Secondary air injection on gasoline engines

The secondary air injection system of gasoline engines ensures a reduced emission of pollutants in the warm-up phase when starting the engine. During this time, the engine requires a mixture with fuel surplus until reaching the operating temperature, with the result that some of the fuel leaves the combustion chamber unburned. Since the lambda control and the catalytic converter don’t have the time to warm up during the cold start phase, the harmful hydrocarbons and carbon monoxides can be released into the environment without aftertreatment. For this purpose, the secondary air system is installed behind the outlet valves.


The main components of the secondary air injection are the secondary air pump and the secondary air valve. To reduce pollutants during cold start oxygen-containing ambient air is blown through the valve into the exhaust system. There, the air makes for a post-oxidation of the unfamiliar exhaust gas constituents, and converts them into harmless carbon dioxide and water. As a result of this thermal afterburning, the catalyst is also heated up and supported until the lambda control steps in.


Pierburg 7.21853.00.0 secondary air injection