Secondary air system
| Secondary air system |
In order to get the catalytic converter to work as fast as possible after a cold start, and thereby maintain good emission values, the surrounding air is pumped into the exhaust manifold with an SAI pump (Secondary Air Injection). The oxygen in the air then initiates a chemical combustion together with the CO and HC compounds, whereby heat is generated.
More fuel is added in order to compensate for the extra air. This extra fuel is added adaptively to the calculated fuel quantity. Trionic calculates the extra amount of fuel using a matrix.
The SAI pump starts when the engine is started provided the charge air temperature and coolant temperature are within the range -11°C - +39°C and the battery voltage and air mass consumption are within limits.
Before the SAI pump starts, the engine must run for a few combustions depending on the coolant temperature and varying between 20 and 70 combustions.
The SAI pump will continue to run for another few combustions after the system has stopped requesting it. This is to avoid unnecessary hydrocarbon emissions once the SAI functions have been turned off.
To prevent exhaust gases leaking back through the SAI system, there is a non-return valve that closes when the pump stops.
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