US3035413A - Thermodynamic combustion device using pulsating gas pressure - Google Patents

Description

y 1962 E. T. LINDEROTH THERMODYNAMIC COMBUSTION DEVICE USING PULSATING GAS PRESSURE Original Filed Jan. 17, 1950 3 Sheets-Sheet 2 m T. m w.

HM Wm R h Mf WM L D MW ma mb May 22, 1962 E. T. LINDEROTH 3,035,413

THERMODYNAMIC COMBUSTION DEVICE USING PULSATINGGAS PRESSURE Original Filed Jan. 17. 1950 s Sheets-Sheet 3 PRESSURE TIME Arryk.

3,035,413 THERMODYNAMIC CUMBUSTION DEVICE USING PULSATING GAS PRESSURE Erik Torvald Linderoth, N. Malarstrand 60, Stockholm, Sweden Original application Jan. 17, 1950, Ser. No. 139,015, now

Patent No. 2,727,535, dated Dec. 20, 1955. Divided and this application Nov. 7, 1955, Ser. No. 553,169

Claims priority, application Sweden Jan. 29, 1949 8 Claims. (Cl. Gil-69.77)

The present invention relates to a thermodynamic blast device preferably for generation of power, e.g., jet propulsion, but it may also find general use wherever a strong blowing efiect obtained by the consumption of heat may be useful.

This application is a division of my application, Serial bio 139,015, filed January 17, 1950, now Patent No. 2,727,535 issued on December 20, 1955.

The present invention is concerned with the type of thermodynamic blast devices in which the pressure is caused to pulsate by intermittent heating, and if desired, by alternate heating and cooling of a gaseous medium, the heating being achieved by intermittent combustion in a combustion chamber in which the pressure pulsations are produced.

Such thermodynamic blast devices, e.g. so-called pulse jets, operate with permanently open gas outlets. As a result thereof, it is not possible to obtain high explosive pressures in the combustion chambers, particularly as the permanently open gas outlets must be given a relatively large area of flow to permit a rapid exhausting of remaining combustion residues, which must be evacuated to make way for a new fuel air mixture.

This type of jet propulsion has heretofore exhibited a very low efficiency compared to the turbojets now used.

This disadvantage becomes still more marked if in order to avoid any moving parts it is attempted to construct a pulse jet with the air inlet also permanently open. The increase of pressure by the intermittent combustion will then be still lower.

The present invention has for its main object to avoid this disadvantage by providing means for achieving a very rapid ignition and rapid combustion of the fuel air mixture in the combustion chambers so that, in spite of a permanently open gas outlet and optionally a permanently open air inlet, high explosive pressures may be obtained.

Another object of the invention is to provide means whereby it will be possible to use relatively small areas of flow in both the gas outlet and the air inlet, which makes it easier for the combustion accelerating device to produce the high explosive pressures which are the main purpose of this invention.

A further object of the invention is to provide means whereby a certain quantity of pure air is sucked in both before and after aspiration of the fuel air mixture. The purpose of the pure air is primarily to prevent direct contact between the aspirated fuel air mixture and the combustion gases remaining in the combustion chamber. It has been found that such contact may result in a premature ignition of the aspirated fuel air mixture which would cause the igniting and combustion accelerating means according to this invention to be less effective or even inoperative.

In addition, the intake of pure air referred to above aims at eliminating another disadvantage inherent in permanently open gas outlets and air inlets, viz. an exhausting of unburnt or partially burned fuel air mixture during the first phase of a combustion period before the entire volume of combustible gas in the combustion chamber has been completely burnt.

The means utilized for achieving the desired intake of States Patent ice pure air is a special configuration of the combustion chamber and of the air inlet which permits a suction relatively free of turbulence and a storage of fuel-free air as well as fuel-admixed air in the combustion chamber without appreciable intermixing of them. Such intermixing and turbulence in the combustion chamber is deferred to a subsequent phase of the operating cycle by the action of the above-named combustion accelerating means. Thus, since fuel air mixture which is ignited is not admixed with combustion residues in advance, the effect of the combustion accelerating means will be enhanced and a very abrupt increase of pressure will be obtained.

The various means described generally above and which will be described in more detail below, are complementary to each other and cooperate to serve a common pose, viz. to obtain a thermodynamic blast device operating with intermittent combustion, in which, notwithstanding the use of continuously open combustion chambers, high explosive pressures may be obtained.

The invention is illustrated by the accompanying drawings in which:

FIG. 1 shows a venturi tube having an edge for the constriction of the reverse flow.

FIG. 2 is a fragmentary sectional view showing the sharp reverse flow resisting edge on an enlarged scale.

FIG. 3 is a view in axial section showing a modified form of venturi tube in which the sharp edge is so shaped and arranged that a powerful constriction of the gas stream is obtained for resisting reverse flow.

PEG. 4 shows means for controlling the supply of fuel.

FIG. 5 is an enlarged fragmentary sectional view showing a modification of FIG. 4.

FIG. 6 is a transverse sectional view taken along the line VIVI of FIG. 5.

FIG. 7 is a longitudinal sectional view of a complete multi-chambered combustion device using a group of devices as shown in FIGS. 5 and 6.

FIG. 8 is a transverse sectional view of the device shown in FIG. 7.

FIG. 9 is an enlarged view of one of the asymmetrically flow resistant nozzles of FIGS. 7 and 8.

FIG. 10 is a time-pressure graph illustrating the overlapping polyphase power pulsations of the multi-charnbered device shown in FIGS. 7 and 8.

For comprehension of the inventive idea and the manner of operation of the suggested devices reference is made to Bernoullis Theorem and to the manner of operation of a venturi tube. A common venturi tube is characterized by a smoothly and gradually curved entrance portion and a long conical (diffuser-shaped) delivery portion. It is possible with such a tube to obtain very high velocities in the narrowest or throat section with a small resistance to flow, due to the recovery of pressure that is obtained in the diffusor shaped delivery portion. In the entrance portion the pressure falls, thus transforming pressure energy to velocity energy and in the conical delivery portion a transformation of energy in the opposite direction is carried out, i.e. from velocity to pressure.

According to the present invention a recovery of pressure during flow in the reverse direction is prevented by an annular sharp forwardly directed edge 2, FIGS. 1 and 2, being fitted at the narrowest section of the venturi tube 1. The inlet portion is in the shape of a curvedly flaring funnel having a radius of curvature R and terminating at its small end in the forwardly directed sharp edge '2. When there is a flow in the reverse direction, this sharp edge causes the flow to be disengaged or diverted inwardly from the surface of the throat portion of the venturi tube, so that the air flow tends to continue in a free jet of reduced cross sectional area as it passes rearwardly beyond the edge. When there is a flow in the forward direction, the flow is only slightly affected by the edge, if it is shaped as shown in FIGS. 1 and 2. The course of pressure will thus remain practically unchanged in the forward direction, while the resistance in the reverse direction is immensely increased. The resistance in the reverse direction can in the construction shown in FIGS. 1 and 2 be about 10 times larger than the resistance in the forward direction. necessary condition for this is that the venturi tube is so shaped that the widening angle of divergence of its conical part is at most 12., but preferably -10 and that the ratio between the areas of the narrowest and widest sections is below the value 0.5 and preferably should be chosen between 0.3 and 0.1. The radius R of the entrance portion should be at least 25% of the smallest section diameter d and should preferably be chosen between 0.3 and 1d. D is the diameter of the largest section.

In the construction shown in FIG. 3 the flow separating edge 2 is fitted a short distance in front of the narrowest part of the venturi tube and shaped like a nozzle having approximately the same inner diameter as the venturi tube. Between said nozzle and the narrowest section of the venturi tube there is an enlarged portion.

Through this shape not only a disengagement of the fiow in the reverse direction is obtained, but also a strong constriction of the emerging jet, the smallest section of which can be reduced to 55% of the passage area of the nozzle 2. In forward flow, on the other hand, there is no constriction. Some increase in the resistance in the forward direction is, however, obtained, for which reason the distance I from the mouth of the venturi tube to its narrow est section should not exceed three times the mouth diameter d and the smallest diameter d of the venturi tube should lie between 0.70 to 1.1, and preferably between 0.8 and 1.0.

FIGS. 5 and 6 show a modification of the apparatus of FIG. 4 and a complete multi-chambered device using five of these units is shown in FIGS. 7 and 8.

Referring to FIGS. 7 and 8, five venturi tubes 1d serving as combustion chambers are mounted in a circle around an ejector comprising a series of secondary air nozzles 30a which serve firstly to cooperate in drawing out remaining combustion gases from the combustion chambers, and secondly to accelerate a quantity of air which is many times larger than the quantity of air taking part in the combustion, thus considerably increasing the motive power. The gases flowing from the combustion chambers are deflected rearwardly by the curved discharge nozzles 5b which are interconnected with the central ejector 30a. Thus the directions of discharge of the reverse flow as well as the main flow coincide. The reverse flow from the venturi tubes is injected in the secondary nozzles 30b mounted around the central ejector and connected thereto. The combustion chambers and the discharge nozzles are surrounded by cooling jackets 8b, connected to the central ejector 30a which consequently draws in cooling air.

The fuel is supplied through an annular distribution chamber 31 (FIGS. 5 and 6) to a plurality of bores 32 circumferentially spaced around the narrowest section of the venturi tube. The fuel supply is otherwise controlled by ball valves in the manner hereinafter described in connection with FIG. 4, so as to ensure that there is a mass of air containing no fuel on either side of the fuelair mixture at the moment of ignition. As in this case the most violent explosions possible are desired, in order to obtain high explosion pressures, the following arrangement may be effected.

From each combustion chamber a pipe 33 is drawn to the adjacent chamber, said pipe having a smoothly curved admission part 34 connected to one chamber and being reduced to a sharp-edged discharge nozzle 35 in the other chamber.

The apparatus works as follows: It is started with compressed air thus charging all the combustion chambers with a fuel-air mixture. Preferably, separate fuel injection nozzles S (FIG. 5) are used for starting, and ignition is then effected by means of electric spark plugs or glow plugs in one of the chambers. The combustion will then spread through one of the pipes 33 to an adjacent combustion chamber, viz. the one into which the nozzle 35 opens. As shown in FIG. 9, the discharge nozzle 35 of the duct 33 is indicated as being sharp-edged at 35a. The other end at 34 is rounded to permit free flow into the duct 33. By reason of this sharp-edged configuration of its mouth, the nozzle 35 is asymmetrically flow-resistant. The need for a positive acting check valve including a I bodily displaceable member is thus avoided. The transfer of the combustion from one chamber to another takes a certain period of time, which is determined by the ratio between the volume of the pipe 33 and the area of the nozzle 35. After still another such a period of time the combustion has reached the third combustion chamber etc. When the combustion has reached the last chamber, the first one has been recharged with a new fuel-air mixture due to the suction effect of the ejector, and the ejector has during this period received five power impulses. The combustion will thus continuously travel around the circle of combustion chambers and cause successive explosions at equal intervals.

FIG. 7 shows how the successive power impulses com bine to produce a substantially constant thrust. An essential advantage reached by the ignition being effected through injection of combustion gases from one chamber to the other is, that the combustion is hereby strongly accelerated, which is of the utmost importance in this case, when high explosive pressure is desired in chambers which are constantly in connection with the atmosphere, and where the suction losses are small due to the venturi shape, thus causing slight turbulence.

For the previously described purposes a too violent ignition is not desirable with respect to silent operation. In jet propulsion, though, the power output is of greater importance than silent operation. The large ejector, however, provides a silencing effect to a certain extent, if it is composed by a large number of relatively short nozzles of different lengths, so that resonance phenomena cannot occur. The streamlined casing 36 enclosing the apparatus also contributes to the silencing etfect. The main purpose of said casing 36 is to catch the wind by means of a diffuser-shaped air inlet 37 in its front end and transfer the ram pressure thus obtained to the jet power unit. So as to permit the power unit to utilize the ram pressure in the best possible way the area of the discharge nozzle should not be greater than the area of the air intake through the venturi tube. Preferably the area of the discharge port should be 0.5 to 1 of the intake of the venturi tube.

A condition precedent for the combustion properly travelling around as described above is, that a certain quantity of air is drawn in both before and after the fuel is supplied so as to avoid self-ignitions, and that the transfer pipes 33 are constructed as indicated above, i.e. with a smoothly curved admission portion and a delivery portion so shaped that constriction is obtained in the reverse direction. Through this constriction and the subsequent formation of turbulence the flarne emerging in the reverse direction will be very short and will not reach through the entire length of the pipe 33, while the smoothly curved admission portion gives a smooth flow in the opposite direction and a slow combustion so that the flame reaches the sharp-edged nozzle 35 and ignites the gas body in the combustion chamber. A further condition for the operation of the device is that the transfer pipes are cooled to a temperature lying slightly below the ignition temperature of the gas mixture. For this reason they are provided with cooling flanges 38.

Also the combustion chambers should be cooled down to below the ignition temperature of the fuel-air mixture. Cooling flanges are not required, however, except at the portion lying nearest the discharge nozzles 5b.

Obviously, the number of combustion chambers may be other than five.

As illustrated in FIG. 10, the firings of the several chambers are displaced in phase because they fire successively. As a result, there is a series of pressure peaks which partially overlap each other with a resulting continuity of pressure. The individual pressure pulsations are thus suppressed or filtered out in the combined output of the five chambers.

Having now particularly described the nature of my invention and the manner of its operation what I claim is:

l. A thermodynamic blast device comprising a plurality of combustion chambers arranged in an endless series, each chamber being adapted for intermittent combustion and each having a ga outlet and an air inlet, each air inlet being in continuous communication with the atmosphere, adjacent ones of said combustion chambers being interconnected with each other by means of ducts whereby said ducts and said chambers form a closed circuit, each one of said ducts having a sharp-edged flow restricting first end constituted by an asymmetrically flow-resistant nozzle and a second end shaped to permit free flow into said duct, said ends of each duct being connected to said two adjacent ones of said chambers between which said duct extends, said duct ends permitting the flow of an igniting and combustion accelerating flame around said closed circuit in one direction and opposing the flow of said flame in the opposite direction, whereby combustion gases in said chambers may be repeatedly fired in a cyclical manner, the gases in the several chambers being fired consecutively in a predetermined sequence.

2. A thermodynamic blast device according to claim 1, wherein said second end of each duct is enlarged and connected to said combustion chamber by means of a flaring and smoothly rounded funnel-shaped part.

3. A thermodynamic blast device according to claim 1, including a common central ejector around which all of said combustion chambers are arranged and into which said gas outlets open, and cooling jackets surrounding the combustion chambers and in communication with said central ejector in order to cool said chambers below the ignition temperature of the fuel air mixture.

4. A thermodynamic blast device according to claim 1, further comprising individual fuel injection means communicating with each combustion chamber, a fuel supply conduit connected to each fuel injection means, and two check valves arranged in each fuel supply conduit, one of said check valves closing in the direction in which the fuel is supplied, the other of said check valves closing in the opposite direction, the first-mentioned check valve being biased to be normally kept open and to limit the flow of fuel for each of the pressure pulsations in the combustion chamber to which its associated fuel injection means is connected.

5. A pulsating thermodynamic blast device comprising a combustion chamber, a continuously open air inlet for said combustion chamber through which said chamber communicates with the atmosphere, said inlet having a constricted throat portion, an annular sharp-edged lip extending around the periphery of said throat portion, said throat portion being smoothly rounded to provide a progressively increasing cross-sectional area for said inlet proceeding away from said lip both inwardly and outwardly with respect to said chamber, said lip being directed toward said chamber for providing an asymmetrical flow resistance opposing reverse flow through said inlet, a fuel supply duct communicating with said chamber, a metering valve included in said duct, said valve including a check member which shuts off fuel flow into said chamher through said duct after a predetermined volume of fuel has been admitted into said chamber, said check member being resettable by an increase in pressure within said chamber to permit a repeated flow of fuel in said duct, ignition means for repeatedly igniting a combustible air-fuel mixture in said chamber, said mixture being formed by said fuel and by air entering said chamber through said inlet, and exhaust means communicating with said chamber for removing the products of combustion produced by ignition of said mixture.

6. A thermodynamic blast device comprising a plurality of combustion chambers arranged in an endless series, each chamber being adapted for intermittent combustion and each having a gas outlet and an air inlet, adjacent ones of said combustion chambers being interconnected with each other by means of continuous open ducts, whereby said ducts and said chambers form a closed circuit, each one of said ducts having a flow restricting first end including an asymmetrically flow-resistant nozzle and a second end shaped to permit free flow into said duct, said ends of each duct being connected to said two adjacent ones of said chambers between which said duct extends, said duct ends permitting the flow of an igniting and combustion accelerating flame around said closed circuit in one direction and opposing the flow of said flame in the opposite direction, whereby combustion gases in said chambers may be repeatedly fired in a cyclical manner, the gases in the several chambers being fired consecutively in a predetermined sequence.

7. A thermodynamic blast device according to claim 6, in which each of said combustion chambers is elongated and comprises a venturi-shaped portion which defines said continuous air inlet passage, the throat portion of said inlet passage comprising an annular knife-edged projection offering an asymmetrical aerodynamic resistance to the flow of gas through said throat portion, said knife edge being directed forwardly with respect to combustion air entering said chamber to minimize resistance to inward fiow and to oppose the outward flow of combustion gases from said chamber.

8. A thermodynamic blast device according to claim 7, in which said venturi-shaped portion extends beyond said throat portion exteriorly of said chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,404,335 Whittle July 16, 1946 2,500,712 Serrell Mar. 14, 1950 2,612,749 Tenney et al Oct. 7, 1952 2,639,580 Stuart May 26, 1953 2,674,091 Malick Apr. 6, 1954 FOREIGN PATENTS 518,453 Germany Feb. 16, 1931 559,370 Germany Sept. 21, 1932 630,180 Germany Sept. 24, 1936 616,481 Great Britain Jan. 21, 1949 OTHER REFERENCES US. Navy Project Squid, Technical Memorandum No. 4, The Aero'Resonator Power Plant of the V-l Flying Bomb, by Ing. Guenther Diedrich, June 30, 1948, Princeton, University, page 39, Fig. 55.

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