The gas which leaves a system after energy exchange or conversion process, e.g. combustion gases from a diesel engine, a boiler, a gas turbine or an incinerator.
The exhaust gases of diesel engines mainly consist of nitrogen, carbon dioxide (CO2) and water vapour with smaller quantities of carbon monoxide (CO), sulphur oxides (SOx ) and nitrogen oxides (NOx), partially reacted and non-combusted hydrocarbons and particulates.