Patent Publication Number: US-2020291853-A1

Title: Pulse drive

Description:
The invention relates to a device and to a method for the repeated generation of explosions for energy conversion, for example for the generation of thrust, in particular in aircraft. 
     Propulsion engines, so-called pulse detonation engines (PDE) are known, concerning which engines instead of a continuous combustion at constant pressure, the temperature and pressure increase of isochoric combustion at a constant volume, i.e. by way of explosions is utilised. In contrast to the internal combustion engine, in which the produced pressure drives the piston in a direct manner, a maximisation of the kinetic energy of the outflowing combustion gases is desired. Hence the combustion gases which are produced with the explosion are to be accelerated to the maximum speed for producing maximal thrust and are to be applied for propulsion purposes. The Holzwarth turbine for generating electricity as well as pulsed jet engines which produced thrust at a high frequency by way of explosions have become known. 
     A method for generating pressure impulses by way of explosions is described in the European patent application EP 2 319 036 A2 (and likewise US 2011/180020 A1). Herein, a mixture of oxidant and combustible is ignited in a container which is closed by a valve and an explosion is produced. The valve is opened shortly before the ignition and the pressure wave of the explosion can be led to its designated location via the outlet opening. The device, also called explosion generator (EG) is applied nowadays for cleaning contaminated steam boilers. 
     A pulse detonation drive is disclosed in the European patent application EP 3 146 270 A1 (and likewise US 2017/082069 A1), said pulse detonation drive comprising an actuating device which given an outflow of explosion gases through an exit nozzle adjusts an area ratio between the nozzle inlet area and the nozzle outlet area, said ratio at least approximately following an ideal area ratio for producing a maximal exit speed of the explosion gases in dependence on the pressure in the explosion space. 
     One possible object of the invention is to provide a device and a method of the initially mentioned type which effect an improved conversion of the energy which is released given the explosion, into kinetic energy of the combusted gas. 
     This object is achieved by a device and a method with the features of the respective independent patent claims. 
     The device serves for the repeated generation of explosions and for converting chemical energy into kinetic energy of outflowing exhaust gases of the explosions, in particular for generating thrust for the propulsion of an aircraft. It comprises:
         a combustion chamber as an explosion space,   at least one feed conduit for feeding a flowable, explosive material or of components which on mixing form an explosive material, to the combustion chamber;   a discharge device for the directed discharge of a gas pressure which is produced in the combustion chamber by the ignition of the explosive material,   a movable nozzle regulation element as a closure element for the partial or complete closure of the discharge device;   an actuating element which is designed to open the discharge device further (successive) after an opening of the discharge device and during the outflow of explosion gases through the discharge device.       

     Herein, the discharge device comprises several part-nozzles for discharging the gas pressure, and a position of the part-nozzles can be adjusted by the actuating element. 
     The part-nozzles each correspond to separate openings of the discharge device. In principle, the individual openings are individually closable, but in an embodiment can be commonly activated and commonly closed. 
     Given the same travel of the actuating element, a larger cross-sectional area can be released on using several individual small part-nozzles than on using only one nozzle with only one nozzle opening. This means that given only one large nozzle, the actuating element needs to be opened significantly further in order to release the same cross-sectional area. This means that the speed of the actuating element must be higher, in order to achieve the same increase of the cross-sectional area per unit of time. In practice, the maximal speed of the actuating element is a critical, limiting variable. For this reason, it can be advantageous if the necessary speed of the actuating element is kept as low as possible and the area which is herein released is kept to a maximum as much as possible. 
     Herewith, in embodiments, a nozzle, in particular a convergent-divergent nozzle is realised by the sum of the part-nozzles, and this nozzle ensures that the optimal, ideal area ratio between the nozzle end (nozzle outlet area) and nozzle neck (nozzle inlet area) is always at least approximately adjusted to during the complete outflow time. By way of this, the outflow speed of the exhaust gases (combusted gases) of the device, or their kinetic energy can ideally be at least approximately maximised. The outflow speed preferably exceeds the speed of sound. If the device or the vehicle is directly driven/propelled by the exhaust gases, then a thrust which affects the propulsion results in accordance with the outflow speed. Herein, the thrust can be maximised in accordance with the inner pressure by way of the respective opening width of the discharge device. If a turbine is driven by the exhaust gases, then only a part of the kinetic energy of the exhaust gases is used for this. Depending on the design and setting/adjustment of this turbine, a remaining part of the kinetic energy at the outlet of the turbine can be used in a direct manner for driving/propelling the device or a vehicle. 
     As a whole, a high efficiency can be realised by the device on converting chemical energy into mechanical energy or work. Chemical energy is defined as the energy form which is stored in an energy carrier in the form of a chemical compound and can be released given chemical reactions. 
     In contrast to the known pulse detonation drive of the European patent application EP 3 146 270 A1 (or US 2017/082069 A1), the speed at which the cross-sectional area of the entirety of all nozzles is changed can be increased. 
     In embodiments, each of the part-nozzles comprises a part valve seat and a part valve body, and a part nozzle inlet area is determined by the position of the part valve body in relation to the part valve seat. Herein, the nozzle regulation element determines the positions of the part valve bodies in relation to the part valve seats. 
     Herein, a part-nozzle can be closable by way of the movement of the respective part valve body towards the respective part valve seat. The sum of the part nozzle inlet areas forms a total nozzle inlet area, and the sum of the part nozzle outlet areas forms a total nozzle outlet area. 
     In embodiments, the part valve bodies are each part of a valve body. A movement of the valve body therefore effects a movement of the part valve bodies with one another, in particular a movement of the part valve bodies towards the part valve seats or away from these. In embodiments, the part-valve seats are each formed on a common valve seat body. 
     In embodiments, openings of the part-nozzles comprise annular openings which are arranged concentrically to one another. 
     In embodiments, the openings of the part-valves each comprise separate circular openings. The openings can all have the same size or the same diameter, or can have different diameters. In embodiments, the openings of the part-valves each comprise separate linear openings. 
     In embodiments, a part-nozzle each comprises a part valve body in the form of a regulation valve needle, and a part nozzle inlet area of the part-nozzle is determined by the position of the regulation valve needle with respect to the part valve seat. 
     In embodiments, the regulation valve needles each have an outer contour which tapers towards a valve tip, in particular an at least approximately cone-shaped outer contour. In embodiments, the part valve seat and the part valve body form a convergent-divergent part of the respective part-nozzle. 
     A flowable, explosive substance or a flowable explosive mixture which is formed by way of mixing components which preferably per se are not explosive is introduced into the combustion chamber. The flowable substances and/or substance mixtures are for example gaseous, fluid, powder-like, dust-like or pulverous or a mixture of such component substances. Typically, one component is a combustible and another component is an oxidiser. For example, a mixture consist of two gases under pressure. Here and hereinafter, all variants and possible combinations of substances and mixtures are simply called “flowable, explosive material”, without this being understood as a restriction to a single substance or to a certain mixture. 
     Given isochoric combustion at a constant volume, greater combustion temperatures are achieved than given combustion at a constant pressure. In the case of an explosive combustion, an enormous pressure increase is additionally achieved. E.g. given a stoichiometric combustion of air and natural gas at a constant volume, a pressure increase by the factor 7.5 can be achieved, i.e. given a preliminary pressure of 10 bar of the mixture, the peak pressure in the explosion space is approx. 75 bar. With such applications with an isochoric combustion, the aim is to produce a gas jet which leaves the explosion space at maximal speed. 
     In embodiments, the device its provided for use with a preliminary pressure which is provided between ambient pressure and twenty-fold the ambient pressure, for example between six-fold and twelve-fold the ambient pressure. 
     In embodiments, the combustion chamber has a changeable volume. 
     respect to a maximal volume. Given a reduced combustion chamber volume, the combusted mixture flows out more rapidly compared to the maximal volume. The shortened outflow duration leads to the thrust being present for a shorter time duration. Herewith, the average thrust of the device over several pulses reduces. The reduced volume simultaneously leads to a smaller quantity of explosive mixture per pulse and also in the temporal average. 
     In embodiments, the device comprises a displaceably arranged separating wall which forms a delimitation of the combustion chamber. 
     By way of this, the variation of the volume of the combustion chamber can be realised in a mechanically simple manner. 
     In embodiments, the separating wall forms a delimitation of the combustion chamber which lies opposite the discharge device. In particular, the actuating element can be led through the separating wall. 
     By way of this, the variation of the volume of the combustion chamber can be realised in a space-saving manner and a rotationally symmetrical shape of the combustion chamber can be retained independently of the position of the separating wall. 
     In embodiments, the actuating element comprises a drive means for the drive of an opening movement of the discharge device, in particular by way of the drive means being realised by way of an auxiliary explosion device, in which an auxiliary explosion produces a force which assists the opening movement. 
     Details concerning the drive of such an auxiliary explosion device are described in the initially mentioned EP 2319036A2. In particular, according to an embodiment, it is possible to synchronise the explosion in the auxiliary explosion device with that in the explosion space by way of a conduit, also called delay conduit. 
     A further force or force component which assists in the opening movement can arise by way of the recoil of the outflowing explosion gases against the actuating element. 
     In an embodiment, the actuating element is configured to temporally completely close the discharge device. Herewith, it is possible to increase the pressure in the explosion space to above ambient pressure before the ignition. 
     In embodiments, the device comprises a compressing device for compressing the flowable explosive material or at least one of the components of the explosive material. By way of this, the pressure of the explosive material can be increased with respect to the ambient pressure before the ignition. The pressure which is produced by the explosion is a function of this pressure before the ignition and is herewith also increased accordingly. Herewith, the thrust which is produced by the device can also be increased. 
     In embodiments, the compressing device is a continuously operated compressor, in particular a rotating compressor, for example a turbo-compressor. 
     The compressor can be a rotating compressor, in particular a turbo-compressor. 
     In embodiments, the compressor is driven by a turbine, and the turbine is arranged to be driven by an exhaust gas jet from a turbine combustion chamber, wherein the turbine combustion chamber is different to the combustion chamber. 
     In other words, the compressor, the turbine and the turbine combustion chamber are herein parts of a gas turbine. The gas turbine is used in order to operate the compressor. The turbine or the turbine combustion chamber can be operated with the same combustible as with the combustion chamber. The explosive material can therefore be the same mixture as in the combustion chamber, but be in a different mixing ratio. 
     In embodiments, the compressor is driven by a turbine, and the turbine is arranged to be driven by exhaust gases of the combustion chamber. 
     In contrast to the topology with a separate gas turbine, here therefore it is the flow of the exhaust gases of the PE which are utilised for the drive of the compressor. This simplifies the device and, thanks to the generally better efficiency of the PE in comparison to a conventional gas turbine, increases the total efficiency of the device. 
     In embodiments, the device comprises an output for delivering mechanical work to a mechanical consumer. 
     In embodiments, the device comprises an output for delivering mechanical work to a flow machine. This can be a propeller, for the propulsion of a vehicle, in particular of an aircraft. 
     In embodiments, the device comprises an output for delivering mechanical work to a generator. Herewith, the mechanical work is converted into electrical energy. 
     In embodiments, the device comprises a compression device in the form of an air inlet, for compressing inflowing air given supersonic speed of the device in relation to the ambient air. 
     Such a compression device can be present alternatively or additionally to a compressor. 
     Herewith, it is particular in the case of an aircraft that the compression in a compressor can be replaced by the compression in the air inlet on reaching supersonic speed. 
     In embodiments, the discharge device is configured, given an outflow of explosion gases through the discharge device, to adjust an area ratio between a total nozzle inlet area and a total nozzle outlet area of the discharge device, said ratio at least approximately following an ideal area ratio for producing a maximal outlet speed of the explosion gases in dependence on the pressure in the combustion chamber. 
     This can be realised by way of the nozzle regulation element being arranged for the variation of a total nozzle inlet area which is the sum of the part nozzle inlet areas. Herein, the actuating elements can be configured to control a movement of the nozzle regulation element for adjusting the total nozzle inlet area at least approximately in accordance with the mentioned ideal area ratio. 
     In embodiments, the actuating device comprises a drive means for the drive of an opening movement of the nozzle regulation element, in particular by way of the drive means being realised by way of an auxiliary explosion device with an auxiliary combustion chamber, in which an auxiliary explosion produces a force which assists in the opening movement. 
     In embodiments, the actuating device comprises a braking means for delaying an opening movement of the regulation valve, in particular by way of the braking means being realised by a gas compression spring or by a camshaft or by a gas compression spring in combination with a camshaft. 
     In embodiments, the nozzle regulation element is configured to temporarily completely close the discharge opening. 
     The method for the repeated generation of explosions and for converting chemical energy into kinetic energy of outflowing exhaust gases of the explosions, in particular for producing thrust for the propulsion of an aircraft, comprises the repeated execution of the following steps:
         feeding a flowable, explosive material or of components which on mixing form the explosive material, into a combustion chamber, wherein a discharge device of the combustion chamber is closed at least partly by way of a movable nozzle regulation element, and generating, in relation to an ambient pressure, an overpressure in the combustion chamber;   opening the discharge device;   igniting the explosive material in the combustion chamber;   leading away explosion gases through the discharge device:   at least partial closure of the discharge device by way of the movable nozzle regulation element.       

     Herein: 
     
         
         
           
             for opening the discharge device and on leading away explosion gases, several part-nozzles are opened synchronously to one another, and 
             for the at least partial closure of the discharge device, several part-nozzles are at least partly closed synchronously to one another. 
           
         
       
    
     In embodiments, the part-steps “opening the discharge device”, “igniting the explosive material in the combustion chamber” and “leading away explosion gases through the discharge device by way of the movable nozzle regulation element” are carried out in a temporally overlapping manner. 
     In embodiments, the part-nozzles each comprise part valve seats and part valve bodies, and the part valve bodies are moved synchronously to one another in relation to the part valve seats by way of the nozzle regulation element. 
     Further preferred embodiments are to be derived from the dependent patent claims. Herein, the features of the method claims where appropriate can be combined with the device claims and vice versa. 
    
    
     
       The subject-matter of the invention is hereinafter explained in more detail by way of preferred embodiment examples which are represented in the accompanying drawings. Shown schematically are: 
         FIG. 1  a pulse drive machine or pulse engine (PE); 
         FIG. 2  an operating mode of the PE with the variable volume of its combustion chamber; 
         FIG. 3  an operating mode with a variable frequency; 
         FIG. 4  increase of an opening speed by way of the use of several part-nozzles with individual nozzle openings; 
         FIG. 5  different nozzle bodies each with several nozzle openings; 
         FIG. 6  a PE with a charging by way of a separate gas turbine; 
         FIG. 7  a PE with a charging by way of a turbine which is driven by exhaust gases of the PE; 
         FIG. 8  a PE with a propeller which is driven by the turbine; and 
         FIG. 9  a PE with a generator which is driven by the turbine. 
     
    
    
     Basically in the figures, the same or equally acting parts are provided with the same reference numerals. 
       FIG. 1  shows a device for the repeated generation of explosions, hereinafter also called pulse engine or PE  15 . A combustion chamber  21  or explosion space can be filled with a flowable, explosive material, for example an explosive gas mixture, via a filling device. For this, the filling device comprises a combustion chamber air inlet  12  for the feed of an oxidant, for example air, and a combustion chamber combustible inlet  14  for the feed of a combustible or fuel, for example hydrogen. The flowable explosive material which is formed therefrom can be ignited and brought to explode by an ignition device, for example by a spark plug  23 . 
     An outlet of the combustion chamber  21  for exhaust gases  17  leads through nozzle openings  27 . The nozzle openings  27  are closable by way of nozzle regulation elements  26  of an actuating element  24 . In a neutral position, the nozzle opening  27  is closed by the actuating element  25 . The actuating element  25  is herein held in this position by way of a gas spring  24 . 
     The nozzle regulation element  26  seals the combustion chamber  21  towards the nozzle openings  27  during the filling of the combustion chamber  21 . By way of this, a preliminary pressure with an overpressure can be produced, with which overpressure in turn a greater explosion pressure can be produced. 
     An auxiliary combustion chamber  22  is likewise fillable with an explosive material via a further filling device with an auxiliary combustion chamber air inlet  11  and with an auxiliary combustion chamber combustible inlet  13 . The actuating element  25  is movable counter to the pressure of the gas spring  24  by means of an explosion in the auxiliary combustion chamber  22  and the nozzle opening  27  can be opened by way of this. 
     On operation of the PE  15 , the auxiliary combustion chamber  22  and the combustion chamber  21  can each be filled with the same explosive material. Basically, different materials or different mixtures can also be applied in both combustion chambers. Firstly, the explosive material is ignited in the auxiliary combustion chamber  22  by way of an assigned spark plug  23 . 
     By way of this, the pressure in the auxiliary combustion chamber  22  increases and the actuating element  25  begins to move and hence begins to release the nozzle opening  27  of the combustion chamber  21 . The explosive material is subsequently ignited in the combustion chamber  21 , for example by a further spark plug  23 . 
     The spark plugs  23  of the auxiliary combustion chamber  22  and of the combustion chamber  21  are therefore ignited shortly after one another. A delay between the two ignition points in time can be selected such that an exit speed of the exhaust gases  17  or a total energy which is converted into kinetic energy of the exhaust gases  17  is maximised. 
     In another embodiment, the material in the combustion chamber  21 , via a conduit or delay conduit, likewise filled with explosive material, is ignited by way of an explosion which comes from an auxiliary combustion chamber  22  and is led through the delay conduit. 
     The filling of the combustion chambers (combustion chamber  21  and auxiliary combustion chamber  22 ) can be effected in stages and in the following sequence, firstly the oxidant through the combustion chamber air inlet  12  or the auxiliary combustion chamber air inlet  11 , then the combustible through the combustion chamber combustible inlet  14  or the auxiliary combustion chamber combustible inlet  3 . Herewith, the respective combustion chamber wall can be cooled with the oxidant during the filling, without a mixture being able to ignite on the combustion chamber wall. The cooling possibility which is created on account of this permits the maximisation of the cycle frequency. Herewith, the power density, thus the maximal thrust per combustion chamber volume can be maximised. 
     Regarding further elements of the design and method aspects for the operation of the device, the initially mentioned EP 3 146 270 A1 is referred to, whose contents are herewith incorporated into the present application. 
     The combustion chamber  21  comprises a separating wall  28  which forms a section of the entirety of the walls of the combustion chamber  21 . The volume of the combustion chamber  21  is changeable by way of displacing the separating wall  28 . The separating wall  28  can be displaced by way of a schematically represented adjusting device  281  and the volume can be varied herewith. In  FIG. 1 , the separating wall  28  by way of example is movable in the same direction, along which the actuating element  25  is moved to and fro. 
       FIG. 2  illustrates an operating mode of the PE  15  with a variable volume in its combustion chamber, each with a temporal course of a thrust F which is produced by the PE  15 : in the upper course with a larger and in the lower course with a smaller volume of the combustion chamber, but with a constant pulse period tc. Given a reduced combustion chamber volume, the combusted mixture flows out more rapidly in comparison to the larger volume. The shortened outflow duration leads to the thrust prevailing for a shorter time duration. The average thrust of the PE  15  over time therefore reduces. The consumption of combustible and oxidiser per pulse as well as its temporal average also reduces due to the lower volume. 
       FIG. 3  shows an operating mode of the PE  15  with a variable frequency, in the upper course with a greater operating frequency (or smaller pulse period tc 1 ) and in the lower course with a smaller operating frequency (or larger pulse period tc 2 ). Herein, it is merely the number of thrust pulses per unit of time which is reduced, whilst the pulse per se is kept the same, i.e. with the same volume. By way of this, the thrust and the consumption in the temporal average also become smaller. 
     On operation, the volume as well as the operating frequency can be varied. Herewith, the same average thrust can be achieved with different combinations volumes and operating frequency, and the operation optimised. For example, the stoichiometry of the mixture can be varied herewith. For example, rapid load changes can be effected by way of adapting the operating frequency and subsequently given a constant load by way of the slow adaption of the volume given a simultaneously compensation by the operating frequency. Given an optimisation, one can take into account the fact that with a thrust regulation over the operating frequency, the individual pulses can all be of a certain optimised temporal course or pulse type. Concerning thermal losses, a large volume is more advantageous compared to a small volume with regard to the ratio of the surface to volume. Given a drive of an exhaust gas turbine, an additional degree of freedom is present with the selection of the operating state: depending on how the efficiency of the exhaust gas turbine behaves as a function of PE frequency and PE volume, it can be advantageous if the PE volume can be reduced in the part-load region. 
       FIG. 4  shows an increase of an opening speed by way of using several part-nozzles with individual nozzle openings. A nozzle with an individual nozzle opening  27  is shown on the left and a nozzle with several part-nozzles  40  is shown on the right. Each of the part-nozzles  40  comprises a part valve seat  41  and a part valve body  42 . The part valve body  42  can bear on the part valve seat  41  and thus close the part-nozzle  40 , and can be moved away from the part valve seat  41  for opening the part-nozzle  40 . The part valve bodies  42  can be moved commonly, i.e. synchronously, by the actuating element  25 , for example by way of the part valve bodies  42  being formed on the same body, or all being fastened to one another in a rigid manner on the actuating element  25  or on a common actuating device. On moving the part valve body  42  away from the part valve seats  41 , given the same travel of the valve bodies or of the actuating element  25 , a larger cross-sectional area is released than on using only one nozzle. Herewith, a temporal change of a total cross-sectional area of all part nozzles  40  is greater than on using only one single nozzle. Hence by way of the nozzle opening  27  consisting of several individual part-nozzles, the speed at which the nozzle opening  27  is opened and a larger cross-sectional area is released can be increased without the actuating element  25  having to be moved more rapidly. 
     The several part-nozzles  40  or the nozzle openings  27  can be shaped differently.  FIG. 5  shows different nozzle bodies  30  each with several nozzle openings  27 , arranged as concentric rings, radial linear jets and as circular openings with different diameters. In other embodiments, the circular openings all have the same diameter (not represented). 
       FIG. 6  shows a PE  15  with a charging by a separate gas turbine. Herein, fuel or combustible is transported from a combustible tank  7  via a fuel delivery device  18  and via fuel inlet valves (auxiliary combustion chamber combustible inlet  13  and combustion chamber combustible inlet  14 ) to the combustion chamber  21  and to the auxiliary combustion chamber  22  of the PE  15 . A further fuel delivery device  18   b  delivers the fuel via a turbine combustion chamber feed valve  10  to a turbine combustion chamber  6  which is operated in a continuous (thus non-pulsating manner) and via a turbine  4  and shaft  3  drives a compressor  2 . This compressor  2  is fed by air from an air inlet  1 , compresses the air and leads it via the air inlet valves (auxiliary combustion chamber air inlet  11  and combustion chamber air inlet  12 ) into the combustion chambers  21 ,  22 . 
     The compressor  2  can be a radial compressor or axial compressor as well be of one or more stages. The turbine  4  and the further turbine  4   b  can be one-stage or multi-stage. The air can already be pre-compressed in the air inlet  1  by way of ram pressure compressing. The higher the mach number of the inflowing air  16 , the greater is this (pre) compressing. Since the air is already adequately compressed in the air inlet  1  given sufficiently high mach numbers, the compressor  2  becomes superfluous at these mach numbers. At mach numbers, at which the compressor  2  is required, a bypass valve  8  is closed and a compressor inlet valve  9  is open. If the compressor is no longer used due to the high speed of the inflowing air  16 , then the compressor inlet valve  9  is closed and the bypass valve  8  is opened. By way of this, the compressor  2  is bridged. In this case a compressor outlet valve  19  is also closed. 
     A vehicle, in particular an aircraft can be propelled by the outflowing exhaust gases  17  of the PE  15  or by the thrust which is produced by way of this. 
       FIG. 7  shows a PE  15  with a charging by way of a further turbine  4   b  which is driven by exhaust gases  17  of the PE  15  via a common shaft  3 . Instead of being driven by a separate gas turbine as an auxiliary assembly, the compressor  2  can also be driven via a turbine  4   b  which is driven by the exhaust gases  17  from the PE  15 . In this case, one can forego the further fuel delivery device  18   b  as well as the turbine combustion chamber  6 . 
       FIG. 8  shows a PE  15 , in which the further turbine  4   b  which is driven by the exhaust gases  17  of the PE  15  drive a propeller or airscrew  201 , in particular via a step-down gear  20 . This propeller can be of a shrouded or a non-shrouded design. The propeller serves for the propulsion of a vehicle, in particular an aircraft, as with a turboprop. An exhaust gas jet  5  of the further turbine  4   b  can likewise contribute to the propulsion. 
       FIG. 9  shows a PE  15 , in which the further turbine  4   b  which is driven by the exhaust gases  17  of the PE  15  drives a generator  202 . When necessary, a step-down gear  20  can be arranged between the shaft  3  and the generator  202 .