Abstract
In Renault's advanced project department, it was decided to study and tune a very low emission concept gasoline engine. The target is the EURO IV regulation level divided by four for each pollutant on the new MVEG cycle.
Because of the light off delay, even with a close coupled catalyst, it is very difficult to fulfil such a target with a conventional three way catalyst. The chosen solution is to use a hydrocarbon trap in front of the first catalyst. As a consequence, because hydrocarbon release occurs before the light off of the downstream catalyst, we use an electrically heated catalyst (EHC) combined with air injection to boost the light off.
Four phases are used by the catalyst system warm-up management : pre heating before cranking by pumping air through the EHC, heating exhaust flow after cranking through the EHC, exothermic heating due to air pump and engine enrichment, hydrocarbon release after treatment.
The originality of this system is that each phase of the warm-up is supervised by the engine electronic control unit (ECU) thanks to an exhaust pipe temperature modelling, which allows one to judge it accurately whatever the driving cycle is. After the warm-up phases, the behaviour of the exhaust system is the same as a conventional closed loop model (the hydrocarbon trap being redundant after light off is achieved).
This total combined approach allows one to reach ones target with a medium class passenger car equipped with a 1.6 litre four cylinder engine.