US2644512A - Burner device having heat exchange and gas flow control means for maintaining pyrophoric ignition therein - Google Patents

Description

lgURR ET AL July 7, 1953 BURNER DEVICE HAVING HEA EXCHANGE AND GAS FLOW CONTROL MEANS FOR MAINTAINING PYROPHORIGIGNITION THEREIN Filed June 7, 1950 INKENTORS WFJJTER BUR-T2 Patented July 7, 1953 BURNER'DEVICE HAVING HEAT EXCHANGE AND GAS FLOW CONTROL MEANS F OR MAINTAINING PYROPHORIC IGNITION THEREIN Walter Diirr, Ludwig Hu her, and Franz Haag,

Uberlingen, Germany assignors to Heizmotoren-Gesellschaft- Uberlingen am Bodensee, Germany,a;German corporation Application June 7, 1950', Serial N o.1 '66,611 In Germany June 13, 194 9 20 Claims.

This invention relates to a burner device having a combustion chamber, an inlet for'injecting fuel charges thereinto for combustion therein, and having a valveless'exhaust duct connected with the combustion chamber, forming therewith an acoustic resonator which is excited by the combustions periodically or intermittently produced therein. The particular object of the invention is toprovide in such a burner heatexchangeand gas-flow control means for promoting and maintaining intermittent ignition of I the fuel charges injectedinto the combustion chamber.

Burners of the type noted above are applicable for heating purposesand may be operated with gaseous fuel or with vaporized liquid fuel. There is a check valve, which admits fuel into the combustion chamber during the decompression phase following each combustion, the check valve being provided within a short inlet conduit to protect it against excessive heating. I

It is desirable, in order to keep the .cycle of the combustions in resonance with the thermally dependent acoustic frequency-assuming suitable cooling of the combustion chamber and the associated exhaust duct'to ignite by extraneous means, e. g., by electric ignition, only thei'irst fuel charge, and to 'maintain'the resulting oscil- 1 lation by back coupling in such'a'way that the reacting residual exhaust gases surgingback from the exhaust duct intothe combustion chain bar after each combustion'cycle cause the igcordance with theparticular form of the inlet neck and of the combustion chamber, as well as in accordance with the heat distribution therein and the combustion temperature of the fuel mixture, all of which are affected by the position of the exhaust conduit. w

The heat-exchange member absorbs heat incident to each combustion cycle, especially at its free end, the heat being conducted to its base, and thereby'being transferred to the fresh fuel mixture admitted during the decompression or suction phase of the burner. The incoming fuel mixture flows along the heated surface of the heat-exchange member in the direction of in-. creasing temperature thereof and is thus preheated to condition it'for ready reaction and ignition. At the same time the fuel mixture is moved toward the walls of the inlet'neck by thermal expansion, and a low gas pressure zone therefore results in direct proximity to the hot' ignition element of theheat-exchange member, in which the mixture cannot ignite, due to insufficient gas pressure, in spite of the high point temperature thereof. This second effect is particularly important and may bev augmented by the provision, ahead of the hot ignition element nition of the succeeding fuel charges meanwhile I supplied thereto. Howeve g the reacting exhaust gases do not alwayshave the temperature reuuired for the ignition ofanorma1 fuel mixture, particularly at low outside temperatures, and'the ignition frequently fails.

1 The invention overcomes this clifficulty and makes it possible to ignite a fresh fuel charge in the combustion chamber by the reacting exhaust gases, even following a cycle of complete combustion, and to maintain thereby automatically the acoustic oscillation, once it has been initiated,

which follows all fluctuations of the resonance frequency. 7 t

The invention employs for this purpose a heat conductive heat-exchange member which projects into the channel formed by the inlet neck vof the device, such member terminating in an exposed ignition element or point which is so dimensioned and approximated to the combustion space that it assumes in operation a temperature lying within a range from about 600 to 1000 C. The length and position of theheat-exchange "member must of course be proportioned in 'acor point of the heat-exchange member, of a deflector, carried thereby which may take-the form of asuitable shield or of a structure which causes thefuel mixture to eddy or to gyrate with respectto the hot ignition point. At'the moment whenthe reacting gases surge back from the ex-.

. haust duct and enter the burned chamber, they compress the preheated highly explosive fuel mixturetherein. By properly proportioning the flow conditions, it is possible to'concentrate the fuel mixture indirect proximity to the hot'ignition point of the heat-exchange member. The ignition of the preheated fuelmixture which has thus been preconditioned for reaction, is in this manner initiated with certainty, and by correct back coupling in proper phase, so that succeeding combustion cycles assume the'chara cter of 'a stable, undamped-oscillation whose periodicity follows automatically all fluctuations of .the resonance frequency that may be caused by thermal or other conditions, and whose amplitude is therefore not noticeably affected by such conditions. I

The inlet'neck of the device thus functions in the nature of a fuel-mixing and fuel-condition- 'ing tube whichterminates in the combustion chamber. v I

The invention will be described below'with reference to the accompanying drawings showing embodiments thereof, to give examples. drawings,

Fig. 1 shows a diagrammatic embodiment of a burner made in accordance with the invention;

Fig. 2 illustrates in diagrammatic representation an embodiment having a modified combustion chamber;

Fig. 3 shows in diagrammatic form 'a further embodiment; v t

Fig. 4 illustrates a heat-exchange element which also functions as a hot wire plug for igniting the first fuel charge; and c Fig. 5 represents in partially elevationalfand partially sectional diagrammatic view an embodiment having an inlet and a combustion chamber of preferred form and employing the hot wire plug illustrated in Fig. 4.

The device shown in Fig. 1 comprises means forming the combustion chamber I which ispro In the vided with the inlet duct 3 having an air inlet controlled by a check valve 2 and carrying a fuel inlet nozzle 4. The inlet 3 thus operates in the manner of a fuel-mixing tube which terminates in the combustion chamber I. From the combustion chamber extends the exhaust tube 5. The exhaust tube 5 and the combustion chamber I thus form a Helmholtzresonatorwith definable resonance frequency which is within a range from 50 to 200 cycles per second.

The combustion chamber l is initially supplied I with a fuel charge, 'e. g., by means of a small hand pump, and such charge 'is ignited by means of the spark plug 8 to cause the first combustion cycle. The check valve 2 closes incident tosuch combustion. The combustion gases are at the fSuctionis at thesame time eff-ectiveto cause the gas; plug in 'th'e'exhaust tube 5 to re'act and, due

to its inertia, tomove inwardly with increasing "velocity; The-duration of this phase of thec'scillation isfdetermined by the-resonance frequency of the resonator. The succeeding combustion *cycles must take placein phase-correctrelationship. 7 p

flnaccor dance with the invention, the'next and all following combusticns are-not initiated by the 'sparli'plug 6,;but by the heat-exchange means which comprises a copper rod '7 disposed within the mixing tube; "and carrying a nickel filament 8 which may form a loopor rnay support a ball forming an'ignition'point. This ignition point isheated tO"flO m" 600 to lOOiP -C inr'espons'e to the combustion of the first fuel charge and trans- "fers-heat to the rod 1, the latter thus being preheated and giving'up the heat to the freshfu'el rnixture so that the latter is preheated on its path to the combustion chamber for reaction and ignition therein. The fuel mixture is at the same time driven by thermal expansion in lateral direction'along the wall of the inlet and'mixing tube 3 towardthe chamber l, as indicated by the dotted lines thereby producing a low pressure cone around the ignition point 8. The gas density in this low pressure zone is insufficient for ignition. But whenthe reacting exhaust gases surge from the exhaust tube 5 inwardly, during the succeeding compression phase, in the direc'-' tion of the full-line arrows, they crowd the fresh fuel mixture, as indicated by the radially inwardly directed arrows at the end of the dotted lines, compressing it in direct proximity to the ignition point 8, causing ignition of the fuel charge exactly at the right moment, with the charge fully in readiness for reaction and combustion.

The operation described above may be effected and improved by the provision of a shield 9 with or without the angular surfaces H3, as shown in Fig; '2', to cause deflection and/or gyrationof the incoming fuel mixture, entering in the direction of the arrow A, relative to the ignition point 8.

The compression of the fuel charge about the ignition body 8 under the action of the exhaust gases reacting inwardly, as described, may be improved by annularly constricting the wall of the combustion chamber, as shown in the figure, 'thusproducing in effect a subchambcr or pocket in which the fresh charge of the fuel mixture is compelled to flow first arcuately about the ignition body it, ready for compression toward such body by the reacting-exhaust-gases to effect ignition within the pocket of the combustion chamber.

Considerable amounts of heat must be transferred from the heat-conductive heat-exchange member 7 to the incoming fresh fuel charges,

' especially in the case of heavy iuel'oils, so as to cause proper preheating and conditioning thereof. In order to meet this requirement, a portion of the inlet and mixing tube may be formed to project into the combustion chamber in the manner of a tubular extension, as indicated in Fig. 8 at 3a, so as to cause preheating of its walls. This ieatureprevents an undesired rapid temperature drop of the heat-exchange device. particularly in back of its i nition point, and forms additional means for preheating the incoming fuel charges. The preheating may be further improved by wholly'or partially omitting the portion or" the heat-exchange member 1 which lies between the valve '2 and the shield 9,'and carrying the exchange member instead upon a bridge *or "yoke disposed across the inlet and mixing tube.

Theheat-e'xchange member is-s'hownin Fig. 3

in the form ofahollow tubular element ib which is closedat its inner end. Thehe'a't-capacity of the he'at.-' exchange element is in this manner reduced; causing Quicker heating and concentrating the heat at thelsuriace thereof. "Thestructureals'o gives the possibility of heating the-end il in the f'rnanner of 'a-g'low hea'd, to obtain the starter the ignition. The 'e'ridti is forthis purpose preferably depressed axially inwardly, as shown. The walls of "thetubular inerhbe'rWb may-be twisted or grooved, as shown, to increase the heatfe'xcha'ng'e surfaces and'at the sam'e't'ime causing theruerharges to ttvistor 'gyrate prior to admission into the combustion "or burner chamber,

The'inlet 'offanyfof-the embodiments includ-= ing the extension (is projecting "into "the cam bustion chamber may be provided with a riblilze wall, or'ribs may be 'suitablysecured thereto in I order to increasethe eiiective heat exchange-and thus improving the preheating of the'fuel charges.

The heat exchange means" may be combined with a hot wireplug, and the ignition portion of the device maybem ade in the form of an incandescent element, to ior'm a particularly suitable'embodiment which is shown in diagrammati'c' perspective View in "Fig. 4. iAsshownfthe metallic rod carries an insulating member Hi from which projects the incandescent filament :rod IS in the manner of a spiral, and thus also operates as a deflector for the incoming fuel charge, corresponding inthis respect to the function of the angular winglike surfaces in Fig. 2. The insulating head I6 operates in the manner of the shield 9 shown in Fig. 2, and therefore prevents direct axial flow of the incoming fuel charge to and upon the ignition wire 11. Current is fed through the rod [5 to the wire I! and through the ribbon I8 to ground from a current feed plug similar to a conventional spark plug. It will be apparent that the struc ture will be at the desired operating temperature immediately after the first ignition, which is obtained by electric current conducted to the wire ii. The embodiment also prevents undesired disturbance in the flow of the fuel charge mixture and the gases in the combustion chamher, which is otherwise unavoidable when using a spark plug entering from the side, as shown in Figs. 1 and 2.

The important effect of the arrangement, according to the invention, resides in carefully keeping the fresh, preheated fuel charges initially properly spaced from the incandescent ignition bodies such as 8, II or H, and then in driving the charges, each in turn, into the immediate proximity of the ignition body. This effect is obtained in particularly favorable manher by terminating the inlet 3a, in accordance with the structure shown in Fig. 5, in a pocket of the combustion chamber, and to connect the exhaust duct 5 to the combustion chamber at such a location that the reacting exhaust gases cause compression of the fresh fuel charges in the direction of the arrows shown in Fig. 5, that is, in the direction of the ignition member ll of the heat exchanger l5.. The inlet is in this embodiment at the same time heated by the combustion gases so as to cause eflicient preheating of the fresh fuel charges. This results from the extension of the inlet 30. in the combustion chamber across the axis of the mouth of the exhaust duct 5. The latter effect may be increased by the provision of small apertures IS! in the wall within and spaced from the walls of said inlet duct and having an inner end which projects into said combustion chamber to a point where it is heated by combustionin said chamber to a temperature of from 600 to 1000 C., whereby the combustible mixture of fuel and air passing through said inlet duct to said combustion chamher is preheated-by heat transferred thereto from combustion in said combustion'chamber by said heat conductive member.

2. Anintermittentcombustion device as defined in claim 1 in which a shield is provided on the heat conductive member adjacent its inner end for deflecting incoming combustion mixture away from such end.

3. An intermittent combustion device as defined in claim 1 in which helically disposed surfaces are provided in theinlet duct for deflecting the incoming combustion mixture and causibng it to gyrate about the heat conductive mem- 4. An intermittent combustion device as defined in'claiml in which the inlet duct includes a tubular extension which projects into the combustion chamber.

- 5. An intermittent combustion device as delined in claim 1 in which the inlet duct is provided with ribs on its walls to increase the cfof the inlet extension 3a, which permit circulation of the reacting exhaust gases through the wall of such extension, as indicated by the arrows in Fig. 5. The flow of the gases heats the relatively cool base portion of the inlet, and at the sametime crowdsthe incoming fuel mixture, compressing it laterally in the direct vicinity of the incandescent body 11, and thus causing ignition in proper phase and at the proper time.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent of the United States. i

We claim:

1. An intermittent combustion device of the type in which a combustible mixture of fuel and air is periodically detonated at acoustic frequency comprising a combustion chamber, an open exhaust tube directly connected to said combustion chamber and forming therewith an acoustic resonator, an air inlet check valve, a tubular inlet duct connecting said combustion chamber to said check valve, a fuel feed nozzle opening into said inlet duct, and an elongated heat conductive member disposed longitudinally -8. An intermittent-combustion device as defined in claim 1 in which means are provided for conducting electric current through the heat.

conductive memberv to heat the same.

9. An intermittent combustion device as de-- fined in claim 1 in which the heat conductive member is provided at the inner end thereof with a wire forming a glow ignition element.

10. An intermittent combustion device as defined in claim '1 in which the heat conductive member comprises a metal rod with a wire forming a glow ignition element at its inner end and an electrically conductive member helically coiled around the rod.

11. An intermittent combustion device as defined in claim 1 in which the heat conductive member comprises a metal rod with an electrically conductive member helically coiled around the rod and serving to cause gyration about the rodof the incoming combustion mixture, and a wire disposed at the inner end of the rod and electrically connected between the rod and the helically coiled conductive member and forming an ignition element.

12. An intermittent combustion device as defined in claim 1 in which a pocket is provided in the combustion chamber, the inlet duct extends within and terminates in such pocket and the fined in claim 1 in which the combustion chamv her is provided with an annular constriction of its walls to form a pocket therein and the inner end of the heat conductive member extends into such pocket.

14. An intermittent combustion device as defined in claim 1 in which the inlet duct includes a tubular extension which projects into the com- 7 bustion chamber, such extension having apertures therein to permit the circulation of a portion of the exhaust gases therethrough.

15. In an internal combustion device of the type in which a combustible mixture of fuel and air is periodically detonated at acoustic frequency, a bulb-like combustion chamber, a tubular inlet duct connected to and extending axially from said combustion chamber at one end thereof, an exhaust tube connected to andextending axially from said combustion chamber at the other end thereof, a metallic element ex tending axially within said inlet duct free of the walls thereof and having an inner end extending into said combustion chamber, and an ignition means carried by said metallic element at its inner end, said metallic element acting" as a heat exchanger to preheat fuel charges enter ing said combustion chamber through said inlet duct.

18. In an internal combustion device of the type in which a combustible mixture of fuel and air is periodically'detonated at acousticfrequency, a bulb-like combustion chamber annularly constricted to form two adjacent chamber por= tions on each side of an annular constriction, an inlet duct connected to one of such chamber portions, an exhaust duct connected to the other of such chamber portions, a. heat conductive member axially disposed within said inlet duct, means carried by said heat conductive member for deflecting the path of flow of fuel charges entering through said inlet duct, and ignition means carried by said heat conductive member.

17. A burner deviceof the class described comprising a bulb-like structure forming a combus tion chamber, an inlet for incoming fuel charges at one end of said chamber, a tubular member forming an extension. of said inlet projecting ax ially into said combustion chamber, the. inner end of said tubular member flaring outwardly at a point within said combustion chamber, an ignition element disposed axially within said 8 burner chamber substantially within and in alignment with the flaring inner end of said tubular member, and a heat-exchange member disposed axially within said tubular member.

18. The structure and combination defined in claim 17, together with means extending from the side of said bulb-like structure and forming a duct for expelling exhaust gases from said burner chamber.

19. An intermittent combustion device as defined in claim 1, in which the inlet duct extends into the combustion chamber free of the walls thereof and in which the elongated heat conductive member extends within the inlet duct free of the walls thereof.

20. An intermittent combustion device as defined in claim '1, in which the inlet duct extends into the combustion chamber free of the walls thereof and across the axis of the mouth of the exhaust duct, whereby the inlet duct is effectiveiy heated by reacting exhaust gases surging inwardly from the exhaust duct mouth.

WAL D i LUDWIG HUBER. FRANZ HAAG'.

References Cited in the filo of this patent UNITED STATES PATENTS

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