Secondary air injection is also known as air injection which is the vehicle emission control strategy that was introduced first in the mid60s. This takes place when fresh air is injected to exhaust stream to produce fuller combustion of the exhaust gases. The mechanism in which the exhaust emission are controlled depend mostly on the injection method and the point at which the air enters the exhaust system and varies during technological advancements.
The first air injected systems is very close to the engine either in exhaust manifold or in the exhaust port of the cylinder head. Such systems provide oxygen to be able to oxidize or burn the unburned and the partially burned fuel in the exhaust prior to ejecting it to 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. The extra heat of recombustion on the other hand particularly with excessively rich exhaust may caused maladjusted carburetor or misfiring, has a tendency to bring damage to the exhaust valves and be seen to make the exhaust manifold to incandesce.
Emission control strategies have grown more sophisticatedly and effectively, the volume of partially burned and unburned fuel in exhaust stream shrunk and particularly when the catalytic converter was created, the function of secondary air injection shifted at the same time.
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 catalytic converter is cold, the air is injected upstream point that is burnt with deliberately rich exhaust. After the catalyst is warmed up, the air is injected to downstream location, the catalytic converter itself, which then assists with catalysis of the unburned hydrocarbons.
The pumped air injection system is using a vane pump referred to as air pump that’s turned by the engine using either an electric motor or belt. The air intake of pump is filtered by the rotating screen to exclude dirt particular huge enough to cause damage to the system. Then after that, the air is delivered under light pressure to injection point/s. A check valve will then prevent the exhaust from forcing its way back to the air injection system which will otherwise damage other components. This is the primary reason why the secondary air injection systems is crucial in cars.