Using monatomic nitrogen induced by a pulsed arc to remove nitrogen oxides from a gas stream Page: 2 of 8
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USING MONATOMIC NITROGEN INDUCED BY A PULSED ARC
TO REMOVE NITROGEN OXIDES FROM A GAS STREAM
Henry K. Ng, Vincent J. Novick, and R. Raj Sekar
Argonne National Laboratory
The effectiveness of monatomic nitrogen, induced by a pulsed
electric arc, in reducing nitric oxide (NO) and nitrogen dioxide
(NO2) was studied. The goal for this research is the reduction of
nitrogen oxides (NO,) from automobile emissions by this alterna-
tive technique, which can be cost-effective (to be demonstrated in
the near future) and has the potential to reduce NOX in exhaust
containing up to 10% oxygen. The initial tests with 100, 500, and
1,000 ppm NO in pure nitrogen have shown that a greater than
50% reduction of NO/NOa is readily achievable. Different flow
rates of the monatomic nitrogen and the gas stream were tested.
The flow rate of the monatomic nitrogen did not have a
significant effect on the reduction efficiency, unlike the flow rate
of the gas stream. The cross-sectional flow area of the gas stream
was varied in order to assess whether the proximity of the gas
stream to the arc would affect NO/NO reduction. Results of the
tests revealed that the smallest cross-sectional area gave the best
reduction, but it also had the greatest chance of contacting the arc.
The composition of the gas stream was also varied to elucidate
the effects of NO2 and 02 on the NO/NO reduction efficiency.
When NO2 and 02 are present in the gas stream, both gases lower
the reduction efficiency significantly by creating more NO or
NO2. Experiments are continuing to improve the reduction
efficiency. The electrical power, a function of pulse frequency,
voltage, and current, was treated as a key parameter in the
investigation. The power consumption of the high-voltage pulser
apparatus for a 100-kW engine was estimated to be 3 kW.
1 INTRODUCTION AND BACKGROUND
Because of the increasing use of automobiles, greater demand
is being placed on the auto industry by the U.S. Environmental
Protection Agency (EPA) to reduce vehicle emissions. Federal
nitrogen oxides (NO,) emissions standards were set at 1.0 g/mi at
50,000 miles in 1992. A standard of 0.4 g/mi is expected to be
phased in between 1994 and 1998 and 0.2 g/mi between 2003 and
2008 (Carlos and Currie, 1992). A more efficient and exhaust-
oxygen-tolerant method of NO. reduction than the present three-
way catalytic method is required to meet these upcoming
emissions standards without fuel economy penalty. Because most
catalytic-reduction reactions require an inlet air temperature of
220-3501C to reach their maximum reduction capability, they do
not work well under cold running conditions.
Such engine combustion modification techniques as lean fuel/air
ratio, stratified charge, and exhaust gas recirculation are used on
mobile sources. A lean-bum technique has been used to
simultaneously control the amounts of NOa, CO, and HC. As the
fuel/air equivalence ratio is reduced to 0.9, CO and HC emissions
drop, but NOz emissions increase, because of higher combustion
temperatures. An extremely lean mixture (0.8 fuel/air equivalence
ratio) results in control of HC, CO, and NOz, but the spark energy
necessary to ignite the lean mixture is at least two orders of
magnitude greater than what is used to ignite a rich mixture
(Bradow, 1982). The stratified charge technique utilizes a rich
fuel mixture in a small chamber containing the spark plug and a
much leaner mixture in the main chamber to reduce the required
combustion temperature. Exhaust gas recirculation (EGR), similar
to that used in stationary sources (e.g. power plants), is also used
in engines. By recirculating the exhaust gas, the postflame gas
temperature is reduced, resulting in a reduction in thermal NO,
These methods can be used to meet present emissions
standards, but they are not adequate to reach the proposed
standards, because their effectiveness for mobile sources is
limited. For example, catalytic reduction methods do not work
well under cold conditions, and engine modification techniques
may reduce the fuel economy of the car. A cost-effective method
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Ng, H.K.; Novick, V.J. & Sekar, R.R. Using monatomic nitrogen induced by a pulsed arc to remove nitrogen oxides from a gas stream, article, December 1, 1995; Illinois. (digital.library.unt.edu/ark:/67531/metadc623062/m1/2/: accessed December 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.