Intra-Catalyst Reductant Chemistry and Nox Conversion of Diesel Lean Nox Traps at Various Stages of Sulfur Loading

Abstract

Due to increasingly stringent emissions regulations, Lean NOX Trap (LNT) catalysts are being researched as a potential solution for diesel engine emissions reduction. LNTs are practical for diesel NOX reduction due to their ability to reduce NOX from the O2 rich environment produced by diesel engines. LNTs function by storing NOX on the catalyst surface during efficient lean operation then, under rich conditions, releasing and reducing the trapped NOX. One method of producing this rich environment which regenerates a LNT involves manipulating the fuel injection parameters and throttling the air intake. This process is called in-cylinder regeneration. Experiments will be described here in which a 1.7 L common rail diesel engine has been used to regenerate LNTs at various stages of sulfur exposure, a known poison of the LNT. In-cylinder regeneration strategies were used to produce a range of reductant chemistries which enabled the study of the role of various reductants as NOX was converted across the LNT. This study gives insight into how to most efficiently regenerate the LNT. Sulfur poisoning of a fresh LNT was accelerated via the use of bottled SO2. Regeneration studies at various states of sulfation and after catalyst desulfation are discussed, highlighting intra-catalyst measurementsmore » of reductant chemistry and NOX conversion through the catalyst. Results showed that as sulfur loading increased, NOX conversion efficiency decreased and reductant utilization shifted downstream. Hydrogen from in-cylinder combustion was consumed over the first half of the LNT then produced from other available reductants over the last half for some strategies and conditions. Hydrogen production over the last portion of the catalyst was found to be affected by sulfur.« less