A Test Method for Evaluating Feasibility of Lean Nitrous Oxide Traps 2011-26-0030
The Lean NOx Trap (LNT) is a technology that could be used to reduce oxides of nitrogen from heavy-duty diesel engines to meet emissions standards (US 2010 and EURO 4/5/6). This paper describes a case-study for evaluating the feasibility of an LNT. LNTs suffer from sulfur poisoning and thermal aging limitations. Catalyst formulations allow reversal of sulfur poisoning through desulfation procedures. A case study was performed using a 7-liter diesel engine equipped with VGT, common rail fuel injection system, cooled EGR, oxidation catalyst and DPF. The LNT was positioned after the particulate filter. Gaseous raw emissions were measured from engine and various stages of aftertreatment. A Fourier Transform Infrared (FTIR) analyzer was used to characterize Ammonia and SO₂. Temperatures were measured in the substrate. Fast response NOx sensor allowed for continuous monitoring of the NOx in the LNT. A wide-range O₂ sensor was also utilized to measure equivalence ratio. An opacity meter was used in developing the initial strategies for LNT regeneration, prior to installation of catalyst. It was used to minimize the smoke production during regeneration. The test cell was equipped with a General Electric eddy current dynamometer to target a 6-mode subset of the 13- mode Supplemental Emissions Test (SET) cycle. Lifetime desulfations and DPF regenerations were performed to demonstrate the effect of aging on the catalyst. Normalized test results indicating reduction of NOx will be presented along with the results of sulfur poisoning and accelerated age testing. At the completion of all testing, the engine had run for a total of 400 hours. The oven-aged aftertreatment was exposed to 34 hours of DPF regeneration and 16 hours of LNT desulfation. The performance of LNT before and after aging will be presented along with changes in engine-out emissions during the LNT aging process.