CATALYTIC AUTOMOTIVE EXHAUST AFTERTREATMENT
Introduction
Diesel engines are presently the most efficient vehicular propulsion systems. Heavy trucks and
buses are powered almost exclusively by diesel engines worldwide. In Europe, diesel powered
cars have been increasingly popular. The high reliability of these engines is an additional
attractive feature. The diesel engine may become even more widely used in the future. However,
significant further progress in diesel emission control is needed. Diesel particulates and nitrogen
oxides, the two most troublesome components of diesel exhaust emissions, have adverse impact
on urban air. The new 2004 emission standards in the U.S. (to be implemented in 2002 after the
consent decree between the manufacturers and the EPA) as well as the tightening regulations in
Europe and East Asia reflect the growing concern with diesel emissions. Recently developed
compact plasmatron fuel converters have features that are suitable for onboard production of
hydrogen for aftertreatment applications. Systems that use these devices in conjunction with
aftertreatment catalysts have the potential to significantly improve prospects for reduction of
diesel emissions.
Compact plasmatron fuel converters have been shown to efficiently reform natural gas
[Bromberg1], gasoline [Bromberg2], diesel [Bromberg3] and hard-to-reform biofuels [Cohn]
into hydrogen rich gas (H2 + CO). Recent developments in compact plasmatron reformer
design at MIT have resulted in substantial decreases in the value of the electrical power
requirements. These new developments also increase the lifetime of the electrodes. The
development of these devices has been sponsored by the DoE Office of Heavy Vehicle
Technologies for the purpose of reducing engine exhaust pollutants by providing hydrogen rich
gas for combustion in spark ignition and diesel engines. Compact plasmatron fuel converter
technology could also be used with NOx absorber/adsorber catalysts and particulate traps.
NOx absorber catalysts and particulate traps have been suggested for the decreasing emissions
from diesel and spark ignition engines. In order to regenerate the catalyst, a reducing agent is
introduced into the exhaust, either directly injected, or in the case of spark ignition engines by
running the engine fuel rich during the regenerating period. Use of compact plasmatron
reformers for generating hydrogen rich gas for regenerating the catalyst could provide important
advantages. This paper describes compact plasmatron fuel converter-aftertreatment catalyst
systems that could provide new opportunities for improved diesel engine emissions control.