Surface Microwave Discharge as Means of Ignition of
Hydrocarbons in Air Streams
A.F.Aleksandrov1, V.M.Shibkov2, L.V.Shibkova3
Department of Physics, Moscow State University, 119992, Moscow, Russia
Influence of non-equilibrium plasma of a surface microwave discharge on processesof ignition of a supersonic propane-air stream with Mach number М=2 is considered.Alcohol, gasoline and kerosene ignition under conditions of subsonic and supersonicair streams is investigated too.
Advances in aviation technology call for research and development aimed at creating new
efficient means for reducing the ignition time and controlling the combustion of supersonic fuel
flow. A new solution to these problems is application of gas discharge. In the paper a surface
microwave discharge was used for ignition of a supersonic propane-air stream and for ignition of
liquid hydrocarbon films under conditions of a subsonic and a supersonic air stream.
For investigation of the possibility of the ignition of high-speed hydrocarbon flows using
a surface microwave discharge an experimental design, which including a vacuum chamber, a
high pressure air receiver, a high pressure propane receiver, a system for propane-air mixing, a
system for supersonic flow creation, a rectangular aerodynamic channel, a high voltage power
supply source, a magnetron generator, a system for microwave energy input to the chamber, a
synchronization unit, and diagnostic equipment, was used [1-9]. A pulsed magnetron generator
of the centimeter wavelength range serves as the microwave power source. The characteristics of
the magnetron generator are: the wavelength λ = 2.4 cm, pulsed microwave power W < 200 kW,
and a pulse duration τ = 5-200 µs.
Ignition of propane-air supersonic flow was studied depending on the pulsed power
(W = 30-70 kW), microwave pulse duration (τ = 5-200 µs), and air mass consumption
(dmair/dt = 25-120 g/s) propane mass consumption (dmpropane/dt = 1-7 g/s); in this case, the
equivalent ratio for propane varied from 0.3 to 2.Experiments were carried out on the installation
consisting of a vacuum chamber, a receiver of a high pressure of air, a receiver of a high pressure
of propane, a system for mixing propane with air, a system for producing a gas flow, a
magnetron, a system for delivering microwave power into the chamber, an aerodynamic channel,
1 Professor, Department of Physics, Moscow State University, 119992, Moscow, Russia, [email protected] Professor, Department of Physics, Moscow State University, 119992, Moscow, Russia, [email protected] Professor, Department of Physics, Moscow State University, 119992, Moscow, Russia, [email protected]
47th AIAA Aerospace Sciences Meeting Including The New Horizons Forum and Aerospace Exposition5 - 8 January 2009, Orlando, Florida
AIAA 2009-690
Copyright © 2009 by Moscow State University. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.
a synchronization unit, and a diagnostic system [1-9]. The scheme of installation is submitted in
Fig. 1.
Fig. 1. Block-scheme of the experimental installation. 1 – vacuum chamber, 2 – synchronizationunits, 3 – magnetrons, 4 – directional coupler, 6 – load, 7 – crystal microwave detector, 8 –waveguide, 9 – dielectric antenna, 10 – Laval nozzles, 11 – electric hydraulic valves, 12 – airhigh pressure receiver, 13 – propane high pressure receiver, 14 – high-pressure cylinder withpropane; 15 – valves, 16 – block of probe measurements, 17 – power supply system, 18 –computers, 19 – digital spectrograph, 20 – video and photo digital cameras, 21 – pulsed powersupply, 22 – pulsed lamp of flash, 23 – lens, 24 − entrance diaphragm, 25 – objective lens, 26 –lens, 27 – exit diaphragm, 28 – digital photo camera, 29 – digital oscilloscope, 30 – pump out.
Fig. 2 shows the integral photo of the burning of the supersonic propane-air flow and
Fig. 3 shows the instantaneous shadowgram of this process. The front boundary of the burning
region, coinciding in configuration with the boundary of the region of supersonic burning
observed in the integral photo, is fixed in the shadowgram. This spatial distribution of the
burning front of the supersonic flow for the propane-air mixture proves our hypothesis on the
possible contribution of ultraviolet radiation of the surface microwave discharge on hydrocarbon
fuel ignition kinetics [2, 11]. It should be noted that gas dynamic perturbations arising in the
course of development of the surface microwave discharge can also strongly influence the
ignition of the supersonic propane-air flow. It was shown experimentally that ignition already
takes place for a pulsed power of 35 kW at a distance of 1.5 cm from the front edge of the
1
9
22
24
23
25
26
27
28
11
15
12
10
2
8
29
21
315
13
14
1
16 17
18
R
2019
306
7
4
antenna. With increasing supplied energy the intensity of supersonic propane-air flow burning
increases; in this case, for a power of 70 kW burning begins approximately at a distance of
0.5 cm from the front edge of the antenna.
Fig. 2. General view of ignition of a supersonic stoichiometric propane-air stream with a help ofa surface microwave discharge created on a quartz antenna at dmair/dt = 55.5 g/s,dmpropane/dt = 3.6 g/s, τ = 120 µs, Wp = 70 kW.
Fig. 3. Instant shadow picture of ignition of a supersonic stoihiometric propane-air stream underconditions of a surface microwave discharge created on the quartz antenna at dmair/dt = 55.5 g/s,dmpropane/dt = 3.6 g/s, τ = 120 µs, Wp = 70 kW. The flashlamp pulse with a duration of 4 µs isdelayed with respect to the microwave pulse front by 120 µs.
The important parameter during the ignition and burning of the air-hydrocarbon fuel is
the mixture composition. In experiments the equivalent ratio for propane was controlled by
either variation of air consumption at a constant propane consumption per second, or variation of
propane consumption per second at a constant air consumption per second. It was established in
the studies performed that the surface microwave discharge results in ignition of both poor and
rich mixtures. The ignition delay for the supersonic propane-air flow changes depending on the
experimental conditions from 5 to 20 µs. The transverse burning front propagation rate was
determined by the known supersonic flow speed and the measured tangent of the inclination
angle of the sharp front boundary of the characteristic glow. It was obtained that the rate depends
on the supplied power and equivalent ratio. It is maximal in the stoichiometric mixture, reaching
about 200 m/s. The fact of ignition was also shown using a double probe placed in the burning
region; in this case, the signal intensity at ignition of the propane-air flow exceeded the intensity
of the signal corresponding to the surface microwave discharge in an air flow by one order of
magnitude. The flame temperature upon burning of the supersonic stoichiometric propane-air
flow for the surface microwave discharge was of the order of 3000 K.
When a liquid is placed in a vacuum chamber, it evaporates intensely, which prevents
investigation of the ignition of hydrocarbon fuel in the liquid phase at air pressures in a pressure
chamber lower than atmospheric pressure. The system of supply of electromagnetic energy to the
antenna developed in [10-13] allows one to create the surface microwave discharge in a wide
range of air pressures up to atmospheric pressure and to study the ignition of liquid hydrocarbons
using the surface microwave discharge under the conditions of high-speed air flow. Liquid
hydrocarbon ignition was studied using alcohol, benzene, and kerosene applied in the form of a
thin layer to the upper and lower surfaces of the quartz antenna as the examples. Air to a pressure
of six atmospheres can be pumped to the high pressure receiver using a compressor; this allows
us to create high-speed air flows with the given speed at atmospheric pressure in the pressure
chamber.
Fig. 4. Alcohol ignition using surface microwave discharge for the microwave pulse duration
τ = 120 µs, is, initial air pressure in the pressure chamber p0 = 1 atm, pulsed microwave power
Wp = 65 kW, and air flow velocities: (a) υblast = 190 m/s, (b) υblast = 390 m/s.
Fig. 4 shows the photos of alcohol burning in the subsonic (upper photo) and supersonic
(lower photo) flows. It was obtained that for a pulsed microwave power of 70 kW the induction
period in kerosene is equal to approximately 10 µs, and the propagation rate of the front
boundary of the burning region in these conditions reaches 100 m/s. The temperature evolution
measured during the microwave pulse demonstrates that kerosene was ignited at 1200 K, and the
temperature increased to 3200 К promptly (during 10 µs). A regime close to detonation burning
developed near the antenna surface (Fig. 5). However, since the active medium in this
experiment is near the antenna only, the detonation regime damped rapidly.
Fig. 5. Transverse alcohol ignition rate under the conditions of surface microwave discharge
(τ = 120 µs, Wp = 65 kW) created in air flow (υblast = 190 m/s).
The obtained results show that a surface microwave discharge can be used to fast ignition
of gaseous and liquid hydrocarbon fuel under condition of high speed air flow.
ACKNOWLEDGMENTS
This work was partially supported by the Russian Foundation for Basic Research, project
# 08-02-01251 and Russian Academy of Science (P-09 program).
REFERENCES
1. V.M.Shibkov, D.A.Vinogradov, A.V.Voskanyan, et al., Moscow Univ. Bull, Ser. 3, Physics,
Astronomy. 2000, v.41, No 6, p. 64-66.
2. V.M.Shibkov, A.F.Aleksandrov, A.P.Ershov, et al., Moscow Univ. Bull., Ser. 3, Phys.
Astron. 2004, v.45, No 5, p.67-69.
3. V.M.Shibkov, A.P.Ershov, V.A.Chernikov, and L.V.Shibkova, J. Tech. Phys. 2005, v.75,
No 4, p.67-73.
0 2 4 60
500
1000
1500
2000
2500v,
m/s
y, mm
4. V.M.Shibkov, S.A.Dvinin, A.P.Ershov, and L.V.Shibkova, J. Tech. Phys. 2005, v.75, No 4,
p.74-79.
5. V.M.Shibkov, A.F.Aleksandrov, A.P.Ershov, et al., Plasma Phys. Rep. 2005, v.31, No 9,
p.857-864.
6. S.A.Dvinin, V.M.Shibkov, V.V.Mikheev, et al., Plasma Phys. Rep. 2006, v.32, No 7, p.654-
665.
7. V.M.Shibkov, S.A.Dvinin, A.P.Ershov, et al., Plasma Phys. Rep. 2007, v.33, No 1, p.77-85.
8. V.M.Shibkov, A.F.Alexandrov, A.V.Chernikov, et al., in Proceedings 43rd Aerospace
Sciences Meeting AIAA-2005-0779, p.1-8 (Reno, NV, USA).
9. L.V.Shibkova, Moscow Univ. Physics Bulletin, Ser. 3, Phys. Astron., 2007, No 5, p.62-64.
10. L.V.Shibkova, Alcohol Ignition under Conditions of Surface Microwave Discharge in Air
(Preprint No. 4, Physical Faculty, MSU, 2007).
11. L.V.Shibkova, "Physical Processes in Moving Plasma of Multicomponent Inert and
Chemically Active Mixtures", Doctoral Dissertation (Phys. Math.) (JIHT RAS, Moscow,
2007).
12. A.F.Aleksandrov, V.M.Shibkov, and L.V.Shibkova. Moscow Univ. Physics Bulletin, Ser. 3,
Phys. Astron., 2008, v.63, No 5, p.365-366.
13. A.F.Aleksandrov, V.M.Shibkov, and L.V.Shibkova. Moscow Univ. Physics Bulletin, Ser. 3,
Phys. Astron., 2008, v. 63, No 6, p.428-430.