A NOX Trap Study Using Fast Response Emission Analysers for Model Validation

Lean burn after treatment systems using NO_X traps for reducing emissions from diesel exhausts require periodic regeneration after each storage stage. Optimising these events is a challenging problem and a model capable of simulating these processes would be highly desirable. This study describes an experimental investigation, which has been designed for the purpose of validating a NO_X trapping and regenerating model. A commercial computational fluid dynamics (CFD) package is used, to model NO_X trapping and regeneration, using the porous medium approach. This approach has proved successful for three way catalysis modelling. To validate the model a one-dimensional NO_X trap system has been tested on a turbocharged, EGR cooled, direct injection diesel engine controlled with an engine management system via DSPACE. Fast response emission analysers have been used to provide high resolution data across the after-treatment system for model validation. Measurements show CO is the primary reductant. After the trap NO and NO₂ spikes (NO_X slippage) were observed both at the beginning and end of the regeneration period. The former is believed to be due to insufficient reductant. Whilst the model can qualitatively describe the main storage and regeneration phases it failed to predict NO_X slippage.