A one-dimensional lean NOx trap model with a global kinetic mechanism that includes NH3 and N2O

Abstract

Eaton has developed an aftertreatment system for medium- and heavy-duty diesel engines in response to the US 2010 regulations. This system consists of a fuel reformer, a lean NO x trap (LNT), and an ammonia selective catalytic reduction (SCR) catalyst in series. A transient, one-dimensional model of the system was developed to improve system performance, reduce experimental testing, and optimize system design. In this paper, the LNT portion of this model is presented. The model simulates flow, heat transfer, and chemical reactions in the LNT catalyst. A global LNT chemical kinetic mechanism was developed to simulate the key catalytic processes with the minimum number of reactions. The model can be used to predict LNT catalyst performance over a range of operating conditions and driving cycles. Simulated species concentrations and gas temperatures at the LNT outlet were compared with experimental data at three steady state engine conditions over a 13-mode test. The conditions were chosen to develop and test the model over a range of gas temperatures, space velocities, and species concentrations. The LNT model predicts species trends and magnitudes with reasonable accuracy in comparison with experimental data. The simulated LNT NO x conversion efficiency over the 13-mode test was 67 per cent, compared with 63 per cent for the experiment.