Intra-catalyst reductant chemistry and nox conversion of diesel lean nox traps at various stages of sulfur loading

Due to increasingly stringent emissions regulations, Lean NO_x Trap (LNT) catalysts are being researched as a potential solution for diesel engine emissions reduction. LNTs are practical for diesel NO_x reduction due to their ability to reduce NO_x from the O₂ rich environment produced by diesel engines. LNTs function by storing NO _x on the catalyst surface during efficient lean operation then, under rich conditions, releasing and reducing the trapped NO_x. 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 NO_x 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 measurements of reductant chemistry and NO_x conversion through the catalyst. Results showed that as sulfur loading increased, NO_x 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.