Secondary air injection is also known as air injection which is the vehicle emission control strategy that was introduced first in the mid60s. Well, this is when the fresh air is injected to the exhaust stream to be able to create a fuller combustion of exhaust gases. The mechanism that the exhaust emissions are being controlled depend largely on the injection method and also, the point at which the air enters the exhaust system and is varying on the current level of technology.
The very first air injected system is so close to the engine either in the exhaust manifold or in the cylinder head’s exhaust ports. These systems are providing oxygen in order to oxidize or burn both the unburned as well as partially burned fuel in exhaust before ejecting it to the tailpipe.
Believe it or not, there was an enormous volume of burned and unburned fuel in the 60s and 70sand with that, secondary air injection significantly reduced tailpipe emissions. On the other hand, the extra heat of the recombustion, especially with excessively rich exhaust caused by maladjusted carburetor or misfiring, tended to bring damage to the exhaust valves and even be seen to make the exhaust manifold to incandesce.
Emission control strategies have become more effective and sophisticated the volume of the partially burned as well as unburned fuel in exhaust stream shrunk and especially when the catalytic converter was made, the function of secondary air injection shifted as well.
So rather than being the primary emission control tool, the secondary air injection was used instead as a support to the catalytic converter. The original air injection point became known as being the upstream injection point. When the catalytic converter is cold, air is injected to the upstream point that’s burnt with deliberately rich exhaust. As soon as the catalyst is warmed up, air will be injected to the downstream location, the catalytic converter itself which will help with catalysis of unburned hydrocarbons.
Pumped air injection system uses a vane pump referred as air pump that is turned by the engine using an electric motor or belt. The air intake of the pump is being filtered by the rotating screen in excluding dirt particles big enough to bring damage to the system. Then after that, the air is delivered under light pressure to injection point/s. There is going to be a check valve that will be preventing the exhaust to force its way back to air injection system which is crucial because if not for it, it might damage other components. This is the reason why the secondary air injection systems play an important role in cars both in the past and today.