CA1150615A - Apparatus for burning liquid fuel equipped with heating-type fuel vaporizer - Google Patents

Abstract

A liquid fuel combustion apparatus for evaporating and vaporizing kerosene, gas oil or like liquid fuel by heating, admixing air with the vaporized fuel in a specified ratio and burning the resulting gaseous mixture in a combustion unit. The vaporizer for the liquid fuel comprises a liquid fuel drawing-up member (15) made of a heat-resistant porous body (8) or heat-resistant inorganic fiber fabric (9) for drawing up the liquid fuel, and a heat generating member (6) including coating layers (22, 23) of heat-resistant metal, heat-resistant alloy or heat-resistant metallic oxide for giving heat to the drawing-up member. To prevent formation of tar-like substances, a catalyst is preferably deposited on the surface of the drawing-up member and/or on the surface of the heat generating member. Further preferably, the outer periphery of the heat generating member (6) is in contact with the drawing-up member (5). The apparatus assures stable combustion over a prolonged period of time and is useful as a heater, kitchen range or the like.

Description

~5~61S

APPA~ATUS FOR BURNING ~IQUID FU~L EQUIPPED
WITH HEATIN~-~YPE FUEL VAPORIZER

The present invention relates to a liquid fuel combustion apparatus for evaporating and vaporizing kerosene, gas oil or like liquid fuel, admixing a specified quantity of air with the vaporized fuel and burning the resulting gaseous mixture in a combusion unit.
A majority of conventional devices for v~porizing kerosene by heating, which are divided generally into the stationary type and the rotary type, operate on the principle that kerosene is vaporized by being applied to the surface of a meta] member having a relatively large thermal capaci-ty and maintained at a temperature sufficiently higher than the boiling point of kerosene as by electrical heat. These devices require a preheating period of several minutes to more than ten minutes for start-up and have a problem from the viewpoint of savings of energy in that the power consumption involved is exceedingly large as compared with the thermal energy needed for -the vapor-ization of kerosene. The conventional devices have another problem that soft carbon, hard carbon, tar and like unburned deposits formed on the kerosene vaporizing '~ ~

:

6~S
portion adversely affect combustion. Additionally the conventional devices are not always adapted for accurate control of the amount of kerosene to be vaporized and are therefore likely to give off an exhaust gas of objection-able composition especially when affording a reduced calorific value. Thus they have various drawbacks.
The object of the present invention is to provide a combustion apparatus equipped with a fuel vaporizer in which a liquid fuel is drawn up by a drawing-up member and then evaporated with the heat energy generated by a heat generating member to form a vaporized fuel rapidly, smoothly and efficiently at the desired rate, the fuel vaporizing portion having reduced susceptibility to the formation of tar and like deposits and being capable of vaporizing the liquid fuel steadily over a prolonged period of time, the fuel vaporizer therefore enabling a combustion unit to burn the fuel in a very satisfactory state, with improved stability and with a greatly reduced likelihood of giving off soot, C0 or noxious odor.
According to the invention there is provided an apparatus equipped with a heating-type fuel vaporizer for burning a liquid fuel and comprising: a member immersed in the liquid fuel for drawing up the fuel in a liquid state, the drawing-up member being capable of drawing up the liquid fuel at a speed of at least 10 mm/30 seconds, means for supplying the liquid fuel to the drawing-up member, a heat generating member embedcled in the drawing-up member in contact therewith`

:
' ~

s ~or giving heat to the liquid ~uel dfawn up by the drawing-up member, and a combustion unit ~or burning the f~el evaporated and vaporized by the heat emitted by the heat generatinq member.
drawing-up member, and a combustion unit ~or burning the fuel evaporated and vaporized by the heat emitted by the heat generating member.
According to a preferred embodiment, the invention provides a liquid fuel combustion apparatus which includes a liquid fuel drawing-up member and a heat generating member and in which formation of tar - 2a -~ - .
. .

' :
- - ~ .
:

~5~361S

and other deposits is inhibited over a s-till prolonged period of time by a ca-talyst deposited at least on the surface of a liquid fuel vaporizing portion of -the ~rawing-up member and/or on the surface of the heat generating member.
According to another preferred embodiment of the invention? there is provided a liquid uel combustion apparatus of the type described above in which the outer periphery of the heat generating member is at least partly in contact with the fuel draw.ing-up member so that the thermal energy of the heat generating member can be used for the vaporization of the liquid fuel wi-th a further improved efficiency for savings in energy.
Various other features and advantages of the invention will be readily understood from -the following description of preferred embodiments with reference to the accompanying drawings, in which:
Fig. 1 is a view in vertical section showing a liquid fuel vaporizer which is a chief component of a liquid fuel combustion apparatus according to this invention to illustrate the principle;
Fig. 2a is a front view showing a liquid fuel drawing-up member for use in the vaporizer of Fig. l;
Fig. 2b is a side elevation showing the arawing-up member of Fig. 2a;

~5~1S

Fig. 3a is a front view showing another liquid fuel drawing-up member use~ul for the vaporizer of Fig. l;
Fig. 3b is a side eLevation showing the drawing-up member of Fig. 3a;
Fig. 4 is a diagram showing the characteristics of various liquid fuel drawing-up members;
Fig. 5 is a view in vertical section showing a specific embodiment of the liquid fuel combustion apparatus of the invention;
Fig. 6a is a fragmen-tary enlarged view in section showing a first embodiment of -the heat generating member;
Fig. 6b is a fragmentary enlarged view in section showing a second embodiment of the heat genera-ting member;
~ ig. 6c is a fragmentary enlarged view in section showing a third embodiment of the heat generating member;
Fig. 7a is a diagram illustrating a process for producing the heat generating member of Fig. 6a;
Fig. 7b is a diagram showing a process for producing the heat generating member of ~ig. 6b; and Fig. 7c is a diagram showing a process for producing the heat generating member of Fig. 6c.
~Yith reference to the liquid fuel vaporizer -4- ~

, ~ !

, ''.' - .' ' ~ ~ . '' ' ~5~?6~LS

shown in Fi~. 1, the wall of a closed container 1 is ~ormed with an inlet 2 for a liquid fuel such as kerosene, an air inlet 3 and an outlet 4 for a fuel-air gaseous mi~ture. Disposed within the closea container 1 is a liquid fuel drawin~-up member 5 made of a heat-resistant porous material or fabric of glass fiber or like heat-resistant fiber ~nd having a capillary action. A heat generating member 6 having a heat-resistant coating layer on its outer surface is provided in intimate contact with the drawing-up member 5. ~y virtue of the intimate contact of the heat generating member 6 with the drawing-up member 5, a predominant' 2mount of the heat emitted from the member 6 is efficientl~ transmitted to the drawing-up member 5 to effectively evaporate and vaporize the liquid fuel drawn up by the member 5. ~y a capillary action the drawing-up member 5 automatically draws up thè liquid fuel at a rate corresponding to the rate of evaporation to maintain a steady state. When the capacity of the member 5 to draw up the liquid fuel, the amount of heat emitted by the heat generating member 6, the surface area of the fuel evaporating and vaporizing portion, etc.
are suitably determined relative to one another, the fuel can be vaporized very efficiently relative to the heat suppl~ by the member 6 with high responsiveness.

. ' ' ~
.

~l~5~l5 Since -the liquid fuel is vaporized mainly at and around the portion of the drawing-up member 5 in contact with the heat generating member 6, the air inlet 3 is so arranged that the air supplied there-through wlll promote vaporization of the liquid *ueland flow out through the outlet 4 as completely admixed with the vaporized fuel. ~he gaseous mixture thus obtained is led to a particular combustion unit suitable for the contemplated use. This provides a convenient and economical liquid fuel combustion apparatus.
The heat generating member 6, when provided within the drawing-up member 5, is advantageous in evaporating and vaporizing the liquid fuel with improved efficiency. When a PTC thermistor coated with a heat-resistant material is used as the heat generating member6 as desired, the member 6 is self-controllable to give a specified heating temperature.
~ ost preferably, the drawing-up member 5 should fulfil the following requirements to attain the objects of the invention.
(1) Having a structure by which the heat emitted by the heat generating member 6 contacting or installed in the drawing-up member 5 can be efficiently converted to the heat of evaporation and vaporization of the liquid fuel.

,. . .

, ~
~ ~' ,, , ~5~6~5

(2) ~eing capable of vaporizing the liquid fuel in a væriable amount in accordance wi-th the amount of heat emitted by the heat generating member 6.

(3) Having an outs~anding capillary action and a small thermal capacity.

(4) Having minimized suscep-tibility to the formation of tar and like deposits at the portion there~f for evaporatin~ and vaporizing the fuel.

(5) ~eing made of a heat-resistant and corrosion-resistar.t material.

(6) ~eing serviceable as a carrier for a catalyst and capable of fully withstanding the process for depositing the catalyst thereon.
A detailed description will now be given of the materials for drawing-up members filfilling theee requirements and the catalysts to be deposited on the surface of the drawing-up members.
~ irst, useful drawing-up members will be described which have a capillary action and made from heat-resistant porous materials.
Heat-resistant porous materials Heat-resistant ceramics are usable as heat-resistant porous materials. Such ceramics must be porous and capable of drawing up the liquid fuel by a capillary action and are preferably foamed bodies.

., ~,.
~ .................................................................. . .

- - . . : . -,.
. ,: ' ~- ' ~ .
. . - :, - . . . . - , ~ .

~L51~6~ 5 Useful ceramic materials are alumina, magnesia, clay, silica and ~irconia which are resistant to heat. Heat-resistant foamed ceramics can be prepared, for example, from a mixture of a ceramic material of -the clay type and a required amount of finely divided graphite for blowing the material during baking at a high temperature, by a known method involving molding, drying and baking.
Preferably the drawing-up member 5 made of such a heat-resistant porous material has the construction shown in ~igs. 2a and 2b. It is seen that the heat-resistan-t ceramic body 8 of the member is formed with a bore 7 extending therethrough for accommodating the heat generating member 6.
Since the porosity of the heat-resistant ceramic body 8 is inherently limited with a limitation on its ability to draw up the liquid fuel, it is preferable to use heat-resistant fibers for drawing-up members for small-sized combustion apparatus with relatively small heat output. ~-Heat-resistant fibers Drawing-up members of heat-resistant fibers, especially heat-resistant inorganic fibers, draw up liquid fuels most efficiently when made of fabric woven from bundled yarns o~ monofilaments in a reti~ular form. However, nonwoven fabrics and mats are still . . . ~ ~ .

~: :, . :-- .
- :. . : .
. ' : . :

~5~61S

superior to the above-mentioned hea-t-resistant porous materials. Extensive research has revealed -that pre*erable heat-resistant inorganic fibers are glass fiber, de-alkalized glass fiber, silica fiber, al~ina fiber, carbon fiber and asbestos fiber, among which glass fiber and dealkalized ~lass fiber are most preferable from the overall viewpoint in respect of the stability of quality, variety, economy, processability, etc. Furthermore such fibers achieve the highest vaporization efficiency. The drawing-up member 5, when made from such heat-resistant inorganic fiber, preferably has the structure shown in Figs. 3a and 3b in which a heat-resistant fiber fabric 9 surrounds the heat generating member 6.
When the drawing-up member 5 is in the form f a heat-resistant ceramic body 8, the member 5 can be made to support thereon a material, such as active alumina, colloidal silica or the like, which is active and has an increased surface area, in order to compensate for the small surface area of the body 8. On the other hand, the heat-resistant fiber material 9 usually has a larger active surface area than ceramics and is therefore fully useful as it is. To be more efficient, however, the fiber material can be made to support active alumina, colloidal silica, or the like thereon.
Preferably the fuel drawing-up member 5 made :. . : -: . .

~1~5{~6~5 of such heat-resistant porous or fibrous material has ability to dra~ up the liquid fuel at a speed of a-t least 10 mm/30 seconds -to inhibit deposition of tar on the fuel evaporating and vaporizing portion of the member 5 that would lead to improper combustion For the selection of materials meeting -this requirement, various materials are cut to a width of 70 mm and a length of 150 mm, immersed the lower ends of the cut pieces into kerosene, an example of liquid fuels, to measure the heights to which the materials draw up the kerosene by the capillary action. The results are shown in ~ig. 4, in which A represents the characteristics of a drawing-up member of clay biscuit. ~ represents the characteristics of a drawing-up member in the form of a porous foam biscuit prepared from a mixture of clay and finely divided graphite by molding, drying and baking. ~ represent those of a member of plain-woven fabric formed from bundled yarns of glass fiber. D
represents those of a member made of a fabric resembling a plain gauze, formed from thicker bundled glass fiber yarns and having larger openings. Fig. 4 reveals that the height to which the kerosene can be dra~n up per unit time differs greatly from member to member in ~ccordance with the material, process of production and structure of the member~
~ ' -10- ~, :

~5~6~5 While the forma-tion of -tar can be inhibitea considerably with the use of drawing-up members having a liquid fuel drawing-up speed of at least 10 mm/30 seconds, the tar can be inhibited more effectively by a catalyst deposited at least on the surface of the fuel evaporating and vaporing portion of the drawing-up men-ber. Such catalysts will now be described~
Catalysts The catalysts to be used in this invention act to crack the liquid fuel to lower-molecular-weight substances and to inhibit the formation of -tar, carbon and other deposits or to decompose such deposits at low temperatures. Although the term "catalyst" generally refers to a material comprising a carrier and a catalytically ~-active substance deposited on the carrier, the term"catalyst" as used in this invention means the catalytically active substance itself for the convenience of descrip-tion since the drawing-up member or -the heat generating member to be described later serves as the carrier in this invention. Typical of catalysts useful in this invention are so-called metallic oxide catalysts such as MnOx, CuOx, NiOX, CoOx, ~eOx, CrOx, AgOX, V0x, etc.;
double oxide catalysts such as ferrite, zeolite, silica-alumina, cement, etc.; and noble metal catalysts such as Pt, Rh, Pd, Ir, Ru, etc. Useful catalysts further :;

.

`~5-~6~L5 inelude those widely used in catal~tic chemistry, examples of which are solid acid catalysts including (l) na-tural clay minerals sueh as Japanese clay aeid, kaolin, monmorillonite, (2) solid aeids sueh as H2SO~, H3P04, etc. as adsorbed to carriers, (3) silica-alumina, siliea-magnesia, etc. and (4) inorganic chemieals such as ZnO, Al203, TiO2, CaS04, CuCl2, etc.; and solid base catalysts lneluding (l) inorganie chemicals sueh as CaO, MgO, K2C03, EaC03, etc., (2) sodium hydroxide as adsorbed to an alumina catalyst and (3) chareoal activated with nitrous oxide. Among these catalysts, noble metal catalysts are espeeialiy effeetive for decomposing tar, carbon and like deposits at low temperatures. With use of a drawing-up member having O.OOl~o to 5.0~0 by weight of sueh a noble metal catalyst deposited thereon, the liquid fuel can be handled as if it were a gas fuel. These eatalysts may be used singly or in admixture as desired.
The catalyst may be deposited on the drawing~
up member direetly or by some other me-thod. In the ease of ~nx catalyst, for ex~mple, a solution of Mn(N03)2 serving as a starting material is applied to the carrier, namely, to the drawing-up member by immersion or spraying, followed by heat treatment to form MnOx. ~urther in the case of Pt eatalyst, the earrier ean be made to support the eatalyst thereon by dissolving chloroplatinie aeid ~5~615 (H2PtC16) in a solvent mix-ture of water and e-thyl alcohol, applying the solution to the carrier by immersion or spraying and heat-trcflting the resulting carrier.
~'lith reference to Fig. 5, a specific embodi-ment will be described in which the liquid fuel vaporizer of Fig. 1 is incorporated in a liquid fuel combustion apparatus. The parts shown in Fig. 5 and substantially identical with those shown in ~i~. 1 are referred to by the same reference numerals and will no-t be described. A combustion unit 11 comprising a burner for a small kitchen range is installed on a fuel-air gaseous mixture outlet 4, with a bacXfire preventing net 10 provided thereb~tween. The fuel-air mixture burns to force out flames through apertures 12 and 13.
Indicated at 14 is a trivet, and at 15 a heat insulator for a closed container 1. A heat generating member 6 has input terminals 16 and 17. Air is fed by a fan 18, while a leveler 19 maintains the liquid fuel, such as kerosene, at a constant level for the supply of the fuel.
The amount of combustion is widely variably by ad~usting the input to the heat generating member 6 and the supply of air by the fan 18.
A combustion experiment was conducted with use of various liquid fuel drawing-up members 5 for the - . : . ,.

6~5 apparatus of Fig. 5. ~ight drawing-up members were tested. They are the drawing-up members A to D already described ~!ith reference to Fig. ~, and drawing-up members A' to D' prepared by causing the same kinds of members to support a catalyst thereon. For this purpose, a platinum catalyst was deposited on each member by dissolving chloroplatinic acid (H2PtC16) in a mixture of water and ethyl alcohol to a concentation of 2g/liter calculated as platinum, spraying -the solution to the member in an amount of 0.01% by weight calculated as platinum and based on the weight of the member, drying the member and thereafter baking the member at 600 C, The heat generating member 6 was prepared by coating a 15-ohm electric heating wire with finely divided alumina to a uniform thickness of 30 to 50~ by arc metal spray method. The output of the heat generating member 6 ~;/as adjusted to 40 W or 60 W -to check the apparatus for the variations in the amount of heat generated in each case. The time taken for the formation of tar on each drawing-up member was also measured.
Table 1 shows the results.

~5~615 o o o q~ , o o U~ o o h ~ ~I r~l o O ~ ~ 0 ~ ~ ~ ~ ~.
h ~ N L~ (~ t~ 0u~ Cq Q~ a ~d~3 rl ~' O O ~ ~~1 ¢ ¢ O
~ ~ ~d o 3 O O O O O O O O~H
-' ~ O L~ 1 S~ O ~ 0 ~ ~ ~ 0 ~D
~D r-lr~l N t~ ~. ~I N
O rl cd :~ O O O O O O O O o~
O 0 0 0 0 1~ 0 (~1 N bD
O ~ ~ O r-l U~ ) ~ '.
~ ~ ~ ' a~
C O
~:
U~
~0 ~ O ~ L~ O O O U~ O O O
U~ h ~ ~I N ~ ~ N
rl Q~ ~
X~ ~ r-l S~
~' U~ U~
~d O : - : .~ ~d _ : -l ' ~- ~d ~ C` :~ O N
Q~
C~
. ~ * bO
C~ C~
C~ ~ C~
l 0 ~1 ~I h h -r bD h h q~
S~ q-~ ' ^ ,Q O t~ ~) td ~ h ,~ o CH ~> tH ~7 17 cd ~7~7 a~ ~rl rl h a~ h ~ h h rlrlh al h 0 C~ C~ ,D .-740 O C~C) ,D ~ U~
~1 U~ U~~.7 r~
o t~ ~ p ~ ~1 o ~ ~,o 4~ U~
~ ~ ~ O ~ ~ C
~1 ~ o ~ ~ c~ c~
~, C~
r1 ~ ~ ~ ~ _ _ _ _ *
¢ ~ C~ q ~ F
.
Z ~ N

, :
~:

~5{~15 ~ased on -the experiment~l resul-ts given in Table 1, the desirable characteristics of liquid ~uel drawing-up members for attaining -the foregoing objects of the invention will be discussed.
~llhile both the members No. 1 and No. 2 are heat-resistant porous bodies made chiefly of clay, No. 2 has a higher porosity and higher ability to draw up kerosene, a~fords increased heat output, namely, an increased amount of heat and is operable ~or a longer period of time free of formation of tar.
Although No. 3 and No. 4 are woven of the same glass fiber, they di~fer in the thickness of bundled glass fiber yarns and in the method of weaving and therefore greatly differ in capillary attraction.
No. 4 is superior in the ability to raise kerosene, heat output and tar formation time.
The drawing-up members No. 5 to No. o, having O . Ol~o by weight of platinum catalyst deposited on the base body, achieved remarkable improvements in all the characteristics over the members No. 1 to No. 4 bearing no catalyst. It is noted that the improved characteristics are substantially dependent largely on the kerosene raising ability of the base bodies.
These results have revealed that drawing-up members having ability to draw up kerosene at a speed ~5~6iS

o~ at least 10 mm/30 seconds are fully useful for the evaporator of the liquid fuel combustion apparatus contemplated by -the present invention. Drawing-up members having lower ability, like the member No. 1 listed in Table 1, will permit deposition of t~r on the porous body thereof within Q short period of time and consequently become unserviceable for the vaporizer. Thus in order to fulfill the objects of the invention, the liquid fuel drawing-up member must be capable of drawing up the fuel at a rate of at least 10 mm/30 seconds. ~specially when having ability o~
not lower than 20 mm/30 seconds, the drawing-up member exhibits stable characteristics for a further prolonged period of time.
Extensive research conducted has indicated that porous ceramics capable of drawing up a liquid fuelJ e.g., kerosene at a rate of at least 10 mm/30 seconds can be prepared by using at least one of the heat-resistant materials exemplified above conjointly with finely divided graphite, CaF2, ~;gF2 or the like serving as a blowing agent for baking at a high temperature.
Although the invention has been described above as embodied for use with kerosene, experiments have shown that exactly the same results are achievable ., -.~

. ,.

-- -....... . ' ' .' ', , ' ~ ' : ::

~ith use of o-ther liquid fuels such as gas oil.
~ he hea-t generating member 6 will be described in greater detail.
Most suitably, the heat generating member 6 should fulfill the follo~ing requirements for attaining the objects of the invention.
(1) Being held in intimate contact with the liquid fuel drawing-up member 5 to the greates-t possible extent and over the largest possible area.
(2) Being capable of subjecting the generated heat to heat exchange with the liquid fuel or the drawing-up member 5.
(3) ~reedom from local heating to a high temperature over the surface thereof.
(4) Freedom from tar-like unburned deposits over i-ts surface.
(5) Having the function of catalytically self-cleaning its surface to eliminate tar-like unburned deposi-ts, if any.
(6) Being capable of maintaining a uniform surface temperature in the range of 200 to 250 ~.

(7) Having its metal portion protectedzgainst corrosion due to cementation.
When the heat generating member 6 comprises a sheathed heater, a usual heating wire, for example, of -',: ' ' ` - ' ''' , ' ' - ~. .,''. ~ '' ' .
. - . . ..

';,' ~S{~6~LS

Fe-Cr-Al, Fe-Ni-Cr or Fe-Ni-Cr-Al-Yt alloy, or the like, tar-like unburned products will be deposited on its surface in a short period o~ timel consequently impairing the heat exchange for affording the heat of vaporization or locally subjecting the sheathed heater or wire to cementation that could lead to local overheating or a break or cause ignition of the gaseous mixture.
Accordingly it is preferable -to coat the heat generating member with at least one layer of a heat-resistant metal such as Al, Zn, Sn, Cr, Cu, Fe, ~i orthe like, a heat-resistant alloy such as Ni-Cr-Al, Ni-Cr, ~e-Cr, Fe-Cr-Al, Fe_Ni-Cr-Al, Fe-Ni-Cr or the like, or a heat-resistant metallic oxide. It is also preferable to cause the coating layer to support a 17 catalyst on its surface.
With reference to Figs. 6a to 6c, heat generating members 6 useful in this invention will be described.
Fig. 6a shows an embodiment comprising a heating wire or resistor 21 coated with a layer 22 of metalli-c oxide (or double metallic oxide). Since the preferred surface temperature of the heat generating member 6 is 200 to 250 C, the thermal expansion of the resistor 21 is not very great, so that this embodiment is formed by coating the resistor 21 directly with a metallic oxide, such as A1205, TiO2, MgA1204 or the like, or a double oxide of .: . . . .
.

~51~LS

metal by the plasma spra~ method.
Fig. 6b shows another embodiment comprising a heating wire or resistor 21, an intermediate layer 23 of heat-resistant alloy coating the resistor 21 and a layer 22 coating the intermecliate layer 23 and made of me-tallic oxide (or double metallic oxide) like the coating layer of ~ig. 6a. ~his embodiment is fully serviceable for a prolonged period of time under heat cycles when the resistor 21 and the metallic oxide layer 22 differ greatly in thermal expansion. Heat-resistant alloys, such as Ni-Cr, Ni-Cr-Al or the like, are useful for the intermediate layer 23.
The embodiment of ~ig. 6b is further treated with a sealant 25 and provided with a catalyst 24 to ~ive the embodiment shown in Fig. 6c.
The heat.generating members 6 of ~igs. 6a, 6b and 6c are prepared by the processes illustrated in ~igs. 7a, 7b and 7c, respectively and to be described below in detail.
Heat generating sources Examples of -the most preferable heat generating sources are coils of nichrome wire, iron wire, chromium wire, ~anthal alloy wire,Ni-Cr-Fe-Y wire and the like.
Although sheathed heaters, PTC thermistors and other heating surces are usable, usual heating wires such as - ~ ~ ' , ' ~5~ 5 nichrome wire are used for the embodiments.
Surface enlargement The surface of the heating wire is fully degreased and cleaned first and subsequently trea-ted for enlargement with a usual abrasive of A1203, SiC
or the like, 20 to 100 mesh in particle size, at a blast pressure of 3 to 5 k ~cm2. Preferably the heating wire is treated to an average roughness (Ra) of 5 to 50 ~ as measured by "TA~ISUR~ 10," an instrument for the measurement of surface roughness by the stylus method.
If the Ra value is lower than 5 ~, the heatin~ wire will not be coated with a heat-resistant material effectively, whereas Ra values exceeding 50 ~ entail difficulties in uniformly coating the heating wire.
~ashin~ and Dryin~
The heating wire is then washed with water to remove abrasive particles and particles of the wire metal and is thereafter thoroughly dried at 100 to 150 C.
Coatin~ ~primar~ coating) I~ the heating wire is held directly in intimate contact with the liquid fuel drawing-up member 5 or the liquid fuel, accelerated formation of tar takes place on the surface of the wire, consequently subjecting the wire to corrosion due to cementation with the tar.
To avoid this, the heating wire is coated with a layer ., -21- ~;

- . ~ , , :

,. ~ , . . . . -. ': . : , , ~, ' , ' , . :

~5~i1S

of heat~re~istant metal, heat-resistant alloy or heat-resistant metallic oxide. Preferably the coating layer is ~ormed from a heat-resistan-t metallic oxide which itself is capable of catalytically cracking liquid fuels,such as kerosene, and tar-like suhstances. Examples of suitable metallic oxides are A1203, SiO2, Fe203, Y O TiO2, CaO, B203, Li20, ~r203, ZrO2, g t ThO2, HfO2, ~a203 and CeO2. Also suitable are double oxides of spinel s-tructure, such as MgA1204, Mn~1204, 2 4~ A1204, ZnA1204, MgCr20~, etc. These oxides are used singly or in admixture. Among these examples, A1203, ~iO2, 2rO2~ SiO2 and ~gA1204 are most effectiYe and also economical.
~hese substances can be applied to the heating wire by the arc, flame, plasma and explosion metal spray methods, while the plasma metal spray method was employed for the present embodiments, using "PLASMATRON,"
(trade name, product of Plasmadyne, a division of Geotel, Inc.) 80 ~l~ type Model SG-100. Argon gas was used as the arc gas 7 and helium as an auxiliary gas. ~he heat-resistant coating material Y~as sprayed onto the wire ~ith a power supply of 1000 A,41 V for coating.
Coating layers of about 10 to about 100 ~ proved effective.
Intermediate co .

s A~ already stated, the intermediate layer, when provided between the heating wire or resistor 21 and the metallic oxide layer 22, renders the wire usable stably for a prolonged period of time under heat cycles.
5 Exarnples of the most suitable materials for the interme-diate coating layer are heat-resistant alloys, such as Ni-Cr, Ni-Cr-Al, ~e-Cr, ~e-Cr-Al, ~e-Cr-Ni-Al, etc., and heat-resistant metals, such as A1, Znl Sn, Cr, ~u, Fe, Ni, etc.
At least one of these heat-resistant alloys and metals is applied to the wire. Preferably the intermediate coating layers are formed by metal spray methods, such as those mentioned above. Good results were obtained when the intermediate layer has a thickness of about 5 to about 30 ~.
Sealin~ `
When the heating wire or resis-tor 21 is coated with the intermediate layer of alloy such as Ni-Cr-Al by the metal spray method and further coated with a ceramic material, such as TiO2, Al203, SiO2 or ZrO2, by the plasma spray method to form a primary coating layer ~;
thereon, the metal spray layers ? which have a substantial porosity of 5 to 30~, will permit the liquid fuel to penetrate therethrough to the surface of -the heating wire. Since the interface between the heating wire or . : '- ' .

~5~6~S

resistor 21 and the intermediate layer involves difficulty in permitting diffusion of air and therefore presence of a substantial amount of oxygen, the liquid fuel penetrating to the wire surface is liable to become tar, which is difficult to oxidize and burn. To avoid such an objectionable result, it is preferable to seal off the interface.
Examples of useful sealants ~or this purpo~e are water ~lass, silica sol, alumina sol, vitreous powder, silicone resin and heat-resistant coating compositions. Among these exa~lples, water glass~ silica sol and alumina sol were found to be especially useful.
De~osition of catalyst Although the metallic oxide coating layer 22 itself has a self-cleaning function by par-tly cracking kerosene and tar-like substances, the layer will have greatly improved ability to crack kerosene and tar-like substancesfor self-cleaning when made to support a noble metal or like catalyst on the surface thereof.
Catalysts useful for this purpose are those already exemplified for deposition on the drawing-up member, among which noble metal catalysts are especially desirable similarly. Such a novel metal catalyst can be deposited on the oxide coating layer by dissolYing a chloride of the noble metal in a solvent mixture of . ' ':

.

~5~

water and ~lcohol to a concentration of 1 to 10 g/liter, impregnating the layer wi-th the solu-tion, drying the wet layer a-t 100 to 150 C and bal;ing the same in an electric oven at 600 C. Fig. 6c shows the coating layer thus supporting the noble metal catalyst on its surface.
For comparison, a commercial nichrome wire 0.4 mm in diameter was wound into a coil having an inside dlameter of 4 mm and an overall resistivity of 15 ohms, and this heat generating member was tested with a power supply of 60 W with use of the apparatus of Fig. 1. Tar was formed about 20 to 30 hours after the start-up, and the heat generating member was found to have been wholly covered with tar when used continuously or about 400 to abou-t 500 hours. By this time, the initial resistivity of 15 ohms had increased to 196 ohms, with a greatly reduced fuel vaporization eficiency.
On the other hand, a nichrome wire of the same size was coated with a metallic oxide layer 22 only by the process shown in Fig. 7a to obtain a heat generating member shown in Fig. 6a. The same kind of ire was also treated by the process shown in Fig. 7c to obtain a heat genera-ting member as shown in Fig. 6c and having an intermediate layer, a primary coating ~5~61~

layer, a sealing layer and a platinum ca-talyst deposited on the coating layer. These heat genera-ting members ~ere continuously used in the same manner as bove. In 2000 hours, the former member with the metallic oxide layer 22 alone was found to have its initial resistivity of 15 ohms increased to 165 ohms although still continuously usable. No changes were found in the resistivity of -the latter heat generating member even aft~r the lapse of 2000 hours.

. .

.-

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An apparatus equipped with a heating-type fuel vaporizer for burning a liquid fuel and comprising:
a member immersed in the liquid fuel for drawing up the fuel in a liquid state, the drawing-up member being capable of drawing up the liquid fuel at a speed of at least 10 mm/30 seconds, means for supplying the liquid fuel to the drawing-up member, a heat generating member embedded in the drawing-up member in contact therewith for giving heat to the liquid fuel drawn up by the drawing-up member, and a combustion unit for burning the fuel evaporated and vaporized by the heat emitted by the heat generating member.

2. An apparatus as defined in claim 1 wherein the drawing-up member is made of at least one kind of fiber selected from the group consisting of glass fiber, dealkalized glass fiber, silica fiber, alumina fiber, asbestos fiber and carbon fiber.

3. An apparatus as defined in claim 1 wherein a cata-lyst is deposited on the drawing-up member at least on a surface portion thereof close to the heat generating member.

4. An apparatus as deined in claim 3 wherein the catalyst is at least one catalyst selected from the group consisting of metallic oxide catalysts, double oxide catalysts, noble metal catalysts, solid acid catalysts and solid base catalysts.

5. An apparatus as defined in claim 1 wherein the outer periphery of the heat generating member is at least partially in contact with the drawing-up member.

6. An apparatus as defined in claim 5 wherein the heat generating member is coated over the outer surface thereof with at least one layer made from at least one member selected from the group consisting of heat-resistant metal, heat-resistant alloy and heat-resistant metallic oxide.

7. An apparatus as defined in claim 6 wherein the heat-resistant metallic oxide is at least one compound selected from the group consisting of metallic oxides including Al2O3, SiO2, Fe2O3, Y2O3, TiO2, CaO, B2O3, Li2O, Cr2O3, ZrO2, MgO, BeO, NiO, ThO2, HfO2, La2O3 and CeO2 and double metallic oxides having a spinel structure and including MgA12O4, MnAl2O4, FeAl2O4, CoAl2O4, ZnAl2O4 and MgCrO4.

8. An apparatus as defined in claim 6 wherein the heat-resistant metal is at least one member selected from the group consisting of Al, Zn, Sn, Cr, Cu, Fe and Ni.

9. An apparatus as defined in claim 6 wherein the heat-resistant alloy is at least one member selected from the group consisting of Ni-Cr-Al, Ni-Cr, Fe-Cr, Fe-Cr-Al, Fe-Ni-Cr-Al and Fe-Ni-Cr.

10. An apparatus as defined in claim 6 wherein the coating layer has a catalyst deposited on the outer surface thereof.

11. An apparatus as defined in claim 10 wherein the catalyst is at least one member selected from the group consisting of metallic oxide catalysts, double oxide catalysts, noble metal catalysts, solid acid catalysts and solid base catalysts.