US2715390A - Resonant intermittent combustion heater and system - Google Patents

Description

Aug. 16, 1955 w. TENNEY ETAL 2,715,390

RESONANT INTERMITTENT COMBUSTION HEATER AND SYSTEM 5 Sheets-Sheet 1 Filed July 18, 1950 WATER Fe'so STEAM 02 HOT WATER OUTLET --H 5 Fusl Irv/n- :III STARTING Am. //vvE/v-ro l V/L LIAML .7'ENNEY C'l/AEL E5 5. MAR/(6 JM M ATTORNEYS Aug. 16, 1955 w. L. TENNEY ETAL 2,715,390

RESONANT INTERMITTENT COMBUSTION HEATER AND SYSTEM Filed July 18, 1950 5 Sheets-Sheet 2 TAM On Her WATER OUTLET h A'rER INLET JVVENTOR'S W/LL MM L. 7L=N-EY CHARLES 15. MARKS 7 O MQQ B M ATTORNEYS Aug. 16, 1955 Filed July 18, 1950 W. L. TENNEY ET AL RESONANT INTERMITTENT COMBUSTION HEATER AND SYSTEM 5 Sheets-Sheet 5 AVVENTORS lA/lu. 1AM L- TENNEY CHAEL E5 5. MAB/(6 ATToB/V YS Aug. 16, 1955 w. L. TENNEY ETAL 2,715,390

RESONANT INTERMITTENT COMBUSTION HEATER AND SYSTEM Filed July 18, 1950 5 Sheets-Sheet 4 J N VEN TO R8 VVILLl/IM L .7Z.=-E Y CHARLES 5. MARKS ATTOBNE Y6 6, 1955 w. TENNEY ETAL 2,715,390

RESONANT INTERMITTENT COMBUSTION HEATER AND SYSTEM Filed July' l8, 1950 5 Sheets-Sheet 5 INVENTOR. W\LL\AM L. TENNEY CHARLES E. MARKS United States Patent 0 RESONANT INTERMITTENT CONIBUSTION HEATER AND SYSTEM William L. Tenney, Vandalia, Ohio, and Charles B. Marks, Dhahran, Saudi Arabia; said Marks assignor to said Tenney Application July 18, 150, Serial No. 174,498

8 Claims. (Cl. 122-24) This invention relates to resonant intermittent combustion heaters and systems wherein the primary heating element is a resonant, intermittent combustion type apparatus, the operating cycle of which is similar to that of the propulsive type of engine known as a pulse jet engine.

It is known that engines of the foregoing type are capable ofburning large amounts of fuel; and, in so doing, quickly produce intense heat. These engines consist essentially of an elongated tube, one end of which functions as a combustion chamber. The combustion chamber may be of the same diameter as the balance of the tube or of larger or smaller diameter. The operating theory of such engines has, to date, been the subject of controversy but it is known from practical engines, employed as propulsive units, that a charge of air and fuel introduced into the combustion chamber may be ignited by auxiliary means for starting, and thereafter ignition of the succeeding charges is carried out spontaneously.

The poducts of combustion formed in the combustion chamber have a temperature of the magnitude of at least 2000 F.; and, following ignition, flow at high speed through the balance of the tube which is known as the exhaust tube. A unique reaction thereupon takes place in this phase of the operation of the engine. The products of combustion from the initial explosion flow at high velocity through the exhaust tube but only a portion of thecombustion products from this initial explosion is expelled from the end of the exhaust tube with jet-like velocity. During the flow of combustion products described a new charge of air and fuel is being drawn into the combustion chamber. After the outward flow of combustion products from the initial explosion the direction of flow of the unexpelled portion of the combustion products reverses and this latter portion then flows toward the combustion chamber where it was formed. The reversal of flow is accompanied by a flow of fresh air into the exhaust tube from the exhaust end thereof. Following'th e reversed flow of combustion gases and the inflow of fresh air, the second charge of air and fuel drawn into the combustion chamber ignites spontaneously. When the second explosion takes place the combustion products from this second explosion likewise flow through the exhaust tube forcing the fresh air and the remaining combustion products from the first explosion toward the exhaust end of the tube with jet-like velocity. Still another charging of the combustion chamber and reversal of the flow of exhaust gases then occurs ashas been described above. The spontaneous ignition of new charges of air and fuel and the rapidly reversing flow of combustion products in the exhaust tube proceeds at substantially fixed frequency for any given pulse jet engine depending upon the design thereof, the operating cycle being dependent on resonant wave conditions controlled by the tube geometry. The charging, combustion, scavenging and exhaust processes are, therefore, cyclic in occurrence and resonant in origin. The exhausting of combustion products and fresh air at jet velocity from til) 2,?l5,39 Patented Aug. 16, 1355 the exhaust tube provides the thrust which renders the engine a propulsive unit.

The combustion heaters of this invention are similar to the resonant jet propulsion engines described above in that they employ the resonant cyclic operating principles of such engines but differ therefrom in structure, design and function. The resonant exhaust tubes of the devices of the present invention function as heating elements and are made with an extremely great length of diameter ratio, and may be curved or coiled as desired for purposes of compactness and directional heat radiation. The length of diameter ratio of the tubes is in the order of about 35/ l or more, resulting in diminution of the jet propulsion function and development of unique characteristics favorable to heater units.

Among the unique characteristics of these intermittent combustion devices having resonant exhaust tubes of greater length to diameter ratio than efficient for jet propulsion, is the suppression of the loud, sharp and irritating exhaust noise characteristics of pulse jet propulsion engines. The high exhaust tube length to diameter ratio of the heater units of the present invention, which serves to reduce the exhaust propulsive energy and convert it into useful heat, also reduces the exhaust sound energy. Reduction in sound level is, of course, essential for stationary devices such as heaters.

At the same time the intake valve endurance, when mechanical intake valves are used, is multiplied many times. The valve head arrangements shown in certain embodiments of this invention hereinafter disclosed result in a valve endurance in the order of 75 hours or more when used in combination with an exhaust tube length to diameter ratio in the order of 60 to 1. The valve endurance of the same valve head arrangement was found to be only a 1% to 2 hours when utilized with an exhaust tube of a 12 to 1 length to diameter ratio, or less, such as is utilized for jet propulsion efficiency. This increase in valve endurance is far out of proportion to that to be expected from the reduction in cycle frequency resulting from increased tube length. With an increase in tube length of approximately 5 times that required for jet propulsion efiiciency, and an accompanying decrease in cycle frequency to approximately one-fifth that of the jet propulsion engine, the valve endurance was multiplied in the order of 50 times.

With reference to valve endurance, it should be understood that the invention is not limited to the use of mechanical intake valves, but may employ air inertia or similar non-mechanical valve means such as suggested in our co-pending patent application Serial No. 661,363,

filed April 11, 1946, now Patent 2,612,749.

In addition to the advantages of reduced exhaust noise and greatly increased intake valve endurance as compared with pulse jet propulsion engines, the intermittent combustion heater units of the present invention exhibit many advantages over heaters of prior types. These advantages include extreme mechanical simplicity, light weight, low cost, compactness and portability, in combination with unusually high heating efficiency.

It is an object of the present invention, therefore, to provide heaters of extreme mechanical simplicity which can be fabricated largely of sheet metal at very low cost. It is also an object of the invention to provide light weight, portable and compact heater units.

It is a further and most important object of the invention to provide heaters capable of converting a maximum amount of the available heat energy of the fuel into useful heat.

The advantages of low cost mechanical simplicity, light weight and compactness are inherent in the automatic charging, ignition, and scavenging resulting from utilizais not uni-directional.

tion of the resonant intermittent combustion system described above.

The advantage of unusual efficiency results from the employment of certain characteristics of resonant intermittent combustion systems of the type described above, for purposes of improved heat transfer. In this invention a resonant intermittent combustion tube, which exhibits extremely rapid combustion, approaching the condition of combustion at constant volume, is utilized as the heat source.

The inherent advantages of high pressure combustion at constant volume are well known. This extremely rapid combustion, resulting in relatively high peak pressures, results in an extremely high velocity, highly turbulent flow of exhaust gases through the exhaust tube. Instead of constant burning in the combustion chamber a series of explosions takes place. The high temperature gases resulting from these explosions are then ex pelled through the exhaust tube with great force and velocity and in a highly turbulent state. high velocity, highly turbulent gases, with consequent scrubbing action of a maximum number of heated gas molecules'against the exhaut tube surface, results in greater efiiciency of heat transfer through the exhaust tube than is had with conventional methods. The exhaust tube is heated to extremely high temperatures, in the order of 1500 -2000 F., and radiates heat at a very high rate from its outer surface.

'In addition to the efficiency of heat transfer resulting from the scrubbing action of the highly turbulent, high velocity gases, there results another unusual characteristic not attainable in steady flow combustion heating devices. This characteristic, which also contributes to superiority of heat transfer through the exhaust tube,

results from the fact that the gas flow through the tube In a properly operating resonant intermittent combustion device of the nature de scribed there exists a reversal of gas flow in the tube following each explosion. This rapid, cyclic flow reversal not only creates turbulence but also brings at least a portion of the hot gases generated by each explosion in 'the combustion chamber into contact with portions of the tube not once but twice or three times. At least a portion of the gases scru the tube not only during their passage from the combustion chamber through the tube toward the exhaust outlet, but also during their reverse motion between each explosion, and again during their motion in the normal direction prior to final ejection. Due to the nature of this cyclic reversing flow process, the regenerative action produced by repeated exposure of given heated gas particles to given portions of the tube wall results in maximum recovery of heat from these particles within a minimum tube. length, with correspondingdy lower exhaust temperatures and higher efliciency of heat transfer through the tube wall.

Thus, the combustion heaters of this invention are similar to resonant jet propulsion engines in that they employ the resonant, cyclic operating principles of such engines but dilfer therefrom in that a high proportion of the available energy is converted into useful heat instead of propulsive energy. This result is attained by elongating the exhaust tube of a resonating type pulse jet engine to the point that its length to diameter ratio is such that the mean exhaust velocity is reduced below a level capable of producing worthwhile efiiciency as a jet propulsion unit. The engine thus modified ceases to be a thrust producing resonant pulse jet engine and becomes a resonant intermittent combustion heating device.

It is an obect of the present invention to provide a resonantintermittent combustion heater and more particularly to provide resonant intermittent combustion heaters and systems for producing quick, intense heat energy and for utilizing such heat energy. It is also an object of the invention to provide water and air heaters, radiant heaters, circulating water and air heaters and combined resonant intermittent combustion heaters and systems wherein no material thrust is developed or wherein only sufiicient thrust is produced to be utilized in the system for circulating the heated medium such as air or water.

Other and further objects of the invention are those inherent in the apparatus herein illustrated, described and claimed.

7 The invention is illustrated with reference to the drawings in which Figure 1 is a longitudinal sectional view of one form of the invention;

Figure 2 is a longitudinal sectional view of another form of the invention, particularly adapted for the production of steam or hot water;

Figure 3 is a longitudinal sectional view of another form of the invention utilized particularly as a space or radiant heater; 7

Figure 4 is a longitudinally sectional view of still another form of the invention particularly adapted for directional radiant heating;

Figure 5 is a longitudinally sectional view partly diagrammatic of a specific valve head unit and combustion chamber of an intermittent combustion heater system applicable to the heaters of this invention;

Figure 6 is a detail plan view of the heater unit valve employed in the valve head unit shown in Figure 5;

Figure 7 is a detail side elevational view partly in section of the fuel injection and air starting means employed in the valve head unit shown in Figure 5.

Throughout the drawings corresponding numerals refer to the same parts.

In all forms of the invention hereinafter more particularly described, the resonant combustion chamber fuel inlets, valve mechanisms and the like may be of any known or suitable type. As examples of the combustion chamber and valve mechanisms, fuel feeding inlets, etc., which may be utilized, reference is made to our copending application Ser. No. 649,882, filed February 25, 1946, entitled Pulse Jet Engine, now Patent No. 2,609,660. One of the forms shown in said application is illustrated in Figure 1 and it is understood that the same or any other appropriate form of resonant intermittent combustion chamber, valve mechanism, or one way restricted air inlet such as described in our copending application Ser. No. 661,363, filed April 11, 1946, entitled Pulse Jet, now Patent No. 2,612,749, fuel and air inlet, etc., may be utilized in each of the remaining forms of the invention.

Referring to Figure 1 there is illustrated a frame having tures 12 and an igniter hand hole aperture 13 through which a high tension ignition wire is attached to the igniter 14 for starting the unit. Upon the cylindrical tube 11 there is an internal hoop 16 having a flange 17 upon which the boiler shell 18 is mounted. The boiler 18 has a water feed inlet pipe 19 and a steam or hot water outlet pipe 20. A plurality of inlet and outlet pipes may be used, if desired. Into the boiler 18 there is built a cylindrical combustion chamber which is smoothly domed at 21 and connected to an exhaust tube heater element 22 which extends through the medium to be heated and finally extends to the exhaust tube 23 which may be exhausted to the air or to an exhaust flue, as desired. In the illustrated embodiment of the invention the tube 22 is in the form of a helix having a plurality of turns 24, although it is to be understood that the tube 22 may extend directly through the medium or have any desired curvature. The heating element or tube 22, taken in conjunction with the combustion chamber and the exhaust tube portion 23, functions as a resonant intermittent combustion system and the heating element tube preferably has a relatively large surface area, as compared to the volume of gases flowing therethrough, so as to provide an adequate heat transfer surface by which the heat of combustion is efliciently transferred to the medium to be heated. The length to diameter ratio of the tube which in this form of the invention includes both the heating element tube 22 and the exhaust tube 23 should be not less than about to l; and, preferably or to l or more, as will be discussed more fully below. If substantially no thrust is required for auxiliary purposes and space permits, length to diameter ratios of 200 to 400 to l or more may be used.

The combustion chamber wall extends downwardly at 25 and is closed by a valve plate 36. In the valve plate there are a plurality of valve ports 23 from which there are a plurality of downwardly extending and converging inlet holes 29 which as they converge together, intersect and extend in the form of a Venturi inlet tube at 30. Into the Venturi inlet tube there extends a fuel inlet pipe 31 which is mounted on the entrance mouth 32 of the Venturi. There is also provided starting air inlet pipe 33 which is positioned so as to direct a blast of starting air over the tip 34 of the fuel inlet pipe so as to provide a fuel-air mixture for initiating combustion. The valve 36 which rests lightly upon the valve plate or is positioned in very close proximity thereto and the valve clamping and supporting plate 37 are attached by means of a bolt 38. These parts of the apparatus may be of the type shown in said Patent No. 2,609,660, above} referred to, and will therefore not be further described. The valve mechanism may also be dispensed with and a one way restricted air inlet such as described in said Patent No. 2,612,749, be substituted. If desired, fuel and air may be introduced into the combustion chamber through separate inlets as is common practice in pulse jet propulsion engines. Combustion is initiated as described in said applications and the exhaust which contains intensely hot products of combustion is conveyed by way of tube 22 through the medium to be heated.

Referring to Figure 2 there is illustrated a modified form of the invention in which the combustion chamber, valve mechanism, and air and fuel inlet are as previously described. From the combustion chamber tube plate 41 there extend several relatively long and slender pipes 42 which terminate in the upper tube plate 43. The boiler shell 45 which is closed over the combustion chamber at 46 has an inlet 47 for the introduction of the medium being heated and an outlet 48 for the heated medium. The boiler shell extends upwardly to form the exhaust gas stack at 50. The operation is initiated and continued as previously described, whereupon the intensely heated products of combustion pass through the tubes 42 and heat the medium within the boiler. In this form of the invention, as required in the form shown in Figure 1, the length to the diameter ratio of the heater element pipes 42 should be not less than about 35 to 1. This ratio is based on the length and diameter of each individual tube 42.

In the apparatus shown in Figure 3 the combustion chamber is of the same type previously described except that it is provided with an exceedingly heavy wall 91- and the single resonant exhaust heater tube 93 having a passage 92 therethrough. The entire mechanism is supported by flange 95 from the exterior frame 96 which may be of any suitable type. Upwardly from the frame 96 there extends a protecting wire grill 98 to prevent accidental touching of the radiant heavy walled resonant exhaust tube 93. In operation the resonant intermittent combustion is started and combustion is continued long enough to raise the temperature of the heavy metallic body 91 and 93 to a high temperature such as red heat or incandescence, as desired. The resonant intermittent combustion system is then turned off. In order to permit preset timing the fuel supply may be by means of a small reservoir, not illustrated, which is simply filled full by a measuring cup. The resonant intermittent combustion is then initiated and continued until all the fuel is burned, the amount of fuel measured into the reservoir being previously determined as just sufficient to produce the prescribed amount of heat desired. The heavy metallic combustion chamber side wall 91 and the resonating heater element tube 93 then serve as radiators and give off heat over a considerable period of time. The unit is very useful in place of a salamander for space heating. This form of the invention, as are the previously disclosed forms of the invention, is a true resonant intermittent combustion heater wherein an intermittent fiow of hot, high velocity and highly turbulent exhaust gases occurs. The scrubbing action of hot exhaust gas particles on the inner surface of the heater element tubes enhanced by the high velocity and turbulence as well as the constant reversal of flow of such particles provides an efficient heat recovery system. The length to diameter ratio of the heater element tubes is, in each instance, not less than about 35 to 1 and is preferably 40 or 50 to 1 and may be as great as 600 to 1 or more. Within the upper limits of this range the thrust developed is negligible while in the lower limits of this range sufiicient thrust is developed to permit the use thereof for auxiliary or secondary purposes.

In Figure 4 the combustion chamber 99, valve mechanism and fuel feeding mechanism, not illustrated in Figure 4, are of any of the types previously referred to. From the upper end of the combustion chamber the exhaust resonant tube continues first along the curve 100 and thence along the open spiral via 101, 102, 103, 104, and thence to an exhaust at 106. The turns of the resonant heater element pipe are arranged to fit the approximate shape of a reflector, and if desired, a metal reflector may be attached to the heating unit as by welding at 111. Combustion in the resonant intermittent combustion heater is initiated and continued as long as is necessary to heat the resonant heater element tube 100 and the unit may be positioned by any suitable mounting bracket so that the larger portion of the heat produced by the unit is directed in a desired direction for best utilization.

In Figures l4 several representative types of resonant intermittent combustion heaters have been illustrated. It will be understood that various combinations of these types fall Within the scope of the invention. For example, the heavy walled space heater shown in Figure 3 may be employed with multiple tail pipes as shown in Figure 2, or the directional radiant heater shown in Figure 4 may employ the heavy walled construction with the resonant combustion operated only long enough to bring the heavy wall to the desired temperature following which resonant combustion is turned off and the heat collected in the heavy wall is given off by radiation.

It has been brought out hereinabove that an essential feature of this invention resides in the construction of a resonant heater element tube having a materially greater length to diameter ratio than that which is employed in eflicient resonant pulse jet propulsion engines. This important requirement provides for an efiicient recovery of the available energy in the form of heat which is transferred to the resonant heater element tube and becomes available for use; and, furthermore, results in a heater unit of the resonant type wherein the exhaust gases produce a negligible amount of thrust.

Theirnportance of this relationship has been established wherein it was found possible to cause a resonant intermittent combustion tube 50 feet in length, with 1% inch inside diameter giving a length to diameter ratio of 480 to l, to exhaust at 100 F. mean temperature while burning 5.6 lbs. of gasoline per hour, corresponding to a total heat release in the order of 110,000 B. t. u./hr. Tube surface temperatures in excess of 1600 F. were measured at the combustion chamber during this test, indicating combustion gas temperatures of 2,000 F. and higher prior to passage through the tube and consequent heat transfer. The differential between an initial tube temperature of 1600 F. and a final tube temperature of 100 F., with a heat input of 110,000 B. t. u./hr., demonstrates the tremendous quantity of heat radiated by the tubes of these heater units. A continuation of this test showed exhaust temperatures of 160 F. at 43 feet tube length (i/d=413 to 1), 230 F. at 33 feet tube length (1/d=317 to 1), 450 F. at 24 feet tube length (1/d=,230 to 1), and so on up to well over 1,000 F. at tube lengths of twofeet or less which give a measure of propulsive efficiency.

A very important feature of the invention lies in the possibility of choosing the most applicable tube length to diameter ratio in accordance with the demands of the application for which the unit is designed. Thus if maximum heat transfer through the tube is required, with minimum waste of heat in the exhaust, a tube of relatively great length to diameter ratio, such as 50 feet length and 1% inch diameter (l/d 480 to 1), will be chosen. If, on the other hand, it is desired to utilize a portion of the exhaust energy for driving auxiliaries such as air or fluid pumps, the tube length to diameter ratio is made correspondingly less in order to retain more energy in the exhaust available for auxiliary uses. A good example of this type of unit is a smoke or fog generator such as that disclosed in application Serial No. 111,308 filed August 19, 1949 of Wm. L. Tenney et al. for Machine for Producing Dispersions of Liquids in Air or Other Gases for the Production of Fogs which utilizes a tube length to diameter ratio in the order of 60:1 for the dual purpose of heating oil and air, and at the same time pumping engine and cabinet cooling air by means of av jet pump or exhaust aspirator. The same type of unit can be used as a hot air blower, using the exhaust gas energy to aspirate a flow of cooling air over the engine and cabinet surfaces and eject a blast of heated air mixed with combustion gases at the outlet end of the device.

It should be emphasized that in all cases of choice of tube length to diameter ratio for the purposes described herein, the ratio is made sufiiciently great so that the exhaust energy is of secondary importance, as for auxiliary use, or is negligible as when no use is to be made of the exhaust. The unit then, in either event for practical purposes, ceases to be a jet propulsion device and utilizes to advantage characteristics of the resonant intermittent combustion process in entirely different fashion than a jet propulsion device.

The line of demarcation between jet propulsion devices and devices of the nature described herein, therefore, lies in the increase of the tube length to diameter ratio which subordinates the jet propulsion function to provide the functions and advantages already described. Tests with a 1 /4 inch diameter exhaust tube and a 2% inch diameter combustion chamber have shown that the pounds of fuel consumed per pound of jet thrust per hour increase rapidly as the tube length to diameter ratio is increased beyond quite narrow limits. The efficiency as a jet propulsion device, of course, decreases correspondingly. In accordance with the tests conducted utilizing a 1% inch diameter exhaust tube, a length to diameter ratio in excess of about 35:1 showed such a marked loss in jet propulsive efficiency that it was out of the question to use such a unit as a jet propulsion device in comparison with length to diameter ratios of 12:1, and less. The increase in specific fuel consumption as measured in lbs. of fuel/lb. of thrust/hour was from 2.7 at the short length to diameter ratios to 3.8 at the 35:1 ratio. Conversely the efficiency as a heating unit was still good at length to diameter ratios as great as 500:1. Thus, an

exhaust tube length to diameter ratio of about, 35:1 may be considered in the range of the lower limit relating to this invention. The upper limit lies beyond 500:1, at whatever point, if any, that the resonant intermittent combustion process can no longer be sustained. There iii exists today no mathematical means by which this upper limit can be determined. I

The determination of exact length to diameter ratios is complicated by the fact that large diameter tubes have thus far, in practical tests, tended to develop best jet propulsive efliciencies at lesser length to diameter ratios than small diameter tubes. However, the lower limit of the length to diameter ratio in resonant intermittent combustion heaters may be taken at about 35 to 1. Another complicating fact in determining length of diameter ratios lies in that the combustion chamber can be made the same diameter as the exhaust tube, in which case there exists no line of demarcation between combustion chamber and exhaust tube from which to start measuring exhaust tube length to diameter ratios. Also, if an enlarged combustion chamber portion is used, it can be made of smaller capacity than necessary, in which case a portion of the fresh charge gases will be inducted into the exhaust tube. The length to diameter ratios herein described are, therefore, determined by measuring the separating point'between combustion chamber and exhaust tube based upon the combustion chamber volume at the intake end which is required to contain the fresh charge gases, and to consider the remainder of the tube as exhaust tube.

In Figure 5 there is shown a combined valve head unit and combustion chamber which may be connected with an exhaust tube to provide heaters of the type shown in Figures 1, 3 and 4. This specific combustion chamber and valve head unit when employed with an exhaust tube having a length of 5 feet and an inside diameter of 1.4" will liberate heat energy at the rate of 250,000 B. t. u. per hour or more, corresponding to a fuel consumption of 12.5 pounds or more of gasoline per hour. Referring to the drawing in detail the head 200 consists of a generally cylindrical finned member about 2 inches in diameter having a plurality of circular cooling fins 202. The cylindrical finned member 200 has a Venturi passage formed therein including an upstream portion 203 and a throat 204 of the Venturi. The throat 204 has a diameter of 0.920 inch. The outwardly flared downstream portion of the Venturi passage leads into ten circular passages 205 which diverge from the throat portion at an included angle of 25 degrees with respect to the longitudinal axis of the generally cylindrical member 200.

The passages 205 are about 0.328 inch in diameter and terminate in the end' of the cylindrical member 200 to provide ten circularly arranged equally spaced valve ports 206. A hole is also drilled along the longitudinal axis of the cylindrical memher 200 to provide a centrally located passage 207 which is internally threaded. A valve 208 formed of 0.006 inch blue tempered spring steel shaped to resemble a plurality of flower petals as shown in detail in Figure 6 is positioned on the end of the cylindrical member 200 with each petallike element thereof resting lightly on and covering one of said valve ports 206. A combined valve retainer and stop 1 209 opposed to the valve 208 rests on the center portion of the valve 208. The face of the member'209 opposed to the valve 208 is provided with a fiat surface adjacent the inner edge thereof which is adapted to clamp the solid central portion of the valve, and a curved surface adjacent the outer edge thereof which is adapted to control the curvature of the valve petals in their open position. This member is countersunk at the center thereof to receive a washer and an Allen screw which engages the threads in the upper end of the centrally located passage 207.

The fuel and starting air supplies are obtained from a central fuel injection stem 211 and an air blowpipe 212 which are shown in detail in Figure 7 The fuel.

injection stem 211 has a threaded cylindrical head 213 which is adapted to be secured in the threaded centrally located passage 207 and adjacent the head 213 there is provided a conically shaped enlarged portion 214, the sides of which blend with the walls of the passages 205. The injection stem 211 is drilled from the end remote with respect to the head 213 to provide a fuel passage 215 and fuel outlets 215a are provided in the fuel injection stem 211 at a point coinciding with the throat portion 204 of the Venturi passage. The lower portion of the fuel injection stem is enlarged to provide a step 211!) which is located below the fuel outlets 215a and over which air flows in passing through the valve head unit. The fuel passage 215 in the fuel injection stem 211 is internally threaded at the inlet end thereof to receive an externally threaded metering jet 216. The metering jet terminates in a frusto conical tip 216:! having a fuel metering orifice 216]; formed therein and the conical face of the metering jet engages and seals against the shoulder portion 211a formed in the passage within the stem 211. A web member 217 secured to the fuel stem supports the starting air blowpipe 212. The longitudinal axis of the fuel stem 211 coincides with that of the cylindrical member 200 while the longitudinal axis of the starting air blowpipe converges toward the cylindrical member longitudinal axis at an angle of about 36 degrees. The fuel outlets 215a are preferably located at a point about 0.25 inch above the level of the fuel in the fuel float chamber 211c which level is kept substantially constant by a float valve 211d. The air blowpipe 212 is threaded at the lowermost end thereof to permit connection to the outlet of any suitable source of air under pressure; such as, for example, a standard tire pump.

The side Wall of the cylindrical member 200 is threaded adjacent the valve supporting end thereof to receive a a ring 218 upon which is mounted the combustion chamher 219. The combustion chamber is about 10 inches in length and has an internal diameter of about 3.5 inches. This combustion chamber length is suitable for use with a heater exhaust tube of about 61 inches in length and 1.4 inches inside diameter. An alloy tubing of a thickness of about 0.049 inch is employed in making the combustion chamber which alloy is capable of withstanding temperatures of at least 2000 F. A locking ring 220 may be used to retain the combustion chamber 219 in engagement with the cylindrical head member 200. The side Wall of the chamber is drilled to receive a single wire spark plug 221. This ignition means is used to initiate the combustion of the first charge of fuel and air and is not employed after resonant combustion in the unit proceeds. A single wire spark plug is preferred since the wide gap between the end of the single wire and the shell portion of the plug provides a wide spark gap.

The uppermost end of the combustion chamber 219 terminates, preferably, in a hemispherical Wall or dome 222 and this is provided with an opening which leads to the heater exhaust tube 223. The latter consists of a tube of alloy metal having a wall thickness of about 0.049 inch and an internal diameter of 1.4 inch. The tube is formed of the same heat resistant alloy employed in the combustion chamber.

The above described valve head unit and combustion chamber may be provided with an exhaust tube to form a resonant intermittent combustion heater of the type shown in either Figures 1, 3 or 4 of the drawings. In operating these heaters fuel is allowed to flow from the float chamber 211]; into the central fuel injection stem 211. Starting air is then obtained from the blowpipe 212 by pumping air therethrough from any suitable means; such as, for example, a standard tire pump. The starting air fiows over the step 211k and over the fuel outlets 215a of the injection stem 211. The fuel is thus aspirated from the fuel outlets 215a and streams of fuel and starting air flow from the Venturi throat 204 into the downstream passage of the Venturi and thence through the several passages 205. The streams of fuel and starting air strike the petal portions of the valve 208 and bend these portions toward the curved face of the combined valve retainer and backstop member 209 thus opening the valve ports 206. The fuel and starting air which have begun to mix pass into the combustion chamber. The mixed fuel and starting air is then fired in the combustion chamber by the spark produced by the spark plug 221 which is connected to a high tension intermittent current. The valve 208 is then closed by combustion pressure leaving only the exhaust tube as a passage for the expanding products of combustion. The products of combustion then flow with high velocity through the exhaust tube. The high tension current may be stopped and the spark plug thus cut-out and the supply of starting air also turned off at this point. The combustion thereafter continues automatically. Thus, as the scavenging of the combustion chamber proceeds air is drawn into the valve head unit through the Venturi by a pumping action. This incoming air aspirates fuel from the fuel outlets 215a. The streams of air and fuel open the valve 208 and flow into the combustion chamber as described above in connection with the starting operation. The ignition of the second charge takes place automatically as does all that of all subsequent charges drawn into the combustion chamber. Throughout the operation of the heater combustion proceeds resonantly with automatic charging, ignition and scavenging and a pulsating flow of exhaust gases accompanied by cyclic reversals of flow of these gases is produced in the exhaust tube. A large proportion of the propulsive energy produced in these resonant intermittent combustion heaters is converted into heat that is recovered by the exhaust tube which functions as a heater element.

This application is a continuation-in-part of our c0- pending application Serial No. 661,364, filed April 11, 1946, and now abandoned.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that We do not limit ourselves to the specific embodiments herein except as defined by the appended claims.

We claim:

1. In a resonant intermittent combustion heater the combination comprising a combustion chamber having at least one inlet for air thereto; pressure responsive valve means for controlling the introduction of combustion air through said air inlet located in direct free communication and in direct pressure responsive relation with said combustion chamber for periodic automatic operation under the action of and in timed relation with the resonant pulsating action of the gases therein; at least one elongated exhaust tube heating element communicating at one end directly with said combustion chamber and at its other end with the surrounding atmosphere for free pulsating inward and outward flow therethrough of said gases, said exhaust tube being open at both ends in substantially free and unrestricted relation with said combustion chamber forming therewith integral parts of a system resonant in gases; means for introducing fuel into said combustion chamber, said exhaust tube heating element having a high length to diameter ratio of about 35 to 1 or more, forming with said combustion chamber a naturally resonant intermittent combustion system wherein automatic charging, ignition and scavenging occurs and a resonant pulsating flow of exhaust gases accompanied by cyclic reversals of flow of said gases is produced in said exhaust tube heating element and a large portion of the propulsive energy of said resonant intermittent combustion system is converted into heat that is transmitted by said combustion chamber and exhaust tube heating element.

2. A resonant intermittent combustion heater as set forth in claim 1 characterized in that the length to diameter ratio of the exhaust tube heating element is from about 35 to l to about 600 to 1.

3. In a resonant intermittent combustion heater the combination comprising a combustion chamber having an inlet for air at one end thereof; means for introducing fuel into said combustion chamber; pressure responsive means for controlling the introduction of combustion air through said air inlet located in direct free communication and in direct pressure responsive relation with said combustion chamber providing for substantially unrestricted periodic flow of air through said inlet into said combustion chamber under the action of, and in timed relation with, the resonant pulsating action of gases in said system while substantially preventing reverse flow of said gases therefrom; an elongated exhaust tube heating element opening at one end in unrestricted relation into said combustion chamber in spaced relation with said air inlet and forming with said combustion chamber integral parts of a self-contained system resonant in gases; the opposite end of said exhaust tube heating element opening freely to the atmosphere and adapting said tube element for the rapidly reversing inward and outward resonant flow of the gases therethrough; said exhaust tube heating element having high length to diameter ratio of about 35 to 1 or more forming with said combustion chamber a naturally resonant intermittent combustion system wherein automatic charging, ignition and scavenging occurs and a resonant pulsating flow of exhaust gases accompanied by cyclic reversals of flow of said gases is produced in said exhaust tube heating element and a large portion of the propulsive energy of said resonant intermittent combustion system is converted into heat that is transmitted by said combustion chamber and exhaust tube heating element.

4. A resonant intermittent combustion heater as set forth in claim 3 characterized in that said exhaust tube heater element is coiled to conform to a curved surface and wherein a curved radiant heat reflecting member is mounted adjacent said coiled exhaust tube heater element.

5. A resonant intermittent combustion heater as set forth in claim 3 characterized in that a jacket having an inlet and an outlet is positioned around said exhaust tube heater element and a portion of said combustion chamber whereby a fluid to be heated may be conducted through said jacket and over said exhaust tube and combustion chamber heater element.

6. A resonant intermittent combustion heater as set forth in claim 3 characterized in that said combustion chamber and exhaust tube heater element are formed of a tube having massive side wall thickness so as to have a large thermal capacity.

7. A resonant intermittent combustion heater as set forth in claim 3' characterized in that said exhaust tube heater element is coiled in a plurality of coils one adjacent another achieving a compact heat dissipating unit.

8. A resonant intermittent combustion heater as set forth in claim 3 characterized in that there is a metal reflector around the heating unit tending to confine and reflect the heat therefrom.

References ited in the file of this patent UNITED STATES PATENTS Re. 17,098 Miner, Jr. Oct. 9, 1928 974,166 Maxim Nov. 1, 1910 1,628,341 Towles et a1. May 10, 1927 1,714,843 Brown et a1 May 28, 1929 1,801,007 Jezler Apr. 4, 1931 1,935,659 Noack Nov. 21, 1933 1,948,540 Noack Feb. 27, 1934 1,953,213 Christensen Apr; 3, 1934 1,974,177 Doucha Sept. 18, 1934 1,986,561 Davis Ian. 1,1935. 2,008,528 Warren July 16, 1935 2,122,280 Diedrich June 28, 1938 2,218,422 Haddock Oct. 15, 1940 2,223,856 Price Dec. 3, 1940 2,227,666 Noack Jan. 7, 1941 2,348,767 Walker et al May 16, 1944 2,414,828 McCollum Jan. 28, 1947 2,496,351 Mazzoni Feb. 7, 1950 2,508,396 Jordan May 23, 1950 2,581,669 Kadenacy Ian. 8, 1952 2,618,246 Rostek 2 Nov. 18, 1952 2,619,941 Rydberg Dec. 2, 1952 FOREIGN PATENTS 436,681 Great Britain Oct. 16, 1935 597,915

Great Britain M Feb. 5, 1948

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