Concept, Loading and Calibration Effects on the Emission Performance of NG-TWC for HD Engines

The environmental impact of heavy-duty vehicles powered by natural gas is considered to be less harmful compared to Diesel vehicles. Consequently, the share of vehicles using either compressed natural gas (CNG) or liquified natural gas (LNG) is expected to increase in the coming years. Since most Euro VI compliant engines operate with stoichiometric air-fuel ratio, the aftertreatment system (ATS) requires efficient three-way catalyst. With ever increasing prices on platinum group metals (PGM) over the past few years, three-way catalysts products have been exposed to wild fluctuations in cost that have had great impact on their affordability. Given that stoichiometric operation is the most widely used calibration of heavy-duty natural gas engines, the trade-off between efficiency, calibration and PGM cost must be constantly reset. This study focuses on the evolution and transition from bimetallic palladium-rhodium (Pd:Rh) concepts to trimetallic platinum-palladium-rhodium (Pt:Pd:Rh) three-way catalyst (TWC) concepts where a reduction in PGM loading through washcoat improvements and catalyst architecture supported by catalyst simulation software can be achieved, while keeping emissions at comparable or better levels and exploring the effects of different calibrations to the overall performance.