Nitrogen Selectivity in Lean NOx Trap Catalysis with Diesel Engine In-Cylinder Regeneration 2005-01-3876
NOx emissions have traditionally been difficult to control from diesel engines; however, lean NOx trap catalysts have been shown to reduce NOx emissions from diesel engines by greater than 90% under some conditions. It is imperative that lean NOx traps be highly selective to N2 to achieve the designed NOx emissions reduction. If selectivity for NOx reduction to NH3 or N2O is significant then, ultimately, higher levels of pollution or greenhouse emissions will result. Here studies of the N2 selectivity of lean NOx trap regeneration with in-cylinder techniques are presented. Engine dynamometer studies with a light-duty engine were performed, and a lean NOx trap in the exhaust system was regenerated by controlling in-cylinder fuel injection timing and amounts to achieve rich exhaust conditions. NH3 and N2O emissions were analyzed with FTIR spectroscopy. Both engine and bench experiments show that excess reductant delivery during regeneration leads to high NH3 emissions and poor N2 selectivity. Specific design of in-cylinder regeneration techniques that minimize excess reductant or allow O2 purge can optimize N2 selectivity of the lean NOx trap catalyst.