Using monatomic nitrogen induced by a pulsed arc to remove nitrogen oxides from a gas stream Page: 3 of 8
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that can reduce emissions at any temperature and not affect the
gas mileage of the car is needed.
1.2 Monatomic Nitrogen Method
Recently, engineers have been developing a membrane for
automotive application that separates the air stream into oxygen
and nitrogen components. The oxygen-enriched stream is fed to
the engine combustion chamber, while the nitrogen-enriched air
is exhausted. The currently available membrane can reach an
efficiency of 99% N2 quite readily. The advantages of an
increase of oxygen to the combustion process are a reduction of
HC and CO and improved fuel economy of the motor (Ng et al.,
1993). However, the concentration of NO, in the exhaust
This paper reports on the ongoing research at Argonne National
Laboratory (ANL) of a method that uses the nitrogen-enriched
stream of the membrane to reduce NO and NO. In this first
phase of the research, only compressed nitrogen was used for the
experiments. The detailed mechanisms involved in energizing the
nitrogen with an electric arc to form monatomic nitrogen (N) are
largely unknown today. Therefore, it is not possible to get an
estimate of the amount of Ns generated. However, it is well-
known that N* atoms generated by an arc can reduce NO
emissions by reversing the Zel'dovich step (Hilliard, 1976):
N* + NO -> N2 + O . (1)
This project examines the applicability of using N to reduce
both NO and NO2. The advantages of using this technology are
that it can be low in cost, works readily under cold-start
conditions, and will likely improve the fuel economy of an
automobile. This control technology will permit the engine to
burn leaner and more efficiently, meet future emission standards,
and not rely on the current three-way catalytic converter (which
requires the engine to run continuously near stoichiometric).
2 EXPERIMENTAL APPARATUS AND PROCEDURE
2.1 High-Voltage Pulser System and Reaction Chamber
Figure 1 presents a schematic diagram of the experimental
setup. The system is used to determine the feasibility of
employing an electric arc to create N' for reducing NO, to
nitrogen and oxygen. For these laboratory tests, a 50-kV charge
from a power supply is used in conjunction with a pulser to create
an electric arc. The pulser, manufactured for ANL by Ion Physics
Corporation, consists of a series of capacitors and resistors
enclosed in a cylindrical aluminum tank. The 50-kV charge from
the power supply travels to the pulser through two external
resistors. Once the charge reaches the pulser, it is stored in the
system's capacitors until the pulser receives a signal from the
trigger to release the charge. The frequency of the trigger can be
altered during an experiment to vary the pulse of the electric arc.
The high-voltage pulse from the pulser is delivered to a needle in
the reaction chamber through a 6.35-mm-diameter metal tube
insulated by Teflon. The electric arc then propagates from the
needle to a ground electrode. A narrow, rounded tip on the
ground electrode helps to reduce the motion of the arc and to
keep it centered along the nitrogen gas stream. The metal tube
provides a current path for the pulser to the reaction chamber,
while simultaneously allowing for introduction of a pure nitrogen
gas to the needle, forming a gas jet. The gas jet impinges on the
ground electrode placed right in front of it.
The reaction chamber that houses the needle and ground
electrode is a metal rectangular box that has a cross section
measuring 100 mm x 100 mm and is 1.22 m long. The chamber
is fitted with two windows, mounted on opposite sides, to allow
observation of the arc, needle, and ground electrode
characteristics. The needle is centered in and surrounded by a
removable glass tube. The ground electrode is aligned with the
needle center at a distance of 19.05 mm from the needle end.
The gas stream is fed from the gas cylinders into the glass tube,
which keeps the gas in close proximity to the arc, as pictured in
Figure 2. The glass tube defines the cross-sectional flow area of
the NOz gas stream. The gas stream and the pure nitrogen jet
always flow in the same direction. Three different diameters of
glass tube were used to investigate the effects of confining the gas
stream at various distances from the arc and to assess the effects
of different exhaust gas velocities on the NO, reduction
efficiency. Perpendicular to the end of the glass tube is a sample
probe, consisting of an 3.18-mm-outside-diameter ceramic tube
connected to Teflon tubing. The probe collects a representative
gas sample that is pumped to the NO/NO, and oxygen analyzers.
2.2 NO/NOX and Oxygen Analyzers and Data Acquisition
A Beckman Model 951A NO/NO, analyzer is used to monitor
the NO and NO, concentrations of the gas exiting the glass tube.
The analyzer has two settings for measuring the exhaust. NO is
measured directly by using the chemiluminescent method, and
NO, is measured by first converting NO2 to NO and then using
the chemiluminescent method for detection. Therefore, the
analyzer measures only NO and the combination of NO2 and NO
as NOz. This analyzer is used to measure the concentrations of
NO and NO, before the arc is turned on and to measure the
amount of NO and NOz left after the gas stream has reacted with
the nitrogen ions produced by the arc. These two measurements
are used to determine the reduction efficiencies of NO and NO,
for each set of experimental variables:
NO Reduction Efficiency= arc-[N laher arc and (2)
[NO ]or arc -[NOxiatter are(3
NO, Reduction Efficiency= [oarc arc (3)
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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/m1/3/: accessed November 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.