22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Performance of 1 kW-class arc jet thrusters with N 2 /H 2 /NH 3 propellants
X. Meng, W. Pan, H. Huang and C. Wu
Institute of Mechanics, Chinese Academy of Sciences, State Key Laboratory of High Temperature Gas Dynamics,
100190 Beijing, P.R. China
Abstract: a 1 kW-class arcjet thruster with natural radiation-cooled nozzle has been
designed and tested, and the performance of the arcjet thruster has been studied and
observed by using pure N 2 , H 2 , NH 3 and mixtures of N 2 /H 2 and H 2 /NH 3 as propellant.
Results show that better performance of the arcjet thruster can be obtained by using
H 2 /NH 3 propellant than that with H 2 /N 2 propellant.
Keywords: arcjet, specific impulse, thrust efficiency, voltage, pressure
1. Introduction
The DC arcjet thruster, which has the advantages of
relatively simple and compact system, moderately high
specific impulse and high energy conversion of input
power to kinetic energy of the exhaust stream, plays an
increasingly noticeable role in satellite applications. In
practical applications, hydrazine (N 2 H 4 ) is often used as
the propellant [1-2], in order to share the storage tank
with ordinary chemical combustion rockets. Ammonia
(NH 3 ) is also a promising propellant for ease of storage
and high performance. In the laboratory, for sake of safety
and convenience, gaseous mixtures of N 2 /H 2 or N 2 /NH 3
in various proportions are often used in experimental
studies to simulate dissociated hydrazine or ammonia. It
is interesting to study the effect of propellant composition
on the performance of the arcjet thrusters.
Specific impulse and thrust efficiency are the two
important parameters characterizing the performance of
the arcjet thruster. In order to improve the performance of
the thrusters, both the power input to the thruster and the
conversion efficiency from input power to kinetic energy
of the exhaust gas should be increased. However, energy
conversion is a very complicated process, which is closely
associated with the gas type, arc-discharge behaviour,
plasma flow pattern, nozzle structure and arc-electrode
interactions, etc. [3, 4].
In the present study, a 1 kW-class arcjet thruster with
natural radiation-cooled nozzle has been designed and
tested, and the performance of the arcjet thruster has been
studied and observed by using pure N 2 , H 2 , NH 3 and their
mixtures as the propellant.
2. Experimental
Fig. 1 shows the schematic diagram of the experimental
setup, which mainly consists of a vacuum chamber of 2m
diameter and 4m length, vacuum pump systems, gas and
power supplies, water-cooled thrust measurement stand,
traversing system, data collecting system, etc. The
ultimate vacuum of the chamber is 10-4Pa, and can be
kept at ~10 Pa for higher operational volume flow rates.
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Fig. 1. Schematic diagram of the experimental setup.
The arcjet thruster is mounted on a three-dimensional
moveable table driven by stepping motors, a heat-resistant
metal plate of 200 mm in diameter on the thrust stand,
used to receive the impact of the jet plume, is set
perpendicular to the jet plume axis. The impulse method
has been applied to measure the thrust in this work [2].
The gas flow rate, arc current and voltage, pressures, etc.
are measured by transducers. The dimensions of the
nozzle are: throat diameter 0.7 mm, constrictor length
0.5mm, half angle of the divergent section 20o, and area
expansion ratio of exit to throat 205.
Fig. 2 shows photographs of the arcjet plasma plumes
of pure NH 3 , pure H 2 and mixture of N 2 /H 2 . It is seen
that the appearance of the plasma plume varies with the
propellants, and the outside nozzle temperature measured
by infrared pyrometer can be as high as 1600 K for
hydrogen propellant due to its high thermal-conductivity.
1
3. Results and discussions
150
H2
H2/NH3
Voltage (V)
NH3
100
H2/N2
50
N2
(a) Pure NH3, 6L/min, 9A, 1130W
0
0
2
4
6
8
10
12
14
N2: H2: NH3 I
1 0 0 7A
1 0 0 8A
3.5 1 0 9A
2 1 0 9A
1 1 0 9A
1 1.8 0 9A
1 2.6 0 9A
1 3.2 0 9A
1 4 0 9A
1 8 0 9A
1 10 0 9A
0 1 0 12A
0 6.1 1 12A
0 4.6 1 12A
0 3.1 1 12A
0 1.6 1 12A
0 1.2 1 12A
0 0 1 12A
0 0 1 9A
Gas flow rate (L/min)
Fig. 3. Variations of arc voltage against volumetric flow
rate.
(c) N2: H2=2:3, 4.0L/min, 7A, 630W
Fig. 2. Photographs showing the appearance of the
plasma plumes.
Fig. 3 plots the variations of arc voltage against
volumetric flow rate for different propellants. It is seen
that the arc voltage increases with volumetric flow rate
for all the propellants, which indicates that the arc column
is restricted to a thinner diameter and extended to a longer
length. The arc voltages with NH 3 propellant and H 2
propellant are higher than that with N 2 propellant, and the
arc voltages of H 2 /NH 3 mixtures arc higher than that with
the N 2 /H 2 mixtures at similar gas flow rates. It could
indicate the combined result of the different thermophysical properties of the propellants, and the complicated
physical-chemical processes within the nozzle, such as
gas dissociation and ionization, chemical reaction, arc
formation and development, ionized gas flow and
heat/mass transfer, etc.
The variations of specific impulse with volumetric flow
rate are plotted in Fig. 4. Within the range of working
conditions of these tests, the thruster with hydrogen
propellant has the highest specific impulse, the next is
with ammonia propellant, and the specific impulse is
lowest with nitrogen propellant. One main reason is that
the molecular weight of H 2 is 2, NH 3 17, while that of N 2
is 28. For similar input power, the thrusters with hydrogen
2
1000
N2: H2: NH3 I
1 0 0 7A
1 0 0 8A
3.5 1 0 9A
2 1 0 9A
1 1 0 9A
1 1.8 0 9A
1 2.6 0 9A
1 3.2 0 9A
1 4 0 9A
1 8 0 9A
1 10 0 9A
0 1 0 12A
0 6.1 1 12A
0 4.6 1 12A
0 3.1 1 12A
0 1.6 1 12A
0 1.2 1 12A
0 0 1 12A
0 0 1 9A
H2
800
Specific impulse (s)
(b) Pure H2, 7.6L/min, 12A, 1000W
propellant has the highest power input per unit mass and
can obtain the highest specific impulse. For the gas
mixtures, the higher specific impulse can be obtained for
the larger volumetric ratio of H 2 /N 2 and H 2 /NH 3 . For
hydrogen and ammonia propellant, the specific impulse
decreases slightly with the increase of volumetric flow
rate. It is known that higher gas temperature can produce
higher velocity at the nozzle exit, which is numerically
equal to the specific impulse. Though the arc voltage
increases with the increase of the volumetric flow rate and
the conversion efficiency may also increase somewhat,
the electric energy input per unit mass decreases, and the
overall result is still a decrease the gas temperature, thus
the specific impulse. On the other hand, the voltage and
efficiency increase with flow rate in nitrogen is large
enough to cause an increase of the specific impulse.
H2/NH3
NH3
600
400
H2/N2
200
N2
0
0
2
4
6
8
10
12
14
Gas flow rate (L/min)
Fig. 4. Variations of specific impulse against volumetric
flow rate.
Fig. 5 shows the variations of thrust efficiency against
volumetric flow rate. The thrust efficiency increases with
the increase of volumetric flow rate. At similar working
conditions, the arcjet thruster with ammonia propellant
has higher thrust efficiency compared with hydrogen and
nitrogen propellant, and the thrust efficiency of the arcjet
thrusters with propellant of H 2 /NH 3 mixture is higher
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than that with H 2 /N 2 mixture. The thrust efficiency is
affected by a number of factors (e.g. [3]) and cannot be
simply explained. One of the factors could be the gas
temperature. As mentioned in the discussion of Fig. 4, the
increase of volumetric gas flow rate generally results in
the decrease of the gas temperature, and thus decrease the
energy losses, such as the frozen loss, heat and friction
losses in the flow through the nozzle, thermal energy
carried by the exhaust gases, and finally result in the
increase of the thrust efficiency. For ammonia, it will
absorb heat during the dissociation process, which may
further decrease the gas temperature, and lead to the
higher thrust efficiency compared with hydrogen and
nitrogen.
Efficiency (%)
60
N2: H2: NH3 I
1 0 0 7A
1 0 0 8A
3.5 1 0 9A
2 1 0 9A
1 1 0 9A
1 1.8 0 9A
1 2.6 0 9A
1 3.2 0 9A
1 4 0 9A
1 8 0 9A
1 10 0 9A
0 1 0 12A
0 6.1 1 12A
0 4.6 1 12A
0 3.1 1 12A
0 1.6 1 12A
0 1.2 1 12A
0 0 1 12A
0 0 1 9A
H2/NH3
40
H2
NH3
H2/N2
20
N2
0
0
2
4
6
8
10
12
14
Gas flow rate (L/min)
Fig. 5. Variations of thrust efficiency against volumetric
flow rate.
4. Conclusions
Experimental results show that within the range of
working conditions of the test, the specific impulse of the
arcjet thrusters with H 2 and NH 3 propellants falls with the
increase of volumetric flow rate, while the thrust
efficiency increases with the volumetric flow rate. Better
performance of the arcjet thruster can be obtained by
using H 2 /NH 3 propellant than that with H 2 /N 2 propellant.
5. Acknowledgements
This work is supported by the National Natural Science
Foundation of China (Nos. 11475239 and 11175226).
6. References
[1] D.A. Lichtin, N.V. Chilelli, J.B. Henderson,
R.A. Rauscher Jr., K.J. Young, D.V. McKinnon,
J.A. Bailey, C.R. Roberts, D.M. Zube and
J.R. Fisher. AIAA, 2009-5364 (2009)
[2] R.L. Sackheim. J. Propulsion Power, 22, 1310
(2006)
[3] C.K. Wu, W.X. Pan, X. Meng and H.X. Wang.
Mechanisms for non-ideal flow in low-power archeated supersonic nozzles. Acta Mechanica Sinica,
accepted (2015)
[4] W.X. Pan, H.J. Huang and C.K. Wu. Plasma Sci.
Techn., 12, 473 (2010)
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