Requirements for lambda sensors
When fuels are combusted, a number of harmless compounds such as water, carbon dioxide and nitrogen are produced, as well as a number of dangerous pollutants. It is the task of the regulated catalytic converter to reduce these emissions. These converters have been installed in new cars with petrol engines since the late 1980s and include at least one lambda sensor. This sensor actually optimises the operating conditions for the catalytic converter.
Catalytic converter and lambda sensor - the team for clean air
Regulated catalytic converters reduce the emission of pollutants by more than 95 per cent. As they reduce the emission of the three harmful gases HC, CO and NOx, they are known as "three-way catalytic converters".
They are coated with the precious metals platinum, rhodium and palladium on the inside. A number of complex chemical reactions take place on these coatings: carbon monoxide (CO) and hydrocarbons are converted to water (H2O), while carbon dioxide is oxidised. Nitrogen oxides (NOx) are reduced to nitrogen (N2), oxygen (O2) and carbon dioxide (CO2).
The lambda sensors – also known as oxygen sensors – ensure that these reactions can take place under optimised conditions, as proper conversion of these noxious gases can only occur at a set air fuel ratio. They thus make sure that nearly all pollutant emissions are converted. Modern cars are normally equipped with at least two lambda sensors, namely a front or control sensor installed in front of the catalytic converter and a rear or diagnostic sensor mounted after the catalytic converter. They measure the oxygen content in the exhaust gas. Based on this information, the engine control system can adjust the air fuel ratio.
Basic principle of the lambda sensor
It measures the residual oxygen in the exhaust gas and feeds a sensor signal to the control unit, which in turn uses this signal to control the carburetion system. Based on the above principle, the lambda sensor technology has made huge progress. Modern systems effectively reduce the harmful emissions, optimise the fuel consumption and ensure a long service life of the catalytic converter.