INFORMAZIONI SU

Combustion (Combustione)

Programma dell'insegnamento di Combustion (Combustione) - cdl magistrale in Ingegneria per l'Ambiente e l'Energia - Integrato con Energetica

Teacher

prof. Pietro GIANNATTASIO

Credits

6 CFU

Objectives:

The aim of this course is to introduce the fundamentals of combustion so as to provide the theoretical basis of most applications of combustion in thermal power plants and process industry. In particular, adequate chemical, physical and mathematical tools are provided so as to enable the student to perform quantitative and predictive evaluations of the combustion processes.

Acquired skills:

- Knowledge of the different types of combustion and their phenomenology
- Computation of the thermochemical parameters of combustion and the equilibrium composition of the combustion products
- Understanding of the main kinetic mechanisms of combustion, computation of the reaction rates
- Skilful application of the conservation equations to multicomponent reacting systems
- Computation of the evaporation and combustion rate of spherical droplets
- Quantitative evaluation of premixed and diffusion flames, both laminar and turbulent
- Knowledge of the flame ignition and stabilization topics and the relevant calculation procedures
- Knowledge of the formation mechanisms of nitrogen oxides and soot
- Knowledge of the main combustion devices and systems

Contents

Introduction to combustion: Presentation of the course. The impact of combustion in the world energy context. Definition and classification of the combustion processes. (2 hours)
Thermochemistry and combustion
: Equations of state. First law of thermodynamics. Reactants and products mixtures: stoichiometry, absolute enthalpy and enthalpy of formation, enthalpy of combustion and heating values. Adiabatic flame temperatures. Chemical equilibrium: second law of thermodynamics, Gibbs function, equilibrium products of combustion, dissociation of CO2 and H2O, water-gas equilibrium. Energy recovery in combustion systems and control of the flame temperature: recuperators and regenerators, FGR and EGR systems. Classification and chemistry of hydrocarbons. (10 hours)
Chemical kinetics and main combustion mechanisms: Review of global and elementary reactions. Reaction rates of elementary and multistep mechanisms. The H2-O2 system. Carbon monoxide oxidation. Methane combustion. Oxidation of higher paraffins. (6 hours)
Conservation equations for multicomponent reacting systems:
Fick's law of diffusion. Molecular basis of diffusion. Multicomponent diffusion. Conservation equations of mass, chemical species, momentum and energy in multicomponent systems. Conserved scalars. (6 hours)
Thermal analysis of reacting systems: Fixed-mass reactors (constant pressure and constant volume reactions). Well-stirred reactors. Plug-flow reactors. Application to the combustion systems. (4 hours)
Laminar premixed flames:
Physical description. Flame geometry. Spalding’s model for the computation of flame speed and thickness. Effect of physical and chemical variables. Flame speed correlations. Quenching, flammability limits, ignition, flame stabilization. Design of burners. (7 hours)
Laminar diffusion flames: Model of isothermal laminar jets and self-similar solution. Physical description and mathematical model of jet flames. Solutions of Burke-Schumann, Fay, Roper. Flame lengths in circular-port and slot burners. Influence of physical and chemical parameters on the length of a jet flame. (7 hours)
Droplet evaporation and burning: Some applications of “spray combustion” (Diesel engines, gas turbines, liquid-rocket engines). Models of evaporation and combustion of spherical droplets. D-square law and droplet lifetime. (6 hours)
Introduction to turbulent flows: Definition of turbulence. Lenght scales of turbulent flows. Analysis of turbulent flows. Axisymmetric turbulent jets. (2 hours)

Turbulent premixed flames: Some applications (spark-ignition engines, gas turbines, industrial gas burners). Turbulent flame speed. Structure of turbulent premixed flames. Flame regimes and correlations for the flame speed.
Damkohler diagram. Flame stabilization.  (4 hours)
Turbulent diffusion flames: Flame types and applications. Jet flames: flame geometry and luminosity, flame temperature distribution, experimental data, simplified analysis, flame length and influencing factors, flame radiation, liftoff and blowout. Practical combustion devices. (4 hours)

Pollutant formation: Nitrogen oxides formation mechanisms (Zeldovich, Fenimore, N2O-intermediate). Formation and oxidation of soot in diffusion flames; smoke point. (2 hours)

 

References

- Stephen R. Turns, “An Introduction to Combustion: Concepts and Applications”, second edition, McGraw-Hill, 2000.
- Kenneth K. Kuo, “Principles of Combustion”, second edition, John Wiley & Sons, 2005.

Type of exam

Written and oral