5. Engine emissions

5.1 Type of emissions

Perfect combustion of a hydrocarbon leads to the formation of carbon dioxide and water. This ideal pattern is rarely realized in an engine: exhaust gases are made up of a large number of molecules, some of which are identified pollutants, such as carbon monoxide (CO), nitrogen oxides (NO, NO ₂ , N ₂ O, represented as NO _x ) and unburned hydrocarbons (HC). The determining parameter for the production of these pollutants is the richness of the carburetted mixture in which combustion has developed (figure 30...