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Technical Paper

Lean Breakthrough Phenomena Analysis for TWC OBD on a Natural Gas Engine using a Dual-Site Dynamic Oxygen Storage Capacity Model

Oxygen storage capacity (OSC) is one of the most critical characteristics of a three-way catalyst (TWC) and is closely related to the catalyst aging and performance. In this study, a dynamic OSC model involving two oxygen storage sites with distinct kinetics was developed. The dual-site OSC model was validated on a bench reactor and a natural gas engine. The model was capable of predicting temperature dependence on OSC with H2, CO and CH4 as reductants. Also, the effects of oxygen concentration and space velocity on the amount of OSC were captured by the model. The validated OSC model was applied to simulate lean breakthrough phenomena with varied space velocities and oxygen concentrations. It is found that OSC during lean breakthrough is not a constant for a particular TWC catalyst and is dependent on space velocity and oxygen concentration. Specifically, breakthrough time exhibits a non-linear, inverse correlation to oxygen flux.
Technical Paper

Diagnostics of field-aged Three-Way Catalyst (TWC) on stoichiometric natural gas engines

Natural gas is one of the most attractive alternate to gasoline and diesel fuels due to its competitive price resulting from its abundant availability and lower GHG emissions. In stoichiometric natural gas engines, three-way catalysts (TWCs) are widely employed to convert the exhaust pollutants CO, HC (including CH4) and NOx to CO2, N2 and H2O. TWCs contain Platinum Group Metals (PGM) as the active centers for various reactions and ceria-zirconia (CeZrOx) material to provide oxygen storage capacity (OSC), which acts as a buffer for maintaining stoichiometric conditions under a broad range of air to fuel ratios. The activities of the PGM and OSC components of TWC degrade upon prolonged real life operation. This degradation could arise due to various factors such as high temperature hydrothermal exposure of catalysts for prolonged periods and masking/poisoning of the catalytic sites by, for example, chemical contaminates originating from lube oil consumption and/or coolant leakage.