AU647892B2

AU647892B2 - Combustion device

Info

Publication number: AU647892B2
Application number: AU12390/92A
Authority: AU
Inventors: Kazutada Momoda
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1991-02-07
Filing date: 1992-02-05
Publication date: 1994-03-31
Anticipated expiration: 2012-02-05
Also published as: WO1992014095A1; JP2811971B2; JPH04257607A; AU1239092A; KR930700805A; KR960012387B1

Description

OPI DATE n7/n9/92 PC. AOJP DATE 15/10/92 APPLN. ID 12390 92 PCT NUMBER PCT/JP9?/001n.Il (51) m 9 l 5 (11) M i WO 92/14095 F23D 11/10, 11/40 Al (43) $IF 1I B 1992f8 fl 20 0(20. 08. 1992) (21) [EB.tS-; PCT/JP92/00114 (22) IWlgtE 199242 5 8(05. 02. 92) AMBF 7 #ZI 3/16304 1991-S.7~ 70(07. 02. 91) JP (71) WRsA (MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.)

[JP/JP)

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(54)Title: COMBUSTION DEVICE 1 (54) R )Vt, (57) Abstract This invention relates to a combustion device used for the oil fan-heater or the like and intends to improve vaporization and combustion performances while lowering the NOx concentration and widening a variable range for combustion. This combustion device is in such a structure that a burner head is fixed to a vaporizing cylinder to vaporize liquid fuel, said burner head is provided with minute burner holes at the upper part and slightly larger burner holes (6a 6b 6c) at the lower part thereof, and a perforated sheet such as a wire net is tightly fixed to the outer periphery of said burner head Thus, flames formed at said burner head are small to reduce NOx concentration, the temperature of the upper part such as the wire net (7) can be kept at a low level even when combustion is on low, and flame stability is good because of the large lower flame holes, whereby a temperature of the vaporizing cylinder susceptible to the influence of said flames can be maintained at a high level and favorable vaporization and combustion performances are ensured.

Y i- j r i (57) L D R Af*t 44 X f L t-Lk TL(4J 6 6D A L (6 a 6 b 6 f -kN 0 x f Lh b M 6 ;5 L L Alf- -C 6 5K~ (1L-C oK9A-t 6 L- T AT 71 ES 4 G-e3'7 A t-A1,9 )Fl 7 9>I M L 1 B B A--P FR MN BE MR T BP t .7 GN A M BG GB 4 A! 1 NL BR .i 1 PL X- CA 75t IE RO f -vT CF 41! 71)h R IT 4 RU -1J CG :i JP Ei SD Y.

CH 4 A KPI* I11 SE 7 Cl KR :k 0rL W SN -L, cm bLI SU v ~r4.L Anl CS 1-~~~rLK 7,9 TD DE I4-1v LU 4 /L T DK -MC =us w COMBUSTION APPARATUS i The present invention relates to a combustion apparatus and in particular to a premixed type combustion apparatus for use in an oil fan heater or the like.

As shown in Figure 6, a prior art combustion apparatus of this kind comprises a cylindrical burner head 23 having a ceiling provided on an upper opening of an Sevaporation cylinder 22 embedding a sheath heater 21 therein. Mixed gas consisting of combustion air and fuel supplied to the evaporation cylinder 22 and evaporated therein is introduced into the burner head 23 and jetted from a plurality of flame holes formed on the entire peripheral wall of the burner head 23, thus forming flame 26 through a metal net 25. Reference numeral 27 of Figure 6 denotes a nozzle for supplying the fuel into the evaporation cylinder 22; 28 represents an air duct for supplying the combustion air to the evaporation cylinder 22; 29 indicates a throat 940131,pAoper\kay,12390.a,I -2connecting the air duct 28 and the evaporation cylinder 22 with each other; denotes a cover, of the evaporation cylinder 22, having an opening 30a for introducing the mixed gas; 31 denotes a resistance plate having a plurality of openings; 32 denotes a cylinder having an opening 32a; 33 denotes an ignition electrode; and 34 denotes a flame rod serving as a flame detecting sensor.

In the prior art combustion apparatus, each flame hole 24 is in an eiliptic configuration of 3mm x 10mm and the area thereof is large. This is because the conventional combustion apparatus is designed according to the maximum combustion amount without paying much attention to the turn down ratio of combustion. As a result, much nitrogen oxide (NOx) is discharged from the conventional combustion apparatus, and the turn down ratio of combustion is as small as 3200 to 1100llOOkcal/h.

That. is, when the volume of the flame 26 formed in the flame hole 24 exceeds a certain volume, the temperature of the flame 26 becomes high in proportion to the volume thereof. Accordingly, the discharge amount of NOx is great in dependence on the atmospheric temperature of the flame 26.

If the minimum combustion amount is reduced to enlarge the turn down ratio of combustion between the maximum combustion amount and the minimum combustion amount, the flame 26 is disposed in the vicinity of the flame hole 24 and the temperature of the metal net 25 positioned in an upper portion of the flame 26 becomes very high. As a result, the metal net 25 is heated at a high temperature and there is a possibility that backfire occurs. Therefore, the turn down ratio of combustion cannot be enlarged.

The load of the flame hole can be increased by making the area of each flame hole small, but the flame 26 is liable to lift due to even a slight disproportion of airfuel ratio during a minimum combustion period of time. As a result, the flameholding performance of the flame 26 becomes weak, which causes the temperature of the evaporation cylinder 22 to become low and gives an unfavourable influence on the evaporation performance of fuel.

According to a first aspect of the present invention there is provided a combustion apparatus comprising: an evaporation cylinder for evaporating liquid fuel and mixing the evaporated 940131,p:\oper\kay,12390.cla,2 L 1 rclc9e -1 -3gas and combustion air with each other so as to form mixed gas; and a burner head having a plurality of flame through-holes formed therein through which the mixed gas is jetted, said flame through-holes being formed in a peripheral wall of said burner head and wherein each flame through-hole comprises an outer hole section and an inner hole section, said outer hole section having a sectional area greater than that of the inner hole section, and the sectional area of the inner hole section of a through-hole positioned at an upper portion of the peripheral wall of said burner head being smaller than the inner hole section of a through hole formed at a lower portion of the peripheral wall, and the sectional area of the outer hole section of a through-hole positioned at the lower portion of the peripheral wall of said burner head being larger than that of the outer hole section o of a through-hole positioned at the upper portion of the peripheral wall of said bo n 00 'burner head; 0°o and a porous plate in close contact with the peripheral wall of said burner head.

According to a second aspect of the present invention there is provided a oo combustion, apparatus comprising: an evaporation cylinder for evaporating liquid fuel and mixing the evaporated .00. o gas and combustion air with each other so as to form mixed gas; and 20 a burner head having a plurality of flame through-holes formed therein :0ooo through which the mixed gas is jetted, said burner head comprising an inner burner head and an outer burner head, a first flame through-hole formed at an upper portion of a peripheral wall of said inner burner head, and a second flame throughhole formed at a lower portion of the peripheral wall of said inner burner head having a larger sectional area than the first flame through-hole, furtier flame through-holes being formed on said outer burner head in opposition to each of said first and second flame through-holes of said inner burner head; and a porous plate in close contact with the peripheral wall of said outer burner head.

In accordance with the teachings of the first aspect of the invention the sectional area of the flame through-holes of the burner head is restricted, the volume of flame formed in the flame hole of the burner head is therefore small.

940131,p:\opcr\kay, 12390cla,3 i -4- Consequently, the amount of NOx generated is small. The sectional area of the flame hole positioned on the peripheral wall of the burner head is greater than that of the flame hole positioned on the inner peripheral wall of the burner head.

Accordingly, the flow velocity of the flame formed in the flame hole positioned on the inner peripheral wall of the burner head is reduced in the larger flame hole positioned on the peripheral wall of the burner head. As a result, the flame is disposed in the periphery of the larger flame hole positioned on the peripheral wall of the burner head. Consequently, a strong flame-holding performance is formed and the flow velocity of the flame in the centre region of each flame hole is higher than that of the flame in the periphery thereof. Therefore, the temperature of the metal net does not rise greatly and no backfire occurs even though the turn down ratio of combustion is enlarged.

Since the lower flame hole of the burner head is larger than the upper flame hole, the flow velocity of the flame formed in the lower flame hole is lower than that of the flame formed in the upper flame hole and the volume of the flame formed in the lower flame hole is greater than that of the flame formed in the upper flame hole. Therefore, the flame formed by the lower flame hole has a higher flameholding performance and thus the neat recovery from the burner head to the evaporation cylinder is accelerated and the temperature reduction of the evaporation cylinder can be prevented even though the turn down ratio of combustion (lowering of the minimum combustion amount) is enlarged. Thus, the combustion apparatus provides favourable evaporation and combustion performances.

i Embodiments of the invention will now be described by way of example only Swith reference to tL, accompanying drawings in which:- 25 Figure 1 is a sectional view showing a combustion apparatus according to an i embodiment of the present invention; ri Figure 2 is an enlarged sectional view showing flame holes of the combustion apparatus of Figure 1; 940131,p:\oper\kay,12390.ca,4 ~c I I_ 1 7 Fig. 3 is a sectional view showing the entire construction of the combustion apparatus of Fig. 1; Fig. 4 is a sectional view of principal portions showing a burner head according to another embodiment of the present invention; Fig. 5 is a sectional view of principal portions showing a burner head according to still another embodiment of the present invention; and Fig. 6 is a sectional view showing a conventional combustion apparatus.

_BEST-=MODE=F AG-QI THE IN.ENTIN i A combustion apparatus comprising a burner head of a double construction according to an embodiment of the present invention is described below.

Referring to Figs. 1 through 3, reference numeral 1 denotes an evaporation cylinder having a bottom and embedding a sheath heater 2 therein and the upper portion Sthereof is opened. Reference numeral 3 denotes a cylindrical burner head, having a bottom, which is screw-fixed to the periphery la of the opening of the evaporation cylinder 1 by means of a flange disposed in the lower periphery of the burner head 3. The burner head 3 comprises a second burner head 3a and a first burner head 3b disposed inward of the second burner head 3a. Larger through-holes 4a, 4b, and 4c, the diameter of which are 3mm, 3.5mm, and 4mm, respectively -I _i i are formed on the entire peripheral wall of the second burner head 3a from an upper portion thereof to a lower portion thereof. Smaller through-holes 5a, 5b, and 5c, the diameter of which are 1.5mm, 1.8mm, and 2.6mm respectively are formed on the entire peripheral wall of the first burner head 3b from an upper portion thereof to a lower portion thereof. The through-holes 4a and 5a are coaxial with each other and opposed to each other, thus forming a flame hole 6a.

Similarly, the through-holes 4b and 5b are coaxial with each other and opposed to each other, thus forming a flame hole 6b.

Similarly, the through-holes 4c and 5c are coaxial with each other and opposed to each other, thus forming a flame hole 6c.

Reference numeral 7 denotes a metal net fixed to the entire periphery of the second burner head 3a by spot-welding the metal net 7 to the lower through-hole 4c.

Reference numeral 8 denotes an evaporation cover i provided in the burner head 3 and covering the opening of the evaporation cylinder 1. The lower center portion, of the burner head 3, which is small in diameter is formed as a gas inlet 8a for introducing the mixed gas into the burner head 3. Reference numeral 9 denotes a resistance plate, having a plurality of small openings disposed in opposition to the gas inlet 8a, fixed to the burner head 3 under pressure.

Reference numer,\l 10 denotes an ignition electrode for igniting the mixed gas which is jetted out from the flame

-I

holes 6a, 6b, and 6c; 11 denotes flame; and 12 denotes a flame rod serving as a flame detecting sensor. Reference numeral 13 denotes an air duct for feeding combustion air into the evaporation cylinder 1. An air hole 14 of a throat disposed at one end of the air duct 13 is provided on the wall surface of the evaporation cylinder 1 and the other end of the air duct 13 communicates with an air blower 15. Reference numeral 16 denotes a nozzle communicating with an oil feeding tube 18 connected with a fuel pump 17 and passing through the inside of the air duct 13 with the leading end thereof disposed in the evaporation cylinder 1.

In the above-described construction, when the evaporation cylinder 1 is heated to a predetermined temperature upon energizing of the sheath heater 2, the air blower 15 is actuated to feed the combustion air from the air hole 14 into the evaporation cylinder 1 through the air duct 13, and the fuel pump 17 is also actuated to jet fuel from the nozzle 16 into the Evaporation cylinder I through the oil feeding tube 18. The liquid fuel jetted into the evaporation cylinder 1 is evaporated on the side wall surface of the heated evaporation cylinder 1 and mixed with the combustion air and then, fed to the burner head 3, and the mixed gas is then jetted out from the flame holes 6a, 6b, and 6c. The mixed gas is ignited by the spark discharge generated by the 4 I ignition electrode 10, thus forming the flame 11. At this 0*1 i. -i I i time, the mixed gas rises along the peripheral wall of the evaporation cylinder i, thus flowing from the gas inlet 8a disposed in the center of the evaporation cover 8 into the burner head 3. Therefore, even though comparatively large unevaporated particles exist, they do not enter into the burner head 3 and as such, the generation of yellow flame can be prevented. The mixed gas which has flowed from the gas inlet 8a to the burner head 3 is dispersed by the resistance plate 9. As a result, the mixed gas is dispersed uniformly in the burner head 3.

The volume of the flame formed in the flame holes 6a, 6b, and 6c of the burner head 3 is very small because the flow rate and flow velocity of the flame are substantially restricted by the smaller through-holes 5a, 5b, and 5c of the first burner head 3b disposed inward of the second burner head 3a.

Accordingly, the temperature of the flame is lower than the flame according to the conventional combustion apparatus and the length of the flame is shorter than that according to the flame of the conventional combustion apparatus. Thus, the atmospheric temperature in the vicinity of the burner can be lowered to a great extent as compared with the atmospheric temperature in the vicinity of the burner of the conventional combustion apparatus. As such, a 25 combustion state in which the atmospheric temperature of the flame is low can be obtained and the amount of the generation of NOx which depends greatly on the temperature of the flame can be reduced.

Since the larger through-holes 4a, 4b, and 4c of the second burner head 3a are disposed outside the smaller through-holes 5a, 5b, and 5c, the flow velocity of the flame j formed in the smaller through-holes 5a, 5b, and 5c is reduced Sin the larger through-holes 4a, 4b, and 4c and the flame is i positioned in the periphery of the larger through-holes 4a, 4b, and 4c. Therefore, a strong flame-holding performance is j formed and the flow velocity of the flame in the center region of each flame hole is k4 ethan that of the flame in the periphery of each flame hole because the flame is not u positioned in the periphery of each flame hole. Therefore, i 15 the temperature of the metal net 7 does not rise greatly. In

L

i addition, no backfire occurs and flame can be reliably formed even though the turn down ratio of combustion is enlarged.

i The lower flame hole of the burner head 3 comprising the first and second burner heads 3b and 3a is larger than the upper flame hole (6a<6b<6c) thereof and the mixed gas which has flowed from the evaporation cylinder 1 collides with the ceiling of the burner head 3, thus spreading along the inner periphery of the burner head 3. Therefore, the blowout pressure of the mixed gas jetted out from the upper flame hole p1 is higher than that of the mixed gas jetted out from the lower ii u, n| I I I mm n i

I\

flame hole. Consequently, the flow velocity of the mixed gas jetted out from the upper flame hole is higher than that of the mixed gas jetted out from the lower flame hole. Accordingly, the flow velocity of the flame formed in the lower flame hole positioned in the vicinity of the evaporation cylinder 1 is lower than that of the flame formed in the upper flame hole, and the volume of the flame formed in the lower flame hole is greater than that of the flame formed in the upper flame hole. Therefore, the flame formed by the lower flame hole has a higher flame-holding performance and thus the heat recovery from the burner head 3 to the evaporation cylinder 1 is accelerated and consequently, the temperature reduction of the evaporation cylinder 1 can be prevented even though the turn down ratio of combustion (lowering of the minimum combustion amount) is enlarged and as such, favorable evaporation and combustion performances can be obtained and tar-resistant performance can be improved.

In addition, since the flow velocity of the flame formed in the upper flame hole is higher and further, the volume of the flame formed in the upper flame hole is smaller, the temperature of the metal net 7 does not rise greatly and thus a burner having a high heat resistance can be provided.

Fig. 4 shows a burner head 3 with a single construction. A plurality of flame holes 6a, 6b, and 6c of the burner Xj\i14 head 3 are formed on a multiple stage through the entire L iii i peripheral wall of the burner head 3 so that in each stage, the sectional area of a flame hole positioned on the peripher- 1 al wall of the burner head 3 is greater than that of a flame Shole positioned on the inner peripheral wall of the burner head 3, and the sectional area of a flame hole positioned at !i an upper portion of the inner peripheral wall of the burner i head 3 is slight, and the sectional area of a flame hole positioned at a lower portion of inner the peripheral wall of the burner head 3 is larger than that of the lame hole positioned 1i 0 at the upper portion of the inner peripheral wall of the i burner head 3 (6a<6b<6c). The operation and effect of the burner head according to this embodiment are similar to those of the burner head according to the above-described embodiment.

15 Fig. 5 also shows the burner head 3 with a single i construction. Different from the above-described embodiments, I each flame hole of this burner head 3 consists of a single iv hole, and the sectional area of the upper flame hole is smaller than that of the lower flame hole (6Ia<6b<6c). In this embodiment, because of the reason described above, the mixed gas flows at a high velocity from the upper flame hole of the burner head 3 and the volume of the flame formed in the upper flame hole is small. As a result, the temperature of the metal net does not rise greatly. The mixed gas is jetted out at a low velocity from the lower flame hole in which the c i -i ICllr*l

WL.

2 flame-holding performance is deteriorated and the volume of the flame formed in the lower flame hole is comparatively great. As a result, the flame-holding performance of the lower flame hole is favorable. Accordingly, the heat recovery from the burner head 3 to the evporation cylinder 1 is favorable and hence the temperature drop of the evaporation cylinder 1 can be prevented. Therefore, favorable evaporation and combustion performances can be obtained. The other operations and effects of this embodiment are similar to those of the embodiment described previously with reference to Fig.

1 except the reliable formation of flame.

Each of the embodiments has been described as an example for efficiently manufacturing the combustion apparatus, but the constructions of detailed portions are not limited to the configuration of the construction of the embodiments. For example, the burner head may be composed of a cylindrical component having no bottom and a ceiling component for closing the ceiling of the burner head. The combustion apparatus may be composed as desired unless the object and effect of the present invention is achieved.

INDUSTRIAL APPLICABILITY As described above, the combustion apparatus of the present invention is capable of improving the flame-holding performance and enlarging the turn down ratio of combustion i with nitrogen oxide formed in a small amount. In addition, I I and combustion pertormances while lowering the NUx concentration and widening a varnaoe range lor comustion. Ins combustion device is in such a structure that a burner head is fixed to a vaporizing cylinder to vaporize liquid fuel, said burner head is provided with minute burner holes at the upper part and slightly larger burner holes (6a 6b 6c) at the lower part thereof, and a perforated sheet such as a wire net is tightly fixed to the outer periphery of said burner head Thus, flames formed at said burner head are small to reduce NOx concentration, the temperature of the upper part such as the wire net (7) can be kept at a low level even when combustion is on low, and flame stability is good because of the large lower flame holes, whereby a temperature of the vaporizing cylinder susceptible to the influence of said flames can be maintained at a high level and favorable vaporization and combustion performances are ensured.

r-

I

-13according to the combustion apparatus, the occurrence of backfire can be prevented even though the turn down ratio of combustion is enlarged, the temperature rise of the metal net and the temperature drop of the evaporation cylinder can be also prevented. Therefore, the burner provided by the present invention can be safely used and a favourable evaporation performance can be obtained.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

940131,p:\oper\kay,12390.ck,13 i i

Claims

1. A combustion apparatus comprising: an evaporation cylinder for evaporating liquid fuel and mixing the evaporated gas and combustion air with each other so as to form mixed gas; and a burner head having a plurality of flame through-holes formed therein through which the mixed gas is jetted, said flame through-holes being formed in a peripheral wall of said burner head and wherein each flame through-hole comprises an outer hole section and an inner hole section, said outer hole section having a sectional area greater than that of the inner hole section, and the sectional area of the inner hole section of a through-hole positioned at an upper portion of the peripheral wall of said burner head being smaller than the inner hole section of a through hole formed at a lower portion of the peripheral wall, and the sectional area of the outer hole section of a through-hole positioned at the lower portion of the peripheral wall of said burner head being larger than that of the outer hole section i of a through-hole positioned at the upper portion of the peripheral wall of said burner head; and a porous plate in close contact with the peripheral wall of said burner Shead. i S2. A combustion apparatus comprising: an evaporation cylinder for evaporating liquid fuel and mixing the evaporated gas and combustion air with each other so as to form mixed gas; and a burner head having a plurality of flame through-holes formed therein through which the mixed gas is jetted, said burner head comprising an inner burner head and an outer burner head, a first flame through-hole formed at an upper portion of a peripheral wall of said inner burner head, and a second flame through- hole formed at a lower portion cf the peripheral wall of said inner burner head having a larger sectional area than the first flame through-hole, further flame througl-holes being formed on said outer burner head in opposition to each of said first and second flame through-holes of said inner burner head; and a porous plate in close contact with the peripheral wall of said outer burner l 940131,p:\oper\kay,12390.cla,14 supplying the combustion air to the evaporation cylinder 22; 29 indicates a throat 9 4 0131,p:\oper\kay,12390.ca,1 IL, I I 15 head.

3. A combustion apparatus according to claim 1 or claim 2 wherein the porous plate comprises a metal net.

4. A combustion apparatus as defined in any one of the preceding claims wherein a cover for said evaporation cylinder is disposed between said evaporation cylinder and said burner head and a small-diameter inlet for introducing mixed gas into said burner head is formed in the centre of said cover. A combustion apparatus as defined in any one of claims 1 to 3 wherein a cover is provided for said evaporation cylinder, said cover having a small-diameter mixed gas-introducing inlet in the centre thereof and a resistance plate having a plurality of small openings formed therethrough in opposition to said mixed gas- introducing inlet.

6. A combustion apparatus substantially as hereinbefore described with reference to Figures 1 to 5 of the accompanying drawings. DATED this 1st day of February 1994 Matsushita Electric Industrial Co., Ltd. By Its Patent Attorneys DAVIES COLLISON CAVE l 940201,p:\oper\ky,12390.ca,1S I 1 ABSTRACT OF THE DISCLOSURE The present invention relates to a combustion apparatus for use in an oil fan heater or the like. The object of the present invention is to enlarge the turn down ratio of combustion and yet suppress the generation amount of NOx so as to obtain favorable evaporation and combustion performances. The combustion apparatus according to the present invention comprises an evaporation cylinder for evaporat- ing liquid fuel and a burner head mounted thereon. A slight flame hole is formed on an upper portion of the burner head and a flame hole larger Than the slight flame hole is formed on a lower portion of the burner head (3) (6a<6b<6c). A porous plate such as a metal net is provided in close contact with the peripheral wall of the burner head Therefore, the volume of flame formed in the burner head is small and thus a small amount of NOx is generated. In addition, the upper portion of the combustion apparatus, for example, the metal net can be maintained at a low temperature. Since the flame hole positioned at the lower portion of the burner head is larger than the flame hole positioned at the upper portion thereof, the flanme- holding performance is favorable. Thus, the evaporation cylinder can be maintained at a high temperature and as I I j such, favorable evaporation and combustion performances can be obtained.