Exhaust gas gas is undesirable, noxious, or toxic substances, such as carbon monoxide (CO) from incomplete combustion, hydrocarbons (properly indicated as CH, but typically shown simply as "HC" on emissions-test slips) from unburnt fuel, nitrogen oxides (NO) from excessive combustion temperatures, and particulate matter (mostly soot). Exhaust gas temperature (EGT) is important to the functioning of the catalytic converter of an internal combustion engine. It may be measured by an exhaust gas temperature gauge. EGT is also a measure of engine health in gas-turbine engines (see below). During the first two minutes after starting the engine of a car that has not
Exhaust gas analyzer analysers for use within the MOT test scheme is listed on the Department of Transport website. The presence of oxygen in the exhaust gases indicates that the combustion of the mixture was not perfect, resulting in contaminant gases. Thus measuring the proportion of oxygen in the exhaust gases of these engines can monitor and measure these emissions. This measurement is performed in the MOT test through Lambda coefficient measurement. The Lambda coefficient (λ) is obtained from the relationship between air and gasoline involved in combustion of the mixture. It is a measure of the efficiency of the gasoline engine by