it is
found that if complete combustion is to occur, air must be supplied in an amount
greater than theoretical air. This is due to the chemical kinetics and molecular
activity of the reactants and products. Thus, we often speak in terms of percent
theoretical air or percent excess air, where they are related by

14
Combustion

15
Combustion

Butane is burned with dry air at an air-fuel ratio of 20. Calculate the percent
excess air, the volume percentage of CO2 in the products, and the dew-point
temperature of the products.

16
Combustion

Butane is burned with 90% theoretical air. Calculate the volume percentage of CO
in the products and the air-fuel ratio. Assume no hydrocarbons in the products.

17
Combustion

Butane is burned with dry air, and volumetric analysis of the products on a dry
basis (the water vapor is not measured) gives 11.0% CO2, 1.0% CO, 3.5% O2, and
84.6% N2. Determine the percent theoretical air.

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