Combustion chemistry — Hydrocarbon-based flames

Combustion is an important phenomenon since it is used as the main source of energy. The major problem with this process is the formation of pollutants (CO, volatile organic compounds (VOCs), nitrogen oxides (NO _x ), polycyclic aromatic hydrocarbons (PAHs), soot...). Indeed, in human activity, these compounds are the ones that predominate in the environment through the discharges of numerous combustion systems: automobile engines, iron and steel industry, chemical companies, fires, urban waste incinerators...

For many years, European and international companies have been trying to reduce air pollution, particularly that caused by combustion processes which can produce polycyclic aromatic hydrocarbons, ultimately leading to the formation of soot. This article focuses on the formation of these hydrocarbon compounds.

Today, the main fuels used are fossil fuels such as coal, oil and natural gas. To understand the formation pathway of the chemical species obtained from the initial fuel to the final products, kinetic studies are carried out using various analytical techniques. The aim of such studies is to determine the reaction rate of each chemical process, and the nature of the various compounds produced. Once this knowledge has been acquired, it is easier to intervene in the combustion of hydrocarbons to reduce pollutants and increase energy efficiency.

Combustion of hydrocarbon species can be analyzed using a variety of techniques and specific equipment: reactors (closed, tubular flow, perfectly stirred), compression systems (rapid compression machine, shock tube) and burners (premixed flame, diffusion flame). These experimental devices can be used to measure kinetic constants, which determine the rate at which a reaction proceeds. These results form the basis for the development of a kinetic mechanism that brings together all the reaction pathways taking place during combustion.

These models simulate the combustion of a hydrocarbon in a given reactor, under defined temperature and pressure conditions. By comparing the calculated results with those obtained experimentally, the mechanism is validated or not: in other words, under the same conditions as those of the operating procedure, it must be able to represent the experiment from a kinetic point of view.

Such a mechanism can then be used in industrial calculations: to optimize the manufacture of a combustion system by reducing pollution and increasing efficiency, to predict pollutant concentrations and their reaction speed...

It's important to understand the different processes by which pollutants are formed, in order to curb them and reduce their production....