33931 - Chemistry of Combustion Processes M

Course Unit Page

Academic Year 2018/2019

Learning outcomes

The course provides students with the thermodynamics and kinetics of the chemical reactions occurring in the internal combustion engines and in the systems for energy production, in view of optimizing working conditions, taking into account also pollutant emissions to the environment.

Course contents

First of all, the course deals with a widening of chemical thermodynamics and kinetics in relation to the chemistry knowledge gained in the three-year degree, in order to understand the reaction schemes relating to the combustion mechanisms of the main fuels used in internal combustion engines; afterwards, these mechanisms are examined and discussed in detail. The main pollutant formation mechanisms and the methods used today to minimize their release into the environment are also illustrated, taking into account the fuel used and the conditions under which combustion (spark ignited or diesel engines) occurs. Finally, a discussion of atmosphere chemistry is carried out in order to understand the effect of pollutants on the environment.

1. Fundamental Chemistry. An outline of the electronic structures of the elements, their properties, the different kinds of chemical bond and their characteristics. Absorption spectra of atoms and molecules. 

2. Chemical Thermodynamics. Standard reaction, formation and combustion enthalpies. The second law of Thermodynamics and Gibbs free energy. The chemical equilibrium on thermodynamic basis; the equilibrium constants for ideal and non-ideal systems. Heterogeneous reactions. Effect of temperature and pression on the equilibrium composition. The electromotive force and the Nernst equation derived by a thermodynamic approach.  

3. Chemical kinetics. Fundamentals of chemical kinetics. Simple and complex reaction mechanisms. Molecularity and reaction order; the special case of monomolecular reactions. Kinetics of complex reactions: competitive, converging and consecutive reactions. The steady-state approximation. Reversible reactions. Kinetics of chain and chain-branching reactions. The partial equilibrium assumption. Effect of temperature on the reaction rate: the collision theory and Arrhenius equation; the activated complex and the steric factor. Other k(T) functional forms. General properties of catalysts; homogeneous and eterogeneous catalysis. Gas-solid catalysis: kinetics of adsorption with (or without) the dissociation of reagent molecules.

4. Combustion. The combustion reactions: fuels and oxidizing agents. Higher and lower heating values; the adiabatic flame temperature. Chain-branching reactions and the conditions for explosion. Explosion limits for hydrogen, carbon monoxide, methane, hydrocarbons, etc. Nitrogen oxides formation during the combustion: thermal and prompt mechanisms. The effect of the presence of nitrogen in fuels. Formation of sulfur oxides and other S-containing compounds. Particulate structure and the effects on human health; an outline of the mechanisms of formation.

5. Enviromental effects of combustion. The structure of atmosphere. The temperature and pressure gradient in troposphere. Thermal stability and thermal inversion conditions. Pollutants in the troposphere: the photochemical smog. Ozone, hydrogen peroxide, PAN and nitric acid formation. Acid rains and their environmental effects. Catalytic systems for the conversion of pollutants in engine exhausts: three-way converters and NSR systems; SCR approach in diesel engines. Particulate traps and regeneration methods. Gas sensors: the lambda probe. The particulate matter removal from diesel emissions. Greenhouse effect and global warming: carbon dioxide and the other greenhouse gases. Characteristics of the main fuels, with special attention to those obtained from renewable sources: energy and fuels from biomass. Methanol and ethanol, biodiesel, hydrogen: favourable and unfavourable features. Production methods of hydrogen and stocking problems.

6. The Chemistry of stratosphere: the ozone layer. The absorption of UV radiation by oxygen and ozone. Formation and destruction of the ozone layer in the stratosphere and thermal effects. Catalytic mechanisms of ozone destruction: the effect of CFC and other pollutants. The annual formation of the antarctic hole.

 

Readings/Bibliography

I. Glassman - “Combustion”, Academic Press, III Ed., 1996.

S.R. Turns - “An introduction to combustion”, Mc Graw-Hill, II Ed., 2000.

C. Baird, M. Cann – “Environmental Chemistry”, 3rd Ed., W.H. Freeman & Co, 2005.

R.A. Michelin, A. Munari - “Fondamenti di Chimica”, III Ed., CEDAM, 2016.

Teaching methods

Lectures

Assessment methods

The final exam is oral and aims to verify that the student is able to:
- discuss, on the basis of available data, any reaction scheme both by a kinetic and a thermodynamic point of view.
- understand the combustion mechanisms of the main fuels used in internal combustion engines and the formation of the main pollutants, with attention to the various methods used today to minimize their emission into the environment.
- describe the effects of the major pollutants on the environment.

The exam usually involves a question for each of the following three blocks of topics:

- Chemical thermodynamics and kinetics.

- Combustion and the main combustion mechanisms; the mechanisms of pollutant formation.

- The effect of the pollutants on environment and the methods of reduction of combustion pollutants; the chemistry of atmosphere.

Teaching tools

Overhead projector. Copies of the most important slides shown during the lessons will be available during the Course at the Teacher website together with some notes on specific subjects.

Office hours

See the website of Andrea Munari