Thermally amplified and stimulated emission radiator fiber matrix burner

A combustion device for producing predetermined radiation spectral output and heat for a variety of applications including lighting, cooking, heating water, electric power generation, and providing inexpensive photons to enhance chemical and physical reactions. A process for the preparation of a porous ceramic burner is described which comprises drawing a solution which contains metal oxide fibers onto a burner skeleton by use of a vacuum to form a base fiber layer. The base fiber layer is dried, after which an additional metal oxide fiber layer, the outer fiber layer, is added over the base fiber layer. In another embodiment of the invention, an intermediate fiber layer is placed over the base layer, prior to the addition of the outer fiber layer. The porous ceramic burners prepared in accordance with the present invention comprise a base fiber layer having a low emissivity in the range of the aluminum oxide, gallium oxide, thorium oxide, yttrium oxide, erbium oxide and zirconium oxide, and an outer fiber layer which is thermally stimulated to emit radiation of a specific wavelength above a threshold temperature wherein the burner produces from about 30,000 to about 3,000,000 watts/m.sup.2 and less than 20 ppm of NOx. An intermediate fiber layer is used to bond the outer fiber layer to the base fiber layer where desired.

The application is also related to U.S. patent application Ser. No. 
07/695,783, filed May 6, 1991 (now abandoned), and to Disclosure Documents 
Nos. 156,490 filed on or about Sep. 22, 1986, and 167,739 filed Apr. 13, 
1987. 
FIELD OF THE INVENTION 
The present invention relates to a porous ceramic burner for use in 
high-heat and photon flux producing devices, which are capable of 
producing selected and/or broad wavelength spectral outputs for a variety 
of applications from lighting, cooking, laser pumps, heating fluids, and 
producing D.C. power when selected wavelengths are collected onto 
photovoltaic materials. A method of preparing such porous ceramic burners 
by differential pressure forming is also provided by the present 
invention. In addition, methods of raising the temperature of combustion 
to increase radiation output for increased photon output which may provide 
higher efficiency electrical production are described. 
BACKGROUND OF THE INVENTION 
The combustion of natural gas (and other low-molecular-weight gaseous fuels 
including oil aerosols) to generate other forms of energy is one of the 
cleanest methods of combustion-based energy conversion. However, in any 
combustion process, some drawbacks are present. One of the most serious 
problems is the generation of pollutants, such as oxides of nitrogen. It 
is well established that nitrogen oxides are a source of ozone generation 
in the atmosphere and that ozone, along with unburned hydrocarbons, leads 
to the eventual formation of other components of photochemical smog, such 
as peroxyacyl nitrates. Current governmental regulations are directed at 
reducing the NO.sub.x levels that are released into the atmosphere, in an 
attempt to reduce the occurrence of photochemical smog. 
To accommodate these regulations, research has been directed at the 
development of more efficient burners and catalysts. One group of 
compounds which have been found to reduce NO.sub.x formation, when 
low-molecular-weight fuels are burned at high temperature, are the 
perovskite-type ceramic oxides. These compounds have been shown to reduce 
the formation of nitrogen oxides during combustion and will be referred to 
as "superemitting" ceramics. Such materials often have an element present 
in a mixed oxidation or mixed valence state, forming a nonstoichiometric 
oxide. Some of the most effective members of this class of compounds are 
rare earth/alkaline earth oxide systems, rare earth/transition metal oxide 
systems, and various other mixed metal oxide systems. 
Superemitters, when heated to a threshold temperature, emit visible or 
infrared radiation. Such radiation can be absorbed by a photovoltaic 
device, such as a silicon cell, to produce output voltage or current. The 
thermally-stimulated superemitters produce radiation in a relatively 
concentrated, narrow spectral band compared to blackbody or "grey body" 
emitters, which typically exhibit a broad band thermal emission. As a 
result of the concentrated, narrow spectral band, the power generated by a 
superemitter is greater than that generated by a blackbody emitter. 
The thermophotovoltaic device used to collect the radiation is designed so 
that the superemitter emits radiation of wavelength near the photovoltaic 
material band gap. For example, silicon has a band gap at about 1,100 nm, 
and InGaAsP and has a band gap at about 1,300 nm. An ytterbia-based, mixed 
oxide emission spectrum is compared with that of holmium oxide and with a 
typical blackbody spectrum in FIG. 1. 
Although general fiber matrix burners have been developed, they have 
generally not been found to be effective at high temperatures to function 
at over 650,000 watts/m.sup.2, producing selected band(s) of radiation as 
well as producing low NO.sub.x levels, i.e., less than about 20 ppm. Some 
such burners are capable of operation at a nitrogen oxide emission level 
of 20 to 30 ppm below 650,000 watts/m.sup.2 in both laboratory and field 
tests. However, when the energy density of such burners is increased to 
above 650,000, they deteriorate and NO.sub.x emissions increase 
dramatically. 
Therefore, there is a need for a high-energy density burner that produces 
low NO.sub.x emissions when operating at a high-energy density. 
Superemitter ceramic burners, which emit radiation in a narrow spectrum 
when heated above their threshold temperature offer the potential for such 
high-efficiency energy production. It is desirable that these superemitter 
ceramic burners have highly active emissive surfaces and low NO.sub.x and 
other combustion products. It is also desirable that these superemitters 
be inexpensive and easy to produce, strong and durable, and have 
high-temperature and high-energy density capabilities. The intensity of 
the light emitted from a superemitter increases dramatically with 
temperature. Therefore, the amount of radiant energy emitted and then 
collected by the photovoltaic cell will also increase dramatically with 
temperature. 
It is also desirable to produce electric power efficiently. The efficiency 
of the electric power goes up if the energy in the exhaust gas is recycled 
by means of a recuperator, which transfers the energy in the exhaust to 
the air inlet. The recuperator may increase the temperature of the air 
above the autoignition point. To provide for this important energy 
feature, a fuel injection system has been invented that allows combustion 
inlet temperature to reach well over autoignition. 
Therefore, there is a need for an improved fiber matrix burner technology 
for a wide variety of applications in heating, electrical energy 
generations, cooking, and providing photons of specific wave bands for 
such purposes as pumping lasers and operating photochemical reactors. 
SUMMARY OF THE INVENTION 
The invention comprises various devices to produce and concentrate photons 
onto a target and methods for constructing these devices. A number of 
examples of novel devices to produce electromagnetic radiation with a 
predetermined spectral characteristic depending on the specific 
application are presented. 
A process for preparing a porous ceramic burner is also described. The 
process comprises placing a base fiber layer suspension (consisting of 
bonding gel, which supports fibers and porosity agents) on one side of a 
burner skeleton; applying a vacuum to the other side of the burner 
skeleton to draw the base layer fibers onto the surface of the burner 
skeleton and to draw the liquid component through the burner skeleton, 
removing the fiber-coated skeleton from the base fiber layer suspension, 
and drying the base fiber layer. An outer fiber layer may also be added to 
the base fiber layer by placing another fiber layer's suspension in 
contact with the side of a burner skeleton containing the base fiber 
layer; applying a vacuum to the other side of the burner skeleton, to draw 
the outer layer fibers onto the surface of the base fiber layer; drawing 
the liquid component through the base fiber layer and the burner skeleton, 
to form an outer fiber layer; removing the burner with the outer layer 
coated onto the skeleton from the outer fiber layer solution; drying the 
outer fiber layer; and firing the coated burner to sublime out porosity 
agents and bond the ceramic together to produce a porous ceramic burner. 
In another embodiment of the invention, an intermediate fiber layer is 
placed on the base layer, prior to the addition of the outer fiber layer, 
by placing an intermediate fiber layer solution on the side of a burner 
skeleton containing the base fiber layer; applying a vacuum to the other 
side of the burner skeleton to draw the intermediate layer fibers onto the 
surface of the base fiber layer; drawing the liquid component through the 
base fiber layer and the burner skeleton to form an intermediate fiber 
layer; and applying the outer fiber layer to the intermediate fiber layer. 
Porous ceramic burners prepared in accordance with the present invention 
comprise a base fiber layer which may have a high emissivity such as 
silicon carbide or a low emissivity such as silicon dioxide, aluminum 
oxide, gallium oxide, thorium oxide, yttrium oxide, erbium oxide and 
zirconium oxide, and an outer fiber layer which consists of at least one 
material that is thermally stimulated to emit radiation of a specific 
wavelength above a threshold temperature; wherein the burner produces 
about 30,000 to about 3,000,000 watts/m.sup.2 and less than 20 ppm of 
NO.sub.x. 
In another embodiment of the invention, the porous ceramic burner further 
comprises an intermediate fiber layer between the base fiber layer and the 
outer fiber layer to bond the outer fiber layer to the base fiber layer. 
In another embodiment of the invention, the photon generator is designed to 
focus the emitted light onto a target placed near the center of a 
cylindrical burner, which consists of an outer chamber to distribute the 
premixed gas/air inward and further comprising a porous skeleton through 
which the gas moving toward the center passes further comprising a porous 
ceramic matrix; the premix gas/air travels through the pores to the 
surface region of the burner where ignition and combustion take place. 
In another embodiment of the invention, the burner contains separate gas 
(fuel injection) and air inlets into the fiber matrix to allow for 
preheating of the air to above the ignition temperature. This fuel 
injection can be used with a number of designs including the cylindrical 
central focused burner.

DETAILED DESCRIPTION 
FIG. 1 illustrates the spectral emittance of two different ceramic 
superemitters when heated above the thermally stimulated quantum emission 
temperature using the same amount of gas (1500 BTU). 
The present invention relates to novel porous ceramic burners and methods 
of preparing such burners. FIG. 2A illustrates the general structural 
features of a simple flat porous ceramic burner 10 formed by the practice 
of the invention. The porous ceramic burner comprises a base fiber layer 
30, an intermediate fiber layer 20, an outer fiber layer 10, and a "burner 
skeleton" 60, which may be metal screen, punched metal, or other suitable 
support material with one or more layers of fiber applied onto the 
skeleton. A porous ceramic skeleton 70, shown in FIG. 2B, is preferred for 
high temperature applications. 
The base fiber layer may comprise a high temperature fiber such as pure or 
doped oxides of uranium, thorium, ytterbium, aluminum, gallium, yttrium, 
erbium, holmium, zirconium, chromium or other high-temperature oxides. The 
base fiber layer is preferably any low-cost, fiber material that can be 
bonded effectively, preferably with thermally-stimulated superemitter 
materials. One of the preferred base fiber layers is of aluminum oxide, 
which is inexpensive and which lasts longer under oxidative conditions 
than do other inexpensive materials such as carbides, silicon oxide, or 
aluminosilicates. 
The intermediate layer functions to bond the outer fiber layer to the inner 
fiber layer. The intermediate fiber layer may be used when aluminum oxide 
fibers are used for the base fiber layer, and ytterbia is used as the 
outer fiber layer, since it is difficult to maintain a bond between 
ytterbia and alumina after thousands of cycles. If fibers other than 
aluminum oxide, such as yttria, are used for the base fiber layer, the 
intermediate layer may be omitted. When the intermediate layer is used, it 
preferably comprises any fiber material which is oxidation resistant and 
which bonds well to both alumina and ytterbia or alumina and holmium or 
mixed oxide fibers containing these materials or other suitable materials 
such as pure or doped uranium, thorium, ytterbium, gallium, yttrium, 
erbium, holmium, zirconium, chromium or other high-temperature oxide 
fibers. 
The outer fiber layer is preferably a high-temperature superemissive 
material. The superemitter comprises a material which has an inner 
electron shell vacancy which upon heating one inner electron below jumps 
into the hole as described in U.S. Pat. Nos. 4,906,178 and 4,793,799 and 
4,776,895, by one of the authors, i.e., perhaps by means of a 
photon-electron interaction. These patents are herein incorporated by 
reference. Materials suitable for use as the superemitter are zirconium, 
yttrium, ytterbium, holmium, thulium, cerium or thorium oxide fibers, or 
thorium-holmium, aluminum ytterbium-yttrium mixed oxide fibers, or 
mixtures thereof and other materials that emit radiation by an inner 
electron shell transition. The use of such materials increases the life, 
reduces corrosion, and changes the emissivity characteristics of the 
resultant burner to those desired for a variety of uses such as 
photovoltaic devices, cooking food, heating water, pumping lasers, 
reacting materials photochemically, etc. 
The method of fabricating such a burner is described below. Fiber may be 
manufactured or purchased. One manufacturing process is incorporated by 
reference to U.S. Pat. No. 4,758,003. Another method in which rayon fibers 
are chopped into short lengths (in the range of from about 1/2 to about 2 
cm) may also be used. The size of the fibers may be from less than 1 .mu.m 
to over 100 .mu.m in diameter. Smaller-diameter fibers are preferred for 
some applications, since they are more rapidly heated and cooled than are 
larger-diameter fibers. For example, to make alumina fiber a solution may 
be formulated with aluminum nitrate. To make superemitting fibers, a 
solution of ytterbium nitrate, yttrium nitrate, alumina and erbium nitrate 
are prepared. Any of the rare earth metal or other metal nitrates may be 
used in appropriate proportions to result in the desired compositions for 
a particular application. Preferably, the cut rayon fibers are impregnated 
with a solution that has concentrations of about 1 mg/ml comprising from 
about 80% to about 99.89% (wt/wt) Yb(NO.sub.3).sub.3.6HO.sub.2, from about 
0% to about 3% Er(NO.sub.3).sub.3, from about 0% to about 5% 
Ai(NO.sub.3).sub.3, and from about 0% to about 8% Y(NO.sub.3).sub.3. 
When the fibers are saturated, they are dried and then are treated with 
ammonia gas to reduce the nitrates. The ammonia reacts with the nitrate to 
form the hydroxide at about 25.degree. C. (+5.degree. or -5.degree. ) and 
20% to 80% relative humidity for several hours. In order to carbonize the 
rayon, the cut fibers are first dried and heated to about 60.degree. C. 
and then fired at several hundred degrees to slowly oxidize the carbon 
containing metal to gaseous products. 
The fibers are added to a specially prepared gel which serves as a ceramic 
binder and a transport medium for the vacuum or pressure forming process. 
One method for the gel preparation (used to suspend methylmethacrylate 
(MMA) and alumina fibers) is from an alumina "sol," which is partially 
reacted with Ai(NO.sub.3).sub.3 to form a viscous gel. The viscosity of 
this gel is important. The gel must be thick enough to suspend a 
relatively-large-porosity agent that is used in formulating the burner 
material. If the gel is too thick, it will entrap air bubbles, thereby 
producing burners of poor quality. Preferably, the viscosity is maintained 
so as to just suspend the fibers and MMA. 
One example of a gel is Gel #1, comprising Alumina Sol AL-20 (AL-20) 
supplied by Nyacol, a subsidiary of PQ Corp, water, and aluminum nitrate 
(60% Al(NO.sub.3).sub.3.9H.sub.2 O by weight solution from Mineral 
Research Corp.), and is prepared by adding about 200 ml of AL-20 per liter 
of water. The mixture is stirred for about 5 minutes, after which time 
about 42 ml of aluminum nitrate, for each liter of water, is slowly added 
to the diluted AL-20 solution, while the mixture is stirred, at the rate 
of about 1 ml/sec or less. After the addition of the aluminum nitrate is 
complete, alumina fibers sold under the trade name "SAFFIL", which may be 
purchased from ICI Americas Inc. of Wilmington, Delaware, may be added and 
a porosity agent is added. About 20 grams of alumina fibers are wetted 
with about one liter of liquid gel. (Changing this ratio has little effect 
on the properties of the burners produced from the fibers.) The wetted 
fibers are chopped and homogenized (from about 1 to about 12 hours of 
stirring time with a low-shear mixer generally produces the best cosmetic 
results) and then dispersed in the remaining liquid gel. About 3 grams of 
alumina fibers per liter of gel are used. 
A porosity agent is then added slowly to prevent clumping. A low-cost, 
water-insoluble subliming material may be used as the porosity agent. 
Methyl methacrylate (MMA) beads supplied by ICI Resins, produce code B728, 
are suitable as the porosity agent, as is camphor or any other 
non-soluble, subliming material. Bead sizes in the range of 400 to 25 mesh 
are suitable for practice of the invention. A bead size of about 40 mesh 
is preferred for low cost burners, since improved burner performance 
results from the use of a smaller bead size. A 100 to 200 mesh agent may 
be used in very high energy density burners and up to 400 mesh in 
recuperator central inward firing burners. A quantity of from about 30 to 
about 35 grams of MMA beads is added per liter of gel. The MMA beads 
initially float on the gel surface and must be folded into the liquid. The 
fibers and the MMA may be added independently of each other, and the order 
of addition seems to be unimportant. Once the components are mixed, the 
gel is ready to be formed into the shape required on the burner skeleton. 
Trapped air bubbles in the gel are undesirable and are removed by gentle 
agitation or by vibration of the gel. 
The burner skeleton comprises a porous material such as porous ceramics, 
punched metal or a stainless steel screen attached to a pipe or other 
structure. The structure is then attached to a vacuum source. The screen 
is dipped into a fiber suspension, and about 2 to 8 cm Hg of vacuum is 
applied to "pull" the solution onto the screen. A positive pressure can be 
used as long as there is sufficient pressure to provide aggregation of 
fiber and porosity agent and allowing the liquid to be pumped through. The 
vacuum pulls the fluid through the burner skeleton, while the screen acts 
like a filter. The fibers and the MMA are trapped on the surface of the 
burner blank, forming an alumina base layer. Most of the excess gel is 
drawn through the screen and captured in a separation tank. 
A small burner, such as a cylinder, about 30 cm long and about 6 cm O.D., 
having a power density of about 125,000 watts/m.sup.2 is formed in about 
10 seconds, while larger burners take longer. The skeleton coated in the 
base fiber layer is removed from the gel suspension and allowed to 
air-dry. The vacuum is maintained for about 10 to 15 seconds or more, to 
aid in the drying process. The used gel solution may be replenished by 
adding the appropriate amount of fiber and porosity agent. 
Alumina fibers, which in this embodiment of the invention form the base 
fibers of the burner, may be replaced with any fiber that can be 
mechanically or chemically bonded directly to ytterbia fibers, such as 
ceria, yttria, yttria alumina garnet, YAG, or mixed oxide fibers. If 
fibers other than alumina fibers are used, which bond directly to 
ytterbia, holmium, ceria/thoria, or mixtures thereof, then the step of 
adding yttria fibers, which in this embodiment of the invention form the 
intermediate fiber layer of the burner, and which are described below, may 
be omitted. 
The next step is to bond a thin layer of yttria fibers, which form the 
intermediate fiber layer, to the alumina fiber layer. The intermediate 
fiber layer provides a means of bonding the ytterbia fibers, the outer 
fiber layer, to the alumina fibers. Gel #2 is prepared by adding 1,000 ml 
of ammonium hydroxide to 1,000 grams of yttrium nitrate per liter of 
water, to produce an yttrium hydroxide gel. The porosity agent, about 30 
to 35 grams/liter, and about 3 grams of yttria fibers/liter are added to 
the yttrium hydroxide gel and are blended by a process similar to that 
described above for alumina fibers. A thin layer, about 0.1 to 1 mm, of 
yttria fibers is then formed onto the alumina base fibers by drawing the 
yttrium hydroxide gel through the burner in the same manner as described 
for the alumina gel. 
An alternative to using fibers such as yttria or a base layers is to coat 
the base fibers, such as alumina, with yttria or a layer of yttria and 
another layer of the emitting material, such as ytterbia containing 
material. Then the outer layer of fibers will bond to the coated base 
fiber. The process to coat the base fiber with one or more layers to 
enhance bonding of the outer fiber involves the use of soluble nitrate to 
coat the fiber by spray, dip or similar process. This coating process is 
the subject of a co-pending application. This coating is followed by 
drying and then a denitration process such as exposure to ammonia to form 
the hydroxide. The hydroxide is insoluble and may be bonded to directly, 
or the hydroxide may be partially or completely converted to the oxide 
first. 
The next step is to form the outer fiber layer. In one embodiment of the 
invention, the outer fiber layer comprises mainly ytterbia. Gel #3 is made 
by adding 1,000 ml ammonium hydroxide to 1,000 grams of ytterbia nitrate 
per liter of water, to form colloidal ytterbium hydroxide, which acts as a 
binder. The gel may be dilute so the gel just supports the MMA. About 12 
grams of ytterbia fibers per liter of ytterbium hydroxide gel are added. 
The fibers are blended, and about 30 to about 35 grams/liter of a porosity 
agent, such as MMA beads, is added. This mixture is then blended and air 
is removed. The burner skeleton containing alumina base and/or yttria 
intermediate fiber layers is immersed in Gel #3, and the ytterbium fiber 
layer is added as described above for the alumina fiber layer. After a few 
seconds, a layer of from about 2 to about 2.5 mm ytterbia fibers is 
formed, completing the porous ceramic fiber matrix. The outer fiber layer 
is preferably from about 1.5 to about 3.5 mm thick. 
The porous ceramic fiber matrix is dried at from about 60.degree. C. to 
about 80.degree. C. Once dry, the porous ceramic fiber matrix is heated to 
about 320.degree. C., to sublime the porosity agent. After about 90% or 
more of the porosity agent is removed (from about 1 to about 5 hours, 
depending on the size of the burner and the size of the porosity agent 
used), the temperature is slowly raised to about 500.degree. C., to set 
the ceramic binder. The outer ceramic may be heated to over 1500.degree. 
C., to "set" the colloidal ytterbia. The heating may be accomplished with 
a torch, as shown in FIG. 4A, or other suitable means, such as burning gas 
on the burner surface. Preheated air may be used to increase the fiber 
matrix temperature. In the case of cylindrical central firing focused 
burners with the ytterbia layer on the inside of the cylinder, reflected 
radiation from the burned gas will cause self-heating and bonding of the 
ytterbia fibers. This occurs very quickly with very little preheating 
required. 
While there is described the preparation of only one type of porous ceramic 
burner, other types, such as those for producing light, for pumping 
lasers, and so on, may be constructed. Different fiber layers being added 
to the surface of the base fiber to produce the desired effect, can also 
be made by practice of the invention. 
One novel application of the present invention is a cylindrical burner with 
the fiber matrix layers being added to the interior of the burner skeleton 
for use in a high flux water tube type boiler. 
FIGS. 3, 4A and 4B show high flux cylindrical outward firing burners, for 
example 330, 430, and 130 respectively, wherein the burners, in FIG. 3 and 
4A, are formed on metal skeletons, screen 260 and punched metal, 
respectively, by practice of the present invention. The fiber layer 236 is 
formed over the screen 260 in FIG. 3. Next an intermediate layer 220 and 
final layer of fiber 110 are formed as illustrated in FIG. 3. FIG. 4A 
shows the high temperature thermal processing 444 of the outer layer 10. 
FIG. 4B is a vacuum form on a porous skeleton made of ceramic foam 279, 
first forming the base 230, middle layer 220, and finally an outer 
emissive layer 110. 
FIGS. 5 and 6 illustrate a self-powered water tube boiler 650 comprising an 
outer distribution chamber 660 made from heat resistant metal or other 
suitable material. A porous material 620 and a plurality of inlets 606 are 
provided, e.g., a structural porous member 620 for the introduction of 
air/fuel mixture from the inlets 606 to the chamber to the inner shell. 
Air and fuel are premixed and fed into the outer chamber (660) by a blower 
or by other means. The air/fuel mixture is distributed into the chamber 
and flows into the inner burner surface consisting of the porous ceramic 
skeleton 620 and porous fiber matrix 610. 
The porous ceramic burner skeleton 620 comprises a material such as ceramic 
foam. Punched metal or a metal screen may also be used if the preheat 
temperature is less than the maximum available by that material. Attached 
to the support's inner surface is a base layer of fibers 610, such as 
aluminum fibers or an emissive fiber. The matrix consists of materials 
such as pure or mixed metal oxides of ytterbia, ceria, holmium, 
dysprosium, cobalt, chromium, and other spectral selective emitters, but 
not excluding black body emitters. 
On the other hand, the base fiber layer 610 may be bonded to an 
intermediate fiber layer not shown in FIGS. 5 and 6 (a material such as 
yttria). An emissive fiber layer may be bonded directly to the ceramic 
skeleton 610. The surface combustion heats the emissive fiber 610 to 
provide the desired radiation spectra. 
An ignition system (not shown) ignites the fuel/air mixture, and the fuel 
is combusted near the surface fiber layer of the porous ceramic burner. 
In a thermophotovoltaic device (one type of application), fibers contained 
within the inner most layer are heated sufficiently to produce radiant 
energy of a narrow wavelength band. The radiant energy passes through an 
optical filter 685 of material such as high temperature glass quartz, 
alumina or sapphire, which separates combustion gases from the 
photovoltaic device 666. The intense focused radiant energy is capable of 
high-efficiency conversion to electricity when concentration type TPV 
cells (666) are used. This thermophotovoltaic cogenerating device 
comprises a plurality of photovoltaic cells 666 attached to a support tube 
656 which contains a heat transfer fluid such as water, ammonia water or 
helium. 
Either a recuperator (shown in FIG. 7 as 703) or other method of increasing 
the temperature of the fiber may be used to heat the fiber to a much 
higher temperature than can be accomplished with room temperature air. 
Oxygen or oxygen enrichment (not shown) may be used either by itself or in 
combination with the recuperator. 
The cylindrical inner side firing is preferred for several applications 
such as thermophotovoltaic cogeneration, photochemical reaction, water 
heating, and other fluid heating, for example, for water heating. This 
design is less expensive because only one water tube need be constructed. 
The entire central firing focus matrix burner system unit is smaller 
because the higher energy density; less expensive to construct and 
simpler; less likely to be damaged because the fibers are protected by the 
outer shell and plates (not shown); and takes less floor space. The 
cylindrical central fired design also meets the low NO.sub.x requirements. 
FIG. 7 illustrates a side section of a photochemical reactor 730 of a 
central fired focus burner design. The fuel/air premix is fed by a blower, 
or other means, to the distribution chamber 777. The fuel/air mixture 
passes through the porous skeleton 799 into the fiber matrix 788, which 
consists of at least one layer of fibers. The fuel/air enters at 700 and 
combusts in a surface zone which may consist of special emissive fibers 
with a predetermined spectral character or a catalytic coating to reduce 
NO.sub.x or both such as La.sub.l Mn.sub.l O.sub.n, AlYCrPdO, AlYCrSmO, 
AlYCrNdO or similar materials. FIG. 7 shows a target material entering the 
intense photon zone (733) where photons 750 are directed upon the target 
material 727 flowing through the chamber and being converted to the 
product. The exhaust gases 795 are directed down and then up through the 
center of the reactor 730. 
FIG. 7 also illustrates the use of a recuperator 703 which may also contain 
a catalyst to reduce NO.sub.x. The exhaust passes through the recuperator 
703 and transfers energy to the fuel/air mixture to increase the 
temperature of the combustion zone and then through the radiation output 
750 to the exhaust 795. The recuperator may also be used to preheat the 
air to well above the autoignition point as implied in FIG. 8 below. 
FIGS. 8A and 8B illustrate a cylindrical inner-side central focused firing 
burner with fuel injection. The fuel is brought in to the fiber matrix 
combustion region by tubes 801, each of which contain small openings 809 
such as slots or holes to emit the gas. This distribution system allows 
for fuel injection. The fuel injection prevents preignition when the air 
is heated to above the autoignition temperature. 
An oxidant such as oxygen or air may be used at temperatures well above the 
ignition point, making recuperation and fuel injection efficient and 
practical. The recuperator, not shown in FIG. 8, may contain a catalytic 
surface which may be used to further reduce NO.sub.x. This surface may 
consist of a coating on the heat exchanger surface or a catalytic bed. 
Also the air may be replaced with or enriched with oxygen to further 
increase the temperature of combustion and the watts/m.sup.2 output of 
this design. The recuperator provides a method to significantly increase 
efficiency by recycling the energy in the exhaust products. 
Operation of the central focus firing cylindrical burner with fuel 
injection as depicted in FIGS. 8A and 8B is as follows. The hot oxidant 
881 enters the outer distribution chamber 880 having outer wall 895 via 
inlets 890 under pressure and flows through the porous structural member 
870 thus connecting holes or pores such as 875 to the fiber matrix 860 in 
which the fuel injection tubes 801 are located. The fuel enters the fiber 
matrix 860 through fuel injection tube holes 809. The exhaust products 
move through the exhaust chamber 818. The photovoltaic cells 830 are 
protected from the combustion products by a filter 850. The narrowband 
radiation passes through the filter 850 and focuses on the photovoltaic 
cells 830. A fluid 845 flows inside the heat exchanger tube 840 to cool 
the TPV cells 830 and provide thermal energy to some other source such as 
a heat pump, boiler, water heater, turbine, etc. 
Another application of the thermally amplified and stimulated emission 
radiator (THASER.TM.) is lighting. In the case of using the THASER.TM. for 
light production, an outside fired tube may be more appropriate. Another 
application not shown is cooking. In the case of cooking on a range, flat 
round shaped burners may be the most appropriate; however, there are both 
cooking and photon emitting applications in which the cylindrical inner 
firing concept may be used effectively. 
The photovoltaic cells are capable of efficiently capturing only 
wavelengths at or just above their band gap. In "gray body" radiators at 
1000.degree. C., the quantum efficiency is from about 4 to about 6 
percent, where quantum efficiency is defined as the ratio of the 
photo-generated carriers to the photon flux incident on the photovoltaic 
device. Three similar fiber matrix burners (outside firing cylinders 
similar to FIG. 3 about 30 cm long and about 7 cm in diameter) are 
compared below, at the same input of natural gas. Each was measured using 
the same photovoltaic panel. 
______________________________________ 
Material Power (watts) 
______________________________________ 
Ytterbia fibers 
9.90 
Alumina fibers 0.036 
Near-blackbody 0.336 
______________________________________ 
The comparison indicates that the superemitter burner produces about 30 
times more power than that of a near-blackbody burner. 
The advantages of the high-temperature ceramic material of the present 
invention are that they: (1) are relatively inexpensive to construct, (2) 
are strong, (3) are durable, (4) are highly porous, (5) produce low levels 
of NO.sub.x, (6) achieve high radiation power densities of desired 
spectral wavelengths(s), and (7) have high-temperature capability. 
The porous ceramic burners of the present invention are capable of a power 
density from as low as 60,000 watts/m.sup.2 to greater than 1,250,000 
watts/m.sup.2 while maintaining low NO.sub.x emissions. Oxygen may be 
substituted for air, in that case zero NO.sub.x is measured and the 
recuperator need only be very small, saving money. 
FIG. 10 illustrates a self-powered boiler deriving its electrical energy 
from photovoltaics (1111) placed on a small section of the heat exchanger 
tube 1100 near the center of the burner. This boiler/water heater may be 
designed with only one heat exchanger tube 1100, or more than one. The 
premix air/fuel 1400 enters the chamber 1255, passes through the structure 
skeleton 1600 , through the superemitting fiber matrix 1700, thereby 
heating the surface to provide incandescent superemitted radiation 1800. 
The radiation powers the TPV cells 1111 by passing through the heated 
barrier filter 1454. The heat exchanger 1100 may contain vertical fins, 
not shown. 
Other preferred embodiments of the invention are capable of delivering high 
photon fluxes. Selected wavelength bands may be used to match the silicon 
photovoltaic band gap of about 1,000 nm. The useful photon fluxes of the 
burners are many times those produced by conventional surface burners and 
may be easily delivered to a variety of targets, such as photovoltaic 
cells, chemical reactors, cooking, heating devices, and optical collection 
means for lighting or growing plants and pumping other devices such as 
lasers. High efficiencies of 10% to 60% in the wavelength bands that 
enhance plant growth promise to replace electric green house lamps. The 
mixtures of Ce(0.4% to 3%), Sm(0.5% to 5%) and thorium with ytterbium have 
been shown to produce the most intense light for growing crops, flowers, 
and plants and at the same time providing the required long life and 
durability under high temperature performance needed to produce the light 
with an efficiency over 4%. 
FIG. 9 schematically illustrates the Small-scale Managed Advanced 
Residential Thermophotovoltaic (SMART) energy system which interfaces with 
a thermal actuated heat pump. The SMART energy system is a method to 
dramatically reduce energy cost and reduce insults to the environment. The 
SMART energy system uses the principle of cogeneration; i.e., instead of 
using a central power plant that generates electricity and discards almost 
2/3 of its energy in the form of thermal pollution; the SMART energy 
system uses the thermal energy for space conditioning, hot water, and to 
meet other thermal requirements. 
The economics of this system depends on the proper sizing of thermal and 
electrical storage, so the thermophotovoltaic cogeneration can be sized as 
small as possible. A typical peak load of a home with a family of 4 is 
about 6 kilowatts; however, using an Advanced Managed Power System 
developed by William Wilhelm (formerly of Brookhaven National Laboratory, 
now President of Alkem Research and Technology), the thermophotovoltaic 
cogeneration unit may be reduced to a size that is competitive with the 
initial capital costs of conventional technologies. Some preliminary 
estimates from a study at Brookhaven National Laboratory show a 50% 
reduction in the current cost of electricity using the SMART energy 
system. The basic concept of electrical generation and storage appeared 
many years ago in a Brookhaven National Laboratory report dealing with 
fuel cells. A very similar system is shown in FIG. 9. 
The house with a SMART energy system is supplied with a fuel such as 
natural gas. The gas is converted to electric power and heat by means of a 
special cogenerator. This cogenerator uses thermophotovoltaic technology; 
i.e., by heating an emissive material to incandescence the electromagnetic 
radiation (light) produced is then converted to electricity by a direct 
conversion device such as a solar cell. The space heat from the process is 
used to provide thermal energy for a variety of applications such as to 
heat or cool and providing hot water. 
The brains of the SMART energy system is the Advanced Managed Power System 
developed by Bill Wilhelm. This management system makes it possible to 
reduce the size of the thermophotovoltaic (TPV) cogenerator from 6 kwe to 
about 0.5 kwe. This size reduction has a major impact on the economics. 
Preliminary estimates indicate about $0.50 to $1.00 per watt cost for the 
TPV cogenerator when sized at the 1000 watts electric level, 15% 
electrical efficiency, and overall efficiency above 75%. This overall 
efficiency is twice that from a typical power plant. The Advanced Managed 
Power System is the brains of the system, it stores some of the electrical 
energy in lead acid batteries (electrolyte starved type can handle 3,000 
deep cycles). The thermal energy from the TPV unit is also stored in a 
thermal storage system either hot or cold. The brain computes the amount 
of thermal storage to minimize energy consumption and manages the battery 
storage and withdrawal to maximize the battery system life. The SMART 
energy system is believed to have tremendous advantages over conventional 
energy systems which include a combination of power plant, furnace, hot 
water heater, etc. 
The advantages include: 
1. Conserve 1/2 of fuel 
2. Reduce insult to the environment 
3. Reduce electricity cost 
4. Reduce thermal energy cost 
5. Increase jobs in U.S.A. 
6. Decrease balance of payment problem 
7. Increase national security 
The benefits to the nations are so great that one can envision tax 
incentives to stimulate the small scale congeneration market. This 
technology will most certainly create many new jobs and industries in 
addition to expanding and revitalizing the lead industry (which is 
dominated by the U.S. lead mining and battery industry, as well as the 
American appliance industry). 
The above claims are based on an estimate of the efficiency of the TPV fuel 
injection central fired burner system which follows. The principle that 
electromagnetic emissions increase dramatically with temperature has been 
well established in physics by Stefan e.g. with the equation I.sub.(t) 
=.sigma..epsilon.T.sup.N when .sigma. is constant, .epsilon., the 
causivity, is a number between 0 and 1, and N equals 4 for a near 
blackbody. Using this principle, an estimate of power potential using data 
from a TPV water heater project is that 40 watts is attainable in this 
configuration without recuperation. Recovering some of the exhaust gas 
energy could raise the pre-combustion gas temperature to about 500.degree. 
C. and does not require fuel injection. The intensity of light emission 
goes up with the 10th power for similar materials. Nelson estimates that 
emission for ytterbia increases with the 8th power of temperature. We 
estimate that the emissive fibers are currently running at about 
1500.degree. K. If we assume that recuperation raises fiber temperature to 
1750.degree. K., an increase of 344% is calculated. In other words, 137.6 
watts would be attainable using the recuperation concept to raise the 
temperature and then the power output. 
The idea of inverting the burner system to central fire has two main 
benefits: it increases the ratio of emissive surface area to collector 
area, thus reducing the number of photovoltaics required because a higher 
photon flux can be obtained; and this configuration also lends itself to a 
more compact design which will cost less, take less space and be more 
durable. 
The TPV water heater project uses an emitter/collector pair that is based 
on silicon as the collection media because of its availability. A holmium 
emitter has shown the ability to produce more than twice of the absolute 
radiant intensity of the estimated ytterbia as shown in FIG. 1. The 
advanced photovoltaic materials (InGaAs) for this emitter are twice as 
efficient as silicon in converting ytterbia energy to electrical power. 
Using the 137.6 watts from FIG. 1 as a basis, 743 watts are estimated to 
be attainable using the advanced emitter/collector pair. 
The recuperation temperature of an air/fuel gas mixture is limited by its 
combustion temperature. For natural gas in air, this point is somewhere 
below 800.degree. C. In order to increase the emissive fiber temperature 
using recuperation, it is desirable to have the combustion air as hot as 
possible without preignition of the mixture. FIG. 8 depicts a 
configuration where natural gas is injected through porous tubes into the 
combustion zone. The recuperated air can then be 1000.degree. C. without 
fear of preignition. If we assume the emissive fibers are 250.degree. C. 
hotter than the situation in FIG. 6 that produced 743 watts, a possible 
2162 watts is calculated. The efficiency is over 20%. Careful electrical 
design of heat exchangers and heat pumps shown in FIG. 9 can lead to an 
overall efficiency of 60% to 70%, which is twice that of the power plant 
system. 
The above descriptions of exemplary embodiments of the preparation of a 
porous ceramic burner and the use of such burners are for illustrative 
purposes. Variations will be apparent to those skilled in the art. 
Therefore, the present invention is not intended to be limited to the 
particular embodiments described above. The scope of the invention is 
defined in part by the following claims.