Browse Publications Technical Papers 2019-24-0074
2019-09-09

Development of a Dedicated CNG Three-Way Catalyst Model in 1-D Simulation Platforms 2019-24-0074

A growing interest in heavy-duty engines powered with CNG dictated by stringent regulations in terms of emissions, has made it essential to study a specific Three-Way Catalyst (TWC). Oxygen storage phenomena characterize catalytic converter efficiency under real world driving operating conditions and, consequently, during strong dynamics in Air-to-Fuel (A/F) ratio. A numerical “quasi-steady” model has been set-up to simulate the chemical process inside the reactor. A dedicated experimental campaign has been performed in order to evaluate the catalyst response to a defined lambda variation pattern of the engine exhaust stream, thus providing the data necessary for the numerical model validation. In fact, goal of the present research activity was to investigate the effect of very fast composition transitions of the engine exhaust typical of the mentioned driving conditions (including fuel cutoffs etc.) on the catalyst performance and on related emissions at the tailpipe. A surface reactions kinetic mechanism, concerning CH4, CO, H2 oxidation and NO reduction, has been appropriately calibrated with a step-by-step procedure in steady-state in the engine work plan at different A/F ratios and during transient conditions through cyclical and consecutive transitions of variable frequency between rich and lean. Model includes a proper calibration of reactions involving Cerium inside Catalyst in order to reproduce oxygen storage and release dynamics. Reactions rate continuous control allowed to evaluate impact of each of them on the exhaust concentration in several operating conditions. The proposed model predicted tailpipe conversion/formation of main species starting from experimental engine-out data and provides a useful tool for evaluation of catalyst performance.

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