Note: Descriptions are shown in the official language in which they were submitted.
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DESPRIPTION
GAS COMBUSTION DEVICE
Technical Field
The present invention relates to a gas combustion device for generating
completely burnt hot air or warm air with high combustion efficiency using
burning
flame caused by, in particular, Liquefied Petroleum Gas (LPG) as a heat
source.
Background Art
Conventionally, a gas combustion device contained in devices such as
portable hair driers and heat guns has been known.
Referring to Figs. 1 to 3, in a gas combustion device 101 contained in a hair
drier, a combustor 103 for burning gas is provided in a cylindrical casing 105
of the
hair drier. The combustor 103 burns combustion gas supplied from a gas tank
(not
shown) in which fuel is stored. The air heated by the combustor 103 is emitted
to the
side of a vent by a fan (not shown) provided at the side of an inlet of the
casing 105.
In Fig. 1, the gas tank not shown is connected to the combustor 103 through a
gas passage 107. Due to flow speed of the combustion gas supplied to the
combustor
103, the pressure in the gas passage 107 becomes negative relative to the
outside
pressure. An ejector 111 with a suction port 109 for sucking outside air from
the
outside of the gas passage 107 by utilizing a difference between the outside
pressure
and the pressure in the gas passage 107 is provided at and end of the gas
passage 107.
In detail, as shown in Fig. 2, supplied LPG, for example, is injected from a
nozzle 113 in the ejector 111 at high speed. Since the pressure in the gas
passage 107
and the ejector 111 becomes negative due to the ejector effect generated by
injection
speed of the injected gas, outside air for mixing gas flows into from the
suction port
109. As a result, mixed gas of the injected gas and air is generated.
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The mixed gas is injected from a wick (wire mesh) 115 provided in the
combustor 103 at the side of the inlet. A spark generated from an ignition
plug
(ignitor) 117 (refer to Fig. 3) by high voltage is blown to the wick 115 which
injects
the mixed gas, thereby igniting the mixed gas.
The combustor 103 is disposed between the fan and the vent of the casing 105.
As shown in Fig. 3, the shape of a cross section perpendicular to the
longitudinal
direction of the combustor 103 is a non-circular cylindrical body in which the
wick
115 is located at the center of the gas combustion device 101 and which has
eight
radial groove-like combustion chambers 119 in the shape of eight-divided star-
like
proj ections around the wick 115 (a first conventional example: Japanese
Patent
Application Laid-open Publication No. 2002-233416).
Since the ejector 111 is provided in the above-mentioned conventional gas
combustion device 101 to supply the combustion gas to the combustor 103,
outside air
is automatically sucked from the suction port 109 due to the ejector effect
generated by
injection speed of the gas injected from the nozzle 113 in the ejector 111 at
high speed.
Thus, since the mixed gas of the gas and air is generated and inj ected from
the surface
of the wick 115, whereby complete combustion is promoted.
However, the ignition performance of the mixed gas and the combustion
performance of the combustion gas after ignition are conflicting one another.
That is,
to improve the ignition performance of the gas, the ratio of the gas to air in
the mixed
gas needs to be increased, and however, when the mixed gas with high gas ratio
is
burnt, a large amount of incomplete combustion gas generates and the
combustion
performance is lowered. As a result, CO concentration is increased.
Conversely, to improve the combustion efficiency, when the amount of air is
increased, thereby decreasing the ratio of gas in the mixed gas, the
combustion
performance is improved and however, it becomes difficult to set a fire,
resulting in
failure to burn.
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Thus, to keep a certain level of ignitability, even when the size of the
suction
port 109 of the ejector 111 is made small to suppress the amount of sucked
air, the
ratio of air in the mixed gas is lowered compared to the mixed gas with good
combustion efficiency for the above-mentioned reason and therefore, the
problem
occurs that air slightly lacks and CO concentration becomes high.
A conventional example 2: Japanese Patent Application Laid-open Publication
No. 2002-249347 discloses that a combustor comprised of a primary combustion
chamber for burning mixed gas injected from a wick and a secondary combustion
chamber for supplying a secondary air from outside air to the gas burnt in the
primary
combustion chamber and firing the combustion gas is provided and that complete
combustion of the combustion gas is promoted in the secondary combustion
chamber.
However, also in the second conventional example, CO concentration is still
high and there is a room for improvement. To solve the above-mentioned
problem,
the present invention intends to provide a gas combustion device capable of
improving
ignitability and combustion performance of gas and decreasing CO
concentration.
Disclosure of the Invention
To achieve the above-mentioned object, a gas combustion device according to
the present invention comprises a combustor for burning combustion gas
supplied
from a gas source, a gas passage for sending the gas supplied from the gas
source to
the combustor, an ejector with a primary air hole for sucking a primary air
due to
negative pressure generated by flow speed of the combustion gas supplied to
the
combustor in the gas passage, an ignitor for igniting mixed gas injected from
a wick
provided ahead of the ejector, a primary combustion chamber provided in the
combustor for igniting and burning the mixed gas injected from the wick
therein, a
secondary air hole provided in the combustor for supplying a secondary air to
the gas
burnt after ignition in the primary combustion chamber, a secondary combustion
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chamber for mixing the gas burnt in the primary combustion chamber with the
secondary air sucked from the secondary air hole and further burning the mixed
gas
therein, and a tertiary air hole for supplying a tertiary air to the gas burnt
in the
secondary combustion chamber.
Brief Description of the Drawings
Fig. 1 is a side view of a conventional gas combustion device.
Fig. 2 is a partial sectional view of an ejector in Fig. 1.
Fig. 3 is a front view of the gas combustion device viewed from the left side
in Fig. 1.
Fig. 4 is a sectional view of a gas combustion device in accordance with an
embodiment of the present invention taken along a line IV IV in Fig. 6.
Fig. 5 is a side view of the gas combustion device in accordance with the
embodiment of the present invention.
Fig. 6 is a front view of the gas combustion device viewed from the left side
in Fig. 5.
Fig. 7 is a back view of the gas combustion device viewed from the right side
in Fig. 5.
Best Mode for Carrying Out the Invention
An embodiment of the present invention will be described below with
reference to figures.
With reference to Fig. 4, a gas combustion device 1 in accordance with this
embodiment has an ej ector 3 for generating mixed gas of LPC~ for example, as
combustion gas and air, an electrode 5 as an ignitor for igniting the mixed
gas
generated by the ejector 3 and a combustor 7 for burning the mixed gas ignited
by the
electrode 5 therein.
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A chamber 9 of the combustor 7 made of aluminum (die-cast) is a
substantially cylindrical body with circular right and left side faces in the
longitudinal
direction of the chamber 7 as shown in Figs. 6 and 7. The inside of the
chamber 9 is
comprised of a primary combustion chamber 11 located on the right side in Fig.
4 and
5 a secondary combustion chamber 13 located ahead of the primary combustion
chamber
11 (left side in Fig. 4). The ejector 3 is attached to the gas induction side
in the rear
of the primary combustion chamber 11 (right side in Fig. 4).
The ejector 3 is provided with a nozzle 19 for injecting gas supplied from a
gas source such as a gas tank (not shown) for storing combustion gas such as
LPG
through a gas supply pipe 17 as a gas passage at the side of an inlet of a
substantially
cylindrical ejector body having a circular cross section.
A pin hole as an injection hole (not shown) having a bore diameter of ~ 60 ~,m
to ~ 200 hum, for example, is provided at a front end of the nozzle 19. The
injection
hole is an orifice formed substantially in the center of a disc-like pin-hole
disc (not
shown) and LPG is thinly discharged at high speed close to sonic speed. A
filter (not
shown) for removing impurities and dusts which block the injection hole is
provided in
the nozzle 19. For example, a sintered metal with a pinhole having a diameter
of 10
to 30 ~,rn is used as the filter.
A mixer for mixing LPG with a primary air and introducing the mixed gas
into the combustor 7 is provided in the ejector body 15 ahead of the nozzle 19
and a
primary air hole 23 for sucking the primary air from the outside penetrates a
side wall
of the mixer 21. Accordingly, the pressure within the mixer 21 becomes
negative due
to the combustion gas discharged from the nozzle 19 at high speed, and the
primary air
is sucked and sent to a forward wick 25 as a gas combustion part while being
mixed
with the combustion gas. This is called as an ejector effect. By adjusting
area of
the primary air hole 23, the ratio of the primary air can be adjusted.
The wick 25 as a gas combustion part is a cylindrical SUS metal mesh of 50
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to 150 mesh, for example, and is attached to the end ahead of the ejector body
15 by
welding or the like substantially in the center of the right half of the
primary
combustion chamber 11 of the combustor 7 in Fig. 4. A wick holder 27 as a
direct-advance suppression part is attached to the end ahead of the wick 25 by
welding
or the like. Since direct advance of the mixed gas discharged from the mixer
21 is
suppressed by the wick holder 27, lateral discharge (in the direction shown by
an
arrow AR1 in Fig. 4) of the mixed gas is facilitated and the mixed gas of LPG
and air
is discharged from meshes of the wick 25. The flame after ignition is blue and
substantially circular.
The electrode 5 is provided within the combustor 7 and ahead of the wick 25
and in the vicinity of the side face of the wick 25. High-tension electricity
generated
in a piezoelectric element for ignition (not shown) is input to the electrode
5 through
an electric wire 29 and.a spark is blown from the front end of the electrode 5
to the
wick 25. The spark ignites the mixed gas discharged from the wick 25, thereby
burning the gas.
Referring to Fig. 6, on an inner wall of the primary combustion chamber 11, a
plurality of groove parts 31 extending in the forward-rearward direction are
radially
arranged around the wick 25. In Fig. 6, six groove parts 31 are formed.
A plurality of secondary air holes 33 for supplying a secondary air from
outside air to the primary combustion chamber 11 are provided on a rear wall
(right
side wall in Fig. 4) of the primary combustion chamber 11. The plurality of
secondary air holes 33 is disposed so that the secondary air is supplied at
the position
slightly separated from the periphery of the wick 25. In other words, the
holes are
disposed so that the secondary air is supplied to the gas after ignition at
the position
where the air does not influence on the mixed gas just discharged from the
wick 25,
that is, the position other than an ignition point. The ignition point means
the area
where a spark generated by the electrode 5 can blow at the side of the
electrode 5 in
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the periphery of the wick 25 as shown by an area surrounded by a dotted line
in Fig. 6.
In this embodiment, five secondary air holes 33 in total are provided so that
the
secondary air is supplied from the rear of the groove parts 31 except for the
groove
part 31 to which the electrode 5 is attached.
A plurality of tertiary air ducts 35 as tertiary air holes for supplying a
tertiary
air from outside air to the secondary combustion chamber 13 are provided in
the wall
of the primary combustion chamber 11 between adjacent groove parts 31. In this
embodiment, six tertiary air ducts 35 in total are provided.
By adjusting area of the primary air hole 23 of the ejector 3, the ratio of
the
primary air can be adjusted. To improve ignitability of the mixed gas injected
from
the wick 25, in this embodiment, the area of the primary air hole 23 is
configured so as
to be an almost half of the area of the conventional primary air hole. For
example,
providing that the diameter of the conventional primary air hole is D, the
diameter of
the primary air hole 23 in this embodiment is 0.73D.
The diameter of five secondary air holes 33 is 0.4D and the diameter of six
tertiary air ducts (tertiary air holes) 35 is D.
A plurality of fins 37 for heat exchange are provided in the outer periphery
of
the chamber 9. The fins 37 has the effect of emitting heat generated when the
mixed
gas is burnt in the chamber 9 and cooling the chamber 9, that is, performing
heat
exchange.
With the above-mentioned configuration, when LPG is supplied into the
nozzle 19 of the ejector 3 through the gas supply pipe 17, LPG passes through
the
filter in the nozzle 19 and injected from the injection hole as the orifice to
the mixer 21
at the speed close to sonic speed. As a result, the pressure within the mixer
21
becomes negative due to the ejector effect and the primary air necessary for
combustion (corresponding to the air-fuel ratio) is sucked from the primary
air hole 23
and flows into the mixer 21. And then, the flowed primary air and LPG are
mixed to
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form the mixed gas and the mixed gas is inj ected into the forward wick 25.
In the mixer 21, in proportion to increase or. decrease in LPC~ the primary
air
necessary for combustion is automatically sucked. Furthermore, by making the
diameter of the primary air hole 23 small to decrease the amount of the
primary air, the
mixed gas with good ignitability is injected to the forward wick 25.
Since the wick holder 27 is provided at the forward end face in the wick 25,
the combustion gas (mixed gas) is mainly injected from the SUS metal mesh on
the
side face to the periphery.
Next, by supplying high voltage through the electric wire 29, a spark is
generated from the electrode 5 in the combustor 7 and surely ignites the mixed
gas
with the suitable gas ratio emitted from the wick 25. Most of burning flame of
the
ignited gas spreads outwards in a circle pattern from the side face of the
wick 25 and
the length of the burning flame remains to be ten-odd mm from the wick 25.
Warm
air is transmitted along the inside of the primary combustion chamber 11 and
eight
groove parts 31 on the inner wall to the forward secondary combustion chamber
13.
At this time, although the mixed gas emitted from the wick 25 has good
ignitability because of high gas ratio, CO concentration is increased, thereby
lowering
combustion performance. However, since the secondary air hole 33 is provided
at the
region other than the ignition point, the amount of air in the region other
than the
ignition point in the primary combustion chamber 11 and CO concentration is
lowered.
That is, since the secondary air is supplied to the combustion gas in the
primary
combustion chamber 11 after ignition, combustion efficiency of the gas in the
primary
combustion chamber 11 is improved, thereby improving combustion performance.
Therefore, in the primary combustion chamber 11, the mixed gas discharged from
the
wick 25 is surely ignited, combustibility of the combustion gas after ignition
is
promoted and CO concentration is decreased.
Furthermore, since the tertiary air from outside air passes through the six
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tertiary air ducts (tertiary air holes) 35, the temperature at the wall part
of the primary
combustion chamber 11 is effectively decreased and the hot tertiary air that
has passed
through the tertiary air ducts 35 is introduced into the secondary combustion
chamber
13. For this reason, combustion reaction of the gas in the secondary
combustion
chamber 13 is further promoted, thereby improving combustion performance. In
other words, since the gas burnt in the primary combustion chamber 11 and the
hot
tertiary air are mixed, combustion reaction easily occurs and complete
combustion is
promoted. With such configuration, combustion performance is improved. As
described above, the tertiary air has the effects of decreasing the
temperature in the
primary combustion chamber 11 and improving combustion performance in the
secondary combustion chamber 13. It is preferred that the number of the
tertiary air
ducts 35 is eight to satisfy both of combustion performance and heat exchange.
As apparent from the above-mentioned matters, since most unburnt gas is
burnt in the secondary combustion chamber 13 in the gas combustion device 1 in
accordance with the embodiment of the present invention, flame is hard to go
out of
the chamber 9.
To validate performance of the present invention, when CO concentration in
the gas combustion device of the second conventional example and the gas
combustion
device 1 of this embodiment was measured under the same condition, in the case
of a
first condition, CO concentration was 94 ppm in the second conventional
example and
41 ppm in this embodiment. In the case of a second condition, CO concentration
was
119 ppm in the second conventional example and 49 ppm in this embodiment.
Therefore, it was confirmed that CO concentration was decreased by
supplying'~the tertiary air to the secondary combustion chamber 13 and the
secondary
air to the primary combustion chamber 11 in this embodiment. In the combustor
of
the second embodiment, although the tertiary air is supplied to the secondary
combustion chamber 13 of the combustor 7 as in this embodiment, the secondary
air is
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not supplied to the primary combustion chamber 11.
The present invention is not limited to the above-mentioned embodiments and
can be carried out according to the other aspects. The gas combustion device 1
in
accordance with this embodiment can be used as the gas combustion device such
as a
5 hair drier and a heat gun used for compression operation of a heat-
shrinkable tube,
drying, adhesion, fusing and soldering and the other gas combustion devices
such as
the other appliances.
Industrial Applicability
10 According to the present invention, even when ignitability of the mixed gas
emitted from the wick is improved by decreasing the amount of the primary air,
combustion efficiency of the combustion gas in the primary combustion chamber
can
be improved, thereby improving combustion performance. Furthermore, since the
tertiary air is introduced into the secondary combustion chamber from the
tertiary air
holes, combustion performance is further improved, thereby improving
combustion
performance. Therefore, complete combustion is facilitated and CO
concentration
can be decreased.
Further, since the amount of the primary air can be decreased to increase the
gas ratio by making the diameter of the primary air hole small, ignitability
of the
mixed gas discharged from the wick can be improved.
Furthermore, since the secondary air holes are provided at the positions other
than the ignition point in the primary combustion chamber, the amount of air
in the
region other than the ignition point is increased without impairing
ignitability of the
ignition point in the primary combustion chamber, thereby improving
combustibility
of the gas as well as decreasing CO concentration.
