SHOCK WAVE GENERATOR

Abstract: A two-phase shock wave generator incorporating a combustion chamber (20) including a first combustion portion (25) having an input port and a second detonation portion (27) downstream of the first portion (25) and having an output aperture (34), an air-fuel supply line (15) operative to feed the input port with an air-fuel mixture, an igniter (16), associated with the air-fuel supply line (15) and a turbulence stimulator (22), mounted in the combustion chamber (20), which enhances and controls burning of the air-fuel. The turbulence stimulator (22) includes a first section (24) having a predetermined first gas dynamic resistance and a second section (27) having a predetermined second gas dynamic resistance. The first resistance is such that burning of the air-fuel mixture in the combustion portion yields a predetermined pressure level suitable for initiating detonation of the remaining air-fuel mixture in the detonation portion. The second resistance supports continued detonation of the remaining air-fuel mixture in the detonation portion. Preferably, the second gas dynamic resistance is lower than the first gas dynamic resistance.

Description: SHOCK WAVE GENERATOR The present invention relates to combustion and explosion processes in general, more particularly, to the use of combustion or explosion processes for industrial application, such as cleaning of industrial equipment and machinery by devices employing these processes. Proper maintenance of industrial machinery generally includes frequent removal of undesired accumulations of particles on different elements of the machinery. Parti¬ cles accumulation on the machinery parts can be minimized by cleaning the environment surrounding the machinery. Various air cleaning devices have been used for that purpose. Although a clean working environment reduces parti¬ cle accumulation on the machinery parts, it cannot pre¬ vent such accumulation completely. Thus, more direct methods for cleaning the machinery parts are often re¬ quired. It is known that efficient cleaning of various machinery parts may be achieved by generating shock waves in the vicinity of the parts thereby "shaking off" dust particles and other accumulations from the parts. Alter¬ natively, the shock waves may be induced onto a machinery part, causing the part to vibrate and "shake off" the accumulations. Shock wave cleaning is particularly useful for elements which are not readily removed for cleaning and/or elements which are particularly susceptible to the use of other cleaning methods and/or cleaning materials. Gas dynamic generators which induce shock wave vibrations in their vicinity are known in the art. When a gas dynamic generator is placed near a machinery element to be cleaned, the shock waves induced in the vicinity of the element can be utilized to clean the element, as described above. Gas dynamic generators are useful aids in the production of construction materials and appara¬ tus, metallurgy, mining, the chemical industry, oil processing and the food industry. Gas dynamic generators have been used in the past, for example, for cleaning dust accumulation and other deposits in a centrifugal compressor. The centrifugal compressor includes a pumping wheel with pumping blades mounted in a pumping chamber. Nozzles, which are connect¬ ed to a source of pressured gas via a gas channel, are mounted in the pumping chamber at a preselected distance from the pumping blades. The source generates high pres¬ sure gas pulses which impinge on the pumping blades thereby removing undesired accumulations from the blades. For optimal results, the distance between the nozzles and the pumping blades is selected to be between 1 and 1.5 times the diameter of the gas channel. Gas dynamic generators have also been used for cleaning contaminated electrodes, particularly for puri¬ fying electrodes of electrofilters. An ignited air-fuel mixture is transported through an elongated detonation chamber, in which the burning mixture develops a high velocity, and is released onto a shock receiving plate which is associated with a shock transporting block. The block carries shock waves produced in the plate to the electrodes, thereby causing high acceleration vibrations in the electrodes to "shake off" the deposits. Although existing gas dynamic pulse generators are useful for some applications, such as for cleaning com¬ pressor blades and removing deposits from electrodes, these systems generally suffer from high energy consump¬ tion and low operating efficiency. The output pressures obtained by devices as described above generally does not exceed 10 - 12 bars and, even then, most of the gas dynamic energy is not utilized since only a fraction of the pulsed gas dynamic energy is converted into shock waves in the part to be cleaned. Additionally, since the burning rate of the air-fuel mixture is relatively low (typically 400-500 meters per second) compared to the expansion rate of the mixture, only part of the mixture (typically not more than 30%) is utilized to produce the gas dynamic pulses. This difference between the burning rate and the expansion rate may also result in undesira¬ ble release of a flammable air-fuel mixture, thereby reducing the efficiency of the system and endangering the persons operating the system. To produce sufficiently powerful shock waves, existing shock-wave generators often employ straight, elongated, combustion chambers, typically having a length of 4 meters or longer. This results in systems which are highly space-consuming and, therefore, imprac¬ tical for various application. It is well known that the life-span of filters, such as the air filters used by heavy-duty diesel en¬ gines, can be somewhat extended by periodic cleaning of the filters. Normally, such filters are cleaned either superficially, by manually shaking the filters, or by applying pressured air in a reverse direction, i.e. in a direction opposite that of the air flow during normal operation. However, since air-pressure cleaning is local in nature, the use of air-pressure cleaning devices is often tedious and damaging to the filters being cleaned and is generally not thorough. It is an object of the present invention to provide a more efficient and more powerful method and apparatus for generating gas dynamic pulses, e.g. shock waves. A shock wave generator constructed and operative in accord¬ ance with the present invention may be utilized to remove various deposits from industrial machinery parts, for example to clear clogged pipes or to ensure free flow of dry materials. It is a further object of the present invention to provide a folded gas dynamic pulse generator wherein the long dimension of the generator is folded, in accordance with a predetermined folding scheme, to provide a rela¬ tively compact shock wave generator having a relatively long effective length. It is yet a further object of the present invention to provide improved apparatus for cleaning filters, particularly air filters, using gas dynamic pulses. In accordance with a preferred embodiment of the present invention there is thus provided a two-phase shock wave generator including a combustion chamber including a first, combustion, portion having an input port and a second, detonation, portion downstream of the first portion and having an output aperture, an air-fuel supply line, operative to feed the input port with an air-fuel mixture, an igniter, associated with the air- fuel supply line, which ignites the air-fuel mixture in the supply line and initiates a burning front which propagates towards the input port and a turbulence stimu¬ lator, fixedly mounted in the combustion chamber, which enhances and controls burning of the air-fuel mixture and includes a first section, situated within the combustion portion of the combustion chamber and having a predeter¬ mined first gas dynamic resistance and a second section, situated within the detonation portion of the combustion chamber and having a predetermined second gas dynamic resistance, wherein the first resistance is such that burning of the air-fuel mixture in the combustion portion yields a predetermined pressure level suitable for initi¬ ating detonation of the remaining air-fuel mixture, in the detonation portion, and wherein the second resistance supports continued detonation of the remaining air-fuel mixture in the detonation portion. Preferably, according to the present invention, the second gas dynamic resistance is lower than the first gas dynamic resistance. In a preferred embodiment of the present invention, the air-fuel supply line is associated with the input port via a perforated nozzle which scatters the burning front substantially upon entry of the burning front into the combustion chamber. Additionally, in a preferred embodiment of the invention, the turbulence generator includes a plurality of gas dynamic obstructers positioned at fixed locations along the combustion chamber to yield the preselected first and second gas dynamic resistances along the com¬ bustion and detonation portions, respectively. Preferably, each obstructer includes a plurality of rods, generally perpendicular to the direction of propa¬ gation of the burning front in the combustion chamber. In a preferred embodiment of the invention, the plurality of rods are arranged along a generally helical path, having a predetermined pitch. In one preferred embodiment of the present inven¬ tion, the combustion chamber of the shock wave generator includes at least one bent portion. The at least one bent portion may be include at least one bend in the combus¬ tion portion of the combustion chamber and/or at least one bend in the detonation portion of the combustion chamber. The locations of the bent portions are prefera¬ bly selected in accordance with a predetermined folding scheme. Alternatively, in accordance with a preferred embod¬ iment of the invention, there is provided a shock wave generator including a combustion chamber having an input port and an output aperture, an air-fuel supply line operative to feed the input port with an air-fuel mix¬ ture, an igniter, associated with the air-fuel supply line, which ignites the air-fuel mixture in the supply line and initiates a burning front which propagates towards the input port, a turbulence stimulator, fixedly mounted in the combustion chamber, which enhances and controls burning of the air-fuel mixture and a perforated nozzle, associated with the input port, which scatters the burning front substantially upon entry of the burning front into the combustion chamber. Further, in accordance with a preferred embodiment of the invention, there is provided a method of generat¬ ing a shock wave using a two-phase burning process, including the steps of supplying an air fuel mixture from an air-fuel supply line to a combustion chamber, igniting the air-fuel mixture in the supply line when the combus¬ tion chamber is filled with a preselected amount of air- fuel mixture, thereby initiating a burning front propa¬ gating towards the combustion chamber and enhancing and controlling the burning process by stimulating turbulence in the combustion chamber, wherein turbulence is stimu¬ lated by the steps of imposing a first, predetermined, gas dynamic resistance in the combustion portion during a first, combustion, phase of the burning process and imposing a second, predetermined, gas dynamic resistance during a second, detonation, phase of the burning proc¬ ess, and wherein the first resistance is such that burn¬ ing of the air-fuel mixture during the combustion phase yields a predetermined pressure level suitable for initi¬ ating detonation of the remaining air-fuel mixture, during the detonation phase, and wherein the second resistance supports continued detonation of the remaining air-fuel mixture. In a preferred embodiment of the invention, the second gas dynamic resistance is lower than the first gas dynamic resistance. Preferably, the method further includes the step of scattering the burning front substantially upon entry of the burning front into the combustion chamber. Alternatively, in accordance with a preferred embod¬ iment of the invention, there is provided a method of generating a shock wave including the steps of supplying an air fuel mixture from an air-fuel supply line to a combustion chamber, igniting the air-fuel mixture in the supply line when the combustion chamber is filled with a preselected amount of air-fuel mixture, thereby initiat¬ ing a burning front propagating towards the combustion chamber, enhancing and controlling the burning process by stimulating turbulence in the combustion chamber, scat¬ tering the burning front substantially upon entry of the burning front into the combustion chamber and detonating the air fuel mixture in the combustion chamber. In a preferred embodiment of the invention, the method further includes the step of removing the detonat¬ ed mixture at an output aperture to form a gas dynamic pulse thereat. Further, in accordance with a preferred embodi¬ ment of the invention, there is provided apparatus for cleaning a filter including a shock wave generator which generates at least one gas dynamic pulse in a given direction and a reflector which reflects the at least one gas dynamic pulse onto at least a portion of the filter. Preferably, the shock wave generator used by the cleaning apparatus includes a two-phase shock wave gener¬ ator as described above. The apparatus preferably further includes an enclo¬ sure for accommodating the filter. The filter is prefera- 6/ 6 8 bly an air filter. In a preferred embodiment of the invention, the cleaning apparatus further including a positioning mechanism which controls the position of the reflector relative to the filter. The apparatus preferably fur¬ ther includes a controller which controls the operation of the positioning mechanism and the activation of the shock wave generator. The controller preferably operates the positioning mechanism and activates the shock wave generator in accordance with a predetermined cleaning sequence. The cleaning sequence preferably includes a prede¬ termined number of activations of the shock wave genera¬ tor at each of a predetermined number of positions of the reflector relative to the filter. Preferably, the prede¬ termined number of activations of the shock wave genera¬ tor includes between 1 and 20 activations at each posi¬ tion of the reflector. In a preferred embodiment of the invention, the filter is a cylindrical filter and the predetermined number of positions are spaced along the height of the cylindrical filter. Preferably, the prede¬ termined number of positions are spaced by a spacing of between 5 and 10 centimeters. The present invention will be better understood from the following detailed description of preferred embodi¬ ments of the invention, taken in conjunction with the accompanying drawings in which: Fig. 1 is a schematic, cross-sectional, illustration of a gas dynamic pulse generator, constructed and opera¬ tive in accordance with a preferred embodiment of the present invention; Fig. 2 is a pictorial, side view, illustration of a two-phase turbulence stimulator useful for the operation of the gas dynamic generator of Fig. 1 according to a preferred embodiment of the present invention; Fig. 3 is a schematic, cross-sectional, illustration of a portion of a folded gas dynamic pulse generator, constructed and operative in accordance with another preferred embodiment of the present invention; and Fig. 4 is a schematic, cross-sectional illustration of apparatus for cleaning a filter using pulse dynamic pulse generation, constructed and operative in accordance with yet another preferred embodiment of the present invention. Reference is now made to Fig. 1, which schematically illustrates a preferred embodiment of the gas dynamic pulse generator of the present invention. As shown in Fig. 1, the gas dynamic pulse generator preferably in¬ cludes a fuel supply line 10, an air supply line 12, a mixer 14, an air-fuel mixture carrier line 15, an igniter 16 associated with a preselected portion of carrier line 15, a perforated nozzle 18 mounted to the end of carrier line 15, a combustion chamber 20 and a two-phase turbu¬ lence stimulator 22 mounted in combustion chamber 22. Fuel, preferably a combustible gas such as Methane (CH 4 ), and air are compressed through lines 10 and 12, respectively, into mixer 14 at suitable pressures so as to provide, at the output of mixer 14, an air-fuel mix¬ ture having a preselected fuel to air ratio. Preferably, the fuel to air ratio provided by mixer 14 is higher than the ratio required for a normal chemical reaction between the fuel and the air. The air-fuel mixture is carried via carrier line 15 and released via perforated nozzle 18 into combustion chamber 20. Igniter 16, preferably a spark plug sealingly mounted into carrier line 15, is activated only after combustion chamber 20 has been filled with a predetermined amount of fuel-air mixture suitable for proper combustion. Activation of igniter 16 initiates burning of the air-fuel mixture in carrier line 15, creating a burning front which propagates towards perforated nozzle 18. When the burning front reaches perforated nozzle 18, the front is broken and a scattered flame front is released into combustion chamber 20. Scattering of the burning front by nozzle 18 is preferred because it provides a considerably larger area of contact between the propagating burning front and the air-fuel mixture in combustion chamber 20. It should be appreciated that the increased contact area between the burning front and the air-fuel mixture pro¬ vides more rapid combustion of the air-fuel mixture in combustion chamber 20. This initiates a first phase of the burning process, hereinafter referred to as the combustion phase. Within combustion chamber 20, the burning front confronts two-phase turbulence stimulator 22 which en¬ hances and expedites combustion of the air-fuel mixture in a controlled manner, as will now be described. Fig. 2 pictorially illustrates turbulence stimulator 22 in greater detail. As shown in Fig. 2, turbulence stimulator 22 is preferably composed of a longitudinal axis 23 and a plurality of radially extending rods 28 which are generally perpendicular to a longitudinal axis 23, i.e. generally perpendicular to the propagation direction of the burning front. In accordance with a preferred embodiment of the present invention, turbulence stimulator 22 includes a first section 24, associated with a first, combustion, portion 25 of combustion cham¬ ber 20 (Fig. 1), and a second section 26, associated with a second, detonation, portion 27 of combustion chamber 20 (Fig. 1) . The spaces between neighboring rods 28 in first section 24 are preferably smaller than the spaces between neighboring rods 28 in second section 26. Additionally or alternatively, rods 28 in section 24 may be thicker than rods 28 in detonation section 26. In a preferred embodiment of the invention, rods 28 of sections 24 and 26 of stimulator 22 are arranged in equiplanar groups, hereinafter referred to as obstructers 30 and 32, respectively. The number of rods in each obstructer may vary but, preferably, each obstructer 30 includes more rods 28 than each obstructer 32. For exam¬ ple, each of obstructers 30 may include four rods 28, arranged in the form of a cross, and each of obstructers 32 may include two radially aligned rods 28. The rods of successive obstructers, 30 or 32, are preferably angular¬ ly shifted such that the outward ends of rods 28 define a helical path having a preselected pitch. The pitch of the helical path defined by the ends of rods 28 is preferably selected, empirically, so as to produce optimal turbu¬ lence of the burning air-fuel mixture in combustion chamber 20. In a preferred embodiment of the present invention, the radially outward ends of rods 28 do not touch the internal surface of combustion chamber 20. Preferably, there is a preselected distance, typically at least 2 - 3 millimeters, between the ends of rods 28 and the internal surface of chamber 20. This provides improved, turbulat- ed, flow of the burning air-fuel mixture in combustion chamber 20. Rods 28, which preferably have a diameter of between 10 and 14 millimeters, are operative to impose a prede¬ termined resistance on the propagating burning gasses in combustion chamber 20 and, thereby, to control the gas pressure in combustion chamber 20 during the burning process. In a preferred embodiment of the invention, obstructers 30 and 32 are positioned along axis 23 with appropriate spacing so as to yield a desired burning sequence of the air-fuel mixture in combustion chamber 20, as described below. Due to the generally thicker rods 28 in first sec¬ tion 24 and/or the greater number of rods 28 in each obstructer 30 and/or the closer spacing between succes¬ sive obstructers 30 in first section 24, the resistance imposed by section 24 on gasses flowing therealong is generally greater than the resistance imposed on gasses flowing along second section 26. This results in a rapid build up of pressure as long as the burning front inter¬ acts with first section 24, reaching a peak suitable for detonation of the air-fuel mixture substantially when the burning front reaches the interface between section 24 and section 26. According to the present invention, the peak pressure reached by the burning front, at the inter¬ face between sections 24 and 26, is sufficient for initi¬ ating detonation of the remaining, unburnt, air-fuel mixture. Thus, the burning process undergoes a transition from the combustion phase, heretofore described, to a second phase of the burning process, hereinafter re¬ ferred to as the detonation phase, in which the remaining air-fuel mixture is detonated. As known in the art, detonation of the air-fuel mixture is initiated only when the pressure of the air- fuel mixture exceeds a suitable, threshold, pressure level. In a preferred embodiment of the invention, this threshold pressure level is exceeded substantially at the 13 interface between portions 25 and 27 of combustion cham¬ ber 20. As described above, the transition from the combus¬ tion phase to the detonation phase preferably occurs when the burning front is substantially at the interface between portions 25 and 27. At this point, the pressure building resistance provided by section 24 of stimulator 22 is no longer required. Nevertheless, in a preferred embodiment of the invention, second section 26 of stimu¬ lator 22 imposes some resistance on the propagating gas, as required for rapid yet complete and controlled detona¬ tion of the unburnt air-fuel mixture in detonation por¬ tion 27. Since the gas dynamic resistance suitable for sup¬ porting detonation is generally lower than that suitable for pressure build-up, rods 28 are generally thinner along section 26 and/or obstructers 30 are less spaced apart then obstructers 32, as described above. Generally, the gas dynamic resistance imposed by a given obstructer 30 or 32 depends on the volume taken up by the given obstructer which, in turn, depends on the thickness and length of rods 28 and the number of rods 28 included in the given obstructer. For given thickness, length and number of rods 28 included in obstructers 30 and 32, the average gas dynamic resistances in portions 25 and 27 depends on the spacing between obstructers 30 and 32, respectively. The detonation phase of the burning process produces a high pressure gas dynamic pulse, i.e. a shock wave, released through an output aperture 34 of chamber 20. The output pressure, in a preferred embodiment of the inven¬ tion, is approximately 80 atmospheres or more. As known in the art, the shock wave released from aperture 34 or, preferably, a series of sequentially generated shock waves, may have various industrial application, such as cleaning of industrial machinery elements. It should be appreciated that the burning process described above, using perforated nozzle 18 and two-phase turbulence stimulator 22, provides a particularly efficient shock wave generator which is considerably more efficient than corresponding conventional shock wave generators. It is appreciated that careful positioning of ob¬ structers 30 and 32 along sections 24 and 26, respective¬ ly, is required in order to produce optimal two-phase shock wave generation. The present inventor has found that satisfactory results are obtained when obstructers 30 and 32 are spaced in accordance with the following empirical equation: X = lOd/m wherein: X is the distance between successive obstructers, 30 or 32; d is the average diameter of rods 28 in each ob¬ structer, 30 or 32; and m is the gas dynamic permeability of each obstruct¬ er, 30 or 32, in portions 25 or 27, respectively. It will be appreciated that permeability m may be determined from the following formula: m = s c s^-, wherein: S.J- is the cross-sectional area of the obstruct¬ er, 30 or 32, perpendicular to axis 23; and s c is the cross-sectional area of combustion chamber 20. A working prototype, designed according to the present invention, was constructed on a combustion cham¬ ber having a diameter of 120 millimeters and a length of 4 meters. The obstructers in the first, 2.5 meter long, section of the turbulence stimulator included four rods, each having a diameter of 14 millimeters. The permeabili¬ ty of each obstructer in the combustion portion, deter¬ mined as described above, was 3.5. Thus, according to the equation given above, the proper distance between succes¬ sive obstructers in the first section was 40 millimeters. The obstructers in the second section, the remain¬ ing 1.5 meters, of the turbulence stimulator included two rods, each having a diameter of 12 millimeters. The permeability of each obstructer in the detonation por¬ tion, determined as described above, was 2. Thus, accord¬ ing to the equation given above, the proper distance between successive obstructers in the second section was 20 millimeters. Experiments with the above described prototype yielded an output shock wave having a power level approx¬ imately 5 - 7 times greater than that of conventional shock wave generators. The energy consumption of the prototype was approximately 2 - 3 times lower than that of conventional generators. In the above described prototype, the combustion chamber has a length of approximately 4 meters, while the diameter of the combustion chamber is only 120 milli¬ meters. It is appreciated that even longer combustion chambers may be required for certain applications of shock wave generators. Such long combustion chambers have a bottleneck effect, resulting in generators which consume considerable space and are hard to move from place to place. Thus, in a further preferred embodiment of the present invention, the combustion chamber is folded to a compact configuration which maintains the effective length of the combustion chamber. Reference is now made to Fig. 3 which schematically illustrates a portion of a folded combustion chamber 120 of a compact shock wave generator, constructed and opera¬ tive in accordance with a further preferred embodiment of the present invention. In analogy to combustion chamber 20 of the shock wave generator of Fig. 1, combustion chamber 120 includes a first, combustion, portion 125 and a second, detonation, portion 127. However, in contrast to the embodiment of Fig. 1, combustion chamber is bent at various locations, in accordance with a predetermined folding scheme, to reduce the over-all length of the generator. Two bends of combustion chamber 120 are shown in Fig. 3, by way of example. A bend 140 is shown in combustion portion 125 and a bend 142 in shown in detona¬ tion portion 127. It is appreciated that a number of bends, similar to bends 140 and 142, may be formed in either or both of portions 125 and 127, to obtain a desired shape of the shock wave generator, in accordance with specific design considerations. The combustion chamber thus formed defines a segmented propagation path for the moving front, whereby a curved propagation path of the burning front is defined at bends 140 and 142 while a straight propagation path is defined at the segments between bends. The shock-wave generator of Fig. 3 further includes a turbulence stimulator 122 having a first section 124 and a second section 126, analog to sections 24 and 26 in turbulence stimulator of Fig. 2. Turbulence stimulator 122 is preferably composed of an axis 123 and a plurality of radially extending rods 128 which are generally per¬ pendicular to axis 123, i.e. generally perpendicular to the propagation direction of the burning front. The arrangement of rods 128 in sections 124 and 126 is preferably analogous to that of rods 28 in sections 24 and 26 of Fig. 2, i.e. the spaces between neighboring rods 128 in first section 124 are preferably smaller than the spaces between neighboring rods 128 in second section 126. Additionally or alternatively, rods 128 in section 124 may be thicker than rods 128 in second section 126. However, in contrast to the embodiment of Figs. 1 and 2, axis 123 of stimulator 122 does not lie along a straight line but, rather, axis 123 is bent at predetermined locations corresponding to the bends in combustion cham¬ ber 120, e.g. at bends 140 and 142. It is appreciated that the gas dynamic resistance imposed by the bent portions, e.g. bends 140 and 142, of combustion chamber 120 is generally higher than the gas dynamic resistance imposed by the straight segments of the combustion chamber. Thus, to avoid undesired deceleration of the burning front at the curved por¬ tions, the controlled gas dynamic resistance provided by turbulence stimulator 122 at bends 140 and 142 is appropriately adjusted so to maintain a substantially homogeneous gas dynamic resistance along each of portions 125 and 127. This is preferably achieved by adjusting the dimensions, i.e. the length and/or the diameter, of rods 128 along the bent portions and/or by adjusting the spacing between rods 128 along the bent portions. More specifically, the length and/or diameter of rods 128 along the bends may be reduced, or the spaces between rods 128 along the bends may be increased. It should be appreciated that by using an appropri¬ ate folding scheme, the gas dynamic generator can be considerably compactized. For example, it has been found that a gas dynamic generator having an effective length of 5.5 meters can be folded into a housing whose largest dimension is only 1.2 meters. This may be obtained by providing 4, substantially equally spaced, 90 degree bends along the combustion chamber, preferably two bends in the combustion portion and two bends in the detonation portion. Reference is now made to Fig. 4 which schematically illustrates apparatus for cleaning a filter using pulse dynamic pulse generation, constructed and operative in accordance with yet another preferred embodiment of the present invention. The apparatus of Fig. 4 includes a shock wave generator 150 which may be any suitable shock wave generator having an output pressure of 30-40 atmos¬ pheres. In a preferred embodiment, however, shock wave generator 150 is constructed in accordance with any of the embodiments described above with reference to Figs. 1 - 3. The activation of shock wave generator 150 is preferably controlled by a controller 152 which also controls the operation of an external positioning motor 154, as described in detail below. Controller 152 prefer¬ ably includes a user interface which enables manual control over either or both of motor 154 and generator 150. Controller 152 preferably also includes an automat¬ ic mode of operation, in which generator 150 and motor 154 are controlled in accordance with a predetermined, preferably selectable, activation program. Associated with the output of generator 150, the cleaning apparatus includes an output extension 156 having an output aperture 158. Extension 156 guides the shock waves produced by generator 150, via aperture 158, into the interior of a filter cleaner enclosure 160 which accommodates a filter 170 to be cleaned. Filter 170 is preferably a cylindrical air filter, for example, of the type used by heavy duty diesel engines. Filter 170 is preferably securely mounted in enclosure 160, by any suitable means, surrounding aperture 158, such that the shock waves from aperture 158 are released into the interior 172 of the filter. In a preferred embodiment of the invention, the cleaning apparatus further includes a shock wave reflec¬ tor mechanism which includes a disc reflector 164, situ¬ ated in the interior 172 of filter 170, and an elongated arm 162 which extends through aperture 158 and a portion of output extension 156. The vertical position of disc reflector 164 is preferably controlled by controller 152 using external position motor 154, as described below. Arm 162 connects between position motor 154 and disc reflector 164 to allow mechanical control of the position of reflector 164. Output extension 156 is preferably formed with a bend 168 which allows linear movement of arm 162, in response to external position motor 154, through an opening 166 in a wall of extension 156. Opening 166 is preferably appropriately sealed to prevent loss of energy therethrough. According to this preferred embodiment of the present invention, shock waves generated through aperture 158 are reflected by disc reflector 164 onto the interi¬ or surface of filter 170, "shaking off" accumulations of dirt, dust, etc., from the filter. It has been found that this indirect application of shock waves using reflector 164 results in a more even distribution of the shock wave energy on filter 170, in comparison to direct application methods. However, since the magnitude of the reflected shock waves is generally a function of distance, the shock waves are generally more intense and, thus, more efficient in the vicinity of reflector 164. Therefore, in a preferred embodiment of the present invention, the vertical position of reflector 164 in filter interior 172 is changed during the clean¬ ing process, whereby a predetermined number of shock waves are generated at each of a predetermined number of reflector positions levels. This allows more even verti¬ cal distribution of the shock wave energy on filter 170 and results in more efficient cleaning of filter 170. In a preferred embodiment of the invention, the number of vertical position levels is between 1 and 15, with a vertical spacing of between 5 and 20 centimeters, depending on the dimensions of filter 170. For efficient cleaning of filter 170, the number of gas dynamic pulses, i.e. shock waves, applied at each vertical position level is preferably 1 - 20, more preferably 15-20 shock waves per level, depending on the condition and type of filter 170. Movement of reflector 164 between the different vertical positions is preferably controlled by controller 152, using external positioning motor 154, whereby the reflector is maintained at each level for a predetermined period of time. The activation of shock wave generator 150 for the predetermined number of times, at each vertical position of reflector 164, is also controlled by controller 152. It will be appreciated by persons skilled in the art that the present invention is not limited to what has been thus far described. Rather, the scope of the present invention is limited only by the following claims:

Claims: C L A I M S 1. A two-phase shock wave generator comprising: a combustion chamber including a first, combustion, portion having an input port and a second, detonation, portion downstream of said first portion and having an output aperture; an air-fuel supply line, operative to feed said input port with an air-fuel mixture; an igniter, associated with said air-fuel supply line, which ignites the air-fuel mixture in said supply line and initiates a burning front which propagates towards said input port; and a turbulence stimulator, fixedly mounted in said combustion chamber, which enhances and controls burning of said air-fuel mixture and comprises: a first section, situated within the combustion portion of the combustion chamber and having a predeter¬ mined first gas dynamic resistance; and a second section, situated within the detona¬ tion portion of the combustion chamber and having a predetermined second gas dynamic resistance, wherein said first resistance is such that burning of the air-fuel mixture in said combustion portion yields a predetermined pressure level suitable for initiating detonation of the remaining air-fuel mixture, in said detonation portion, and wherein said second resistance supports continued detonation of the remaining air-fuel mixture in the detonation portion. 2. A shock wave generator according to claim 1 wherein said air-fuel supply line is associated with said input port via a perforated nozzle which scatters said burning front substantially upon entry of the burning front into said combustion chamber. 22 3. A shock wave generator according to claim 1 or claim 2 wherein said turbulence generator comprises a plurality of gas dynamic obstructers positioned at fixed locations along the combustion chamber to yield said preselected first and second gas dynamic resistances along said combustion and detonation portions, respectively. 4. A generator according to claim 3 wherein each ob¬ structer includes a plurality of rods, generally perpen¬ dicular to the direction of propagation of the burning front in said combustion chamber. 5. A generator according to claim 4 wherein said plurality of rods are arranged such that they define a generally helical path, having a predetermined pitch. 6. A shock wave generator according to any of claims 1 - 5 wherein the combustion chamber comprises at least one bent portion. 7. A shock wave generator according to any of claims 1 - 6 wherein said combustion portion comprises at least bent portion. 8. A shock wave generator according to any of claims 1 7 wherein said detonation portion comprises at least bent portion. 9. A shock wave generator according to any of claims 6 - 8 wherein the location of said at least one bent portion is selected in accordance with a predetermined folding scheme. 10. A shock wave according to any of claims 1 - 9 where¬ in said second gas dynamic resistance is lower than said first gas dynamic resistance. 11. A shock wave generator comprising: a combustion chamber having an input port and an output aperture; an air-fuel supply line operative to feed the input port with an air-fuel mixture; an igniter, associated with said air-fuel supply line, which ignites the air-fuel mixture in said supply line and initiates a burning front which propagates towards said input port; a turbulence stimulator, fixedly mounted in said combustion chamber, which enhances and controls burning of said air-fuel mixture; and a perforated nozzle, associated with said input port, which scatters said burning front substantially upon entry of the burning front into said combustion chamber. 12. A method of generating a shock wave using a two- phase burning process, comprising the steps of: supplying an air fuel mixture from an air-fuel supply line to a combustion chamber; igniting the air-fuel mixture in said supply line when said combustion chamber is filled with a preselected amount of air-fuel mixture, thereby initiating a burning front propagating towards said combustion chamber; and enhancing and controlling the burning process by stimulating turbulence in said combustion chamber, wherein the turbulence is stimulated by the steps of: imposing a first, predetermined, gas dynamic resistance in said combustion portion during a first, combustion, phase of said burning process; and imposing a second, predetermined, gas dynamic resistance during a second, detonation, phase of said burning process, and wherein said first resistance is such that burning of the air-fuel mixture during said combustion phase yields a predetermined pressure level suitable for initiating detonation of the remaining air-fuel mixture, during said detonation phase, and wherein said second resistance ensures controlled detonation of the remaining air-fuel mixture. 13. A method according to claim 12 wherein said second gas dynamic resistance is lower than said first gas dynamic resistance. 14. A method according to claim 12 or claim 13 and further comprising the step of scattering the burning front substantially upon entry of the burning front into said combustion chamber. 15. A method of generating a shock wave comprising the steps of: supplying an air fuel mixture from an air-fuel supply line to a combustion chamber; igniting the air-fuel mixture in said supply line when said combustion chamber is filled with a preselected amount of air-fuel mixture, thereby initiating a burning front propagating towards said combustion chamber; scattering the burning front upon entry of the burning front into said combustion chamber; enhancing and controlling said burning process by stimulating turbulence in said combustion chamber; and detonating the air fuel mixture in said combustion chamber. 16. A method according to any of claims 12 - 15 and further comprising the step of removing the detonated mixture at an aperture to form a gas dynamic pulse there¬ at. 17. Apparatus for cleaning a filter comprising: a shock wave generator which generates at least one gas dynamic pulse in a given direction; and a reflector which reflects the at least one gas dynamic pulse onto at least a portion of the filter. 18. Apparatus according to claim 17 wherein the shock wave generator comprises a shock wave generator according to any of claims 1 - 11. 19. Apparatus according to claim 17 or claim 18 and further comprising an enclosure for accommodating the filter. 20. Apparatus according to any of claims 17 - 19 wherein the filter comprises an air filter. 21. Apparatus according to any of claims 17 - 20 and further comprising a positioning mechanism which controls the position of the reflector relative to the filter. 22. Apparatus according to claim 21 and further compris¬ ing a controller which controls the operation of the positioning mechanism and the activation of the shock wave generator. 23. Apparatus according to claim 22 wherein the control¬ ler operates said positioning mechanism and activates said shock wave generator in accordance with a predeter¬ mined cleaning sequence. 24. Apparatus according to claim 23 wherein said clean¬ ing sequence comprises a predetermined number of activa¬ tions of the shock wave generator at each of a predeter¬ mined number of positions of the reflector relative to said filter. 25. Apparatus according to claim 24 wherein said prede¬ termined number of activations of the shock wave genera¬ tor comprises between 1 and 20 activations at each posi¬ tion of the reflector. 26. Apparatus according to claim 24 or claim 25 wherein said filter is a cylindrical filter and wherein said predetermined number of positions are spaced along the height of the cylindrical filter. 27. Apparatus according to claim 26 wherein said prede¬ termined number of positions are spaced by a spacing of between 5 and 10 centimeters.

Inventors: FRIDMAN IGOR, FRIDMAN, IGOR
Applicants: FRIDMAN IGOR, HORAN SHAUL, SEDITEC LTD, FRIDMAN, IGOR, HORAN, SHAUL, SEDITEC LTD.
Application year: 1995
Main classification: B01D46
IPC codes: B08B7, F23C15, F23M9