Electricity vs Fire
See also : BLOMGREN :
Electrostatic Cooling // WARD : Magnetic Beam vs Fire
March 28, 2011
Fires could be extinguished using
beams of electricity
Scientists have developed a device that uses beams of electricity
to extinguish flames
It's certainly an established fact that electricity can cause
fires, but today a group of Harvard scientists presented their
research on the use of electricity for fighting fires. In a
presentation at the 241st National Meeting & Exposition of the
American Chemical Society, Dr. Ludovico Cademartiri told of how
they used a unique device to shoot beams of electricity at an open
flame over one foot tall. Almost immediately, he said, the flame
was extinguished. On a larger scale, such a system would minimize
the amount of water that needed to be sprayed into burning
buildings, both saving water and limiting water damage to those
Apparently, it has been known for over 200 years that electricity
affects fire – it can cause flames to change in character, or even
stop burning altogether. According to Cademartiri, a postdoctoral
fellow in the group of Prof. George M. Whitesides at Harvard
University, what hasn't been looked into much is the science
behind the relationship. It turns out that soot particles within
flames can easily become charged, and therefore can cause flames
to lose stability when the local electrical fields are altered.
The Harvard device consists of a 600-watt amplifier hooked up to a
wand-like probe, which is what delivers the electrical beams. The
researchers believe that a much lower-powered amplifier should
deliver similar results, which could allow the system to worn as a
backpack, by firefighters. It could also be mounted on ceilings,
like current sprinkler systems, or be remotely-controlled.
Cademartiri believes the technology would work best for fires in
confined spaces, such as aboard submarines, but not so much for
wide-open areas like forests. As it was additionally found that
electrical waves can affect the heat and distribution of flames,
he also thinks their discovery could be used to boost the
efficiency of devices that involve controlled combustion, such as
engines, power plants, and cutting and welding torches.
Taming the flame: Electrical wave
“blaster” could provide new way to extinguish fires
Fighting out of control fires could become faster and more
eco-friendly with an unusual technique that snuffs out flames
using blasts of electrical waves.
ANAHEIM, March 27, 2011 — A curtain of flame halts firefighters
trying to rescue a family inside a burning home. One with a
special backpack steps to the front, points a wand at the flame,
and shoots a beam of electricity that opens a path through the
flame for the others to pass and lead the family to safety.
Scientists today described a discovery that could underpin a new
genre of fire-fighting devices, including sprinkler systems that
suppress fires not with water, but with zaps of electric current,
without soaking and irreparably damaging the contents of a home,
business, or other structure. Reporting at the 241st National
Meeting & Exposition of the American Chemical Society (ACS),
Ludovico Cademartiri, Ph.D., and his colleagues in the group of
George M. Whitesides, Ph.D., at Harvard University, picked up on a
200-year-old observation that electricity can affect the shape of
flames, making flames bend, twist, turn, flicker, and even
snuffing them out. However, precious little research had been done
over the years on the phenomenon.
“Controlling fires is an enormously difficult challenge,” said
Cademartiri, who reported on the research. “Our research has shown
that by applying large electric fields we can suppress flames very
rapidly. We’re very excited about the results of this relatively
unexplored area of research.”
Firefighters currently use water, foam, powder and other
substances to extinguish flames. The new technology could allow
them to put out fires remotely — without delivering material to
the flame — and suppress fires from a distance. The technology
could also save water and avoid the use of fire-fighting materials
that could potentially harm the environment, the scientists
In the new study, they connected a powerful electrical amplifier
to a wand-like probe and used the device to shoot beams of
electricity at an open flame more than a foot high. Almost
instantly, the flame was snuffed out. Much to their fascination,
it worked time and again.
The device consisted of a 600-watt amplifier, or about the same
power as a high-end car stereo system. However, Cademartiri
believes that a power source with only a tenth of this wattage
could have similar flame-suppressing effect. That could be a boon
to firefighters, since it would enable use of portable flame-tamer
devices, which perhaps could be hand-carried or fit into a
But how does it work? Cademartiri acknowledged that the phenomenon
is complex with several effects occurring simultaneously. Among
these effects, it appears that carbon particles, or soot,
generated in the flame are key for its response to electric
fields. Soot particles can easily become charged. The charged
particles respond to the electric field, affecting the stability
of flames, he said.
“Combustion is first and foremost a chemical reaction – arguably
one of the most important – but it’s been somewhat neglected by
most of the chemical community,” said Cademartiri. “We’re trying
to get a more complete picture of this very complex interaction.”
Cademartiri envisions that futuristic electrical devices based on
the phenomenon could be fixed on the ceilings of buildings or
ships, similar to stationary water sprinklers now in use.
Alternatively, firefighters might carry the flame-tamer in the
form of a backpack and distribute the electricity to fires using a
handheld wand. Such a device could be used, for instance, to make
a path for firefighters to enter a fire or create an escape path
for people to exit, he said.
The system shows particular promise for fighting fires in enclosed
quarters, such as armored trucks, planes, and submarines. Large
forest fires, which spread over much larger areas, are not as
suitable for the technique, he noted.
Cademartiri also reported how he and his colleagues found that
electrical waves can control the heat and distribution of flames.
As a result, the technology could potentially improve the
efficiency of a wide variety of technologies that involve
controlled combustion, including automobile engines, power plants,
and welding and cutting torches, he said.
The Defense Advanced Research Projects Agency (U.S. Department of
Defense) and the U.S. Department of Energy funded this study.
Geo. M Whitesides Group @ Harvard U.
MANIPULATION OF FLAMES AND RELATED METHODS AND APPARATUS
[ PDF ]
Inventor(s): CADEMARTIRI LUDOVICO [US]; MACE
CHARLES R [US]; SHEPHERD ROBERT FOSTER [US]; MAZZEO AARON D [US];
BISHOP KYLE J M [US]; CHIECHI RYAN C [US]; WHITESIDES GEORGE
Applicant(s): HARVARD COLLEGE [US]; CADEMARTIRI
LUDOVICO [US]; MACE CHARLES R [US]; SHEPHERD ROBERT FOSTER [US];
MAZZEO AARON D [US]; BISHOP KYLE J M [US]; CHIECHI RYAN C [US];
Classification: - international:
F23D14/00; F23D14/84; F23D99/00; F23N5/00
Manipulation of flames is described using electric fields. In
those instances in which electric fields are used, the electric
fields may be time-varying gradient electric fields, and in some
instances may be oscillating electiic fields. The manipulation may
include extinction, suppression, control of mixing of the flame,
concentration, and/or bending, among other types.
This application claims priority under 35 U.S.C. $ 119(e) to U.S.
Provisional Application Serial No. 61/491,836 filed May 31, 2011
entitled "CONTROL AND
EXTINCTION OF FLAMES BY OSCILLATING ELECTRIC FIELD GRADIENTS" and
U.S. Provisional Application Serial No. 61/559,677 filed November
14, 2011 as Attorney Docket No. H0498.70424US00 and entitled
"MANIPULATION OF FLAMES AND RELATED METHODS AND APPARATUS," the
entire contents of both of which is incorporated herein by
Research leading to various aspects of the present invention were
sponsored, at least in part, by the Department of Defense under
DARPA Award #w911nf-09-l-005. The U.S. government has certain
rights in the invention.
Combustion processes, and the flames associated therewith, are
common. Yet, our understanding of fire, and how to control it
According to one aspect, manipulation of flames using electric
fields is described. The manipulation may be performed by applying
a time-varying gradient electric field to the flame. The flame may
be any of various types, as the present aspect is not limited in
According to another aspect, a method comprises extinguishing a
flame by applying an oscillating gradient electric field to the
flame. According to another aspect, a method comprises suppressing
a flame by applying an oscillating gradient electric field to the
flame. According to another aspect, a method comprises bending a
flame by application of an oscillating gradient electric field to
the flame. According to another aspect, a method comprises
controlling mixing in a flame by application of an oscillating
gradient electric field to the flame. According to another aspect,
a method comprises concentrating a flame by application of an
oscillating gradient electric field to the flame.
Further aspects and embodiments are described below.
BRIEF DESCRIPTION OF DRAWINGS
Various aspects and embodiments of the technology will be
described with reference to the following figures. It should be
appreciated that the figures are not necessarily drawn to scale.
Items appearing in multiple figures are indicated by the same or a
similar reference number in each of the figures in which they
FIG. 1 illustrates a non-limiting embodiment of a system which
may be used to manipulate a flame by application of a
time-varying electric field to the flame.
FIG 2 shows a graph of the values of the probability
of extinction, P, and the angle of deflection (a) in degrees as
a function of frequency in Hertz (Hz) for the voltage V= 20 kV
of the signal applied to an electrode and the distance [delta]=
6 mm of the electrode from the a flame.
FIG. 3 shows the dependence on electric field frequency of
the probability of extinction, P, of a methane/air conical
diffusion flame as a function of the peak voltage of the
sinusoidal voltage signal applied to the electrode.
FIG. 4 shows the dependence of the critical electric field
frequency (in Hz) at which flame extinction ensues on the peak
voltage (in kV) applied to the electrode, as obtained from the
data shown in FIG. 2.
FIG. 5 illustrates dependence on electric field frequency
of the probability of extinction, P, of a methane/air conical
diffusion flame as a function of the distance between the tip of
the metal electrode and the mouth of the burner.
Fig. 6 shows the dependence of the critical frequency on
the distance between the tip of the Pt electrode and the mouth
of the burner as obtained from the data shown in Figure 4.
FIG. 7 illustrates a non- limiting example of a
configuration for concentrating a flame using an electric field.
FIGs. 8A-8D each illustrate a photograph of a
non-limiting configuration for concentrating a flame with an
electric field as well as a plot of temperature data resulting
FIG. 9 illustrates a non-limiting configuration in which a
time-varying electric field may be used to suppress a flame.
FIG. 10 illustrates a non-limiting example of a
configuration which may be used to increase flow of a fluid by
creating a plume.
FIGs. 11 A and 11B illustrate non-limiting examples of a
suitable configuration for the electrode 104 and sheath 116 of
FIG. 12 illustrates a non-limiting example of a
configuration which may be used to suppress or extinguish flames
using a combination of thermal quenching and electric fields.
FIG. 13 illustrates a non-limiting example of a
configuration in which a mobile electrode may be used to
manipulate a flame.
According to various aspects of the present application,
methods and apparatuses for manipulating flames are provided. The
manipulation may take various forms, including, but not limited
to, extinguishing a flame, suppressing a flame, bending a flame,
controlling mixing of the flame, and concentrating the flame. Such
manipulation may be useful in various applications in which
control of a flame is desired.
According to a first aspect of the present application, a flame
may be manipulated by applying an electric field to the flame. The
electric field may be a time-varying electric field, and in some
embodiments may be an oscillating electric field (e.g.,
oscillating between a positive electric potential and a negative
Moreover, in some embodiments the electric field may have a
gradient associated therewith, rather than being a uniform
electric field. In some embodiments, the electric field may
exhibit a gradient in three dimensions, though not all embodiments
are limited in this respect. Thus, according to a non-limiting
embodiment of the present aspect, a flame may be manipulated with
an oscillating gradient electric field. The electric field may be
applied to the flame with one or more electrodes, as non-limiting
The aspects described above, as well as additional aspects, are
described further below. These aspects may be used individually,
all together, or in any combination of two or more, as the
technology is not limited in this respect.
Manipulation of Flames Using Time- Varying Electric Fields
According to a first aspect, manipulation of flames is
accomplished using time- varying electric fields. In one
embodiment, the time-variation may be sinusoidal, and the electric
field may be an oscillating electric field. The electric field
may, in some embodiments, have a gradient, which may facilitate
achieving certain types of manipulation. Various non-limiting
examples are described further below.
Manipulation of flames using a time- arying electric field may
depend, at least partially, on some parameters of the flame as
well as some parameters of the electric field. For example, flame
parameters which may influence whether, and to what extent, the
flame may be manipulated by application thereto of a time-varying
electric field include the amount of soot in the flame and the
size of the flame source (e.g., the size of the burner used to
create the flame if a burner is used) Parameters of the electric
field that may impact the effectiveness of manipulation include
the field strength, field gradient, and field frequency (e.g., in
those embodiments in which an oscillating electric field is used).
The distance of the electric field source (e.g., an electrode)
from the flame as well as the electrode configuration may also
impact the effectiveness of manipulation.
Applicants have appreciated that flames are charge neutral
polarizable media. The effect of electric field stimulation on a
flame can be understood by considering the concentration of ions
that is present in most flames, which may range, for example, from
approximately 10<8> to approximately 10<11> ions per
cubic centimeter (ions/cm<3>). Despite their low
concentration, the driven motion of these ions in response to an
external electric field, and the consequent transfer of momentum
to neutral molecules, imparts upon the flame a collective
behavior. For sufficiently strong electric fields, this process
can result in macroscopic gas flows-so-called ionic or electric
wind-with speeds of up to ten meters per second. When placed in
the proximity of a flame, the resulting gas flows may serve to
manipulate the flame. However, not all embodiments described
herein relating to manipulation of flames with electric fields are
limited to manipulation arising from generation of an electric
wind, as other physical mechanisms may also or alternatively be
implicated. In fact, in at least some embodiments, manipulation of
a flame is achieved without an ionic wind.
According to one non-limiting embodiment, a flame may be
extinguished by application thereto of a time-varying gradient
electric field. The electric field may be applied by an electrode
placed in proximit to the flame. Various types of electrodes may
be used. According to one embodiment, a rod-shaped electrode may
be used (e.g., a wand-shaped electrode). According to one
embodiment, a point electrode, e.g., from a wire, may be used.
According to another embodiment, a wire electrode may be used.
Alternatively, plate shaped electrodes may be used in some
embodiments. The electrode may be covered/insulated in some
embodiments, for example to minimize or prevent formation of a
corona on the electrode. The electrode may have any suitable size,
shape, and material to provide a desired electric field. As will
be appreciated from the following non-limiting examples,
manipulation of flames (e.g., extinction) may be achieved 5
according to some non-limiting embodiments with one or more
electrodes (e.g., with one electrode, two electrodes, three
electrodes, or more). Extinction may occur when lift off is
achieved, which may represent the displacement of the combustion
zone of the flame from the burner
In some embodiments, the electrode (or electrodes) used to apply a
10 electric field may be stationary. In other embodiments, the
electrode(s) may be mobile.
Further explanation of a non-limiting example of the use of mobile
electrodes to apply a time-varying electric field to a flame is
provided in FIG. 13.
A non- limiting example of a configuration in which a flame may be
extinguished using an oscillating gradient electric field is
illustrated in FIG. 1. The illustrated system 100 includes a
chamber 102, an electrode 104, a counter electrode 106, an
electric signal source 108, a burner 110, and a flame 112.
Diffusers 114 are also included to introduce oxygen into the
chamber. A sheath 116 (e.g., made of borosilicate glass or any
other insulating material) encloses at least one end of electrode
104 proximate the flame. The electrode 104 may be spaced from the
flame by a distance [delta].
20 A non- limiting example of a suitable configuration for the
electrode 104 and sheath 116 is illustrated in FIGs. 11A and 11B,
which include various dimensions. It should be appreciated that
other configurations are also possible.
As shown, the flame 112 may be deflected from the vertical 118 by
an angle a in response to application thereto of an oscillating
gradient electric field from the electrode
25 104. The electric field may have any suitable frequency and
magnitude to deflect the flame by a desired angle a, as the
various aspects described herein are not limited to use of
electric fields having any particular magnitude and or frequency.
For purposes of explanation, some non-limiting examples arc
described further below.
It should be appreciated that the illustrated electrode
configuration is non-limiting.
30 While a wire-shaped electrode is illustrated, other shapes may
be used, including rod- shaped electrodes, and in some embodiments
plate shaped electrodes, though these are only non-limiting
examples. In the illustrated configuration, the resulting electric
field may exhibit a gradient in three dimensions, though not all
embodiments are limited in this respect. The configuration may
allow for achieving larger fields strengths and/or field gradients
than may be possible in configurations in which the electric field
gradient is limited to only two dimensions. Thus, a configuration
in which a gradient is exhibited in three dimensions may
facilitate achieving various types of manipulation of a flame,
such as extinction.
Also worth noting is that in some embodiments (e.g., the
configuration of FIG. 1), the flame may be positioned
substantially between the electrode and the counter electrode (e g
, the flame may be located on a line between the electrode and the
counter electrode) Such a configuration may facilitate achieving
the types of manipulation described herein.
A non- limiting example of the operation of system 100 is now
provided for purposes of illustration. It should be appreciated
that the manner of operation and the specific parameters listed
The methane burner 110 was enclosed in a 0.1 m<3> cubic
chamber 102 of 0.5 cm- thick panels of ROB AX(R), a refractory,
electrically insulating, and highly transparent glass ceramic. The
top panel was instead a glass-filled PTFE sheet (0.32 cm x 61 cm x
61 cm) with a hole 120 (15 cm diameter) in its center, which
served as a chimney for the combustion products. The burner
comprised a cylindrical tube of machinable A1203 (0.32 cm inner
diameter; 2 cm outer diameter; 25 cm in length) and was lodged
tightly into a hole in the center of the bottom panel of the
chamber. Methane was introduced from the bottom hole of the burner
through a one-way valve, and the flow was monitored by a gas flow
meter. The methane flow was kept at 5 0+-23 ml/min for all
experiments reported here.
Air was introduced into the system via two flexible bubble
diffusers (Flexible Bubble Wand, Marineland), which lined the
bottom inside perimeter of the chamber. The diffusers were covered
with a PTFE mesh (635um x 127um rhombic-shaped holes) to further
diffuse the inlet air flow and connected to a compressed air tank
through a flow meter. The air flow rate was maintained at 19+-2
1/min for all experiments.
The electrode 104 was a Pt wire (0.5 mm diameter) with a rounded
parabolic-like tip created via chemical etching, though the
aspects described herein as utilizing a rounded parabolic-like
electrode are not limited to the manner in which the electrode is
created. Furthermore, other electrode geometries are also
possible, as a rounded parabolic-like electrode tip is a
non-limiting example. The electrode was encased in custom-made
borosilicate glass sheath (2 mm thick on the sides of the wire, 5
mm thick at the tip). The purpose of the sheath was to (i)
electrically insulate the flame from the electrode (e.g., to
prevent arc formation between the electrode and the flame) and
(ii) to prevent the formation of the so-called ionic wind
emanating from the corona discharge at the electrode tip. The
electrode was connected to an AC power amplifier (TREK 30/20A),
driven by a signal generator (Agilent 33220A). The amplifier's
output current and voltage were monitored with an oscilloscope
(Tektronix TDS 2024D)
The electrode 104 was positioned horizontally at a height of 1.5
cm above the burner 110, and its tip was oriented towards the
center of the burner (cf. Fig. 1) The sheathed electrode was
supported by a stack of glass slides positioned 7 cm from the
burner and fastened with insulating tape.
The counter electrode 106 was a 45 cm x 45 cm x 1 cm aluminum
plate, fastened to the interior side of the chamber opposite the
electrode and the flame. The distance between the electrode tip
and the plate was [delta] = 25.5 cm.
Before an experiment, the interior of the chamber was cleaned of
soot. The flame and the air flow were turned on at least one hour
before the beginning of the experiment to allow the thermalization
of the setup. The temperature at the internal surface of the side
panels of the box was found to stabilize at 39+-2 [deg.]C.
The flame was subjected to AC fields using a sinusoidal waveform
of various amplitudes (15-30 kV) and frequencies (10-2000 Hz). The
distance between the tip of the electrode (i.e., the outer surface
of the glass sheath) and the mouth of the burner was varied from 6
to 15 mm.
For a constant voltage and a distance [delta] < 11 mm, as the
frequency of the oscillation of the voltage (and therefore the
electric field) was increased, the flame was increasingly
deflected. This deflection of the body of the flame is constant in
time and no obvious turbulence is observed. As the frequency is
further increased and the deflection approaches 90[deg.] the flame
is extinguished with increasing probability.
For a given voltage, V, frequency, f, and distance, [delta], the
angle of deflection a and the probability of extinction, P, were
measured. Movies (at 1 frame per second) were collected of all
events. The angle of deflection a of the flame for a certain set
of experimental parameters was determined by averaging all of the
stills (still images) from all events performed under those
conditions. The resulting image was then analyzed to determine the
major axis of "inertia" of the flame. The manner of analysis is
described in the Appendix of the present application, though it
should be appreciated that the various aspects of the technology
described herein are not limited to the manner in which deflection
is calculated, or to calculating deflection of the flame at all.
The probability of extinction, P, was estimated as the fraction of
successful extinction events (within a set of 10-30) following the
application of the field for 10 sec. If the flame was extinguished
by the field, it was reignited, and the flame was left burning
undisturbed for 30 seconds before attempting another extinction
event If the flame was not extinguished by the field within 10
seconds following the application of the field, the field was
turned off. The flame was then left undisturbed for 30 seconds
before starting another event. These 30 second pauses between
events prevented correlation between events.
Manipulation of flames using time- varying electric fields may
apply to various flame types (i.e., flames resulting from
combustion of various types of fuels), unless otherwise stated,
including liquid, gas, and solid flames, flames categorized as
National Fire Protection Association (NFPA) Class A (e.g., paper,
wood, plastic, etc.), Class B (liquid and gaseous fuel sources),
and or Class C, flames from gels, or any other types of flames.
Ethanol, methanol, toluene, and hexane are non-limiting examples
of liquid flame types to which one or more aspects of the present
application may apply. In some embodiments, diffusion flames may
be used. In some embodiments, flames having conductive
particulates may exhibit the greatest degree of response to an
applied electric field. The breadth in flame types to which the
presently described techniques may apply is due at least in part
to the fact that oscillating gradient electric fields operate on a
minority component of the flame which has a characteristic which
is shared across flames of the most diverse kinds: electric
charge, and not on parameters such as fuel and oxidizer
availability, heat, or the radical chain reaction. Thus, again,
ethanol, methanol, toluene, and hexane are only non-limiting
examples of fuel sources to which aspects of the present
application may be applied. Other types of flames are also
The electric field may have any suitable magnitude and frequency
to extinguish a given flame. In some embodiments, such as that of
FIG. 1, the electric field may be an alternating current (AC)
electric field having a sinusoidal waveform. The signal generating
the electric field may have any suitable voltage to generate a
suitable magnitude electric field. As a non-limiting example, the
voltage of the applied signal maybe between 15-30 kV, between
10-50 kV (e.g., 10 kV, 15 kV, 20 kV, etc.), between 20-25 kV, or
have any other suitable value. The frequency of oscillation of the
applied signal (the signal applied to the electrode 104), and
therefore of the electric field itself, maybe, for example,
between 10-2000Hz, between 100-50000 Hz, between 100-300 Hz,
between 300-600 Hz, between 400-500 Hz, between 100-1000 Hz (e.g.,
100 Hz, 200 Hz, 300 Hz, 400 Hz, 500 Hz, 600 Hz, etc.), or any
other suitable value, as these are non- limiting examples.
According to a non-limiting embodiment, an electric field having
the following parameters may be used to manipulate, and in some
instances extinguish, a flame: E = 1 MV/m, dE/dr = 10<8>
V/m<2>, and f = 1000 Hz). Other values are possible.
The electric field may have any suitable gradient. According to
some embodiments, the gradient may be a three-dimensional
gradient, while in others the gradient may exist in fewer than
three dimensions (e.g., two dimensions). The gradient may range,
in some non-limiting embodiments, between approximately dE/dr =
10<6> V/m<2> and dE/dr = 10<10> V/m<2>
(e.g., dE/dr = 10<7> V/m<2>, dE/dr = 10<8>
V/m<2>, dE/dr = 10<9> V/m<2>, etc.). Other
gradient values are also possible.
The distance from the electrode generating the electric field to
the source of the flame (e.g., to a burner when a burner is used)
may take any suitable value. According to some embodiments, the
closer the electric field source is to the flame the more easily
the flame may be extinguished. Accordmg to some embodiments, the
source electrode may be between approximately 5 mm and 30 mm from
the source of the flame (e.g., between 6 mm and 15 mm, between 10
mm and 25 mm, etc.), or any other suitable distance.
The impact of the electric field characteristics and the distance
from the electrode to the flame on the deflection and extinction
of flames is illustrated in some non-limiting example graphs, and
now explained. Generally, both the angle of deflection, a, and the
probability of extinction, P, increase with increasing frequency.
More specifically, the dependence of P on frequency exhibits a
threshold-like behavior, whereby the flame is reliably
extinguished primarily, and in some situations only, above a
certain "critical" frequency, which we define as the frequency at
which P = 50%.
FIGs. 2 and 3 illustrate data indicative of this generalization.
Figure 2 shows a graph of the values of P and a (in degrees) as a
function of frequency (in Hz) for V= 20 kV and [delta]= 6 mm.
Above the graph is a set of three pictures of the flame 210 taken
at the indicated frequencies (20 Hz, 310 Hz, and 400 Hz), showing
the increasing deflection in the flame 210 with increasing
frequency. The positions of the burner 212 and of the electrode
214 are also indicated.
The probability of extinction, P, increases with increasing
voltage of the applied signal, and therefore with increasing
electric field strength. FIG. 3 illustrates a graph showing a
non-limiting example of data supporting this statement. This plot
shows the dependence on frequency (in Hz) of the probability of
extinction, P, of a methane/air conical diffusion flame as a
function of the peak voltage of the sinusoidal voltage signal
applied to the electrode. No extinction was observed for V < 16
kV within the range of frequencies experimentally tested.
The critical frequency, decreases with increasing voltage (see
also FIG. 4, which shows the dependence of the critical frequency
(in Hz) at which flame extinction ensues on the peak voltage (in
kV) applied to the electrode, as obtained from the data shown in
FIG. 2), in a manner that can be fitted by a decaying exponential
(see FIG. 4):
(fc = ae<"bv>, where [3/4] is the critical frequency, V is
the voltage of the applied signal, a = 1.1 X 10<5> Hz and b
= 0.28 V<"1>) or with a power law (see FIG. 4) (fc =
cV<d> with c=3.2 X 10<9> Hz and d=5.4).
FIG. 5 illustrates dependence on frequency (in Hz) of the
probability of extinction, P, of a methane/air conical diffusion
flame as a function of the distance between the tip of the metal
electrode and the mouth of the burner. The data represent five
distances: 6 mm, 10 mm, 11 mm 12.5 mm and 15 mm. It can be seen
that P decreases with increasing distance. The extinction behavior
is similar for [delta] = 6, 10, and 11 mm, while there is no
extinction for [delta] > 12.5 mm. While at 11 mm of distance,
the response of the flame to the field is repulsive, at 12.5 mm
the response is a mixture of attractive and repulsive, with the
flame becoming shorter and wider, as if stretched horizontally by
the field. The critical frequency of suppression may be
independent of distance, as long as the distance is sufficiently
small to elicit the suppressive "response" (see Fig. 6, which
shows the dependence of the critical frequency (in Hz) on the
distance (in mm) between the tip of the Pt electrode and the mouth
of the burner as obtained from the data shown in Figure 4). Such
behavior may arise from a very sharp distance dependence (e.g., a
power law with large exponent) of the effective force operating on
Extinction of a flame by application of a time-varying electric
field thereto, when P = -50%, may progress in stages. The flame is
initially strongly deflected (-70-90 degrees). The flame loses all
traces of soot emission (possibly due to cooling, or more
plausibly due to the efficient removal of soot particles from the
hot zone). The flame front oscillates erratically at about 2-5 cm
from the burner, as if pushed by two opposing driving forces. On
one side the flame propagation which drives the flame front back
to the burner. On the other side, the effective force generated by
the electric field is pushing it away from the burner. This
behavior fades as P increases to 100% with increasing frequency.
In such conditions extinction happens within the first second of
the application of the field At frequencies much lower than the
critical frequency (P~0), the flame remains "attached" to the
burner and is only deflected.
Though the various aspects described herein are not limited to
utilizing any particular physical mechanism for extinguishing
flames, it is noted that in at least some embodiments the
extinction of the flame may be caused at least in part by forcing
the combustion region away from the fuel source using an
oscillating gradient electric field. The electric field may
accelerate the ions within the flame, resulting in a transfer of
momentum having a non-zero net average, and thus leading to
repulsion of the flame from the electrode applying the electric
field. When the speed of repulsion of the flame is less than the
speed of propagation of the flame to the burner, the flame may not
be extinguished but rather may be deflected. When the speed at
which the flame is projected away from the burner (the fuel
source) is greater than the speed at which the flame can propagate
to the burner (which happens to be approximately 1 m/s for a
CH^air diffusion flame), the flame may be blown off the fuel
source and thus extinguished.
The behavior of flames in response to the application of a
time-varying electric field may be due, at least in part, to the
Ponderomotive Force. The Ponderomotive force, Fp, may take the
where m and q are, respectively, the mass and charge of the
particle, E0 is the magnitude of the electric field given by
K(r,t) = E0(r) cos(ait), and [lambda] is a damping factor which
accounts for the viscous drag due to the surrounding fluid (e.g.,
The Ponderomotive Force may cause ions of either polarity
(positive or negative) to be repelled from the electrode applying
the oscillating gradient electric field. The particles may
oscillate and drift towards regions of low electric field density.
When the amplitude of the oscillations is small with respect to
length scales of the electric field gradients, the oscillation
center moves as if acted upon by a force, which is the so-called
Ponderomotive Force. The Ponderomotive force acts symmetrically on
both positive and negative charged species, may require
oscillating electric fields in at least some situations, and
generally increases with increasing field gradients. The
Ponderomotive Force may also act most effectively in at least some
embodiments on large particles, such as soot in a flame
It is also noted that the manipulation of flames using oscillating
gradient electric fields, as described herein, need not require
contact between the electrode(s) applying the electric field and
As should be appreciated from the foregoing, application of a
time-varying gradient electric field may bend (or deflect) a
flame, for example prior to extinguishing the flame. Thus,
according to one embodiment, a flame may be manipulated by bending
the flame via application of a time-varying (e.g., oscillating)
gradient electric field thereto. The field have any suitable
frequency, magnitude, gradient, and spacing from the flame to
generate a desired degree of bending. Similarly, a flame may be
squashed (e.g., minimized) or stretched if a time-varying electric
field is applied parallel to the direction of the flame.
According to another non-limiting embodiment, mixing of a flame
may be controlled at least in part by application thereto of a
time-varying gradient electric field. As explained previously,
application of a time- varying gradient electric field to a flame
may generate motion of ionic particles within the flame, which may
itself give rise to collective motion of the flame, for example as
a result of ionic particles of the flame transferring momentum to
neutral particles of the flame. The resultant motion may enhance,
or alternatively suppress depending on the conditions, mixing of
the flame. Thus, various applications in which control over flame
mixing is desired may be realized.
According to another non-limiting embodiment, concentration of a
flame may be achieved by application of a time- varying gradient
electric field thereto. FIG. 7 illustrates a non-limiting example
of a configuration which may be used. As shown, an electric field
source may be configured substantially parallel to the direction
of flow of the flame. For example, a burner 702 may have an
electrode 704 configured with respect thereto such that an
electric field 706 is generated in a direction substantially
parallel to the direction of propagation of the flame 708. A
time-varying applied signal 710 (e.g., an alternating current (AC)
signal) may be applied to the electrode to generate the electric
field. A grid 712 may be positioned a distance d from the top of
the burner. The distance d may be between approximately 5-15 cm
(e.g., 10 cm), or have any other suitable value, as these are
non-limiting examples. Application of the electric field may
result in concentration of the flame across a smaller area of the
grid 712 than would occur absent the electric field. Thus, in some
non-limiting embodiments, the width (from left to right in FIG 7)
of the flame 708 may be greater when no electric field is applied
than when the electric field 706 is applied (i.e., the electric
field 706 may "shrink" the width of the flame, thus concentrating
the flame). A non-limiting example of operation of the
configuration of FIG. 7 is now described, together with results
therefrom in FIGs. 8A-8D.
FIGs. 8A-8D illustrate the setup of an apparatus conforming to the
general configuration of FIG. 7, and which may be used to
concentrate a flame. The bottom photograph in each of FIGs. 8A-8D
illustrates the physical setup, showing a perspective view of the
metal grid. The dark spot in the center of the metal grid
represents the area of the grid contacted by the flame. As
described further below, it can be seen that the area changes
depending on the parameters of the applied electric field. The top
image in each of FIGs. 8A-8D represents a thermal image taken of
the metal grid for the corresponding physical setup.
The setup comprises a ceramic burner flowing ~ 1 L/min of methane.
The methane is lit. The flame is then arrested by the thick metal
grid placed flat above the flame. The grid functions as the
ground, while a ring electrode is applied to the burner.
FIG. 8A illustrates the scenario in which no electric field is
applied. The maximal temperature observed on the top of the grid
was 631[deg.] C.
FIG. 8B illustrates the scenario in which a voltage of 18 kV at
100 Hz is applied to the ring electrode surrounding the burner, as
mentioned previously in the manner illustrated by the
configuration of FIG. 7. Thus, an electric field is applied to the
flame. The maximal temperature increased by approximately 100
degrees to 731[deg.] C (which appeared to be the equilibrium)
compared to that of FIG. 8A within 40 seconds. In these conditions
there is the occurrence of slight sparking between the electrodes.
To verify if the sparks are responsible for this increase in
temperature, the conditions of FIG. 8C and 8D were tested. FIG. 8C
illustrates a scenario in which no 5 electric field is applied, as
in FIG. 8A. FIG. 8D illustrates the scenario in which a voltage of
9 kV at 100 Hz (a voltage at which no sparking occurred) is
applied to the ring electrode surrounding the burner. The
temperature still increased by 50 degrees compared to that of FIG
8C in approximately 40 seconds
Thus, it should be appreciated from FIGs. 8A-8D and the data
illustrated therein 10 that according to one or more embodiments a
flame may be concentrated over a smaller area when an electric
field is applied.
According to another non-limiting embodiment, a flame may be
stabilized by the 15 application of a time-varying electric field,
and in some instances a time- varying gradient electric field,
thereto. The flame may be stabilized in that its ability to remain
in existence when it otherwise would be extinguished may be
increased. A non-limiting example of a configuration resulting in
stabilization of a flame is that illustrated in FIG. 7.
Application of the electric field to the flame as illustrated may
allow the flame to exist at 20 higher fuel flow rates than would
be possible absent the electric field. The electric field may have
any suitable strength and frequency to accomplish this result.
According to another non-limiting embodiment, an electric field
may be used to suppress a flame. The electric field may, for
example, be configured to create a boundary between a fuel source
and a flame, such that the fuel source does not ignite. A non- 25
limiting example is illustrated in FIG. 9.
As shown, a flame 902 may be positioned near a fuel source (e.g.,
a burner) 904. The fuel 906 emitted by the fuel source 904 may
initially propagate toward the flame 902. However, application of
a time-varying gradient electric field, in the manner described
previously herein, from an electrode 908 (as a result of
application of an applied signal 30 910) may prevent the flame
from igniting the fuel source, thus suppressing the flame.
The electric field may create an outflow from the flame (in the
direction of the arrows) which may divert the fuel from the flame.
This, however, is a non-limiting example. According to another
non-limiting embodiment, a time-varying electric field may be used
to increase the flow and nebulization of a fluid. A non-limiting
configuration is illustrated in FIG. 10. As shown, container 1002
may include a fuel 1004 and a plume 1006. Application of a
time-varying gradient electric field thereto in the manner
previously described herein, using an electrode 1008 may increase
According to another non-limiting embodiment, a Davy Lamp
configuration is used to manipulate a flame. In some such
embodiments, a flame arrester grid may be used as one electrode A
combination of thermal quenching and electric fields may be used
to extinguish the flame. FIG. 12 illustrates a non-limiting
As shown in FIG. 12, the apparatus 1200 may include a first
electrode 1202 and a second electrode 1204. A power supply 1206
may apply a voltage difference between the electrodes 1202 and
The electrode 1202 may be a metal mesh structure having a mesh
size sufficient to allow a fuel source to pass through. In some
non-limiting embodiments, the electrode 1202 may be considered a
flame arrestor grid, as will be further appreciated from the
discussion below. The mesh size should be such that liquid can
rapidly pass through, but not so large that the flame is not
quenched (as described below). Non-limiting examples for suitable
mesh sizes are between 1 mm and 1cm.
The electrode 1204 may be any suitable electrode formed of any
suitable material. The power supply 1206 may apply a direct
current (DC) or AC signal to the electrodes 1202 and 1204.
Non-limiting examples of suitable voltages for AC signals include
greater than 5 kV at a frequency greater than 1 Hz (e.g., between
1 Hz and 1 kHz, or even greater). Non-limiting examples of
suitable DC signals include -5 kV, between 5 kV and 50 kV, 50 kV,
greater than 50 kV, or any other suitable voltages.
If fuel on the electrode 1202 catches fire 1208, a suitable
electric potential may be applied to the electrode 1202 by the
power supply 1206. The fire may be extinguished, for instance
because contact with the electrode 1202 may thermally quench the
fire 1208 resulting in extinguished fuel 1210 passing through the
mesh of electrode 1202 to the electrode 1204. The thermal
quenching may separate the flame from the liquid fuel and allow
the liquid fuel to pass through the mesh. The electric field from
the electrode 1202 may also facilitate extinguishing the flame, in
addition to the thermal quenching. For instance, the flame may be
extinguished in approximately 1/3 the time as would occur without
the field (e.g., in approximately 4 seconds compared to 12 seconds
which may be required without the electric field). Applying the
electric field may also stabilize the flame.
The electrodes 1202 and 1204 may take any suitable configuration
with respect to each other. For example, they may be separated by
between 1 mm and 1 meter, greater than 1 m, or any other suitable
distance. The electrode 1204 may be below the electrode 1202 or
above it, as the relative orientation is not limiting.
The configuration of FIG. 12 may be used in various products. For
example, a floor or flooring system may be constructed in the
configuration illustrated Other applications are also possible.
In some embodiments, an electrode may be moved relative to a
flame, for example by swiping the electrode across a flame. A
non-limiting example of a suitable configuration is illustrated in
FIG. 13. As shown, the apparatus 1300 includes a fuel source 1302
(e.g., gal, liquid, solid, etc.) which may create multiple flames
1304. Ten flames 1304 are shown, but the number is non-limiting,
and may even include only a single flame in some embodiments. An
electrode, such as the sheathed wire electrode of FIGs. 11A and 1
IB may be oriented as indicated at 1306 (i.e., with the electrode
oriented into and out of the page) and may be moved in the
direction indicated by arrow 1308 across the flames. The electrode
may be connected to a current source (AC or DC) of any suitable
potential (e.g., greater than 5kV in some non-limiting
embodiments). Moving the electrode in the direction shown may
deflect the flames and may extinguish the flames in some
embodiments (e.g., with an oscillating signal of approximately 1
kHz and electric potential greater than 30 kV, as non-limiting
examples). The closer the electrode is to the origin of the
flames, the greater the likelihood of extinguishing the flames.
For example, positioning the electrode within approximately 1 cm
of the flame origin may increase the likelihood of extinguishing
From the foregoing, it should be appreciated that various types of
manipulation of flames using electric fields may be achieved. In
some non-limiting embodiments, the electric fields may be
oscillating electric fields having a gradient in three dimensions
(referred to herein as "three-dimensional gradient fields"). In
some embodiments, the electric fields are generated using fewer
than three electrodes. The electrode(s) may be insulated to
prevent generation of an ionic wind. Thus, the manipulation
described according to various embodiments may be achieved without
the need for an ionic wind. Various techniques for manipulating
flames have been described. As mentioned previously, it should be
appreciated that the various aspects described herein may be used
individually or in any combination of two or more, unless
As mentioned previously, one or more aspects of the present
application may relate to manipulation of flames, and the
manipulation may take one or more of various forms. Non-limiting
examples of manipulation may include extinguishing a flame,
suppressing a flame, bending a flame, controlling the mixing
within the flame, and concentrating the flame However, other forms
of manipulation may also be possible, and the various aspects
described herein are not limited to any particular form of
manipulation unless otherwise stated.
Also, as mentioned previously, the aspects described herein may
apply to various flame types (i.e., flames resulting from
combustion of various types of fuels), unless otherwise stated.
For example, ethanol, methanol, toluene, and hexane are
non-limiting examples of fuel sources to which aspects of the
present application may be applied. Other types of flames are also
Moreover, various benefits may be realized by the application of
one or more of the aspects described (though it should be
appreciated that not all aspects necessarily provide each
benefit). For example, one or more aspects may be used to put out
a fire without the need for adding a suppressant (e.g., a chemical
suppressant), which may reduce damage to items (e.g., personal and
real property) as well as avoiding the need for toxic chemicals.
In some embodiments, a fire may be put out from a distance.
Moreover, manipulation of flames of different compositions may be
achieved with the same technique of manipulation. Other aspects
may provide improved combustion, e.g., more efficient combustion
with the production of fewer combustion byproducts. Various other
benefits, alternatively or in addition, may be realized by one or
more aspects, as those listed are non-limiting examples.
One or more aspects and embodiments of the present application
involving the performance of methods may utilize program
instructions executable by a device (e.g., a computer, a
processor, or other device) to perform, or control performance of,
the methods. In this respect, various inventive concepts may be
embodied as a computer readable storage medium (or multiple
computer readable storage media) (e.g., a computer memory, one or
more floppy discs, compact discs, optical discs, magnetic tapes,
flash memories, circuit configurations in Field Programmable Gate
Arrays or other semiconductor devices, or other tangible computer
storage medium) encoded with one or more programs that, when
executed on one or more computers or other processors, perform
methods that implement one or more of the various embodiments
discussed above. The computer readable medium or media can be
transportable, such that the program or programs stored thereon
can be loaded onto one or more different computers or other
processors to implement various ones of the aspects discussed
above. In some embodiments, computer readable media may be
Having thus described several aspects and embodiments of the
technology, it is to be appreciated that various alterations,
modifications, and improvements will readily occur to those
skilled in the art. Such alterations, modifications, and
improvements are intended to be within the spirit and scope of the
Accordingly, the foregoing description and drawings provide
non-limiting examples only.
Also, the phraseology and terminology used herein is for the
purpose of description and should not be regarded as limiting. The
use of "including," "comprising," or "having," "containing,"
"involving," and variations thereof herein, is meant to encompass
the items listed thereafter and equivalents thereof as well as
Quantifying Flame Deflection
In order to measure the angle of deflection, the flame is filmed
during the application of the electric field using a digital
camera at a frame rate of 1 fps. The frames are then superimposed
on one another to create a composite, grayscale image as shown
The angle of deflection is then measured by calculating the
principle axes of "inertia" of the flame's image. First, the
center of "mass" is calculated as
where My is the intensity of pixel (ij). The inertial tensor is
then calculated as
The eigenvectors of the inertial tensor represent the "principle
axes" of the flame; the one of interest, v, points along the long
axis of the flame. The angle of deflection is then calculated as
[Theta] = tan<">'(¦ vx Iv ¦).
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