US2719580A - Fuel feed apparatus for resonant pulse jet combustion device - Google Patents

Description

Oct. 4, 1955 F. A. HAAG ET AL 2,719,580

FUEL. FEED APPARATUS FOR RESONANT PULSE JET COMBUSTION DEVICE Filed March 11, 1953 Z ODWG R HUB)??? 'FUEL FEED APPARATUS FOR RESONANT PULSE JET COMBUSTION DEVICE Franz A. Haag and Ludwig R. Huber, Uberlingen am Boden See, Germany, assignors, by mesne assignments, to Swingfire (Bahamas) Limited, Nassau, Bahamas, a corporation of the Bahamas to resonant pulse jet combustion devices and more particularly to the provision of means in such devices insuring w a uniform richness of the air-fuel mixture supplied thereto.

The invention of the present application constitutes an improvement over that disclosed in the copending application of Ludwig Huber, Serial No. 291,367, filed June 3,

1952, of the same assignee.

A resonant pulse jet combustion device comprises generally a combustion chamber having connected thereto an unrestricted or valveless exhaust pipe or resonance tube.

Fuel for combustion (preferably in liquid form) is periodically drawn into the combustion chamber and detonated therein at the natural acoustic frequency of the chamber and exhaust pipe, and air to support combustion of the fuel is drawn in with, or at the same time as, the fuel through a suitable check valve or check valves connected to the combustion chamber. The combustion chamber pressure fluctuates periodically at the natural frequency of the device between superatmospheric and subatmospheric values, and the fuel and air for combustion are drawn into the chamber when this pressure is subatmospheric. The periodic interval when the pressure is subatmospheric may be termed the suction phase of operation, and the interval when the pressure is superatmospheric may be termed the detonation phase of operation. Resonant pulse jet combustion apparatus of this nature is disclosed, for example, in the copending application of Walter Diirr et al., Serial No. 166,611, filed June 7, 1950, now Patent No. 2,644,512 and entitled Burner Device Having Heat Exchange and Gas Flow .Control Means for Maintaining Pyrophoric Ignition Therein. Apparatus of this nature is useful in heating devices, to provide a reaction drive for airplanes, in apparatus for atomizing and spraying liquids, and for other purposes.

For stability of the oscillatory process of combustion it is desirable that uniformity be maintained in the richness in the air-fuel mixture admitted to the combustion chamber for each cycle of operation not only with respect to the average mixture obtaining over the cycle but with respect to the instantaneous value of the mixture at every instant throughout the cycle.

In the pulse jet combustion device disclosed in the copending application of Ludwig Huber above identified the air and fuel are admitted during the suction phase through separate inlet ports which communicate with a mixing tube leading to the combustion chamber. The air is drawn in through a check valve having a non-streamlined opening or openings, and the fuel is aspirated at the throat of a Venturi tube formed of two conical passages, the fuel being supplied to a ring-shaped channel surrounding the throat of the Venturi tube. While the check valve closes during the detonation phase, the flow of air through the Venturi tube is merely reversed, and fuel is continuously drawn from the ring-shaped channel. In this way fuel is maintained at the mouth of the channel so that United States Patent ice on the beginning of the suction phase fuel is without delay drawn into the Venturi tube for passage into the combustion chamber.

It is a disadvantage of the construction described in the preceding paragraph that the rate of flow of air through the check valve opening varies with pressure differential across the check valve in a manner distinctly different from that which describes the variation in the rate of flow of air through the Venturi tube (and hence the rate of aspiration of fuel thereat) with difference in pressure between the ends of the Venturi tube. Accordingly use of a Venturi-type opening for aspiration of the fuel as disclosed in the copending application of Ludwig Huber above identified results in a ratio of fuel to air which varies over the combustion cycle.

According to the present invention instead the fuel is aspirated into the combustion chamber by the flow of air through a passage provided with 'a sharp-cornered partition-type constriction, into the radially inner portion of which there open one or more fuel inlet passages connecting with a suitable reservoir. By this means the quantities of air passing through the air-inlet check valve per unit time and of fuel passing through the aspirating apparatus per unit time are brought into a substantially constant ratio at every instant during the suction phase of the combustion cycle.

The invention will now be described in connection with the accompanying drawings in which:

Fig. l is a partial sectional view in elevation through a pulse jet combustion device according to the present invention;

Fig. 2 is a partial sectional view in elevation at an enlarged scale of the fuel supply apparatus of the pulse jet combustion device of Fig. 1;

Fig. 3 is a graphical representation useful in explaining the operation of the apparatus of Fig. 2, and

Fig. 4 is an enlarged view of the air-intake valve.

The pulse jet combustion device illustrated in Fig. 1 includes a combustion chamber 1 connecting with an exhause gas tube 3 open to the atmosphere. The combustion chamber and exhaust tube together form a Helmholtz resonator. An air-fuel mixture is introduced into the combustion chamber through a mixing tube 5. The mixing tube may be provided at its mouth 7, within the chamber 1, with an ignition device such as the coil of wire 9 which may be brought to incandescence by a suitable source of electric energy, not shown. The mixing tube is closed at the end thereof outside the combustion chamber.

Air is admitted to the mixing tube at a check valve generally indicated at 11, having one or more openings 13. The openings may for example take the form of cylindrical holes in an obturating wall having flat parallel faces. The

'salient characteristic of the openings is that they are not streamlined. The valve 11 opens during the suction phase by operation of a flexible diaphragm 15 and closes during the detonation phase of operation. The fuel is drawn into the mixing tube 5 from a float chamber 17 at an aspirating apparatus generally indicated at 19 which is connected between the mixing tube and a condensation chamber 21. The aspirating apparatus, shown in further detail in Fig. 2, operates continuously. During the suction phase it draws fuel into the mixing tube 5, and during the detonation phase it draws fuel into the condensation chamber 21, from which the fuel is returned to the float chamber via line 23.

The aspirating apparatus of Fig. 2 comprises a tube 25 having an apertured partition or constriction 27, preferably of substantial thickness, disposed crosswise thereof. The elongated aperture 29 in partition 27 is substantially cylindrical in shape and joins the flat parallel faces of the partition at sharp angular boundaries. While the aperture 29 is preferably cylindrical, it need not be circularly Cylindrical. Hydrodynamically therefore the aperture 29 is similar to the openings 13 of the air-inlet valve 11.

A plurality of bores or passages 31 lead from the exterior of tube 25 into the cylindrical face of the aperture 29, and it is through the bores 31 that the fuel is aspirated by the flow of air through the opening 29. A jacket 33 surrounds the tube 25 and forms therewith an annular channel 35 which communicates with the aperture 29 by means of the bores 31. A supply tube 37 connects the channel 35 with the float chamber 17 in which fuel is maintained at an appropriate level by means of a float valve. Both the condensation and float chambers are closed.

The. aspirating tube 25 opens at one end into the mixing tube and at its other end into the condensation chamber 21. Upon the passage of air through the tube 25 toward the mixing tube, during the suction phase of operation, the difference in pressures between the aperture 29 and the. condensation chamber (and hence the difference in pressures between the aperture 29 and the float chamber) causes the fuel to flow from the line 37 through the passages 31 and into the opening 29 where it is entrained as a vapor and drawn into the mixing tube. The fuel entrained at the opening 29 during the detonation phase by air passing out of the mixing, tube through the aspirating tube 25 is passed to the chamber 21 where it is condensed and returned. to the float chamber for reuse.

In a preferred embodiment of the invention the tube 25 has a larger bore on the side of the partition 27 adjacent the mixing tube than on the side opposite. In. this way the change in pressure of the fuel-laden air upon its passage from the tube 25 into the mixing tube is reduced, with consequent reduction in condensation of fuel at the junction of the tubes 25 and 5.

The operation of the fuel aspirating apparatus of the present invention may be understood with reference to Fig. 3. In Fig. 3, time is plotted horizontally to the right with zero. time representing the beginning of the suction phase of a combustion cycle. Differences in pressure Ap between the interior of the mixing tube and the exterior of .the combustion chamber are plotted vertically downward while the time rates of flow of air and fuel through the check valve and aspirating apparatus are plotted vertically upward at separate scales. Curve I therefore. represents the course of pressure differentials between the interior and the exterior of the combustion device during the suction phase while references 11 and III respectively represent the Weights per unit time of air drawn in at the check valve 15 and of fuel drawn in at the aspirating tube: 25., also during the suction phase.

The scale of ordinates for curve III is expanded some twenty-fold withrespect to the scale of ordinates for curve Hi.

It is apparent that curves II and III are. of substantially the same shape, their ordinates at various times during the suction phase being releated by a single constant of proportionality. This is to say that curves II and III can be made substantially to coincide by multiplying the ordimates; of. curve. III, at each value of time by a suitably chosen constant of proportionality. Consequently, at every time during the suction phase, the time rate of aspiration of fuel is related to the time rate of entry of air in constant proportion, and therefore the air-fuel mixture delivered by the mixing tube to the combustion chamber is of uniform richness.

This may be contrasted with the relation between curve II and curve IV, the latter of which represents, to the same scale of ordinates as curve III, the weight of .fuel drawn in per unit time by the Venturi tube disclosed in the copending application of Ludwig Huber, Serial No. 291,367, filed June 3, 1952. Curves III and IV are seen to have opposite convexities and to be of very different shape, so that the ratio of air to fuel admitted per unit time varies widely over the suction phase.

We claim:

1. A pulse jet combustion device comprising wall means forming a combustion chamber, an elongated exhaust conduit extending from said combustion chamber and forming therewith a resonator, air intake means through which air for combustion passes to said combustion chamber, a check valve controlling the passage of air through said air intake means, conduit means communicating with the interior of the combustion chamber for the passage of gases to and from said combustion chamber, a partition extending across the passage of said conduit means and substantially normal thereto, said partition having an axially elongated opening therethrough of substantially uniform cross-sectional area and terminating at the sides of the partition in relatively sharp corners, the passage through said conduit means being open for the passage of gases both on the suction phase and the detonation phase of the combustion device, and means for supplying a liquid fuel to the opening in said partition intermediate the ends thereof.

2. A pulse jet combustion device as set forth in claim 1 in which said partition has substantially parallel opposite faces.

3. A pulse jet combustion device as set forth in claim 1 in which the elongated opening in the partition is cylindrical.

4. A pulse jet combustion device as set forth in claim 1 in which the diameter of the conduit means at the side of the partition nearer the combustion chamber is greater than the diameter of the conduit means at the side remote from the combustion chamber.

5. A pulse jet combustion device as set forth in claim 1 including means forming a condensation chamber communicating with the opening through the partition at the side remote from the combustion chamber, means forming a float chamber, conduit means connecting the condensation chamber With the float chamber, and conduit means connecting the float chamber with the opening in the partition, whereby fuel may be supplied to said opening from the float chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,106,914 LOrange Feb. 1, 1938 2,427,845 Forsyth Sept. 23, 1947 FOREIGN PATENTS 270,782' Switzerland Dec. 16, I950

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