22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Rotating arc technology for diesel emission control
Y-H. Song, H.S. Kim, K.T. Kim, J.O. Lee and D.H. Lee
Korea Institute of Machinery & Materials, Plasma Laboratory, Daejeon, South Korea
Abstract: Diesel after-treatment technologies, which are a diesel burner assisted by
rotating arc and a plasma fuel reformer, have been studied. A small-scale experiment to
characterize the fundamental aspects of the technologies and a feasibility study based on
engine and vehicle tests has been conducted.
Keywords: plasma assisted burner, plasma fuel reformer, diesel emissions, soot, NOx
1. Introduction
Considering the forthcoming strict regulations on diesel
emissions, such as Euro 7 and IMO (International
Maritime Organization) NOx emission regulation, the
current conventional diesel after-treatment technologies
are sufficient. For example, as pointed out in the recent
study [1], although the European diesel NOx emissions
have been tightening up for the last 15 years,
improvement of real emissions has not been noticeable.
One of the reasons for such poor improvement is that the
present test cycle to evaluate the diesel after-treatment
technologies is not appropriate to simulate the real driving
conditions, especially, cold start, rural and urban driving
conditions. Under these conditions, temperatures of the
diesel exhaust gases are too low to activate the catalysts
for regenerating DPF (Diesel Particulate Filter) and for
reducing NOx.
Therefore, innovative diesel aftertreatment technology that can be operated under the low
temperature conditions is needed to meet the forthcoming
regulations.
Emission control technology based on plasma
chemistry, which is less relevant to temperature condition,
could be alternative to the current diesel catalyst
technology. The objective of the present study is to
investigate the feasibility of the rotating arc technology
for diesel emission control. Especially, the rotating arc
technology has been applied to solve the low temperature
issues on diesel after-treatment technologies.
To
investigate the feasibility, in addition to fundamental
experiments, engine and vehicle tests have been
conducted, which provide practical engineering data such
as power consumption for plasma generation, the physical
scale and the durability of the mechanical parts of the
rotating arc reactor, etc.
2. Burner and reformer assisted by rotating arc
Geometrical configuration of a rotating arc reactor and
the development of rotating arc are shown in Fig. 1, and
are discussed in detail elsewhere [2]. Here, one of the
important characteristics of the rotating arc is the
evolution of the arc. Initially, the arc is ignited at the
shortest distance between the inner electrode and the outer
tube, which is located at the lower part of the reactor.
After ignition, the arc is pushed upward and is rotated by
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tangentially injected gas flow motion. Eventually, the
rotating arc is anchored between the upper part of the
inner electrode and the edge of the outer tube, and the arc
length reaches its maximum. Under this condition, the
energy transfer from the arc to the reactive gases is
optimized [2].
Fig. 1. Geometrical configuration of rotating arc reactor
and development of a rotating arc: (1) ignition, (2)
evolution, and (3) anchoring.
The present rotating arc reactor is operated with the bifunctional operating modes, one is a diesel burner for
adequate thermal management of the diesel aftertreatment system (De-NOx catalyst and DPF), and the
other one is a diesel fuel reformer to supply reducing
agents to the De-NOx catalyts. Fig. 2 is the schematics of
a typical diesel after-treatment system and the rotating arc
reator that can be operated for both burner and fuel
reformer. As reported in technical papers [3, 4], thermal
management of the diesel after-treatment system is one
the the key issues in developing advanced diesel aftertreatment technologies. For example, in the case of the
cold start of a heavy-duty truck [3], a relatively long time,
i.e., about 10 minutes, is needed for heating up the DeNOx catalyst. In order to reduce this heat-up period,
which is necessary to meet the future emission regulations,
application of a compact diesel burner can be one of the
effective measures. In addition to this fast start-up
purpose, the diesel burner can be operated for
regenerating DPF [4] and for managing urea injection
system.
1
light hydrocarbons are also produced through the plasma
diesel
(a) fuel lean (Φ = 0.55) flame
Fig. 2. Schematics of a typical diesel after-treatment
system with a plasma burner and fuel reformer.
2
(b) fuel rich (Φ = 1.85) flame
Fig. 3. CH 4 flames at differernt electrical power
conditions for rotating arc; picture was taken at 0.25 sec
of shutter speed; supplied air : 15 lpm.
25000

Plasma on
Plasma off
20000
C2
C2
O
H
N
NN
Intensity (a.u.)
In general, diesel exhaust gases are quite harsh
conditions to keep a stable flame [5]. Due to high mean
gas velocity up to 30 m/sec and oxygen deficient
conditions, very sophiscated burner operation and bulky
burner design are inevitable to avoid unstable flame and
flame extinction [4]. Since the flammability limits for
both fuel lean and rich conditions can be significantly
extended by rotating arc, the plasma burner can be
operated with a simple operating procedure and a compact
design. Physical scale of the diesel burner assisted by
rotating arc will be shown in later section. Fig. 3 shows
an example of CH 4 flames stabilized by rotating arc. In
the cases of electrical power off, flame was not observed
due to flame extiction. When the power on, the flame can
be observed for both fuel lean and rich conditions. In the
case of the fuel rich condition, the oscillating and sooty
flame turn into the short and stable flames, right after
50 W of electrical power was supplied to the retating arc
reactor.
Fig. 4 shows the optical emission spectrum from the
flames with and without rotating arc. As shown in the
figure, strong emission spectrum for N, O, H α , CN are
detected from the flame assisted by rotating arc. On the
other hand, these emsission signals are not that strong in
the case of the flame without arc. This difference implies
that the temperature and the reaction pathways of the
combustion assisted by rotating arc is quite different from
theose of the normal flame.
The geometrical configuration of the plasma fuel
reformer is the same as the diesel burner assisted by
rotasting arc. One noticeable differernce between the
burner and the reformer is the amounts of the air supply to
the rotating arc reactor. In the case of the fuel reformer,
the amounts of the air supply is reduced by half. Thereby,
the present fuel reforming process can be called as
partical oxidation process. However, the product gases
reformed by the present rotating arc are quite differernt
from those reformed by catalyst. As shown in Fig. 5, in
addition to syngas (H 2 and CO), numerous species of
O
15000
OH
CN CH
10000
5000
0
300
400
500
600
700
800
Wavelength(nm)
Fig. 4. Optical emission spectrum from the flame with
and without rotaing arc. Air/fuel ratio: stoichiometiric
condition.
fuel reformer. A recent study has revealed that effects of
these light hydrocarbons on hydrocarbon SCR (Selective
Catalytic Reduction) performance is superior to typical
diesel fuels [6]. Therefore, it could be expected that the
De-NOx performance with plasma fuel refomer is high,
compared to those with catalytic fuel reformer.
3. Engine and vehicle test
Fig. 6 shows the diesel flame assisted by rotating arc,
and also shows the burner installed inside of the diesel
exhaust pipe. The volume of this compact burner is less
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than 100 cc. Owing to this compact size, the burner can
be installed inside of the exhaust pipe. Unlike typical red
14
gases consist of H 2 , CO, and light hydrocarbons. The
power consumption for the rotating arc is 120 W, which is
higher than that of plasma burner.
O2/C 0.4
Concentration [%]
12
O2/C 0.5
O2/C 0.6
10
O2/C 0.7
O2/C 0.8
8
O2/C 0.9
6
4
2
4
2H
6
C
2H
4
C
3
n - H8
C
4H
10
C
2H
2
C
3H
i- C 6
4H
10
C
2
H
O
C
C
2
H
C
O
0
Fig. 7. Temperature of the exhaust gases right after the
plasma burner and DPF.
Gases
Fig. 5. Concentrations of product gases reformed by
rotating arc.
or yellow diesel flames, the color of the flame assisted by
rotating arc is blue, which implies that the soot can be
quickly oxidized by the assistance of rotating arc. The
flame assisted by rotating arc could be stable under any
engine load and speed conditions.
P
Fig. 8. Engine test configuration of the plasma reformer
and the De-NOx catalyst reactor.
Fig. 6. Rotating arc and diesel flame (left), plasma burner
installed in exhaust pipe of 3000 cc diesel engine (middle),
diesel after-treatment system at the underbody of the
vehicle (right).
Fig. 7 shows the diesel exhaust gas temperatures right
after the plasma burner and the gas temperatures in front
of the DPF. As shown in the figure, the initial
temperature of the DPF is about 100 °C, which is far
below the soot oxidation temperature, i.e., 550 °C. The
figure shows that the temperature of the DPF reaches
550 °C in less than one second. So far, the DPF
regeneration test has been conducted with more than
20,000 km of vehicle test, which demonstrated the
feasibility of the plasma burner for regenerating DPF.
Typically, the electrical power consumption for rotating
arc is about 35 W that is acceptable for the current
automobile battery capacity. Because of the small
electrical power consumption, additional cooling of the
electrodes is not necessary.
Fig. 8 shows the De-NOx system that consists of the
diesel fuel reformer and the De-NOx catalyst reactor.
3,000 cc Euro 4 engine was used to supply diesel exhaust
gases to the De-NOx system. The diesel reformed gases
are produced by the rotating arc reactor, and then supplied
to the De-NOx catalyst. As shown in Fig. 5, the refomred
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For the De-NOx test, two differernt types of catalyst
have been tested, one is the catalyst based on Pt and the
other one is the catalyst based on Ag/Al 2 O 3 . In the case
of the Pt catalyst, the catalyst can be activated at the lower
temperature range. The De-NOx rates is sensitively
varied depending on the O 2 /C ratios, which implies that
the light hydrocarbons play a important role on De-NOx
process. In the case of Ag/Al 2 O 3 catalyst, relatively high
temeprature conditions are needed to activate the catalyst.
The De-NOx rates, however, are higher than those of
Pt catalyst (Fig, 9). A recent test shows that the De-NOx
rate can be noticeably increased by changing the catalyst
materials, which means that the De-NOx performance
could be increased without further improvemnet on the
reformer.
4. Conclusion
The present plasma technique for diesel emission
control is based on a rotating arc technology, and is
different from a non-thermal plasma technology proposed
by Penetrante [7]. Although these plasma technologies
have different reaction pathways and methodologies, the
purpose of both technologies are to effectively control
the diesel emissions at the low temperatures, which are
too low to activate the conventional diesel catalysts. The
power consumption, the physical scale, and the durabiliy
of the rotating arc installed in a vehicle have been
3
revealed in the present study. Also, the present study
provides realistic performance of the plasma burner and
DeNOx efficiency [%]
50
Pt catalyst
self HC
O2/C ratio 0.4
40
O2/C ratio 0.8
30
20
10
0
150
DeNOx efficiency [%]
80
250
200
self HC
O2/C ratio 0.4
300
Temperature [oC]
350
Ag/Al2O3 catalyst
O2/C ratio 0.8
60
40
20
0
200
250
300
350
400
450
Temperature [oC]
Fig. 9. De-NOx rates with differernt catalysts, SV:
40,000 hr-1.
fuel reformer installed in a diesel engine, which
demonstrate that the the plasma technology has great
potential to cope with future strict diesel emission
regulations.
5. Acknowledgement
The present study is supported by KIMM and Korea
Research Council for Industrial Science & Technology.
6. References
[1] T. Johnson. “Vehicular Emissions in Review”. SAE
paper No. 2014-01-1491 (2014)
[2] D.H. Lee, K.T. Kim, M.S. Cha and Y-H. Song.
Proc. Combustion Inst., 31, 3343-3351 (2007)
[3] M. Kimura, T. Muramatsu, E. Kunishima,
J. Namima, W. Crawley and T. Parrish. SAE Paper
No. 2011-01-0295 (2011)
[4] X. Fang, D. Mastbergen and C. Paterson. SAE
Paper No. 2011-01-2210 (2011)
[5] N.K. Hwang, J.G. Lee, D.H. Lee and Y-H. Song.
Plasma Chem. Plasma Process., 32, 187-200 (2012)
[6] V. Houel, P. Millington, R. Rajaram and A.
Tsolakis. Appl. Catalysis B: Environm., 77, 29-34
(2007)
[7] B.M. Penetrante, R.M. Brusasco, B.T. Merritt,
W.J. Pitz, G.E. Vogtlin, M.C. Kung, H.H. Kung,
C.Z. Wan and K.E. Voss. SAE Paper No. 982508
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