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Emission Performance Improvement on a Light-Duty Diesel Engine With an LNT-Based Aftertreatment System Via Use of a Pox Reformer System
Technical Paper
2006-05-0306
Sector:
Language:
English
Abstract
Modern diesel automotive engines can improve the fuel efficiency
of passenger cars and light-duty trucks compared to the current
port-injected, spark-ignited gasoline engine. Unfortunately, the
stringent North American NOx emissions standards pose a major
challenge for the rapid expansion of diesel engines in the North
American market.
Although urea selective catalytic reduction (SCR) systems have
demonstrated good NOx control performance and fuel sulfur
tolerance, the lack of urea-dispensing infrastructure and
regulatory uncertainties concerning urea re-fill strategies have
limited the adoption of this technology for the North American car
and light-truck market.
The lean NOx trap (LNT) offers an alternative to urea SCR, but
it faces a different set of challenges such as: limited temperature
NOx performance, low tolerance to sulfur and the need for high
precious metals loadings.
The LNT chemically stores NOx during lean operation, and then
requires frequent "NOx purging" with rich exhaust
reductants. In the fuel-rich environment, the NOx is released and
can then be converted to N2 using an oxidizing-reducing catalyst.
To understand the performance capabilities and limitations of lean
NOx traps with diesel exhaust, several approaches to generating the
rich exhaust feedstream were evaluated on experimental light-duty
diesel trucks. Tests were conducted using rich diesel exhaust
feedstreams generated by modifying the combustion modes, or by
processing diesel fuel on-board with a partial oxidation converter.
The results were analyzed to better understand the chemical and
physical factors that limit diesel LNT performance.
The results from this activity lead to greater understanding on
the role of reductant type on resulting catalyst and aftertreatment
system performance. By incorporating the positive features of the
development activity into future system designs, lower emissions
and improved performance can be achieved.