US2581902A - Resonant gas compressor and method - Google Patents

Description

Jan. 8, 1952 A. G. BODINE, JR

RESONANT GAS COMPRESSOR AND METHOD Filed April 23, 1945 6 Sheets-Sheet l INVENTOR. ,4; 55276. flow/v5, 177a,

Anne/Vin Jan. 8, 1952 A. s. BODINE, JR

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RESONANT GAS COMPRESSOR AND METHOD 6 Sheets-Sheet 5 Filed April 25, 1945 GEAR BOX GOVERNOR INVENTOR. A4552)" 6. flop/Ms, U76,

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RESONANT GAS COMPRESSOR AND METHOD Filed April 25, 1945 s Sheets-Sheet 4 Arm/aver.

Jan. 8, 1952 A. G. BODINE, JR

RESONANT GAS COMPRESSOR AND METHOD 6 Sheets-Sheet 5 Filed April 23, 1945 IIIIHIIIHHIIIIHIII! m I mllm ||Ill|IIIIIIIHIIIIHIIIIIlllll III III l IIIIIIJIHIIIIINIIIII INVENTOR. 445.5976. flop/m5, z/k.,

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RESONANT GAS COMPRESSOR AND METHOD '6 SheetsSheet 6 Filed April 23, 1945 INVENTOR. 445506: flop/ME, Ufa, BY

ATTOEA/EK Patented Jan. 8, 1952 UNITED STATES PATENT OFFICE BESONANT GAS COMPRESSOR AND METHOD Albert G. Bodine, Jr., Van Nays, Calif. Application April as, 1945, Serial No. 589,753

This invention relates to a novel method and apparatus for compressing or pressuring gases for various purposes; also, to a novel cavity resonator employing sonic principles and capable of producing extreme pressure variations and, if desired, a relatively-constant-pressure stream of gas, in some instances comprising products of combustion. The invention has numerous uses and the title hereinemployed is not to be considered as limiting but, rather, exemplary of one use of the device. Pressured gas from a resonating cavity may advantageously be used for purposes of jet propulsion, or to drive a gas turbine, or for pumping a liquid, etc.

In general, the invention employs sound waves in a fluid-filled cavity to establish therein pressure; and velocity undulations varying in intensity in different portions of the fluid. If a pressure disturbance is caused within any cavity, certain' frequencies, said to be resonant, tend to be amplified and to establish a standing wave pattern throughout the fluid, while all other frequencies tend to be damped out. The certain frequencies which tend to maintain themselves are determined by the shape and dimensions of the particular cavity. If pressure pulses are repeated at a resonant frequency, preferably in a region of maximum pressure variation, the resonating wave tends to increase until a condition of equilibrium is reached at which the input energy equals that dissipated in the form of frictional losses.

Such a system maybe used as a pump or compressor by introducing new fluid into the chamber during a period of rarefaction at the point of intake. Discharge may be either continuous or only during periods of a selected recurring phase and may be located at any point within the. 'cavity. The pressure pulses are preferably generated by the intermittent combustion of fuel,

the hot gases produced thereby being permitted ugmenting a Controlled Thrust, Serial No. 439,926, the latter now abandoned, a resonating cavity was disclosed consisting of a Pipe closed at end and opening at the other'into a capacichamber. The sound waves are generated within the closed pipe end so as to produce a 24 Claims. (Cl. Gil-35.6)

plane wave normal to the axis of the pipe. When this wave emerges into the capacitance chamber from the opposite end of the pipe it diverges and the wave front changes from a plane to a curved surface. It is to be noted that in this and other previously proposed applications utilizing resonating combustion chambers, an important portion of the system has generally been designed for one dimensional vibration. It is a novel feature of the present invention that the standing wave diverges immediately from the generator, in certain versions in all directions. Furthermore, in most embodiments, a generator which preferably functions substantially as a spherical-wave point-source is used whereas in previous devices utilizing resonating gas systems, it was usually desirable to produce a wave as nearly planar as possible, particularly in" that portion adjacent the source. In fact, one identifying feature of long, small cross-section pipes is that they tend to generate plane waves by multiple wall reflection regardness of generated wave form. Helmholtz resonators are in the same analogous class as pipes because they also deal with one dimensional motion, even though they must be short in all directions relative to a quarter wave length.

It is an object of this invention to provide a novel combustion resonator for any purpose and in which the wave front is not everywhere a plane of substantially constant area (nonplanar), e. g., to provide a sonic .resonator in which the desired resonant wave radiates divergently from the generator. Such an acoustic system tends to set up a standing wave having a pressure antinode of maximum energy density in the region of the generator. This feature makes possible a highly eflicient thermal excitation since the effective compression-expansion-ratio in the zone of intermittent combustion is very high.

In a tube-confined column of fluid subjected to an energizing disturbance, a condition of standing wave resonance establishes in the column one or more zones of large or maximum pressure variation, in which zone or zones the velocity variations are a minimum. Spaced one quarter wave length from any such zone of maximum pressure variation, or spaced midway between two such zones, is a zone of large or maximum velocity variation. In other words, the energy in a resonating column changes in form (but not in quantity) from section to section along the length thereof, being primarily potential or pressure energy at the zone of large or maximum pressure 'variation and primarily I These factors tend-to limit the power which can be generated by the sonic vibration in such a column, and tend in some instances to interfere with the desired wave pattern.

It is accordingly an object of the present invention to establish a'zone of large or maximum velocity variationin space with a minimum of contact with the fluid confining surface.

By way of example, if a sound wave generator is disposed in the center of a hollow fluid-filled sphere and if the frequency is such as to produce sound waves having a wave length equal to 1.4 times the radius, a condition of standing wave resonance will be maintained within the sphere, as may be ascertained, for example, by reference to any edition of Lord Rayleighs Treatise on Sound. Zones of pressure loops or antinodes will exist at the center of the sphere and adjacent the inner surface of the spherical wall. For the condition of resonace at fundamental frequency, the zone of large or maximum periodic velocity is revealed by Lord Rayleigh's equations to be located approximately a half wave length from the center, that is, in an envelope about two thirds the radial distance from the center to the spherical wall. In this latter spherical zone, the gas molecules will oscillate along paths radiating from the center of the sphere, but the only friction will be between the gas molecules themselves, and substantially no shock waves will be established.

It is to be understood that the term wave lengt as used herein always means the quotient of velocity divided by frequency. When plane waves are propagated in one direction only (i. e., without divergence) the distance between successive particles of the medium which are in phase with one another-corresponds to this quotient. Particles 180 out of phase with one another are half this wave length apart ina onedimensional vibrating system. The term ceases to have this significance when applied to waves propagated in more than one direction, however. If waves diverge, particles in phase with one another are separated by a distance which is greater than the one-dimensional wave length. If, for instance, a point source generates sound waves in a medium which propagates the waves equally well in all directions, then the loci of all particles in phase with the source is a series of concentric spherical surfaces having the source at their common center. The distance from the point source to the first spherical surface is substantially greater than the distance from the first spherical surface to the second; the distance between successive spherical surfaces decreases and as the spheres become large, and plane wave conditions are approached at high overtones, the separating distance approaching a one-dimensiona wave length as a limit.

In many of its preferred embodiments. the invention employs cavities which have the peculiar property that pressure waves originating therewithin and reflected by the bounding surfaces thereof are concentrated in a focal zone, usually a point or a line rather than a surface. A spherical cavity presents the simplest case in which all reflected waves converge to a focal point. An important advantage of the spherical resonating chamber results from the fact that a sound wave reflected in a converging wave from the concave spherical surfaces increases progressively in energy density and therefore in the degree of pressure variation as it approaches the focal point at the center of the sphere. Pressure variations existing at the reflecting surfaces arethus enormously amplified as they approach the center. In standing wave systems using one dimensional vibration only the sound waves are generated and transmitted in a plane. The maximum pressure attained at any pressure antinode is no greater than that periodically exerted on all reflecting surfaces normal to the wave (except for attenuation). In a spherical standing wave system, on the other hand, the maximum pressures attained in the region of the centrally located pressure antinode are many times those exerted against the reflecting surfaces of the cavity. A conical sector of a sphere, having a solid angle at its vertex of any'desired magnitude less than 41, has similar properties. 5

Another example, comprehended by the present invention, involves a substantially cylindrical resonator having an elongated or cylindrical focal zone coaxial with the cylinder. If an elongated sound-wave generator is disposed in or adjacent this focal zone, sound waves will move radially outward from the focal zone with substantially cylindrical wave fronts and will be reflected by the inner surface of the cylindrical wall to concentrate in the focal zone. Convergence from the reflecting surface has an amplification efl'ect similar to butsomewhat less than in the case of the sphere.

The invention also comprehends other shapes of resonant cavities in which amplification of a reflected wave is achieved by means of surfaces disposed about a focal zone; also resonant cavities in which sound generators are distributed at points other than that of maximum pressure variation. Less symmetrical cavities have more complicated standing wave patterns but if they are such as to have one or more foci, an ellipsoidal cavity for example, then the establishment of a standing wave in the contained fluid will create pressure antinodes at said foci and the pressure variations at these points will exceed those occurring in any other region of the cavity.

The invention is not limited to focusing surfaces, however, but comprehends broadly resonating cavities of whatever shape, in which sound waves are radiated divergently from the generator and in which the standing wave created thereby is utilized for the performance of mechanical work, such as pumping fluids. Even in the absence of points within the cavity which constitute foci, if vibration occurs in more than one direction certain pressure antinode regions will be characterized by a wider variation in pressure than others. Preferably, however, the sound waves are generated adjacent a focal zone, or in the absence of a focal zone. near a pressure antinode of maximum strength in order that reflected sound waves will reinforce the undulations ofthe sound-wave generator.

Certain later-described peculiar advantages of resonating cavities which have one or more pressure antinode regions of maximum energy density may be explained in terms commonly used with reference to vibrating systems whether they be electrical. mechanical, or acoustical, and for accuses convenience these will here be defined. A dimensionless figure of merit represented by the letter Q is used to express the ratio of energy stored in a vibrating system to the energy dissipated by it during each half cycle. Since energy is stored only to the extent that reso- :nance exists, Q reaches a maximum at each resonant frequency and declines in value with departure to higher and lower frequencies. The :term acoustic impedance Z, represents the ratio of alternating pressure component to the volume velocity, the latter beingthe integral of particle velocity over thearea of a surface past which itoccurs. In a standing wave system the impedance quotient has a maxima in the pressure antinode regions since an added increment in the applied alternating pressure results in very little increased velocity at this antinode. The terms Q" and Z are related in that a system having a high Q will exhibit an impedance at its pressure antinodes which is relatively large in comparison with the impedance at its velocity "arltinodes. In fact, as attenuation approaches zero, Q" and the pressure antinode impedance approach infinity and the impedance at the velocity antinode approaches zero.

When a standing wave in a fluid is caused to perform mechanical work it is damped or attenuated; such as by the substraction of vibrating fluid and its replacement by static fluid which must be compressed, or accelerated, depending on whether intake is near a pressure or velocity antinode region. In order that the standing wave may continue to exist, new energy 'must be added, generally once in each cycle, and, in the preferred embodiments of this invention, this is accomplished by the intermittent combustion and expansion of fuel and air. In such a, system, it is desirable that the stored energy of the standing wave be large in proportion to the energy lost in the pumping of fluid and in normal frictional attenuation. The standing wave must carry a sufficient reservoir of stored energy to compress each newly introduced charge of fluid despite these losses. It is seen that the standing wave performs functions exactly analogous to those of a flywheel, the energy being stored for part of the cycle in the fluid mass at the velocity antinode. The two energy storage device differ from one another in that the fly- ,wheel stores its energy wholly in the form of kinetic energy whereas the standing wave alternateiystores energy as kinetic energy at the velocity antinodes and as potential energy of elastic deformation at the pressure antinode. They resemble each other, however, in that for a given frequency, the capacity for energy storage .goes up with the magnitude of the moving mass. Ina, spherical cavity, for example, the moving fluid mass is in the shape of a thick walled hollow sphere whereas in the ordinary one-dimensional resonator it is in the shape of a cylinder or prism. It is seen that for an apparatus of a givenbulk and for a given size of combustion chamber, the sphere has a much heavier flywheel," and, therefore, one which provides a greater energy reservoir at a given alternatin velocity. --Furthermore, the wall drag encountered in a one-dimensional resonator is totally absent in a sphere, and in other diverging wave cavities is. substantially less for a given mass of moving fluid. Such cavity resonators, therefore, provide a flywheel of considerably less friction. Stating exactly the same point in a slightly different manner, a cavity resonator, particular ly a sphere, has a higher Q than a one dimensional resonator of the same bulk since attenuation is reduced by the elimination or reduction of wall drag and by reduction of internal friction since kinetic energy, is stored by a large mass moving at a relatively low velocityrather than by a small mass moving at a high velocity. Partly because of this higher Q and-v partly because of the increased energy density (decreased wave front area) at the focal zone; antinode, pressure variation amplitudes attainable there are much higher than could be attained in a one-dimensional resonator of. similar bulk-and with the same exciting force; for example, the focal zone pressure antinode of a sphere has a higher acoustic impedance than any other type of resonator, other things being equal. If the sound wave is generated by the intermittent combustion of fuel in this region of high impedance, then the advantages of a high compression engine are attained since high pressure variations occur there. In effect the high impedance provides the expanding gases with a loading which more nearly approaches the pres.- sure which may be exerted by a gas expanding in an isentropic manner. Low impedance systems permit free expansions to a large extent. with resulting increases in entropy and'los'ses in thermodynamic efficiency.

In high-energy sonic systems, it is often-desirable to employ intermittent combustion to establish the sound waves. The present invention has among its objects the burning of increments of fuel in a sonic cavity to establish. and maintain the desired sound wave pattern in the cavity. Another object of the invention is .to burn increments of fuel at a position near .the focal zone of a reflecting surface in such a man:- ner as to establish a condition of standing wave resonance giving rise to pressurev variations-at the focal zone which, if desired, can be extremely large. Other objects reside in the utilization of the sound waves in a sonic cavity to aid in the intake of air and fuel, the compression and ignition of the fuel-air mixture, the expansion of the fuel, and/or the exhaust of gases, comprising products of combustion, from the sonic cavity. One of the general objects of the invention is the provision of a novel internal-combustion resonator useful for many purposes.

Other objects of the invention reside .in th utilization of sound waves or some energy in the compression of fluids, particularly gases. Thus, it is an object of the invention to provide a gaspumping or compression system in which the pressure-increasing means is combined with a storage vessel; also, to provide a simple, highly eflicient, internal-combustion compressor. 3 In this latter connection, it is an object of the invention to burn increments of fuel, mixed with appropriate amounts of air, at a position-spaced from reflecting surfaces in such manner as to utilize a reflected. wave to produce large variations in pressure at a focal zone and to remove compressed gas, usually comprising products of combustion, from a position removed from the point of fuel burning, whereby. the gases at the point of withdrawal are not subject to the. large pressure variationsin the focal zone.

Certain general objects of the invention in clude the provision of a novel method and apparatus for maintaining large pressure variations within a container without transmitting equal pressure variations to the walls of the container; provision for the introduction'of-relaasenaoa 7 tively-low-pressure gases to a sonic cavity and for the discharge of relatively-high pressure gases therefrom; provision for intermittent intake of gases to, and a relatively constant-flow discharge of gases from, a sonic cavity; provision of a resonating system including a sonic cavity in which increments of fuel can be burned at a natural resonant frequency of the sonic cavity or at a frequency which is a multiple or sub-multiple of its resonant frequency; provision for the timed intake of fuel and combustionsupporting air to a sonic cavity and, if desired, a supply of auxiliary air thereto; provision for the confinement of fuel-burning to a small zone, usually near the focal zone of a curved reflecting surface; employment of the burning of increments of fuel for the development of pressure to discharge a relatively constant pressure stream of the products of combustion diluted, if desired, by another gas, such as air; provision for the maintenance of a high mean pressure in the sonic cavity, conducive to desirable wave patterns and high-energy outputs; provision for a novel control of valves in a sonic system; and provision of an automatic control to compensate for differences in load or amount of gas withdrawn. It is an object of this invention to provide a sonic engine which utilizes to full advantage the natural spherical expansion pattern of explosions.

Other objects of the invention reside in the provision of a system for turning a rotary shaft in step with the sound waves in the sonic cavity, 1. e., at a speed proportional to the sound-wave frequency; the turning of such a rotary shaft by a turbine receiving a pressured stream of gas from the sonic cavity; and the utilization of at least a portion of the power transmitted by such a shaft for driving a supercharger or compressor for forcing air into the sonic cavity, or for timing the intermittent introduction of fuel to, or the burning of fuel in, such a sonic cavity. It is also an object of the invention to conduct any desired portion of the gases from a sonic cavity of the internal-combustion type for use in driving a turbine, any desired portion of the power developed by the turbine being used to drive a compressor aiding in the forcing of gases into the sonic cavity, anyremaining portion of the power developed by the compressor being used for any desired purpose, and any residual energy in the gases discharging from the turbine being embodiment, namely, an internal-combustion cavity resonator employed as a compressor.

Referring to the drawings:

Figure 1 is a vertical cross-sectional view of a simple form of internal-combustion spherical resonator employed as a compressor;

Figure 2 is a fragmentary vertical sectional view of an alternative air and fuel intake system useful in the system shown in Figure 1;

Figure 3 includes graphical representations of pressure and velocity variations in the sphere of Figure 1;

Figure 3a is a detail sectional view on an enlarged scale of the fuel ressure regulator;

Figure 4 is a diagram illustrating the timing relationships of an internal-combustion resonator operating as a two cycle system;

Figure 5 is a vertical sectional view of a spherical resonator employing novel valve and combustion means;

Figure 6 is a vertical sectional view of an alternative form of spherical resonator;

Figure '7 is a vertical sectional view of the combustion chamber in the center of the sphere of Figure 6, taken along the line 1-1 thereof;

Figure 8 is a diagram illustrating the timing relationships of an internal-combustion resonator operating as a "four-cycle" system;

Figure .9 is a fragmentary view similar to Figure '7 and showing an alternative form of combustion chamber;

Figure 10 is a vertical sectional view of an alternative internal-combustion resonator operating as a compressor and employing a cylindrical cavity;

Figure 11 is a vertical sectional view of a conical sonic cavity which can be employed instead of the spherical or cylindrical forms;

Figure 12 is a vertical transverse section taken through the cone of Figure 11 along line |2l2 in the direction of the arrows;

Fig. 13 is another vertical transverse section through the cone on plane |3-l3 of Figure 11;

Figures 14 and 15 show a set of reed valves in open and closed position, respectively;

Figure 16 is a sectional view of a pipe and apparatus for supplying combustible mixture to a resonating chamber;

Figure 17 is a sectional view of another intake pipe means; and

Figure 18 is a graph of the pressure cycle of a fuel intake opening of the type shown in Fig. 16 or Fig. 17.

Referring particularly to Figure 1, wherein is shown a simplified spherical resonator'or com,- pre'ssor, the apparatus includes a hollow sphere in defining a closed sonic cavity H, the hollow sphere providing a curved reflecting surface I! which, in this embodiment, is substantially spherical. The curvature of this surface I! is such as to reflect sound waves towards, and

concentrate them in, a focal zone inor at the center of the sphere, the focal zone inthis instance being substantially spherical and being suggested by the dashed line ii. If the curved surface I2 is truly spherical and if sound waves are generated in the center of the sphere, the sound waves reflected by the curved surface l2 will concentrate at a focal point exactly in the center of the sphere. The sphere l0 may be supported by any suitable means, such as supports l4.

A sound-wave generator I5 is disposed within or adjacent the focal zone II. The preferred sound-wave generator comprises means for intermittently burning increments of fuel to create pressure pulses. It will be clear, however, that various types of sound generators can; be employed so long as they'transmit pressure pulses to the fluid in the sonic cavity ll.

As shown, the device includes a carburetor l8 for producing a combustible'fuel-air mixture,

the air being supplied through an air duct l1 and-the fuel being supplied through a fuel line l8. This carburetor may be of conventional design and may have the usual throttle IS. A blower, supercharger, or compressor 20 increases the pressure of the fuel-air mixture and forces it along a pipe 2| into the focal zone l3. The compressor 20 may be driven at a aoaneoa proportional or han-proportional "to the. frequency of the sound-wave generator l and.

this drive maybe from any suitable means, for example from a turbine 22 interconnected with the compressor by a shaft' indicated by dashed line-122a.

An'inlet'xzheck valve is preferably provided at some position along. the pipe 2|, being shown as including-a poppet valve 23 urged toward closed position by a spring 24; it has been found, however, .that the apparatus will function if no valve is provided, the combustible mixture being admitted ingulps because of the pressure variationsin the, standing wave. By the same token, valve 23 can-be provided with sufficient inertia and damping so that it will remain open while the system is operating, and will automatically close as a check valve to retain storage of. static pressure-when the system is not operatlng.;- An ignition device, such as a spark plug 2.5, is. positioned adjacent or within the focal zone I 3, being here shown as carried by the inner-end of pipe 2|; and this ignition device may be. energized through lead 26 extending through insulator 21 to a buzzer spark coil, step-up transformer, or other energizing source, indicated by the number 28. Closing an ignition switch 29 establishes a spark in the gap of the spark plug 25. The spark may be used continuously if desired, but in most embodiments the spark is required for starting only, since under operating conditions there isusually a small amount of continuous combustion providing a tail-flame for igniting each successive charge.

A discharge pipe 30 extends through the wall of the sphere". .The inner end of this discharge pipeterminates' preferably in a zone of the cavity llin which pressure variations are smaller than infthe focalzone l3 or adjacent the reflecting surface. II. In. the particular system illustrated, the'wave length'of the'sound waves for fundamental resonance is equal to 1.4 times the radius of the s'phereand, in this circumstance, the innerendof-the discharge pipe 30 preferably terminates approximately two-thirds the way from thecenter of the sphere to the reflecting surface 2, this being in the locus of a pressure node ivelocity anti-node) of the system, so that a may be closed and the spring of valve 3'! adpressure or valve 31 may be highly damped and not responsive to each momentary pressure but serving only to restrict discharge and permit the establishment of high mean pressure within the cavity II. The highly compressed gas may be carried away'through pipe 31a.

The operation of the simplified embodiment shown in Figure 1 can best be illustrated by assuming, first, that the pipes 2| and 30 are absent and that a single minor explosion is initiated at the center of the sphere when filled with a gas, such-as air. For example, if a blank cartridge or an explosive cap were detonated at the center of the sphere, the resulting minor explosion would establish a steep wave front sound wave? moving radially outward toward the reflecting. surface I2 at a speed c rresponding to the speed of sound in the gas filling the sonic'cavity l I. It is important to note that the wave front of such a sound wave is substantially spherical and corresponds to the curvature of the surface l2. Correspondingly, the wave front of this sound wave will reach all portions of the curved surface l2 substantially simultaneously. Since the wave impinges normally against the surface at all points, it is reflected normally inwards. When reflected,

the wave converges from all parts of the spherical surface with increasing pressure as it approaches the focal zone I3.

The sound wave thus transmitted from the center of the sphere to the surface l2 and reflected back toward the center of the sphere can be considered as a steep wave front pressure pulse. The actual intensity of the pressure pulse when first generated in the focal zone may be, for example, several hundred pounds per square inch. However, due to the inverse square law, the actual unit pressure of the pulse decreases during outward travel so that the internal pressure on the curved surface l2 will be very substantially less substantially constant pressure discharge is achieved. The innermost end of the discharge iilDe may openly communicate with the fluid in the sonic .cavity ll but, in some instances, I prefer that this communication be through a damping screen n, thereby tending to prevent resonance inthe discharge pipe 30. The discharged gases drove through a main valve 33 and thence through a' .valve'34. to be utilized for any desired purpose, such ja s'driving air drills, pneumatic machinery, etc. .Any desired portion of the discharged gases may move. through valve 35 to the turbine 22 for driving same, the power from the turbine being use.d..at least in part in driving the compressor any residual power from the turbine being available for driving auxiliary equipment or for any desired. purpose. The gases discharging from the turbine 22 may also be used for any desired Col purpose and are shown as discharging through than the initiating pressure. However, it is important to notice, also, that the reflected pressure pulse is concentrated and amplified as-it retraverses the sonic cavity toward the focal zone because of the focusing action of the curved surface l2. Correspondingly, the pressure in the focal zone l3 will again be built up because of the reflecting wave to a value which is lower than the initiating pressure only by the losses in wave transmission and reflection. This will cause a compression of the gas in the focal zone which, upon subsequent expansion, will again send a pressure pulse outward toward the curved surface l2. Actually, the pressure pulse traverses and re-traverses the sonic cavity repeatedly. In fact, if a blank cartridge or cap is detonated at the center of such a sphere, the sound waves will continue for a substantial period of time, dying out only because of losses in the system. 1 On the other-hand, it follows from elementary principles of sonics that the pressure pulse thus generated in the focal zone tends to create, upon its expansion, a rarefaction of a magnitude sub stantially equal (actually equal pressure values only if mean pressure is sufiicient) to the pressure pulse and having a peak negative pressure one-half cycle after the peak positive pressure, Correspondingly, if the distance between the focal zone and the curved surface I2 is such that pressure anti-nodes are established at the center and at the reflecting surface, then at fundamental resonance a rarefaction exists in the focal zone at theinstant the pressure pulse reaches the curved surface l2 for reflection. It also follows that, when the reflected pressure pulse again raises the pressure in the focal zone I 3 to a maximum, a rarefaction will exist immediately inside the curved surface l2.

Assume, next, that the pipes 2| and 30 are in place and that a small combustible charge is forced through the valve 23 into the focal zone l3 and is ignited by the spark plug 25. A pressure pulse similar to that previously described will move outward and be reflected by the curved surface l2 and the pressure in the focal zone l3 will vary widely about a mean pressure value, increasing when a pressure pulse is present in the zone 13 and decreasing when a rarefraction is present. The system can be designed to open the valve 23 momentarily and admit an additional increment of fuel when a sufficient rarefraction exists in the focal zone [3, preferably by virtue of the occurrence of such rarefraction. In

the present illustrative arrangement, the valve 23 is urged toward closed position by the pressure in the focal zone and by the spring 24, and is urged toward open position by the atmosphere plus compressor-induced pressure in the pipe 2|. As the pressure in the focal zone l3 decreases,

a point is reached, depending upon the adjustment of the spring 24, at which the forces holding the valve normally closed are overcome and the valve opens to admit an additional increment of combustion charge. Due to the cyclic variations in pressure in the focal zone I3, this additional increment of fuel-air mixture tends to be compressed'either before or soon after ignition is initiated by the spark plug 25.

By way of analogy to the operation of a twocycle engine, I have termed as a two-cycle operation the introduction and burning of a fuel charge in step with each pressure variation in the focal zone I3. The relationships are illustrated in Figure 4. in which is shown a sine wave 38 drawn about an abscissa base 39. Ordinates can be considered as representing pressure and abscissa as representing time, in which event the sine wave 38 approximately represents pressure variations in the focal zone when the system is operating under idling conditions or when it is resonating following a single explosion in the focal zone. The abscissa base 33 in this instance is a representation of mean static pressure in the sonic cavity which may be many times atmospheric pressure. Usually, I prefer to employ the invention with a mean pressure above atmospheric pressure and, in high output systems, more than twice atmospheric pressure, a high mean pressure having advantages described elsewhere herein.

In Figure 4, one complete cycle is represented between points I and 5, a rarefraction being present between points I and 3 and a condensation or pressure pulse being present between points 3 and 5. The reduced pressure between points I and 2 is suflicient to open the valve 23 to admit an additional increment of fuel-air mixture. Preferably, the intake period is very short, as suggested in Figure 4. It is followed by compression and ignition between points 2 and 4 pressure curve tends to rise sharply. In practice, a graphical representation of the actual pressure in the focal zone will not follow a true the curve follows more nearly the dotted line v curve 4| during this period of the cycle and, in the second place, the burning of the additional increment of fuel tends to increase and sharpen the positive pressure peak 4. so that the curve approaches more nearly the dotted curve 42 in the compression portion of the cycle. However. this distortion of the sine wave (even in filtered systems with one degree of freedom) from impulse excitation and irregular combustion rates is far less radical with the three dimensional resonators of this invention as compared with pipes, principally because of better Q loading. Also, with spherical resonance the harmonic frequencies are in a proportion of substantially 3. 5, 7, etc. This means that periodic combustion controlled for one frequenc is less apt to excite overtones than in resonators such as pipes with harmonic series of 1. 2. 3, 4, etc.

It is important to understand that, if resonant conditions are established in the sonic cavity Ii. the peak pressures in the focal zone l3 can be built up to a value many times higher than the peak pressure of a single explosion. This is true because of the automatic timing of subsequent explosions-to reinforce the pressure peaks existing because of reflection of previous pulses. Thus, even minor explosions in the focal zone can be made to reinforce resonantly the pressure undulations therein existing, thereby building up enormous pressures in this zone. Further, such momentary pressures exist, in effect, in space and need not be confined by extremely massive walls. The invention is capable of producing very large pressure variations in the focal zone l3,.while pressures substantially less than lbs/sq. in. are applied to the inner wall of the sphere.

If resonant conditions are established in the sonic cavity H, the focal zone l3 will be a zone of large or maximum pressure variation, indicated by the letter P in Figure 3. Likewise, the zone immediately inside the reflecting surface l2 will be another zone of maximum pressure variation, indicated by the letter F, though the pressure variations at P will be substantially less than at P. At spherical zone V, approximately two-thirds the way from P to ,P', pressure variations will be a minimum and the sonic energy will be primarily kinetic or velocity energy. Zone V is a zone of-large or maximum velocity variation and small or minimum pressure variation. .The relationship of pressure and velocity is shown in the curves of Figure 3, in which the abscissa scale represents the radius of the sphere, the lines A-A and B-B respectively corresponding to the center of the sphere and the side wall or reflecting surface l2. Ordinates of the upper curve represent pressure and the envelope between the two curves represents pressure variations at different radii. It will be noted that the pressure is a minimum at zone V. In the lower curve, ordinates represent velocity, and it will be noted that the envelope of the curves shows maximum velocity at zone V. This is the fundamental frequency standing wave pattern. I flnd the fundamental frequency to have an advantage over the higher harmonics because it simplifies the problem of automatic valves.

These relationships exist for a sphere resonating at its natural frequency, i. e., a sphere having a radius equal to .715 times a wave length. However, the invention contemplates that the sphere quency, there will be two or more zones V between the center and periphery of the sphere and the inner end of the dischargepipe -will in such event preferably be positioned to open on ohe ofthese. In other instances, however, pressure fluctuations in the discharge are not disadvantageous and, in some instances, these are desirable, particularly when valve 31 is adjusted for periodic opening at peak pressures for discharge of elevated pressu es, or tuned inductively or capacitatively for discharge-at other chosen phase relationship. Broadly.'therefore, the inner end of the discharge pipe 30 can communicate with'the sonic cavity H at any desired position. If, for instance, the dlscharge'is' located at the inner surface of the sphere, the discharged fluid is subject-to minor pressure variations since the bounding surface constitutes a pressure node. The alternating wave .energy is, however, at a minimum at this surface; fluid may therefore be abstracted under proper conditions with small eil'ect on the standing wave within the cavity.

Although most of the embodiments herein disclosed provide for the intermittent introduction of fuel or air, or both, it is also possible to initiate and maintain resonance with fuel and air which is supplied continuously if the combustible mixture is introduced into a region of the cavity which is subject to large pressure variations under conditions of resonance. When constant combustion occurs in such a region, an unstable evzulilibriu n exists; the slightest variation in the rate of combustion initiates a. pressure pulse which tends to be succeeded by local alternations in pressure which increase in amplitude until a condition of equilibrium is reached. During each compression period the inflow velocity of fuel and/or air is momentarily suppressed by the increase in back pressure and combustion rates are momentarily furtheraccelerated by the increase in the density and pressure of the burning gases. These two eflects thus combine to cause a period of maximum combustion during the compression period followed by a substantial decline in combustion as the rarefaction period begins. During the rarefaction period, the lowered local pressure permits high velocity inflow of fuel and air which may be faster than flame propagation, thus combustion is not at a high rate until after a period of some ignition delay which the next succeeding compression period again increases local pressures and densities. The occurrence of combustion during the compression cycle under conditions wherein combustibles are introduced during the preceding rarefactions relies in part upon ignition lag or delay which latter can be aided by the chemical properties of the fuel and temperature and uniformity of incoming fuelair mixture. Under these operating conditions, combustion continues during rarefaction periods but at a rate which is extremely small in comparison with that occurring during compression periods. This continuing combustion, however, does make it possible to dispense with any ignition system except for purposes of starting.

substantially constant 5 pressure stream of gas comprising the products of com- 'bustion can be withdrawn;

If the sphere is resonating at 'an overtone fre- In some instances, it is desirable -'to supply the air and fuel separately to the sonic cavity, and this can be accomplished by thesystem shown in Figure 2, in which no carburetor I6 is employed, the compressor or supercharger 26 merely forcing a stream of air through the pipe 2| and the valve 23. The fuel is injected in time rela-' tionship with the wave, e. g., during the intake period indicated in Figure 4, properly by a suitable injection pump forcing an increment of fuel through a fuel line 44 and an injection nozzle 45. The fuel ignites either by pressure ignition or, if

desired, by impingement on a hot spot provided, for example, by a member 46 supported on arm 41 to lie in the path of the injected fuel. The surface I2 is preferably smoothly polished or plated in order that heat radiated from the focal zone during combustion will be reflected back to the focal zone, thereby increasin the efficiency of thermal excitation.

Figure 5 illustrates a resonating sphere l0 similar to that shown in Fig. 1 but having .two coaxial pipes 25l and 252 which enter the sphere ID from opposite sides which may intermittently deliver a combustible charge into 'the central focal zone indicated by dashed line l3. A spark plug 25' and auxiliaries are shown and may be used eitherv continually or for starting only, as previously explained in connection with Figure 1.

Combustion is found to be more effective in reso-.

and numbered 439,926.

Each of the pipes 25l and 252 is supplied with a fuel and air mixture through identical apparatus. Pipe 25| for example, opens at the opposite end to the atmosphere and is provided at some convenient point along its length with a reed type check valve indicated generally by the arrow 256 and comprising a resilient metal flap 25! attached at its upper edge to an internal annular shoulder 258 disposed in a plane oblique to. the axis of pipe 25!. When a rarefaction occurs at focal zone l5 and causes the pressure within sphere III to fall below atmospheric pressure, this rarefaction is transmitted through pipe 25l so thatflap 251 is deflected to a position indicated by the dotted lines 259 and a charge of air is inducted through 25l into the sphere.

Gaseous fuel, supplied through a pipe 260-, is passed through pressure regulator 263 to fuel pipe 26I at a rate which isxcontrolled automatically by air pressure in air intake pipe 265. Pressure regulator 263 is separated into upper and lower chambers 263a and 263D by a dia phragm 264 to the lower side of which is attached 15 262 in a manner common to all pressure regulators. Fuel-air mixture ratio may be manually controlled by adjusting the openin of orifice 261 by means of needle valve 268. Air intake pipe 265 and gaseous fuel intake pipe 26| merge into a single pipe 269 which in turn enters pipe 25| at some point between check valve 256 and the opening of pipe 25| into focal zone I3. Air intake pipe 265 and fuel intake pipe 26! are provided with reed type check valves 210 and 21 I, respectively, which are constructed in the same manner as check valve 256, and like it, open to permit the induction of fuel and air during'the occurrence of rarefaction in focal zone l3. Since both air orifice 265a and fuel orifice 261 discharge. into the same negative pressure transmitted from zone 3, the fuel-air ratio will remain stable no matter what may be the degree of pressure reduction at zone l3 because the mixture is controlled by the ratio of orifices 261 and 265a and the equivalent introduction pressure established by regulator 263. If desired, one or more pipes for excess air may be provided in addition to the pipes 25I and 252 which deliver a combustible mixture. One such pipe 212 is illustrated and is provided with a reed type check valve 213.

The various check valves 213, 256, 210, and 2", may be located at various distances from focal zone l3 in order that their openings may occur in any desired sequence. In the arrangement illustrated, the excess air valve 213, is nearest focal zone l3 and will, therefore, open to admit fuel-free air for purposes of scavenging before the opening of the other valves.

' more, such a mode of operation can operate on Fuel valve 21| is positioned most remotely from focal zone 13' in order that it may open last during each rarefaction period because of wave transit time from zone l3, thereby delaying the entrance of fuel until after substantial scavenging has occurred.

A throttle 214 controls the intake of air through pipe 265 and, indirectly, by means of pressure regulator 263, and orifice 261, the amount of gaseous fuel admitted through pipe 26|.

In some embodiments, it is convenient to provide a plurality of reed type intake valves 215 at the surface of the sphere. In this way it is possible to pump large volumes of air at low pressure differential. These valves are remote from destructive flame'temperatures; and therefore can be of many different materials, mounted stressed, as reeds, or relaxed to be forceddriven by the wave pulses.

As previously noted, it is usually desirable that a discharge from the resonating cavity occur with a minimum of pressure fluctuation in the eiilux. In this particular embodiment the discharge pipe 216 withdraws fluid from a region of minimum energy density near the inner surface of sphere i6. Discharge pipe 216 is specially shaped and dimensioned to function as an acoustic band stop filter of the wave length at which sphere I6 is resonating. ,Thus pipe 216 is approximately a half wave length long and has in a plane normal to its axis at its mid-point (i. e., x/4 from each end) a short section in the shape of a cylinder having a radius of such dimensions that it reflects band-stop waves 180 out of phase. A more complete embodiment of the invention. employing mechanically-timed intake and ignition, is shown in Figures 6 and "I. As there shown, a hollow sphere provides a sonic cavity 5| and a curved reflecting surface 52 having a central focal zone 53 and being supported by a somewhat different cycle, for example, the four-cycle operation to be described with reference to Figure 6. The resonant frequency of a two-cycle" simplified system, such as shown in Figure l, is sometimes limited by the rate of fuel burning with certain fuels, the occurrence of tail flame, etc. If a modified cycle of operation is employed with reinforcing explosions occurring at a rate lower than the rate of occurrence of the pressure pulses in the focal zone, many advantages are present, including the presence of time intervals for combustion blowdown" scavenging between successive explosions. It is possible to obtain more complete combusr tion of the individual fuel increments without the occurrence of tail fiame carry over into subsequent cycles, or any continued burning during the operation of the apparatus. Good thermal efiiciency results from any method for burning the charge substantially in separate definite pulses, preferably in step with all or a portion of the number of recurring wave cycles.

Many advantages accrue from the substantial confinement of the burning to a zone which is relatively small compared to the volume of the sonic cavity. Thus, in a sphere, it is desirable that combustion be confined to a relatively small zone in the center of the sphere, the remaining radius of the sonic cavity representing a wave path. In many of the embodiments of this invention focal zone confinement of combustion is accomplished by introducing the reagents directly into the desired zone and providing means for rapid local combustion immediately after entry (usually substantially completely burning the then existing charge on each wave cycle). To aid in confining combustion to such a central zone, the embodiment of Figure 6 includes an orificed body 56 forming a part of a soundwave generator 55. This oriflced body 54 is shown as including a cylindrical side wall 56 with end flanges 51 extending a short distance inward to provide orifices 56 and to provide a peripherally confined zone 59 forming a part of a combustion chamber 66 in which the fuel increments are burned. To prevent concentrated jet effects through the orifices 56, curved baffle elements 6| may be disposed concentric with each orifice 58 to spread expanding gases into conelike shape. Each of these curved elements 6| may be mounted on an arm 62 which, if desired. may be fiexible to permit small sidewise move ment of the elements 6| to transmit sound waves directly to the gas in the sonic cavity 5| around the body 56 by actual movement or vibration of the elements 6|. In this way, these movable elements serve as periodic energy transmitting diaphragms similar to the diaphragm feature for maintaining separate the products of com bustion and auxiliary pumped fluid, as shown in my copending applications Serial Nos. 439,926 and 589,754, both now abandoned, a feature 17 which I find can be used in this invention. While the sound waves generated by such an intermittent-explosion system will not have exactly spherical wave fronts, the gas-spreading action and movement of the elements GI tend to produce a wave front which is substantially spherical, that is, a wave front sufficiently spherical to produce the results desired.

An intake pipe 65 conducts air or a fuel-air mixture to the combustion chamber 80 and discharges substantially tangentially thereinto, as best shown in Figure 6, whereby the incoming stream is whirled by deflection in the peripherally-confined zone 58 to prevent escape from the, combustion chamber 60 before ignition. This tangential entry permits much higher velocity of the incoming charge without giving problems from exceeding the rate of flame propagation and dislocating the actual combustion as must be safeguarded against with unbailled combustion zones. Disposed at some point along the intake pipe 85 is a spring-loaded check valve 51 which may operate in accordance with the pre-.

vious disclosure regarding the valve 23 of Figure l but which is preferably mechanically actuated by a push rod 68 engaging a rocker arm 68 carrying a roller I engaging a cam II on a, rotating shaft 12. This shaft is driven at a speed proportional to the combustion or oscillation frequency by means later to be described, and extends into a gear box 14 containing step-up gears driving a shaft 15 at a higher speed. This shaft is connected in driving relationship with a blower, supercharger, or rotary compressor 18 discharging into the intake pipe 55 and intaking from an induction unit 11 equipped with a suitable throttle, such as a butterfly, and operated by throttle arm 18. A suitable carburetor 80 feeds a fuel-air mixture to the induction unit 11, air entering the carburetor through an induction pipe 8| and fuel entering through a fuel line 82. If a fuel-air mixture is being supplied by the carburetor 80, the amount thereof entering the blower I6 and subsequently delivered to the combustion chamber 60 is controlled by the position of the throttle arm I8 which, in turn, is connected to a cable 83 extending to a suitable throttle control.

The fuel-air mixture may be ignited in the combustion chamber 60 by one or more spark plugs 85 at the periphery of the combustion chamber 60 and preferably firing together. These spark plugs may be energized by means of leads 88 extending through an insulator 81 mounted in the sphere and extending to a magneto 88 driven at a speed proportional to the shaft 12 from suitable gearing in the gear box II. On the other hand, if the supply of fuel through fuel line 82 is shut off, the throttle arm 18 merely controls the amount of air discharged into the combustion chamber 60. In this instance, liquid fuel may be injected into the combustion chamber 80 through a suitable fuel injector 80 acting to atomize the discharged fuel. Increments of liquid fuel are fed to the injector 80 through a pressure line 9| communicating with the discharge of a fuel injection pump 82 driven by a cam 83 on the shaft I2. For mixture control, the displacement control of the injector pump 92 can be linked to the air flow control in well known internal combustion engine design procedure.

The main discharge of gases from the sonic cavity can be through a discharge pipe 84, the inner end of which preferably terminates either 18 in the region of a pressure node .(velocity antinode), as has been indicated in Fig. 6, or in a region of minimum alternating wave energy density (i. e., adjacent an outer wall), as previously described. The gases thus discharged can be used for any purpose, including those described with reference to Figure 1 and including -the driving of the turbine-compressor arrange- 1 ments suggested. In this embodiment of the invention, the gas discharge orifice is controlled by a valve at the inner end of the pipe 84 and comprising a rotatable valve member 85 secured to a rod 88 threaded in a spider 98 and operable by a handle 88 outside the sphere. Since closing down of this valve reduces the outflow and increases the back pressure on the system, the mean pressure within the sphere may be elevated thereby. One or more suitable pressure relief valves I00 may take the place of the valve 31 in Figure 1 to relieve undue pressure in the spherical cavity or to make possible an idling of the system, assuming that the valve 95 is closed.

Discharge pipe 8| may be enlarged at some section near its outer end to provide a chamber a. Preferably the dimensions of this chamber and the length of pipe between it and the valve are selected to resonate at the frequency at which the cavity is operated, or at some frequency above or below the resonant frequency of the cavity at which an impedance can be obtained at the valve 85 which result in minimum energy losses from the resonating cavity. The

.bulb 94a also serves as a surge chamber to smooth out the discharge.

The shaft 12 is driven by a turbine I03 or other means insuring that the speed of rotation of the shaft shall be proportional to the frequency of the desired sonic oscillations in the cavity 5|. If a condition of standing wave resonance is to be maintained in this sonic cavity 5|, the speed of the shaft l2'will be proportional to the natural resonant frequency of the sonic cavity if cam-timed fuel introduction and ignition are to be used. When employing the turbine I03 to drive the shaft 12, a portion of the compressed gases may be removed from a zone of small or minimum pressure variation in the sonic cavity through an orifice I04 into a pipe I05, the orifice serving to prevent tendency for sonic oscillations within the pipe. This pipe feeds the substantially constant-pressure gases to the intake of the turbine I03 to drive same, the discharge from the turbine being either into the atmosphere or being used for other purposes such, for example, as forming a jet for propulsion or other purposes. For instance, the turbine discharge may be conducted to a nozzle I06 by opening a valve I01, or, as is often desirable, a heat exchange can be arranged with the incoming air by opening a valve I08 to conduct the turbine discharge to a jacket I09 around a portion of the intake pipe 65 preparatory to discharge through nozzle IIO. To maintain the speed of the shaft 12 constant, a governor H2 is provided having a governor arm II3 connected by link I It to a throttle arm II5 controlling the position of a throttle 6,, such as a butterfly valve positioned in the pipe I05. The governor controls the throttle H6 in such way that the shaft 12 will run at fixed speed regardless of the load placed on the shaft I2 by various settings of the throttle arm 18 associated with the blower 16. During starting of the device, the shaft 12 can be driven by auxiliary means at the desired speed.

The system thus far described with reference .type internal combustion engine.

memos to Figure 6 can be operated-on a" four-cycle" principle, the term being used as somewhat analogous to the four-cycle operation of a piston- With this mode of operation, the frequency of explosions will be one-half of the fundamental frequency of the sphere and one explosion will occur instep with alternate pressure pulses in the focal zone It should be understood, however, that modifie timing will permit other cycles of operation'in which an explosion occuraonly' after a predetermined number of. pressure pulses, the resonating qualities of the sonic cavity allowing it to fly-wheel between intervening explosions. In this connection, a large amount of energy is stored in the resonating cavity 50 and this is somewhat analogous to the flywheel of a piston-type internal combustion engine.

The four-cycle operation can best be explained with reference to Figure 8, which is similar to Figure 4 in that a sine wave S represents pressure variations in the focal zone under low-load, idling, or "fly-wheeling" conditions. Points I, 2, 3, Land 5 long this wave designate one complete some cycle, while points 5, 6, 1, ,8, and I designate a second complete sonic cycle. Together, these sonic cycles represent one complete operating cycle. The valve 61 is timed to admit combustion-supporting air at a time between points I and 3 of Figure 8. If desired, the valve 61 can be maintained open for the entire time between points I and 3, or it can be opened for any fractional length of time. As previously mentioned, fuel can be introduced along with this combustion-supporting air or it may be injected by the injection nozzle 90 near point 3. If the fuel spray hits a hot 'spot in the combustion chamber 60, the initiation of combustion is automatically controlled by the timing of the fuel injection. However, if a closer control of ignition is desired, this can be accomplished through energization of the spark plugs 85, this normally occurring around point 3. The combustion reinforces pressure peak 4, after which expansion toward negative wave peak 6 occurs. Thereafter, the pressure rises to a second peak 8, by wave resonance unaided by any additional explosion, and then drops to point I' preparatory to starting another operating cycle. An actual plot of the pressure variations in the focal zone will not be truly sinusoidal. In fact, admission of the combustion-supporting air through valve 61 will tend to make the curve between I and 3 follow more nearly the dotted line curve II1. Similarly, the explosion, reinforcing the otherwise-present pressure peak 4, will tend to raise the pressure more nearly to dotted line curve II8. Admission of auxiliary air between points 5 and 1, in a manner presently to be described, will make the curve approach more nearly the dotted line curve H9.

Returning to Figure 6, it is often desirable to supply -a stream of auxiliary air to the sonic cavity 5| in addition to the combustion-supporting air supplied through pipe 65. A stream of auxiliary air thus introduced may blend with and dilute the products of combustion and will be discharged at higher pressure through the pipe 94 or the pipe I05 along with the products. of combustion. Figure 6 shows three systems for introducing such auxiliary air, these systems being usable singly or together. In all three Systems, it is usually desirable to introduce the auxiliary air into a zone of substantial pressure variations. thereby avoiding the necessity mean pressure in the sonic cavity SI.

'of a'iiy pump for the auxiliary air-particularly when a high mean static pressure is maintained in the cavity.

' The first system for introducing a stream of auxiliary air operates in timed relationship with the shaft 12. It includes an auxiliary air-intake pipe I20, terminating adjacent the focal zone 63 just outside the vcomubstion chamber 60. A "valve IN is disposed at some position along this pipe. this valve being shown as of the poppet type, tending to remain closed because of the action of a spring I22. The valve is operable by longitudinal movement of a push rod I23 traversing the pipe I20 and bearing against a cam I24 on the shaft 12. In a four cycle operation, it is usually preferable to open the valve I2I between points 5 and 1 of Figure 8, thus tending to reduce the rarefaction toward the dotted line II9, as previously mentioned. The valve can, however, be opened during each rarefaction pulse. if desired. In any event, it should be closed before the pressure moves up too high on the subsequent pressure pulse curve.

The second system for introducing a stream of auxiliary air includes an auxiliary air-intake pipe I25 providing a spring-operated valve I26 opening upon each rarefaction pulse of sufficient magnitude to overcome the biasing action exerted by springs I21 and I28 on the valve I26, taking into account pressure variations on opposite sides of the valves. The spring I21 is stronger than the spring I28, thus tending normally to hold the valve I26 closed, the double spring arrangement is desirable because it is easier to provide any degree of valve bias against the seat independent of the spring-constant which tunes with the mass of the valve.

The third system for introducing a stream of auxiliary air to the sonic cavity 5| includes an auxiliary air-inlet pipe I30 communicating with the zone P immediately inside the reflecting surface 52 of the sphere. A valve I3I, biased toward closed position by spring I32, is employed to admit air each time a rarefaction pulse exists in the zone P' suilicient to overcome the action of the spring.

I have found that an auxiliary air system such as the second or third above mentioned will permit continued operation even if the first mentioned system is used for mechanical control of discharge phasing by selecting a desired phase setting of cam I24 for discharge at a certain pressure region on the wave curve.

Some advantages arise from employing auxiliary air-intake pipes I20 or I25 of selected length with reference to the sonic wave pattern. By appropriate control of length, a column of the auxiliary air within such pipe may be caused to resonate with such phasing as to assist pumping because of sonic energy transmitted rearwardly through the associated valve during the time that it is opening, open, or closing. A relationship aiding in the operation of the valve is one in which such a pipe has a length corresponding to one half wave length of the sound waves in the contained column of air; although lengths substantially corresponding to a multiple of sphere radius can be employed, particularly when the sphere is resonated at its fundamental. One desirable resulting phase response is that which provides a, positive pulse in the pipe adjacent the intake valve at opening time.

Figure 6 also discloses an automatic control for the system, operating in response to change in For this purpose, a control pipe I extends into the sphere and terminates in a restricted orifice I36. preferably-near a zone of low pressure variation. ,The control pipe I may also contain another restricted orifice I31, these orifices tending to smooth out any remaining pressure undulations so as to supply a constant pressure, substantially corresponding to the mean pressure in the sonic cavity 5|, to a bellows I working against a spring MI. The bellows is connected by cable or rod I42 to the throttle arm 10. The arrangement is such that the throttle is moved toward open position when the mean pressure falls. On the other hand, when the mean pressure increases, the throttle is closed, ultimately to an idling or stop position. Such a control system is shown with particular reference to the control of combustible mixtures formed by the carburetor 80. If fuel injection is utilized, the bellows I40 can be also connected to any of the well known means for varying the amount of fuel injected with each stroke of the pump 92.

Figure 9 shows an alternative construction of a combustion chamber which can be employed in the embodiments of Figures 1 and 6 to produce sound waves having a more nearly spherical wave front. Here, the orificed body is indicated by the numeral I44 and is, in itself, a small hollow sphere providing a combustion chamber I45 therein. Into this combustion chamber, the

combustion-supporting air or the fuel-air mix-..

ture is introduced tangentially through the pipe 65, previously described, and no other perforations are provided in the body I44 in the peripheral zone to which this pipe is tangential. Other portions of the body I44 are orificed by employment of short pipes I46 mounted in the walls thereof and extending a slight distance within the combustion chamber for purposes similar to the flanges 51 previously mentioned regarding Figure '7.

Figure 10 shows an embodiment of the invention employing a cylindrically-shaped resonator. Here, a cylindrical Wall I defines a cylindrical sonic cavity I5l closed at its ends by heads I52. The cylindrical wall I50 provides a curved surface I59 tending to concentrate reflected sound waves toward a focal zone which, in this instance, extends along the central axis of the cylindrical wall I50. A sound wave generator I is disposed in the sonic cavity I5I, preferably adjacent the focal zone. This generator is shown as including an orificed body I55 in the form of a small cylinder closed by the heads I52 and coaxial with the focal zone.

Increments of fuel are burned intermittently in a combustion chamber I51 within the body I56, this being accomplished, for example, by delivering combustion-supporting air to the combustion chamber I51 through plurality of intake pipes I60 spaced longitudinally along the axis of the cylinder I50, each pipe being equipped with a valve I6I, the opening of which is timed by a corresponding cam I62 on a shaft I03 turned by a suitably governed gasoline engine I64. The governing system may include a governor I65 The shaft I63 is tion chamber I51, this energization of the spark plugs being timed with respect to the sound waves. The shaft IBS-also-drives a-fuel-iniectlon 22 pump I00 feeding, by divided lines, a plurality of injection nozzles IBI, also spaced along the combustion chamber I 51. These nozzles, the spark plugs I15, and the valves I6I are disposed in such relative-position that a combustible fuel-air mixture is. ignited substantially simultaneously at spaced longitudinal positions of the combustion chamber I51. The products of combustion escape through a multitude of nippled orifices I85, these orifices preferably increasing in size in a direction away from the closest nozzle IOI so that the products of combustion are distributed substantially uniformly into that portion of the sonic cavity I5I around the orificed body I56. Such combustion products establish sound waves in the sonic cavity I5I having substantially cylindrical wave fronts, as compared with the substantially spherical wave fronts in the previously-described embodiments. Such sound waves move outward to, and are reflected by, the cylindrical surface I53, being thereby returned toward, and concentrated in, the focal zone.

A stream of auxiliary air can be supplied through one or more pipes I90, controlled by spring-loaded or cam-driven valves I9I, all in the manner previously described. Compressed gases comprising products of combustion can be withdrawn through one or more pipes I92 under control of a valve I93.

Sucha system can function on any of the operation cycles previously described. There will be a zone of large or maximum pressure variation in the focal zone. This zone is suggested by the letter P of Figure 10 and a similar zone of pressure variation is indicated at P near the reflecting surface I53. If the distance between the focal zone and the reflecting surface is approximately of a'wave length, a single cylindrical zone of large or substantial velocity variation will be established between zones P and P as indicated by .V, and the pipe I92 may desirably discharge compressed gases either from a pressure node region in or near the cylindrical zone V or from a low energy density region near the cylinder wall. It will be understood that the embodiment of Figure 10 is diagrammatically shown and that the control and auxiliary features suggested in Figure 6 may be applied thereto. Also, simplified combustion control apparatus shown for Figure 1 may also be used.

Figure 11 shows a sonic cavity in the form of a spherical sector and comprisin a cone 200 having its large end closed by a spherical refleeting surface 20I braced as at 20Ia and 20Ib for rigid reflection and having in its small end a transversely positioned grill 202, comprised of a number of horizontal bailies 204 which have an airfoil cross section as seen in Figure 11. A number of fuel nozzles 205 are disposed in rows between baffles 204 with their openings directed into the conical cavity.

Figure 12 shows a sectional view of grill 202 along the line I2-I2 as viewed normally from the cavity. The fuel nozzles 205 are supplied with fuel from fuel pump 206 by pipes 201 whenever the air pressure nearthe fuel nozzle openings falls below a certain delivery pressure. A second grill 203, parallel to the first grill 202 and located directly behind it away from the conical cavity, contains a large number of small rectangular openings 208 as seen in Figure 13.

- Small metal flaps 209 are attached at the upper and lower edges of each rectangular openin so as to-project from the grill in the direction of which large pressure variations occur.

arms

the conical rca-vity ft The: llamas-"tare slightly bowed-:toward one another. so zthat when um stressed' theirouterv edges touch-along'a' line and they form arpointed arch-as shown in the =fragmentary perspective viewv Figure-"14; .Grlil' 203 is cast with a small arch-shaped projectionall! from the verticalwsides oflzeachrectangularopening. 4 These projections provide seats forthe lateral-edges of the" flaps"! and also help to forma closure of the. rectangular opening when .theflaps are'in their archedpositiorn: 71f the-pressure within the small end. of conical cavity falls-below that on the outer side of-the grill 203 the flaps 2.09 'areresiliently bent away from arch-shaped. projections 2 I and open iikedouble doors (see Fig. 15) to permit .the passage-of fluid. Reverse flow, however, is effectively checked when the valvesassume a closed position. Valves of this type are particularly er..- fective for operation at high frequencies.

-W hen-a standing wave exists within the cavity, the small end constitutes" a focal zone 212 in When a rarefaction period begins theflaps 209 open and admit air, which flows between baflles 204 and vaporizes fuel from nozzles 205. v If desired-the the pressure of the infiowing air may be increased f above atmospheric pressure by means of a pump bustion gases remaining from burning the im-- mediately previous charge.

As the rarefaction period draws to 'a close and the compression half of-the cycle begins, the rising pressure closes the flaps .209 andrstops or reduces the flow of fuel. The fuel-and aircharge may be ignited either 'by spark plug 2|! excited by magneto 2l6, or by flameslingeringfromthe previous combustion or byflcanyq-other suitable method providing" the explosion-is timed reinforce the compression .pe'akpf .thestandin'! L Following the compression 'part'; of the wave. cycle, a new rarefaction ensues.andi'jthe, cycle is repeated if the devicesisoperating as, a*two cycle. engine; a scavengingjcycle may =be allowed-to] intervene if four cycle operation is-desired, To

prevent the occurrence ofcertainf' harmonics (such as all those above the fundamental) one or more spoiler" tubes 2l9 maybeused which in focal zone 24v sourceis negligible and-the apparatus functions mereiyasaLclosed-pipe-a Various auxiliary equipment. such as previously described, may extend into the sonic cavity and theasystem may be designed for positivemechanical controloffuel and air introduction, ignition,

etc; in'accordance with the previously described opens only during. rarefaction periods. It was assumed that no appreciable sound waves were 'generatedwithin the intake pipe itself, or that .if they were generated. they were so attenuated within the apparatus as to have little effect on thesystem; It is possible, however, to design a system in which the sound waves generated within the cavity are transmitted into the, intake pipe and are reflected therein in such a manner as to .produce large variations in pressure at the .point of supply to the cavity. These alternations occurjwith the. same frequency as the alternations in pressure within the cavity but are not necesv.

' any time, relative to the pressure cycle in the combustion zone within the cavity.

The, discussion which follows will be confined to the-case in which a gaseous mixture of fuel andair is used but it is to beundejrstood that the same methods may be applied to the. intro- 'duction of fuel and air separatehr or of one of them ali'ine. This method is particularly useful .in usingcertain hydrocarbon fuels such as butane,

which 'be eflicientlyjused when mixed with air before being introduced into the combustion region Combustible mixtures of air and fuel "dtb cavity will be referred to s the intake pipe; its

are open into the cavity while closedat the other end, and of length equal to A/fi forithe' rre quency being cancelled is cause, reflection"180 out of phase. -Also these spoiier ttubes prefer preferablylocated toward the large end of. the

ably open into a' pressure antinode for the. un-

desirable harmonic. The compressed air and combustion products may be withdrawn through a discharge pipe 2l8 preferably )./4'longand inner'end; at-which discharge into the cavity occurs, will be referred to as the inner end; its

opposite end, whether open or closed, will be referred to as the outer end.

Inany of theQembodi-ment s herein described, cavity-pipe interconnection such as the intermittent introduction of fuel and air into the cavity. is certain to generate a series of powerful pulses travel from their point of generation, i. e..

cone in order that gas having a minimum-of-al,-.

ternating energy density may be .discharg'edfi' Also similar pipe 218a in single, multiple, or in the form of an ex i ;endedslot-passage, may be directed so as to give a rad'iation pressure pro .pulsion component with the open ends at a ve-g locityantinode.

The solid angle subtended at the apex of the 'cone may be of any value provided it is not so small that the effect f. divergence from the.-

the inner end. backwards along the pipe until it is-'reflected'either by encountering a rigidwall surface'lor hy sudden expansion'into an enlarged chambeiz; If the fuel and. air' supply apparatus has within it anumber' of small obstructions and apertures atvarious distances from the opening into the cavity a number of small amplitude waves will be reflected and each will be attenuated so that no substantial pressure variations result therefrom at; the-inner en'd. .lfphowever. the intake pipe is smooth and generallv free from obe-ignit'e if brought into the cavity duringgth ,rarefaction period. This method pro- Lvides .a ineans for introducing the bulk of the charge immediately before peak compression. f

V 'Thpipe used for introducing the fuel into the continuity, and if this discontinuity is such as to reflect almost entirely any wave impinging upon it then such reflected waves will return to the inner end' to produce large pressure variations thereat. These pressure variations would occur exactly in phase with the pressure variations within the cavity at the pressure antinode region adiacent the pipe's inner end if the length of the intake pipe from its inner end to the discontinuity is precisely a half wave length, or multiple thereof, of the cavitys resonant frequency. If, however, this distance is other than a half wave length, or multiple thereof, the returned pressure pulse will be out of phase with the pressure variations in the cavitys combustion zone. The pipe length may be made adjustable and may be selected so that the reflected pressure pulse occur in such a manner as to force an increment of fuel into the cavity at any desired time with reference to pressure variations in the combustion region. As previously pointed out, best operation with fast burning fuel is achieved if fuel is introduced after the occurrence of rarefaction and just previous to peak compression.

Figure 16 is a diagrammatic illustration .of an apparatus for utilizing pressure pulses within the fuel intake pipe to introduce fuel at any desired time. Fuel intake pipe 233 is mounted in the wall of a combustion chamber l0' (indicated only fragmentarily) and opens at its inner end 28! into a combustion region indicated by the dotted line l3" which is also a pressure antinode region or cavity Ill". The outer end 232 of fuel intake pipe 280 is internally threaded to receive the externally threaded section ofpipe 283. The opposite end of pipe section 293 projects into a tank 234 through a closely fitting opening 231- Tank ing through pipe 233. When pipe section 293 is rotated in its threaded connection, its longitudinal movement makes it possible to adjust the distance from the combustion region l3" within the cavity l0" to the opening of pipe-section 283 into tank 284. Thus in one mode of operation for example, this distance may be made slightly less than wave length in which casea rarefaction at I3" will cause an insurge of fueland air mixture into region l3" almost of a period later at a time shortly before peak-compression. It will be noted that no valve is necessary for the intermittent introduction of fuel in-this device.

In Figure 17 is shown a fuel intake-pipe which uses a rigid wall surface in its outer end inorder to reflect sound waves.- A fuel intake pipe 290 is mounted in the wall of a resonating chamber jlfl, and projects inwardly So asto open into the resonating cavity at a combustion region indicated by the dashed line |3' which is al so=a pressure antinode region of chamber "1". Fuel half wave length of the cavitys resonant frequency then a pressure pulse I3" will travel down pipe 290, be reflected at surface 293 and return .40 293 is supplied with fuel and air mixture enterslightly less-than one period so as to introduce an increment of fuel slightly before the compression p ak.

It.,is frequently desirable to prevent backfireinto the fuel intake pipe by means of a screen transversely positioned in the pipe near the inner and. Such a screen i indicated by numeral 281 in Figure 16 and by numeral 295 in Figure 17.

In the graph of Figure 18 the solid line 300 in-' dicates the pressure cycle within combustion zone I31" and the dashed line 3M indicates the occurrence of pressure pulsesjust within the inner end of the fuel intake pipe and resulting from the reflection of previous pulses from the end of said pipe. The induction of fuel from the fuel intake pipe into the combustion zone of the resonatingficavity at the fuel intake opening is aided when the pressure Just within the inner end occurs before the pressure within the cavity a slight distance from the fuel pipe opening, Although the pipe length may be adjusted to cause any des i red phasing, including in-phase resonance, in this case the length has been selected so that a reflected pressure pulse 302 appears at the fuel intake opening slightly before the occurrence g f peak compression 393 in cavity "1". The maximum intake period is indicated in the graph by the time abscissae 394 to 305. Although the embodiments of Fig. 16 and Fig. 1'7 do not employ intake valves, it is to be understood that such valves whether mechanically driven or pressure responsive may under proper circumstance be used in connection with such a system. Any of the embodiments described in previous figures may likewise be converted to a system of this type. For example, the embodiment of Fig. 6 may operate in the manner of Fig. 16 if the turbine casing is sufiicient ly enlarged, or if a sufllciently large chamber is interposed between the turbine and the air intake pipe 65, or if air from the turbine enters .the air intake pipe 65 from a side branch, the end of the air intake pipe being closed by a solid wall. In all embodiments of the invention, there will be a remarkably complete combustion of the fuel employed for generating the sound waves. The described sonic standing wave established in the chamber creates very large variations in pressure adjacent the focal zone, and these appear to aid combustion as well as to give large expansiontien capable of high outputs and excellent.

thermal -;efllc iencies. One consideration in obtaining high output from the sonic systems herein disclosed is the maintenance of a relatively high mean-pressure-in the sonic chamber. This mean pre sure ,is controlled largely bythe discharge of gases from-the sonic cavity and by the automatic throttlecontrolof Figure 6. If this discharge of gases is-against athrottling valve or other means for maintaining a back pressure. on the system, it is very easy to obtain the mean pressures of two atmospheres or above desired for high output systems.

. invention is not limited to the use of up pipe 290 toward combustion region I3"- in oxygen-free. fuels, but comprehends the possibility ef'injecting explosive type reagents to generate the wave pattern.

In the present specification, the term sound waves is usedwith reference to elastic waves transmitted through a deformable medium, typically gases in the present instance, the waves travelling therethrough at the speed of sound in this medium, the frequency being usually, though not necessarily, within the frequency range of audibility for the human ear. Similarly, terms such as sonic, acoustic, and similar terms are herein used without limitation as to humanly audible frequencies. Actual test operation has proven that many practical sizes and modes of operation of the apparatus results in frequencies recognized as within the human audible range. For human comfort, this invention comprehends the provision of sound deadening covering over the apparatus as well as conduit muiliers such as standard engine exhaust mufflers connected with the various intake and discharge pipes.

Certain of the broader subject matter of the instant application is disclosed and claimed in my copending applications, Serial Nos. 439,926 and 589,754, both now abandoned, which disclose and claim certain of the broader aspects of a thermally excited resonator without limitation to the employment of diverging waves only.

Various changes and modifications including combining any one or more embodiments of this invention into series multi-stage or parallel multiple combinations can be made without departing from the spirit of the invention as defined in the appended claims.

I claim as my invention:

1. In combination: walls defining a closed cavity and asubstantially curved sound-wavereflecting surface shapedto reflect sound waves originating within a predetermined zone spaced from said reflecting surface, toward a focal zone of said reflecting surface, said cavity being adapted to contain a fluid; a thermally excited sound-wave generator located within said predetermined zone for establishing sound waves in said fluid, said generator being operable at a frequency high enough to produce sound waves whose quarter wave length is less than the distance between focal zone and reflecting surface, and which is such as to establish standing wave resonance, with sound waves. launched toward said reflecting surface reflected and concentrated in said focal zone to produce a pressure antinode at said focal zone and a velocity anti-node between said focal zone and said reflecting surface; means for intermittently introducing fluid to said pressure anti-node region of said cavity in response to decreasing pressure of said sound waves; and discharge means leading from the velocity anti-node region of said cavity.

2. In combination: walls defining a closed cavity and a substantially curved sound-wavereflecting surface disposed geometrically about a focal zone to reflect toward said zone sound waves which originate therein, said cavity being adapted to contain a fluid; a thermally excited sound-wave generator located within said closed cavity at a position adjacent said focal zone for generating said waves, said generator being operable at a frequency to produce standing wave resonance in the cavity, with a wave train moving from said generator through said fluid to said reflecting surface to be reflected to and concentrated in said focal zone, all in a manner to produce a pressure anti-node region at said surface, another pressure anti-node region at said focal zone, and a velocity anti-node between'said pressure anti-nodes; means for intermittently 28 introducing fluid to the pressure anti-node region at said focal zone of said cavity in response to decreasing pressure of said sound waves; and fluid discharge means leading from said velocity anti-node region of said cavity.

3. A combination as defined in claim 2, in which -said reflecting surface is substantially spherical in shape, and wherein the radius of said sphere is greater than a quarter wave length.

4. A combination as defined in claim 2, in which said reflecting surface is substantially cylindrical in shape to provide an elongated focal zone, and in which said sound-wave generator is elongated to occupy a substantial portion of the length of said focal zone.

5. A combination as defined in claim 2 in which said cavity is substantially conical in shape and said reflecting surface comprises the base of said conical cavity and corresponds substantially to the surface of a sphere having its center at the apex of said conical cavity.

6. In combination: walls defining a cavity, said walls including a reflecting surface shaped to reflect sound waves originating adjacent a focal zone of said reflecting surface, said cavity being adapted to contain a fluid; a sound wave generator within said closed cavity at a position adjacent a focal zone of said surface; means for operating said sound wave generator at a frequency which resonates said cavity; means communicating with a pressure antinode region for delivering a fluid to said closed cavity during periods of low pressure; and discharge means for withdrawing fluid from said closed cavity at a position near a zone of substantial velocity variation.

7. In combination: walls defining a cavity bounded at least in part by a reflecting surface shaped to reflect resonant sound waves therein toward a region of relatively high energy density; means for resonating fluid in said cavity; intake means for introducing fluid into said cavity near a region of large pressure variation during rarefaction periods at said region; discharge means leading from a pressure antinode region of relatively low energy density, said discharge means being rearwardly directed to provide a propulsive jet and having a length sufificient to produce a velocity antinode at the outer opening to produce alternate jetting and sucking.

8. In combination: walls defining a cavity bounded at least in part by a reflecting surface shaped to reflect sound waves toward a region of relatively high energy density; means for introducing fluid into said cavity; means for resonating fluid in said cavity; and brace means for connecting said reflecting surface walls to other support means, said brace means being sufficiently rigid to substantially reduce any vibration of said reflecting surface; and means for discharging compressed fluid from said cavity.

9. In combination: walls defining a cavity bounded at least in part by a reflecting surface shaped to reflect sound waves originating in a focal region of said reflecting surface toward a region of relatively high energy density; means for resonating fluid in said cavity; intake means for introducing fluid into said cavity near a region of large pressure variation during rarefaction periods at said region, said intake means comprising a plurality of reed valves having a frequency not less than the resonant frequency of the cavity; and discharge means from said cavity.

19. A combination as in claim 9 in which said

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