Patent Publication Number: US-6210149-B1

Title: Pulse combustion system and method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of U.S. Provisional Application Ser. No. 60/086,697, filed May 26, 1998, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to pulse combustion, and more particularly, to a combustion chamber assembly for generating thermal and acoustic pulses and a resonant exhaust manifold system for propagation and application of the thermal and acoustic pulses to a material. 
     BACKGROUND OF THE INVENTION 
     Many industrial processes are effected to provide heat and mass transfer to a material. Increased rates of heat and mass transfer are desired to increase the efficiency and productivity of such processes. Applications for such processes include food processing, carpet and textiles manufacturing, packaging and sealing, wood fiber processing, glass forming, sheet metal forming, and drying, curing, baking, sintering and like heat treating processes for a wide range of materials and compositions. 
     Many such industrial processes are implemented by the use of a conveyor that moves the material through a space where it may be impinged or otherwise acted upon by a combustion system to accomplish the desired heat and mass transfer. One known arrangement provides an enclosure heated by a combustion system and having entrance and exit apertures for conveying material therethrough to direct and apply heat to the material, as illustrated by the drying and curing oven of U.S. Pat. No. 4,061,463 to Bennett. 
     Additionally, there are known combustion systems that provide a pulsating combustion cycle. The general operational principle of such pulse combustion systems is that a fuel/air mixture is ignited within a combustion chamber which increases the pressure therein resulting in exhaustion of the combustion products from the combustion chamber causing a subsequent pressure decrease which draws additional fuel and air into the combustion chamber for ignition, thereby setting up a cycle of pulsing detonations. 
     Such pulse combustion systems generally provide several advantages over most non-pulsating systems, including the advantages of self-aspiration and higher thermal efficiency of the process. These systems may be self-aspirating because the above described pressure fluctuations cyclically draw combustion material into the combustion chamber to sustain the combustion process. Therefore, a blower is not required for supplying air after start-up. Additionally, these systems may provide a higher thermal efficiency because the pulsating cycles create acoustic pulse waves that break down boundary layers and thus provide for greater heat and mass transfer rates. Also, thermal efficiency may be increased by the pulsating cycles producing a greater mixing of fuel and air and thus providing for a more complete burning of the combustion materials. 
     One known type of pulse combustion system provides two burners connected in parallel to an air intake, with each burner operating at a phase difference of 180 degrees from the other burner, as illustrated by U.S. Pat. No. 2,838,102 to Reimers, U.S. Pat. No. 4,808,107 to Yokoyama et al., and U.S. Pat. No. 4,840,558 to Saito et al. These systems commonly include a heat exchanger for. heat transfer to a fluid for use in applications such as water and oil heating. There are no known anti-phase type self-aspirating or forced air pulse combustion systems adapted for directing and applying thermal and/or acoustic energy to a material in a conveyor type application. 
     Another known type of pulse combustion system provides a spherical combustion chamber with an air intake tube extending radially into the combustion chamber to provide a more central point of combustion within the chamber, and a resonant exhaust tube extending from the chamber, as illustrated by U.S. Pat. No. 2,719,710 to Haag et al. and U.S. Pat. No. 4,260,361 to Huber. Such centralized point of combustion generally does not promote complete combustion within the combustion chamber prior to exhaust because such systems generally do not produce the desired turbulence achieved by a fully developed thermal and acoustic pulse wave. 
     Additionally, there is known the combustion system of Saito et al., as described above, and the gas furnace system disclosed in U.S. Pat. No. 3,540,710 to Urawa, that each provide a combustion chamber with tangential air intake orifices. Neither of these combustion systems, however, have a resonant exhaust pipe system that efficiently propagates an acoustic and/or thermal pulse wave for application to a material, provide a point of combustion within the combustion chamber that sets up and fully develops the desired turbulence of an acoustic and/or thermal pulse wave, nor provide a combustion chamber that advantageously directs an acoustic and/or thermal pulse wave toward such an exhaust pipe system. 
     An additional deficiency of many known pulse combustion systems is the complicated valve and/or control systems employed to control combustion and heat output by regulating the flow rate and ratio of air and fuel, as illustrated by U.S. Pat. No. 4,808,107 to Yokoyama et al. discussed heretofore. Such complicated valve systems are often difficult to maintain in proper adjustment and operating order. A further deficiency of many pulse combustion systems is that generally the systems are necessarily designed for a specific application such as water heating, because the combustion chamber and exhaust pipe must be specifically designed to set up the desired natural harmonic frequency at which the system should operate. 
     Accordingly, what is needed but not found in the prior art is a combustion system and method that embodies pulse combustion principles in an apparatus for conveyor type heat and mass transfer processes for achieving increased thermal efficiency and self-aspiration, that provides a combustion chamber for setting up and fully developing high turbulence, high velocity thermal and acoustic pulse waves, that provides a resonant exhaust piping system for propagating and directing without impeding the thermal and acoustic pulse waves to a material, that provides for temperature control without the need for a complicated valving and control system, and that has a design that is modular, simple, and cost-effective to manufacture and use for a variety of different applications. 
     SUMMARY OF THE INVENTION 
     Generally described, the present invention provides a pulse combustion system. A preferred embodiment of the present invention has at least one generally cylindrical combustion chamber having at least one endwall, at least one curved sidewall, and an exhaust outlet defined in the curved sidewall at a position generally proximate to the endwall. 
     At least one air conduit is preferably provided extending coaxially through the endwall of the combustion chamber and extending coaxially into the combustion chamber such that an outlet end of the air conduit is spaced apart from the exhaust pipe outlet to the combustion chamber. At least one fuel nozzle is preferably provided extending into the combustion chamber and spaced apart from the exhaust pipe outlet to the combustion chamber. At least one igniter is preferably provided associated with the combustion chamber. The spaced apart relationship of the air conduit outlet and the exhaust pipe outlet to the exhaust pipe outlet is preferably provided by the exhaust pipe outlet being arranged within a second half of the combustion chamber and the air conduit outlet and the fuel nozzle each arranged within a first half of the combustion chamber. 
     At least one resonant exhaust manifold is preferably provided having at least one primary exhaust pipe with a first end extending from the combustion chamber and in alignment with the exhaust outlet. The primary pipe comprises a distribution member, and the manifold includes a plurality of secondary exhaust pipes extending from the distribution member. At least one heat exchanger fin is preferably removably coupled to the primary exhaust pipe. 
     An enclosure is preferably provided generally disposed about the combustion chamber and exhaust pipes, the enclosure having at least one cooling air inlet, at least one cooling air outlet, and at least one partition interposed between the combustion chamber and the secondary exhaust pipes. A blower is preferably provided associated with the cooling air inlet of the enclosure. 
     In operation, fuel is entered into the combustion chamber through the fuel nozzle orifices, air is entered into the combustion chamber through the air conduit and mixes with the air, and the fuel/air mixture is ignited by the igniter to generate thermal and an acoustic pulse waves. The burning mixture expands in a helical swirl about the air conduit and along the length of the combustion chamber and then the burnt mixture/exhaust gas tangentially exhausts from the combustion chamber through the tangential primary exhaust pipe. The hot exhaust gas then propagates through the primary and the secondary exhaust pipes, and the hot exhaust gas exits from the outlet ends of the secondary pipes and is directed toward a material. 
     The present invention also provides a pulse combustion method of transferring heat to a material. The method preferably comprises the steps of forcing air through an axial conduit into a first half portion of an elongated cylindrical combustion chamber, injecting fuel into the first half portion of the combustion chamber wherein the fuel mixes with the air, igniting the fuel/air mixture generally within the first half portion of the combustion chamber such that the ignition of the combustion mixture generates thermal and acoustic pulse waves and the burning combustion mixture expands in a helical swirl about the air conduit and along a length of the elongated chamber from the first half of the combustion chamber toward a second half portion of the combustion chamber, exhausting the swirling burnt mixture from the combustion chamber in a tangential direction and into a primary resonant exhaust pipe attached tangentially thereto generally at the exhaust outlet of the chamber second half, propagating the thermal and acoustic pulse waves of the burnt mixture/exhaust gas through an angled distribution member of the primary resonant exhaust pipe, propagating the exhaust gasses through a plurality of secondary resonant exhaust pipes extending from the distribution member, and directing the exhaust gasses out of the secondary pipe outlet ends and toward a material, directing the thermal and acoustic pulse waves of the exhaust gas from the resonant exhaust pipe toward a material, and drawing a subsequent cycle of air through the axial conduit into the first half of the elongated cylindrical combustion chamber for sustaining cycles of a pulsating combustion. 
     Accordingly, it is an object of the present invention to provide a pulse combustion system for heat and mass transfer processes, the system having a design that is modular, simple and cost-effective to manufacture and use for a variety of different applications. 
     It is another object to provide a pulse combustion system that has a high thermal efficiency and is self-aspirating. 
     It is yet another object to provide a pulse combustion system that provides a combustion chamber with an off-center point of combustion for setting up a helical swirl of combustion gases along an axial length of the combustion chamber, and filly developing high turbulence, high velocity thermal and acoustic pulse waves associated with the swirling gases. 
     It is a further object to provide a pulse combustion system having an exhaust manifold with at least one primary exhaust pipe tangentially attached to the combustion chamber for exhausting the combustion gases from the chamber without impeding the associated thermal and acoustic pulse waves. 
     It is still another object to provide a pulse combustion system having an exhaust manifold with a plurality of secondary exhaust pipes extending from the primary exhaust pipe for propagating without impeding the thermal and acoustic pulse waves therethrough, and for directing and applying the thermal and acoustic pulse waves to a material. 
     It is a further object to provide a pulse combustion system having a plurality of thermal conductive fins removably coupled to the primary exhaust pipe, an enclosure with partitions therein forming air passageways therethrough, and a blower for directing air into the enclosure for temperature control of the combustion system. 
     These and other objects, features, and advantages of the present invention are discussed or apparent in the following detailed description of the invention, in conjunction with the accompanying drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features and advantages of the invention will be apparent from the attached drawings, in which like reference characters designate the same or similar parts throughout the figures, and in which: 
     FIG. 1 is a perspective view of a first preferred embodiment of the present invention; 
     FIG. 2 is a side view of the combustion chamber of the first preferred embodiment; 
     FIG. 3 is a side view of the fuel nozzle of the first preferred embodiment; 
     FIG. 4 is a side view of an alternate fuel nozzle of the first preferred embodiment; 
     FIG. 5 is a section view of the alternate fuel nozzle taken at line  5 — 5  of FIG. 4; 
     FIG. 6 is a side view of the combustion chamber and exhaust manifold of the first preferred embodiment; 
     FIG. 7 is a side view of an alternate exhaust manifold arrangement of the first preferred embodiment; 
     FIG. 8 is a detail perspective view of the secondary exhaust pipes of the exhaust manifold; 
     FIG. 9 is an end view of the combustion chamber and exhaust manifold of the first preferred embodiment; 
     FIG. 10 is an amplitude-time plot of an acoustic wave of the first preferred embodiment; 
     FIG. 11 is an end view of the combustion chamber and exhaust manifold of the first preferred embodiment; 
     FIG. 12 is a plan view of a sidewall of an enclosure of the first preferred embodiment; 
     FIG. 13 is an end view of an endwall of the enclosure of the first preferred embodiment; 
     FIG. 14 is a plan view of the enclosure of the first preferred embodiment; 
     FIG. 15 is a schematic of directed airflow for temperature control of the first preferred embodiment; 
     FIG. 16 is a perspective view of temperature control fins of the first preferred embodiment; 
     FIG. 17 is a detail perspective view of a fin of the first preferred embodiment; 
     FIG. 18 is a side view of a combustion chamber of a second preferred embodiment of the present invention; 
     FIG. 19 is a detail perspective view of a fuel nozzle of the second preferred embodiment; 
     FIG. 20 is a detail perspective view of an alternate fuel nozzle of the second preferred embodiment; 
     FIG. 21 is a perspective view of a combustion chamber and exhaust manifold of a third preferred embodiment of the present invention; 
     FIG. 22 is a side view of an alternate combustion chamber arrangement of the third preferred embodiment; 
     FIGS. 23-29 are side and end views of the operational sequence of the combustion chamber of the first preferred embodiment; 
     FIG. 30 is a side view of the first preferred embodiment showing its operation in a conveyor-type heat and mass transfer process; 
     FIG. 31 is an end view of the first preferred embodiment of FIG. 30; and, 
     FIG. 32 is a schematic of directed airflow for temperature control of the first preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 here and throughout, there is illustrated a first preferred embodiment of the pulse combustion system  10  of the present invention. The invention hereof will now be described in particularity and with reference to the corresponding figures. 
     Referring now to FIG. 2, there is provided a combustion chamber  12  for combusting fuel and air and for generating thermal and acoustic pulse waves. The chamber  12  generally has a first endwall  14 , a second endwall  16 , and a sidewall  18 , and is preferably elongated with a generally cylindrical shape. Optionally, the chamber  12  may be provided in an ellipsoidal, parabolic, spherical, conical, or other regular or irregular geometric shape such that at least a portion the sidewall  18  is curved. The chamber  12  is typically provided in a horizontal position, though the chamber  12  is freely arrangement in other configurations, one of which will be described hereinafter in a third embodiment. The chamber  12  may be constructed of a metal, ceramic, synthetic, or like high-heat resistant material, using fabrication techniques known by those skilled in the art. 
     Preferably, two chambers are provided in the combustion system  10 , shown in FIG. 1 as  12   a  and  12   b  and collectively referred to hereinafter as chamber  12 . Optionally, any number of chambers  12  may be incorporated into the system depending on the amount of heat transfer desired and the area over which the heat is to be directed. The size of the chamber  12  is selected based on the desired combined velocities of the thermal and acoustic pulse waves within the chamber  12  and the amount of heat to be delivered to the material. The chamber  12  has an interior length  20 , the midpoint of which may be thought of to divide the chamber into a first half portion  22  and a second half portion  24 . 
     An exhaust outlet  25  is provided in the second half  24  of the combustion chamber  12 . Preferably, the exhaust outlet  25  is defined in the sidewall  18  generally adjacent the first endwall  16  of the chamber  12 . The exhaust outlet  25  preferably allows for tangential attachment of an exhaust pipe, as described in detail hereinafter. 
     An ignitor  26  is provided preferably extending into or flush with an inner sidewall of the chamber  12 . The ignitor  26  preferably comprises a conventional spark plug with ignition wiring and controls. Optionally the ignitor  26  may be provided by a pilot burner, piezoelectric, electronic, or another ignition device known to those skilled in the art The ignitor  26  is preferably removably installed, for example, by providing a threaded portion that engages a threaded portion of the first endwall  14  or sidewall  18 . Optionally, the ignitor may be permanently installed, as may be preferable for a pilot burner. 
     The ignitor  26  is spaced apart from the exhaust outlet  25  of the second half  24  of the chamber, where the spaced apart relationship is preferably provided by the ignitor being positioned in the first half  22  of the chamber  12 . The exact location of the ignitor  26  is not critical, for example, the ignitor  26  may be positioned on most any portion of the first endwall  14  or the sidewall  18  of the combustion chamber  12 , or even positioned outside the combustion chamber  12 . 
     A flame sensor  28  is preferably provided that senses the presence of a flame in the combustion chamber  12 , and in the absence of a flame, cuts off fuel to the combustion chamber  12 . The flame sensor  28  is of a conventional type such as a high temperature metal alloy provided with a small sensing current, an ultra-violet sensor, or another flame sensor known to those skilled in the art. The flame sensor  28  is preferably positioned in the first half  22  of the chamber  12  generally proximate the ignitor  26 , but may be positioned in any location selected such that it may sense the presence of a flame. 
     An air conduit  30  is provided for intaking air into the combustion chamber  12 . The air conduit  30  is preferably tubular and extends through the second endwall  16  and coaxially at least partially into the chamber  12 . The air conduit has an inlet end  32  and an outlet end  34 . The inlet end  32  may be tapered outward and the outlet end  34  may be tapered inward in order to prevent a backflow of combustion products, to reduce sound emissions, and to increase the velocity and turbulence of the combustion products. The air conduit  30  is preferably provided without any movable constrictions therein such as valves or the like, thereby providing for a free flow of air through the conduit  30  into the chamber  12  to permit the pulsating combustion to freely draw air into the chamber  12  for sustaining the pulsating combustion. Optionally, the outlet end  34  may be provided with a surface having angled orifices defined therein or protuberances extending therefrom for inducing a rotary airflow from the conduit  30  into the chamber  12 , and/or the conduit  30  may have a generally rifled exterior surface, to promote a helical swirl about the air conduit  30  as described in more detail hereinafter. 
     The outlet end  34  of the air conduit is spaced apart from the exhaust outlet  25  of the second half  24  of the chamber  12 , where the spaced apart relationship is preferably provided by the outlet end  34  being positioned in the first half  22  of the chamber  12 . In other words, the air conduit  30  has a length  36  within the combustion chamber  12  that is preferably between about 50 to 100 percent of the length  20  of the combustion chamber  12 . Optimally, the air conduit  30  has a length  36  within the combustion chamber  12  that is preferably between about 70 to 75 percent of the length  20  of the combustion chamber  12 . The exact axial position of the outlet end  34  within the first half  22  is not critical. It should be noted that optionally the outlet end  25  may be arranged within the second half  24  of the chamber  12  with lesser, but nevertheless desirable pulsed combustion results. 
     In a pulse combustion system  10  having two horizontal combustion chambers  12 , the chambers  12  may be oriented such that the second endwalls  18  are face-to-face with the air conduits  30  in an oppositely faced and axially aligned position. Such an arrangement provides for reduced sound emissions and for anti-phase self-aspirating operation. 
     Referring now to FIGS. 2 and 3, a fuel nozzle  40  is preferably provided for steady state injection a fuel into the combustion chamber  12 . Orifices  42  are defined in the nozzle  40  for permitting the passage of fuel therethrough, with the size, arrangement and density selected based on the amount of fuel desired to be injected into the chamber  12 . The fuel nozzle  40  is preferably of a conventional type that is known in the art. The fuel nozzle  40  extends preferably through the first endwall  14 , or optionally through the sidewall  18 , into the chamber  12 . The fuel nozzle  40  may be removably installed by providing a threaded portion (not shown) that engages a mated threaded portion (not shown) of the first endwall  14  or sidewall  18 . 
     The fuel nozzle  40  is spaced apart from the exhaust outlet  25 , where the spaced apart relationship is preferably provided by the fuel nozzle  40  being positioned in the first half  22  of the chamber  12 . Thus, the air conduit outlet  34 , the fuel nozzle  40 , and the ignitor  26  are all arranged within the fist half  22  of the combustion chamber  12  such that fuel/air mixing and ignition thereof also occurs generally in the chamber first half  22 . This provides a point of combustion within the chamber  12  that is generally off-center and remote from the exhaust outlet  25 , allowing the ignited mixture to expand and bum to completion as the coaxial chamber  12  and air conduit  30  arrangement induce a helical swirl of the burning mixture about the air conduit  30  and along the length of the chamber  12  toward the exhaust outlet  25 . It should be noted the positional interrelationship between the air conduit outlet  34 , the fuel nozzle  40 , and the ignitor  26  within the chamber first half is not critical. 
     Different nozzles  40  each having different sized and arranged orifices  42  may be interchangeably used with the pulse combustion system  10 . The combustion system  10  may thereby utilize a variety of different gas and liquid fuels, including natural gas, liquid propane, oil and the like. Thus, a nozzle  40  having larger orifices  42  may used for providing a dispersion of a gas fuel, and then the combustion system  10  may be converted to burning a liquid fuel such as oil simply by installing a nozzle  40  having smaller orifices  42  with no other significant adjustment required to convert the combustion system  10  amongst various conventional fuels. The combustion system  10  may achieve similar resulting thermal and acoustic pulse waves with gas and liquid fuel, though a liquid fuel may tend to take longer to fully combust than a gas fuel in the same combustion chamber  12 . Referring to FIGS. 4 and 5, the fuel nozzle  40  may alternatively be provided with angled orifices  44 , preferably arranged with an axis thereof at an angle relative to a longitudinal and/or radial axis of the combustion chamber  12 . The angled orifices  44  provide for injecting fuel into the chamber  12  at a rotary angle to induce a rotary flow of the fuel/air mixture in the chamber  12  and thereby promote the helical swirl of the burning mixture about the air conduit  30 . 
     Turning now to the exhaust of the burnt fuel/air mixture, i.e., the hot exhaust gases, from the combustion chamber  12 , and referring to FIGS. 6-8, there is preferably provided an exhaust manifold  46  for exhausting the hot exhaust gasses from the chamber  12 . The exhaust manifold  46  preferably has a resonant primary exhaust pipe  48  with a first end  47  tangentially attached to the combustion chamber  12  at the exhaust outlet  25 . Such a tangential exhaust arrangement is particularly desirable when utilized in conjunction with the heretofore described combustion chamber because the tangentially arranged primary exhaust pipe  48  advantageously receives the helically swirling exhaust gasses without impeding the thermal and acoustic pulse waves associated therewith, thereby efficiently delivering the gas and pulse waves into the exhaust manifold  46 . 
     As described heretofore, the exhaust outlet  25  is arranged in a position generally adjacent the chamber second endwall  16  and is thus positioned generally offcenter and remote from the point of combustion. This arrangement allows the ignited fuel/air mixture to fully combust as it helically swirls along the length of the chamber  12 , and to set up and fully develop the associated thermal and acoustic waves prior to exhaustion from the chamber  12 . This arrangement thereby provides for increased thermal efficiency of the combustion process and also limits any backflow of the exhaust gases during a subsequent air intake cycle. 
     It is preferable to provide the primary exhaust pipe  48  of a high temperature resistant metal alloy such as stinless steel, though other high temperature resistant materials such as ceramics, synthetics or like may be employed as is known by those skilled in the art The primary exhaust pipe  48  may include one or more pipe angle portions  49  (best shown in FIGS. 1,  9  and  11 ), such as elbows or the like, for arranging the primary pipe  48  in the desired direction. Any such angle portions are preferably minimal in number and without acute angles. 
     The primary exhaust pipe  48  preferably includes a distribution member portion  50  having a plurality of spaced apart orifices  51  defined therein. The distribution member  50  allows propagation of the exhaust gases therethrough for a smooth dispersion over a wide area, without impeding the associated thermal and acoustic pulse waves. The distribution member  50  may be arranged at an angle  55  relative to the primary pipe  48  in order to achieve the desired dispersion area, which exact angle degree is not critical as long as it is not acute. The distribution member  50  may be provided in the shape of an inverted V, as shown in FIG.  6 . Optionally, the distribution member  50  may be provided as a single length of angled pipe, as shown in FIG. 7, or in like angled configurations. 
     A plurality of secondary exhaust pipes  52  are provided, each having an inlet end  53  and an outlet end  54 . Each inlet end  53  is attached to and extends from the distribution member  50 , and is in alignment with one of the orifices  51 . The outlet ends  54  direct the exhaust gases toward a material. The secondary exhaust pipes  52  may be substantially collateral and the outlet ends  54  may be substantially coplanar, though the pipes  52  may be provided in any regular or irregular arrangement as may be desired in a given application. At least one row of secondary pipes  52  is preferably provided, such as the two rows of secondary pipes  52  shown in FIG. 8, though any number rows may be provided as allowed by the size of the primary pipe  48  and based on the desired distribution area of and heat delivered from the directed exhaust gases. Where more than one row of secondary pipes  52  are provided, the rows may be staggered to provide for a uniform distribution area of exhaust gases. Optionally, the diameter, spacing, and uniformity of the secondary pipes  52  may be provided in other arrangements selected based on the desired distribution area of and heat delivered from the exhaust gases. 
     The primary pipe  48  and secondary pipes  52  preferably have a circular cross-section, though oval or the like cross-sectional shapes may be employed. In order to achieve the optimal efficient propagation of the pulse waves through the manifold  46 , the primary exhaust pipe  48  has a cross-sectional inlet area  56 , and the secondary exhaust pipes  52  have a cumulative cross-sectional outlet area  58  that is about equal to or greater than the primary exhaust pipe cross-sectional inlet area  56 , but no more than about 20 percent greater than same area  56 , and more preferably, less than about 10 percent. It should be noted that other relationships between the cross-sectional inlet area  56  and the cumulative cross-sectional outlet area  58  may be provided with lesser but nevertheless desirable benefits. 
     Referring to FIGS. 9-11, in order to further achieve the desired efficient resonant harmonic propagation of the pulse waves through the manifold  46 , the exhaust manifold  46  is preferably provided with specific lengths of primary and secondary piping  48 ,  52 . For example, it is preferable for the total average length  60  of the exhaust manifold  46 , which is defined as the length from the exhaust outlet  25  through the primary pipe  48  to the outlet end  54  of an average length secondary pipe  53  (see FIG. 9) to be generally about one quarter of a wavelength  62  of an acoustic pulse wave  64  (see FIG. 10) generated by the pulse combustion system  10 . Furthermore, it is preferable for the primary pipe  48  to have a length  68 , defined between the combustion chamber outlet  25  and the distribution member  50 , that is generally about two-thirds of the average total exhaust pipe length  60 . 
     Where the system  10  comprises a horizontally oriented combustion chamber  12  with multiple exhaust manifolds  46 , the primary pipe  48  may need to be asymmetrically arrangement with the chamber not centrally positioned therebetween in order to accomplish the preferred lengths  60 ,  68 , as shown in FIGS. 9 and 11. It should be noted that these dimensional criteria are suggested to provide optimal harmonic resonance and thus to propagate the pulse waves through the manifold with a minimum of impedance, but deviations therefrom may produce lesser though nevertheless desirable results. 
     Referring back to FIG. 1, an enclosure  70  may be provided for housing the combustion chamber  12  and exhaust manifold  46 , and is preferable for conveyor-type processes. The combustion system  10  when disposed within an enclosure  70  may thus be provided as a modular unit, with the number and size of modular units selected based on the desired heat output and the distribution area over which the heat output is desired to be applied. The size and shape of the enclosure  70  is selected to accommodate the number and size of chambers  12  provided in a particular combustion system  10  and as well as the number and size of exhaust manifolds  46  provided per chamber  12 . The enclosure  70  is preferably made of a rigid material such as a metal or composite using fabrication techniques known to those skilled in the art. 
     Turning now to temperature control of the pulse combustion system  10 , and referring generally to FIGS. 12-17, there is preferably provided a generally rectangular enclosure  70  having four sidewalls  72  and two endwalls  74 . A layer of insulation material  75  may be provided, such as fiberglass, a ceramic material, or a like non-flammable material with good insulation properties. The insulation layer  75  may line the enclosure  70  to substantially retain within the enclosure  70  the heat and noise generated by the combustion system  10 . 
     As shown in FIG. 12, at least one sidewall  72  has a plurality of apertures  76  defined therein in accordance with the number, shape, size, and location of the outlet ends  54  of the secondary exhaust pipes  52 , such that air is substantially sealed within the enclosure  70 . The apertures  76  may be defined in a single bottom sidewall, in two opposing sidewalls, or in other configurations as may be beneficial in a given application. 
     As shown in FIGS. 13-14, at least one endwall  74  has at least one air inlet  78  defined therein, with the number of air inlets  74  generally selected based on the number of aligned sets of exhaust manifolds  46 . At least one air outlet  80  is provided, preferably defined in the same endwall  74  as the air inlet  78 . At least one partition  82  is preferably provided within the enclosure  70 , and is coextensive with the vertical sidewalls  72  of the enclosure  70  except longitudinally where an opening  81  is provided adjacent an endwall  74  opposite from the air inlet  78  and outlet  80 . The partition  82  thereby compartmentalizes the enclosure to block the lateral movement of air within the enclosure  70  except through the airflow passageway formed by opening  81 . Any air entered through the air inlet  78  is thereby directed to flow across at least a part of the exhaust manifold  46 , through the opening  81 , across the combustion chamber  12 , and out of the enclosure  70  through the air outlet  80 . 
     Referring now to FIG. 15, a blower  84  or other positive pressure creating device may be connected to the air inlet  78  by ductwork or the like for forcing cooling air into the enclosure  70  in an airflow direction  86 . Temperature control of the exhaust gas and the heretofore described components of the combustion system  10  may thereby be provided by adjusting the volume flow rate of air from the blower  84  into the enclosure  70  and across the exhaust manifold  46  and combustion chamber  12 . One or more conventional temperature sensors  88  and control wiring as known in the art may be positioned within or without the enclosure  70  at various locations as desired for providing temperature feedback and control for adjusting the blower  84 . Also, a valve  90  or the like may be provided for redirecting a portion of the heated air out to another application or use, and a valve  92  or the like may be provided for redirecting heated air from another application into the enclosure air inlet  78  as preheated air. 
     Referring now to FIGS. 16-17, additional temperature control may be provided by at least one heat exchanger fin  96  removably coupled to the primary exhaust pipe  48  (which includes the distribution member  50 ). Any number of fins  96  may be provided as desired for temperature control and limited by the length of the primary pipe  48 . The fins  96  preferably have a concave curved portion  98  for receiving the tubular exhaust pipe  48 , and extended surfaces  100  therefrom providing an increased surface area for increased heat transfer. The removable couplings are preferably provided by conventional clamps or the like. It is desirable that the fins  96  be made of material having a greater thermal conductivity than the material of the primary pipe  48 . For example, the fins  96  may be provided of copper or aluminum where the primary pipe  48  is of stainless steel. 
     The combustion system  10  preferably includes for temperature control both the fins  96  and the enclosure  70  as described heretofore. Optionally, only the fins  96  or only the enclosure  70  may be provided. The enclosure  70  may be provided with a sidewall  72  that is removable for access to the fins  96  for removing or adding fins  96  as determined by the temperature requirements of a given application. 
     It should be noted that while the pulse combustion system  10  as described herein provides a manifold for directing the heat output toward a material in a conveyor-type application, the system  10  may be suitably provided in various other forms thereof. For example, the primary exhaust pipe  48  may optionally act as a heat exchanger for heat transfer to a fluid such as oil or water in which the exhaust pipe is immersed. Also, a single primary exhaust pipe  48  may direct the heat output toward a material without the use of a secondary exhaust pipe network, for example, in applications where it is desired to provide a focused high intensity heat output. 
     Referring now to FIG. 18, a second embodiment of the present pulse combustion system  103  comprises the pulse combustion system  10  described heretofore except having a modified introduction of fuel and air into a combustion chamber  101 . In this embodiment, a coaxial fuel/air conduit  102  extends coaxially into the chamber  101 . The coaxial fuel/air conduit  102  comprises a generally tubular air conduit  104  having an air inlet end  106  and an air outlet end  108 , and a generally tubular fuel conduit  110  having an fuel inlet end  112  and an air outlet end  114 . The fuel conduit  110  is generally concentrically disposed about the air conduit  104  such that the fuel conduit  110  and the air conduit  104  are radially spaced a sufficient amount to allow the passage therethrough of a desired flow of fuel. The fuel/air conduit  102  extends coaxially into the combustion chamber  101  such that the air outlet end  108  and the fuel outlet end  114  are spaced apart from an exhaust outlet  115  of the combustion chamber  101 , similar to the first embodiment as described heretofore. 
     Referring now to FIGS. 19 and 20, there are illustrated various arrangements of the fuel/air conduit  102  for introducing fuel into the chamber  12 . Generally, the fuel outlet end  114  of the fuel conduit  110  has an endwall  116  and a curved sidewall  118 . As shown in FIG. 18, a plurality of orifices  120  are preferably provided in the curved sidewall  118  generally adjacent the endwall  116  for injecting fuel generally radially into the chamber  12 . Optionally, as shown in FIG. 19, a plurality of orifices  122  may be provided in the endwall  116 , for injecting fuel generally longitudinally into the chamber  12 . It should be noted that both endwall and sidewall orifices  120 ,  122  may be combined into a single fuel/air conduit  102 , and additionally, any of these arrangements may be provided with the orifices  120 ,  122  angled relative to a longitudinal and/or radial axis of the elongated combustion chamber to induce a rotary flow of fuel therethrough to promote the helical swirl of the expanding, burning fuel/air mixture about and along the fuel/air conduit  102 , similar to the first embodiment described heretofore. Also, the orifices  120 ,  122  may be provided with sizes, shapes, spacing, density, and uniformity selected primarily based on the fuel type and rate desired to be used. 
     Referring now to FIG. 21, a third embodiment of the present pulse combustion system  123  comprises the combustion system  10  of the first embodiment except having a modified combustion chamber  124  incorporated into the system  10 . The combustion chamber  124  is generally arranged in a vertical or upright position, with a coaxial air conduit  126  extending generally upward or downward from the chamber  124 . Any number of exhaust manifolds  128  may be provided, preferably having the secondary exhaust pipes  129  generally collateral thereto. The exhaust manifolds  128  are thus generally equidistant from and symmetrical about the chamber  124 , an arrangement generally not be available with the horizontal combustion chamber  12  of the first embodiment. A greater number of combustion chambers  124  may be included in the modular unit because the lateral space required per chamber  124  is reduced, thereby providing for an increased total and/or intensity of heat output as may be desired in a given application. 
     Referring to FIG. 22, in the case where a system  10  or  123  is provided with two vertical or upright chambers  124 , the air conduits  126  may optionally have an angled portion  130  such that inlet ends  131  of the air conduits  126  are oppositely faced and axially aligned. Such an arrangement may provide for an anti-phase self-aspirating operation, as described heretofore in the first embodiment. 
     The operation of the pulse combustion system  10  will now be described in detail, with reference to FIGS. 23-32 and the component parts described heretofore. As shown in FIG. 23, fuel  132  is injected into the combustion chamber  12  through the fuel nozzle  40  and combustion air  134  is introduced into the chamber  12  through the air conduit  30 . As shown in FIG. 24, the fuel  132  and combustion air  134  mix in the first half  22  of the chamber  12  to form a fuel/air mixture  136 . As shown in FIG. 25, the fuel/air mixture  136  is detonated by a spark  138  from the spark plug ignitor  26  (or flame from a pilot ignitor) producing a burning fuel/air mixture  140  having an associated thermal and acoustic wave. As shown in FIG. 25, the burning fuel/air mixture  140  expands in a pulse along the length of the chamber  12 , with the cylindrical shape of the chamber  12  and the coaxial air conduit  30  inducing a helical swirl  142  about the conduit  30 . As shown in FIGS. 26 and 27, the burning fuel/air mixture  140  expands along the length of the chamber  12  in a toward the exhaust outlet  25 . 
     The air conduit outlet  34  and the fuel nozzle  40  are arranged within the first half  22  of the combustion chamber  12  such that mixing of the fuel  132  and combustion air  134 , and the ignition thereof, occur generally in the chamber first half  22 . This results in a point of combustion within the chamber  12  that is generally off-center and remote from the exhaust outlet  25 , providing the opportunity for the mixture  140  to fully burn and generally complete the combustion thereof within the combustion chamber  12 . The process as described thereby extracts substantially all the available energy content of the fuel  132  prior to exhausting the mixture  140  from the chamber  12  for increased thermal efficiency of the combustion system  10 . 
     Additionally, the thermal and acoustic pulse waves associated with the exploding mixture  140  provide turbulence which promotes a more complete mixing of the fuel  132  and combustion air  134 , and which results in a more complete combustion of the fuel/air mixture  136  for increased thermal efficiency. The elongated combustion chamber  12  further provides the opportunity to set up and fully develop high velocity, high amplitude thermal and acoustic pulse waves, the advantage of which will be further addressed hereinafter. 
     For startup of the combustion system  10 , the combustion air  134  is provided to the chamber  12  by the blower  84  forcing cooling air  150  into the enclosure  70  through the cooling air inlet  72 . Because the air conduit  30  is free of constrictions such as valves, a portion of the cooling air  150  is forced through the air conduit  30  into the chamber  12 . It should be noted that the flow rate of the cooling air  150  is not critical as long as at least some air is introduced into the chamber  12  for combustion. 
     After startup of the combustion system  10 , that is, after a few pulsed combustion cycles, the pressure reversals of the pulsating combustion achieve a sufficient magnitude such that the combustion process becomes self-aspirating, with combustion air  150  being drawn into the chamber  12  upon the pressure drop therein resulting from exhaust of the fully expanded and burnt fuel/air mire  136 . In an arrangement having two chambers  12  with oppositely faced and axially aligned air conduit inlets  32 , the combustion pulses will achieve an equilibrium anti-phase state, that is, with the pulse waves at a phase difference of 180 degrees, for more spontaneous acoustic pulsations and a smoother combustion to reduce sound emissions from the chamber  12  to the environment. 
     Referring still to FIGS. 28 and 29, the exhaust pipe end  47  extends tangentially from the combustion chamber  12  at the exhaust outlet  25 . As the helically swirling burning mixture  140  approaches the exhaust outlet  25 , the mixture will preferably completely burn prior to exhaustion from the chamber  12 , with the resulting heated exhaust gas  144  therefore containing thermal energy representing a high percentage of the available energy content of the fuel  132 . The tangential exhaust arrangement advantageously receives the helically swirling exhaust gas  144 , as the tangential exhaust pipe and the helically swirling exhaust gas  144  have the same rotational direction. 
     Turning now to the operation of the exhaust manifold  46 , and referring to FIGS. 30 and 31, the heated exhaust gases  144  and associated thermal and acoustic pulse waves, having been efficiently exhausted from the combustion chamber  12  by the tangential arrangement of the primary exhaust pipe end  47 , are delivered into the primary exhaust pipe  48  of the resonant exhaust manifold  46 . Because of the lengths  60 ,  68 , cross-sections  56 ,  58 , and angles  49 ,  55  selected for the primary and secondary exhaust piping  48 ,  52 , the pulse waves resonantly propagate through the exhaust manifold  46  with minimal impedance and losses therefrom. 
     The heated exhaust gases  144  are dispersed through the distribution member  50  into the secondary pipes  52  and exhausted therefrom in a direction toward a dispersion area of a material  146  on a conveyor system  148 . The resonant propagation of the thermal and acoustic pulse waves from the point of combustion to the point of application to the material  146  provides fully developed, high amplitude, high velocity, reversible thermal and acoustic pulse waves acting on the material  146 , thereby breaking down the boundary layer to permit the thermal energy to act more directly on the material  146 . Such boundary layer breakdown allows for a greater heat and mass transfer rate and as a consequence produces an increased thermal efficiency. 
     Turning now to the operation of the temperature control components, and referring to FIG. 32, temperature control of the exhaust gas  144  and the components of the combustion system  10  may be provided by adjusting the volume flow rate of cooling inlet air  150  into the enclosure  70  and across the exhaust manifold  46  and combustion chamber  12 . An increased volume flow rate of cooling inlet air  150  provides increased heat transfer from the manifold  46  to the cooling inlet air  150  to reduce the temperature of the exhaust gases  144 . An increased volume flow rate of cooling inlet air  150  also provides cooling of the combustion chamber  12  and exhaust manifold  46  to prevent overheating and premature failure therefrom. The flow rate of cooling inlet air  150  is adjusted by the blower  84 , which adjustments are made based on temperature feedback from the temperature sensors  88 . 
     The temperature control features described also provide increased thermal efficiency of the system  10  by recovering and utilizing waste heat from the cooling process described above. The cooling inlet air  150  from the blower  84  becomes heated by passing across the heated exhaust manifold  46 , and a portion of the heated air is drawn into the combustion chamber  12  through the air conduit  30  during each air intake cycle of the pulsating combustion process, thereby providing pre-heated air for combustion. The remaining heated air exits the enclosure  70  through the air outlet  80  as output air  152 , and all or a portion thereof may be directed back to the blower  84  as recirculated air  156 . The valve  90  may be provided for redirecting a portion of the heated output air  152  to another application or use as redirected air  154 . Also, the valve  92  may be provided for redirecting heated air  158  from other applications into the air input  150  stream for additional preheating of inlet air  150 . 
     Additional temperature control may be achieved by adding or removing the heat transfer fins  96 . In practice, the number and/or size of fins  96  is determined based on the specifications and system configuration for a given application, and then temperature control during operation of the system  10  is made by adjusting the volume and/or direction of airflow from the blower  84 . 
     It should be noted that for optimal performance the features described as the preferred embodiments herein are provided combined into the pulse combustion system  10 . It may also be desirable to provide the combustion chamber  12  for setting up and developing the helical swirl  142  of the burning mixture  140  with other exhaust arrangements. It may further be desirable to provide the tangential exhaust pipe  47  for a swirling mixture  140  set up by another type combustion chamber and delivered into another type exhaust system. The combustion chamber  12  and tangential exhaust pipe  47  may also be effectively utilized in an application for exchanging heat with a fluid, for example, in a hot water heater type application. Moreover, it may be desirable to provide the exhaust manifold  46  incorporated into another type combustion system. 
     For installation of the pulse combustion system  10 , the modular system  10  may be mounted by brackets or the like attached to the enclosure  70 . The modular system  10  may be mounted in any orientation as may be required by a given application. Any number of modular units may be provided, with the number and size of modular systems  10  selected based on the desired heat output and the distribution area over which the heat output is desired to be applied. It should be noted that, in contrast to many known combustion systems for conveyor type heat transfer processes, the enclosure  70  of the present invention is not an oven where material to be treated passes therethough, but rather is a modular unit that may be oriented in a wide variety of arrangements to direct heat in a desired direction over a desired dispersion area. 
     Accordingly, there are a number of advantages provided by the present invention. The present pulse combustion system  10  for heat and mass transfer processes provides a design that is modular, simple and cost-effective to manufacture and use for a variety of different applications. The system  10  produces a high thermal efficiency and is self-aspirating. 
     The present pulse combustion system  10  additionally provides a combustion chamber  12  with an off-center point of combustion that sets up a helical swirl  142  of burning fuel/air mixture  140  along an axial length of the combustion chamber  12 , and fully develops high turbulence, high velocity thermal and acoustic pulse waves associated with the exploding mixture  140 . 
     The present pulse combustion system  10  further provides an exhaust manifold  46  with at least one primary exhaust pipe  48  tangentially attached to the combustion chamber  12  for exhausting the burnt gases  144  from the chamber  12  without impeding the associated thermal and acoustic pulse waves. 
     The present pulse combustion system  10  still further provides an exhaust manifold  46  having a plurality of secondary exhaust pipes  52  extending from the primary exhaust pipe  48  for propagating without impeding the thermal and acoustic pulse waves therethrough, and for directing and applying the thermal and acoustic pulse waves to a material  146 . 
     The present pulse combustion system  10  additionally provides a plurality of thermal conductive fins  96  removably coupled to the primary exhaust pipe  48 , an enclosure  70  with partitions  82  therein forming passageways for airflow therethrough, and a blower  84  for directing air into the enclosure  70  for temperature control of the combustion system  10 . 
     While the invention has been described in connection with certain preferred embodiments, it is not intended to limit the scope of the invention to the particular forms set forth, but, on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the true spirit and scope of the invention as defined by the appended claims. All patents, applications and publications referred to herein are hereby incorporated by reference in their entirety.