Increasing population and a rising necessity for mobility and transportation require a growing environment protection. In the USA and in Europe legislative concluded new emission limits to reduce cold start emissions for passenger cars.
A useful method to reduce HC and CO during the cold start of combustion engines is secondary air injection. Secondary air injection feeds fresh air into the exhaust system during cold start and achieves an oxidation of unburned HC and CO. This exothermal oxidation elevates the exhaust gas temperature and decreases light-off time of the catalyst.
A large portion of the emissions in the FTP 75 cycle is produced during the first seconds of the cold start. This requires a fast rising secondary air mass flow during the cold start of the engine. Electrically driven secondary air pumps achieve this requirement with a high cut-in current.
Mann+Hummel developed the so called secondary air charger with a very short response time. In principle the secondary air charger works as a turbocharger, driven by the pressure drop at the throttle valve. First aluminum prototypes have been tested very successfully. Further improvement was achieved with a secondary air charger with plastic wheels.
The first part of this paper describes the performance of the secondary air charger in a passenger car compared with an electrical secondary air pump. The second part of the paper compares secondary air chargers with plastic and aluminum wheels. Reduction of rotating mass and decreased friction in the bearings affects short response time and increased secondary air flow with plastic wheels.