Three-Way Catalyst System Design and Emission Characteristics Study with Precious Group Metal Loadings for CNG Vehicles

In this research, the three-way catalysts after-treatment system design enhancement for flow uniformity index, backpressure as well as flow distribution near the lambda sensor is analyzed using computational fluid dynamic (CFD) technique. The transient emission (WHTC) characteristics of three-way catalyst (TWC) on the engine rig are studied based on the design enhancements aforementioned above, along with the precious group metals (PGMs) loadings and specific PGM ratios. However, the catalyst with higher PGM loading and specific PGM ratio supported significantly to light-off swiftly for the TWC after-treatment system as well as for reduction of peak emissions. Though, in this study, NOx and CH4 emissions are considered as the key emissions, and the air–fuel ratio parameters are optimized accordingly. Furthermore, for the selected PGM concentration, the NH3 emission is observed to increase in cold-start cycle, due to steam reforming reactions over the TWC system, and the catalyst effectiveness is recognized in hot-start cycle with NH3 reduction. Nevertheless, in the TWC formulation, the Pd is indispensable to meet the emission regulation limit. However, to minimize the cost for TWC as well as to maintain higher emission conversion margin, bringing down the Rh content as well as enhancing the Pt/Pd ratio could be a viable solution. A right balance between the cost and performance of TWC is provided as the scientific reference in this paper. Overall, the emissions met the legal limits with good engineering emission margin.