CN113390765B - Method for researching influence of shock wave on evaporation process of fuel liquid drops under supersonic airflow - Google Patents
Method for researching influence of shock wave on evaporation process of fuel liquid drops under supersonic airflow Download PDFInfo
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Abstract
The invention belongs to the technical field of scramjet engines and detonation engines, and particularly relates to a research method for influence of shock waves on a fuel liquid droplet evaporation process under supersonic airflow, wherein the research method comprises the following steps of 1, calculating a pressure value of critical gas in a high-pressure section; step 2, pre-pressurizing the high-pressure section; step 3, measuring initial light intensity; step 4, atomizing; step 5, measuring the particle size distribution of the fuel droplets in the shock front; step 6, generating shock waves; step 7, measuring the particle size distribution of the fuel droplets in the interaction process of the shock waves and the fuel droplets; step 8, measuring the particle size distribution of fuel liquid drops after shock wave; step 9, releasing pressure; and step 10, data processing. The invention can generate shock waves in experiments and realize the generation of the particle size of the fuel droplets and the measurement of the particle size of the fuel droplets.
Description
Technical Field
The invention belongs to the technical field of scramjet engines and detonation engines, and particularly relates to a research method for influence of shock waves on a fuel liquid droplet evaporation process under supersonic airflow.
Background
The scramjet engine is a power device of an air-breathing supersonic aircraft and generally comprises an air inlet channel, an isolation section, a combustion chamber and a tail nozzle. When the scramjet engine works, incoming flow is decelerated and pressurized through the air inlet channel and then enters the combustion chamber through the isolation section at supersonic speed, and is mixed and combusted with propellant carried by an aircraft in the combustion chamber, so that chemical energy of the propellant is converted into heat energy, and the combusted high-temperature and high-pressure gas expands through the tail nozzle to do work to convert the heat energy into kinetic energy. The scramjet engine has high specific impulse because of not carrying an oxidant, and is favored in the fields of aerospace and national defense.
Because the air flow speed at the inlet of the combustion chamber of the scramjet engine is supersonic, the residence time of combustible mixture in the combustion chamber is extremely short, and in addition, the supersonic air flow at the inlet of the combustion chamber can generate shock waves under the action of the inner wall of the combustion chamber, so that the environment in the combustion chamber becomes worse, and great difficulty is brought to the mixing and combustion of fuel and incoming air. How to make the fuel complete injection, atomization, evaporation, mixing and combustion in a limited space and a very short time also becomes a difficult problem in the research field of scramjet engines. Wherein the evaporation process takes a longer time in the whole process and affects the mixing and combustion process and finally the release of chemical energy of the fuel. Therefore, the method has important significance for researching the influence of the shock wave on the liquid drop evaporation process under the supersonic airflow.
Due to the existence of shock waves, when the particle size of the fuel liquid drop is larger, the liquid drop is broken by the shock waves, and the evaporation rule of the liquid drop cannot be researched by measuring the change of the particle size. The related theory shows that when the particle size of the liquid drop meets the condition that the Weber number is below the critical Weber number, the liquid drop is not broken, and the problem of breaking the liquid drop can not be considered when the problem of evaporation of the liquid drop is researched. However, the diameter of the liquid drop is reduced to micrometer level, and the traditional measuring method is difficult to be adequate for the particle size measuring task in the moment due to the interference of the laser wave. In addition, the droplet generation method used in ordinary times produces droplets having a large particle diameter, and thus it is difficult to meet the experimental requirements. Therefore, when the influence of shock waves on the fuel droplet evaporation process under supersonic airflow is researched, the existing experimental device is difficult to simultaneously meet the requirements of generating shock waves, generating small droplets and measuring the particle size of the small droplets under the interference of the shock waves.
Disclosure of Invention
The invention provides a method for researching influence of shock waves under supersonic gas flow on a fuel liquid droplet evaporation process, aiming at overcoming the defects of the prior art, and the method for researching influence of the shock waves under supersonic gas flow on the fuel liquid droplet evaporation process can realize generation of fuel liquid droplets and measurement of the particle size of the fuel liquid droplets while generating the shock waves in experiments.
The technical scheme adopted by the invention for solving the technical problems is as follows: a research method for influence of shock waves on a fuel liquid droplet evaporation process under supersonic airflow is characterized by comprising a shock tube, wherein the shock tube comprises a high-pressure section, a low-pressure section and an experimental section which are sequentially arranged along the movement direction of an incident shock wave, and a diaphragm is arranged between the high-pressure section and the low-pressure section; the research method comprises the following steps:
step 1, calculating the pressure value of critical gas in a high-pressure section: critical gas pressure value in the high pressure section is p 4 The pressure value of the gas in the low-pressure section is p 1 ，p 4 And p 1 Has a ratio of p 41 (ii) a Determining the Mach number Ma of the required shock wave s Measuring p 1 Through p 41 And Ma s To obtain the pressure value p of the critical gas in the high-pressure section 4 ；
As a further preference of the present invention, p in step 1 1 The pressure is atmospheric pressure or a preset specific pressure value; p is a radical of 41 And Ma s The relation of (A) is as follows:
in the formula a 14 For the sound speed ratio, it can be expressed as:
wherein, γ 1 Specific heat ratio of gas in low-pressure section, gamma 4 Specific heat ratio of gas in high pressure section, M 1 Molecular weight of the gas in the low-pressure stage, M 4 Is the molecular weight, T, of the gas in the high pressure section 1 Is the initial temperature, T, of the gas in the low-pressure section 4 Is the initial temperature of the gas in the high pressure section.
As a further preferred mode of the invention, after the fuel droplets sprayed into the experimental section in the step 4 reach the set concentration, the space between the ultrasonic atomization system and the experimental section is closed.
As a further preferred aspect of the present invention, the multi-wavelength extinction method particle size measurement system includes an optical fiber coupler, a diffraction grating, a photodetector, a signal conditioning circuit, and a data acquisition card; in the steps 3, 5, 7 and 8, the optical paths with multiple wavelengths are coupled into a beam of optical path through the optical fiber coupler and output to pass through the experimental section, and then the optical path with the same path number and wavelength number is divided into the optical paths through the diffraction grating; the photoelectric detector converts detected light intensity signals of various wavelengths after light splitting into electric signals, and the electric signals are transmitted to the data acquisition card through the signal adjusting circuit, so that the change of the particle size and the concentration of the fuel droplets is inverted, and a corresponding change curve of the particle size distribution of the fuel droplets along with time is obtained.
As a further preferred aspect of the present invention, in step 7, the actual shock Mach number Ma s Δ v/a, a is the speed of sound。
As a further preferable aspect of the present invention, the low-voltage section piezoelectric sensors are a low-voltage section I piezoelectric sensor, a low-voltage section II piezoelectric sensor, and a low-voltage section III piezoelectric sensor, which are sequentially arranged along the incident shock wave movement direction; the actual shock velocity Δ v is calculated as follows:
in the formula:
the installation distance between the low-voltage section I piezoelectric sensor and the low-voltage section II piezoelectric sensor is delta L 1 ，
The response time difference between the low-voltage section I piezoelectric sensor and the low-voltage section II piezoelectric sensor is delta t 1 ，
The installation distance between the low-voltage section I piezoelectric sensor and the low-voltage section III piezoelectric sensor is delta L 2 ，
The response time difference between the low-voltage section I piezoelectric sensor and the low-voltage section III piezoelectric sensor is delta t 2 ，
The installation distance between the low-voltage section II piezoelectric sensor and the low-voltage section III piezoelectric sensor is delta L 3 ，
The response time difference between the low-voltage section II piezoelectric sensor and the low-voltage section III piezoelectric sensor is delta t 3 。
Through the technical scheme, compared with the prior art, the invention has the following beneficial effects:
1. during an experiment, micron-sized fuel droplets are generated by an ultrasonic atomization system and are sprayed into an experiment section, and then a diaphragm is broken by pressurizing a high-pressure section, so that shock waves are generated in the low-pressure section and the experiment section; and simultaneously, the particle size of the micron-sized fuel droplets in the experimental section is measured in real time according to a multi-wavelength extinction method particle size measurement system.
2. The invention can select diaphragms with different strengths according to experimental needs to generate shock waves with different strengths, and because the inner sections of the shock tubes are all rectangular, the generated shock waves do not need to go through a circular-square section in the previous design scheme, so the quality of the generated shock waves is better.
3. The invention detects the time difference of pressure change between each low-voltage section piezoelectric sensor and other low-voltage section piezoelectric sensors through a plurality of low-voltage section piezoelectric sensors, calculates a plurality of shock wave speeds according to the time differences and the installation distance between each low-voltage section piezoelectric sensor and other low-voltage section piezoelectric sensors, and then calculates the average value of the shock wave speeds so as to reduce the error.
4. The first detachable observation window and the second detachable observation window can provide measurement channels for various measurement modes, and can meet measurement requirements under different experimental conditions.
5. The atomizer switching section can connect the ultrasonic atomizer with the shock tube, and can drive other structures such as a sealing rod to move quickly through the cam handle to realize quick sealing; the cam handle does not need an extra control device and can be locked by the self gravity of the cam handle, so that the failure rate is low and the reliability is high.
6. The selection of the laser light source array in the multi-wavelength extinction method particle size measurement system has flexibility, and light sources with different wavelengths can be selected to be combined according to the extinction characteristics of substances in an experimental section; the data acquisition card may be selected as required by the sampling frequency.
Drawings
The invention is further illustrated by the following examples in conjunction with the drawings.
Fig. 1 is a perspective view of the overall structure of the present invention.
Fig. 2 is a front view of the overall structure of the present invention.
Fig. 3 is a top view of the overall structure of the present invention.
Fig. 4 is an assembly view of the lamination section, diaphragm, high pressure section and low pressure I section of the present invention.
FIG. 5 is an exploded view of the membrane clamping section and membrane of the present invention.
Fig. 6 is an assembled view of a second removable viewing window of the present invention.
Fig. 7 is an exploded view of a second removable sight glass of the present invention.
Fig. 8 is a front view of the atomizer adaptor of the present invention.
Fig. 9 is a top view of an adapter of the atomizer of the present invention.
Fig. 10 is a perspective view of an atomizer adapter of the present invention in a sealed state.
Fig. 11 is a perspective view of the atomizer adapter of the present invention in an open state.
Fig. 12 is a perspective view of a second blind hole plate of the present invention.
Fig. 13 is a perspective view of the adaptor section cavity of the present invention.
Fig. 14 is a perspective view of the seal bar support plate of the present invention.
FIG. 15 is a perspective view of a sealing rod linkage plate of the present invention.
Fig. 16 is a perspective view of the seal bar of the present invention.
Fig. 17 is a perspective view of the cam handle of the present invention.
Fig. 18 is a perspective view of a packing gland nut of the present invention.
In the figure: 1. a high pressure gas cylinder; 2. a pressure control cabinet; 3. a first blind hole plate; 4. a high pressure section; 5. a high voltage section piezoelectric sensor; 6. a film clamping section; 7. a low-pressure I section; 8. a low-voltage section I piezoelectric sensor; 9. a low-pressure II section; 10. a low-voltage section II piezoelectric sensor; 11. a low-voltage section III piezoelectric sensor; 12. a laser light source array; 13. an optical fiber; 14. an experimental section; 15. a second blind hole plate; 16. a switching section cavity; 17. a sealing rod support plate; 18. a signal conditioner; 19. a photodetector; 20. a diffraction grating; 21. a data acquisition card; 22. a diversion pipeline; 23. an ultrasonic atomizer; 24. a computer host; 25. a display; 26. an air pump; 27. an air exhaust pipeline; 28. a three-way pipe joint; 29. a high pressure pipeline; 30. an air intake duct; 31. an exhaust duct; 32. a sealing rod linkage plate; 33. a sealing rod; 34. a cam handle; 35. a piezoelectric sensor signal transmission line; 36. a fiber coupler; 37. a first viewing window outer frame; 38. a first observation window inner frame; 39. a second viewing window outer frame; 40. a second observation window inner frame; 41. a photodetector signal transmission line; 42. a membrane; 43. adjusting the screw; 44. a first sight glass; 45. a connecting screw; 46. a cotter pin; 47. a socket head cap screw; 48. a nut; 49. a first O-ring; 50. a second O-ring; 51. the sealing ring compresses the nut; v-ring 52.
Detailed Description
The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams each illustrating the basic structure of the present invention only in a schematic manner, and thus show only the constitution related to the present invention.
Example 1
The present example provides a preferred embodiment, as shown in fig. 1 to 18, an apparatus for studying the influence of shock waves on the liquid droplet evaporation process under supersonic airflow includes a control device, a shock wave pipe system, an ultrasonic atomization system, a pressure detection system, and a multi-wavelength extinction method particle size measurement system, and the specific structures of these systems are as follows:
as shown in fig. 1, the control device includes a computer 24 and a display 25, the display 25 is connected to the computer 24, and the computer 24 is connected to the pressure detection system and the multi-wavelength extinction method particle size measurement system via data lines. The shock tube system comprises a shock tube and a pressure control system, wherein:
as shown in fig. 1, the shock tube includes a high-pressure section 4, a low-pressure section and an experimental section 14, which are sequentially arranged along the movement direction of the incident shock wave, and preferably, the shock tube may be a shock tube with a rectangular cross section; a first blind hole plate 3 is hermetically installed at one end of the high-pressure section 4 far away from the low-pressure section, and a diaphragm 42 is hermetically arranged at the joint of the high-pressure section 4 and the low-pressure section; the low-pressure section comprises a low-pressure section I7 and a low-pressure section II 9 which are sequentially arranged along the movement direction of the incident shock wave; two opposite side faces of the experiment section 14 are respectively provided with a first detachable observation window and a second detachable observation window, so that the observation windows can be conveniently installed and opened at corresponding positions of the experiment section 14. Preferably, the inner section of the experimental section 14 is designed to be rectangular, so as to ensure the flatness of the inner surface while windowing, and avoid introducing a complex wave system due to the influence of the unevenness of the inner surface on the shock wave front; the two detachable observation windows and the experimental section 14 between the two detachable observation windows form a measurement channel convenient for the particle size measurement system by the multi-wavelength extinction method to measure.
The present embodiment further includes a clamping section 6, the clamping section 6 being used to clamp the diaphragm 42 and being disposed between the high pressure section 4 and the low pressure section, the design being such that the high pressure section 4 and the low pressure section are isolated to create different initial pressures before the diaphragm 42 ruptures. Preferably, the internal cross sections of the high-pressure section 4, the film clamping section 6 and the low-pressure section and the shape of the diaphragm 42 are all rectangular, so as to avoid the influence on the shock wave quality caused by the change of the geometrical shape of the shock wave front due to the fact that the shock wave needs to go through a circular-square section in the prior art.
As shown in fig. 3, 6 and 7, the first detachable viewing window includes a first viewing window inner frame 38, a first viewing window outer frame 37 and a first viewing pane, and the second detachable viewing window includes a second viewing window inner frame 40, a second viewing window outer frame 39 and a second viewing pane 44. The first windowpane is disposed between the first windowpane casing 38 and the first windowpane casing 37, and preferably, the inner surface of the first windowpane coincides with the inner surface of the first windowpane casing 38 by adjusting the 12 adjusting screws 43, it being noted that the adjusting screws 43 are adjusted diagonally during the adjustment. The second detachable viewing window is identical in structure to the first detachable viewing window, the second viewing window pane 44 is located between the second viewing window inner frame 40 and the second viewing window outer frame 39, and preferably, the inner surface of the second viewing window pane 44 coincides with the inner surface of the second viewing window inner frame 40 by adjusting the 12 adjusting screws 43, and it is noted that the adjusting screws 43 are adjusted diagonally during the adjustment process. After the first detachable observation window or the second detachable observation window is assembled, the first detachable observation window or the second detachable observation window is fixedly connected with the experiment section 14 through 14 connecting screws 45 as a detachable whole, and the inner surfaces of the first detachable observation window and the second detachable observation window after installation are flush with the inner surface of the experiment section 14. After the installation, the inner surface of the first observation window glass, the inner surface of the first observation window inner frame 38 and the inner surface of the experimental section 14 are in the same plane, the inner surface of the second observation window glass 44 and the inner surface of the second observation window inner frame 40 and the inner surface of the experimental section 14 are in the same plane, and no obvious gap exists at the matching position because of high part processing precision, so that the introduction of a complex wave system due to uneven inner surfaces is avoided as much as possible.
As shown in fig. 1 and 2, the pressure control system is used for controlling the pressure of gas introduced into the shock tube, and comprises a high-pressure gas cylinder 1, a high-pressure pipeline 29, a pressure control cabinet 2, a gas inlet pipeline 30, a gas outlet pipeline 31 and a three-way pipe joint 28. The high-pressure gas bottle 1 is connected with the pressure control cabinet 2 through a high-pressure pipeline 29, the pressure control cabinet 2 is connected with an air inlet pipeline 30 and an air exhaust pipeline 31, a hole is formed in the high-pressure section 4, preferably, the hole is formed in the lower side of the high-pressure section 4, the hole, the air inlet pipeline 30 and the air exhaust pipeline 31 are connected through a tee pipe joint 28, and the pressure control system controls air inlet and air exhaust in the high-pressure section 4 through the tee pipe joint 28 so as to control the pressure in the high-pressure section 4. Preferably, the high-pressure gas cylinder 1 provides a pressure source for the high-pressure section 4, and the pressure control cabinet 2 is provided with a pressure gauge, a pressure reducing valve and a stop valve for regulating and controlling the pressure in the high-pressure section 4.
As shown in fig. 1 and fig. 2, the ultrasonic atomization system is used for injecting micron-sized fuel droplets into the experimental section 14, and the ultrasonic atomization system includes an ultrasonic atomizer 23, a flow guide pipe 22, and an atomizer adapter section, wherein: the ultrasonic atomizer 23 stores liquid fuel, and the ultrasonic atomizer 23 has the advantages of small particle size of generated liquid mist (the particle size of the generated liquid mist is in the micron order) and uniform particle size distribution of the generated liquid mist, so that the problem of large particle size generated by a nozzle type atomizer is solved, the generated liquid mist has small particle size, and the problem of liquid drop breakage does not need to be considered in an experiment. One end of the diversion pipeline 22 is connected with the ultrasonic atomizer 23, the other end of the diversion pipeline is connected with the atomizer switching section, and the atomizer switching section is connected with the experiment section 14.
As shown in fig. 8 to 11, the atomizer adaptor includes a second blind hole plate with holes 15, an adaptor cavity 16, a sealing rod support plate with holes 17, a sealing rod linkage plate with holes 32 and a plurality of sealing rods 33. The second blind hole plate 15 with the hole, the switching section cavity 16 and the sealing rod support plate 17 are assembled to form a cavity communicated with the shock tube, and the cavity is used for transferring liquid mist generated by the ultrasonic atomizer 23 into the shock tube.
As shown in fig. 1, 8, 9 and 12, the second blind hole plate 15 is connected to the experimental section 14 on the shock tube, a boss is provided in the middle of the side of the second blind hole plate 15 with a hole contacting the experimental section 14, the boss is provided with a plurality of through holes, preferably, an orifice at one end of the plurality of through holes, which is far away from the cavity 16 of the adapting section, is countersunk into a cone shape, and the number of the through holes is 6, so that the fuel droplets are uniformly distributed after entering the shock tube. Preferably, the second blind hole plate 15 with holes is made of stainless steel, and a sealing ring groove is milled on the surface of the second blind hole plate 15 with holes, which is connected with the experimental section 14, and is used for installing the first O-ring 49 to ensure the air tightness of the shock tube.
As shown in fig. 8, 9 and 13, the adaptor section housing 16 is machined from stainless steel and is located between the second perforated blind hole plate 15 and the sealing rod support plate 17. Preferably, the adaptor cavity 16 is fixedly connected to the second blind hole plate 15 through the matching of a hexagon socket head cap screw 47 and a nut 48, and sealing ring grooves are milled on two end faces of the adaptor cavity 16 respectively and are used for installing a second O-ring 50 respectively to ensure the air tightness of the atomizer adaptor.
As shown in fig. 8, 9 and 14, the sealing rod support plate 17 is fixedly connected to the adaptor section cavity 16 through the matching of a hexagon socket head cap screw 47 and a nut 48, and the sealing rod support plate 17 is provided with a plurality of holes coaxial with the plurality of through holes provided on the boss, and the number of the holes is 6 correspondingly. Preferably, the sealing rod support plate 17 is made of stainless steel, and functions to provide support for the sealing rod 33 to meet the requirement of axial movement of the sealing rod 33. A smooth hole portion for mounting the V-ring 52 is formed in the seal rod support plate 17, and a screw for mounting the packing gland nut 51 is formed. The sealing ring compression nut 51 has two functions, namely, the compression of the V-shaped ring 52 meets the sealing requirement; secondly, the sealing rod 33 is supported together with the sealing rod support plate 17 to eliminate the rotation of the sealing rod 33 around the direction vertical to the axis thereof, thereby playing a role in limiting.
As shown in fig. 8, 9 and 15, the sealing-rod linkage plate 32 is disposed on a side of the sealing-rod support plate 17 away from the adaptor cavity 16, a plurality of holes coaxial with the plurality of through holes disposed on the bosses are disposed on the sealing-rod linkage plate 32, the number of the holes is 6, and rotating shafts are disposed on two opposite sides of the sealing-rod linkage plate 32.
As shown in fig. 9, 10 and 16, the sealing rods 33 are provided with a tapered structure at one end and threads at the other end, and the number of the sealing rods 33 is 6 accordingly. One ends of the six sealing rods 33 provided with the threads are connected with the sealing rod linkage plate 32; the conical surface structure on the sealing rod 33 can be matched with one conical end of the through holes arranged on the boss to form sealing, and when the sealing is formed, one surface of the boss facing the experimental section 14 and the bottom surface of the sealing rod 33 are overlapped to form a reflecting surface of the shock wave, so that the shock wave tube is sealed. Because the conical surfaces are matched and shock waves are rushed towards the bottom surface of the sealing rod 33, the conical surface matching is more and more compact in the shock wave impact process, and the requirement on the air tightness of the shock tube is met. Since the seal bar 33 in this embodiment is an elongated bar, the die steel having a high hardness is selected during machining to prevent deformation that may easily occur during machining, and is chrome-plated after grinding to prevent rusting.
As shown in fig. 8 to 11 and 17, the present embodiment further includes two cam handles 34 symmetrically installed on the sealing-rod linkage plate 32, and the cam handles 34 serve to control the on/off between the experimental section 14 and the adaptor section cavity 16. The cam handle 34 comprises a cam and a handle, the middle part of the cam is provided with a hole, the handle is fixedly connected with the cam, the hole in the middle part of the cam on the cam handle 34 is sleeved on the rotating shaft and is fixed, and the rotation of the cam handle 34 can be realized only by pushing the handle. The rotation of the cam handle 34 drives the sealing rod linkage plate 32 to move along the axial direction of the hole on the sealing rod support plate 17, and further drives the six sealing rods 33 to move along the axial direction of the through hole, so that the sealing rods 33 are in contact with and separated from the second blind hole plate 15 with the hole, and the start and stop of liquid mist entering the shock tube are further controlled. Preferably, a cotter pin 46 is installed on the rotating shaft of the cam handle 34 and located on the cam handle 34 away from the sealing-rod linkage plate 32, and the cam handle 34 is restricted from moving axially along the rotating shaft by the cotter pin 46. The sealing rod linkage plate 32 can be moved quickly by means of the cam handle 34 and can be locked by means of the gravity of the cam handle 34, so that the phenomenon that other unreliable factors are introduced due to the fact that a separate control mechanism is used for controlling the movement and the locking of the sealing rod linkage plate 32 is avoided.
As shown in fig. 11, when the sealing rod 33 is out of contact with the second blind hole plate 15 with a hole, the adaptor cavity 16 is in communication with the experimental section 14, and liquid mist can enter the experimental section 14 from the adaptor cavity 16 of the atomized adaptor; as shown in fig. 9 and 10, the sealing rod 33 is engaged with the second perforated blind plate 15, and the adaptor section cavity 16 and the experimental section 14 are closed.
As shown in fig. 1 and 3, the pressure detection system includes a plurality of low-voltage piezoelectric transducers and a high-voltage piezoelectric transducer 5, and the low-voltage piezoelectric transducers are sequentially disposed on a low-voltage II section 9 along the movement direction of the incident shock wave. The low-voltage section piezoelectric sensors comprise a low-voltage section I piezoelectric sensor 8, a low-voltage section II piezoelectric sensor 10 and a low-voltage section III piezoelectric sensor 11 which are sequentially arranged along the movement direction of the incident shock wave. Preferably, three instrument holes are sequentially arranged above the low-voltage section II 9 at intervals, and the low-voltage section I piezoelectric sensor 8, the low-voltage section II piezoelectric sensor 10 and the low-voltage section III piezoelectric sensor 11 are sequentially and respectively installed in the three instrument holes along the movement direction of the incident shock wave. An instrument hole is arranged above the high-voltage section 4, and the high-voltage section piezoelectric sensor 5 is arranged in the instrument hole.
The high-voltage section piezoelectric sensor 5, the low-voltage section piezoelectric sensor 8, the low-voltage section piezoelectric sensor 10 and the low-voltage section piezoelectric sensor 11 are respectively connected with one end of a piezoelectric sensor signal transmission line 35 through data lines, and the other end of the piezoelectric sensor signal transmission line 35 is connected with a computer host 24. Preferably, the piezoelectric sensor signal transmission line 35 transmits the signals of the high-voltage section piezoelectric sensor 5, the low-voltage section piezoelectric sensor No. I8, the low-voltage section piezoelectric sensor No. II 10 and the low-voltage section piezoelectric sensor No. III 11 to the computer host 24 through processing, and displays the signals on the display 25. The high-pressure section piezoelectric sensor 5 is used for more accurately measuring the pressure of the high-pressure section 4 so as to record the actual working condition of the experiment; the low-voltage section I piezoelectric sensor 8, the low-voltage section II piezoelectric sensor 10 and the low-voltage section III piezoelectric sensor 11 are used for detecting the pressure of the corresponding low-voltage section piezoelectric sensor on the low-voltage section II 9, and the computer host 24 records the pressure change time of the low-voltage section piezoelectric sensors at three positions. The speed delta v of the shock wave can be calculated according to the installation distance delta L between any two low-voltage section piezoelectric sensors and the time difference delta t when the pressure change is detected between any two low-voltage section piezoelectric sensors, and the speed delta v is equal to delta L/delta t, and then the values of a plurality of groups of delta v are averaged to reduce the error.
As shown in fig. 1 and fig. 3, the multi-wavelength extinction method particle size measurement system includes a laser light source array 12, an optical fiber 13, an optical fiber coupler 36, a diffraction grating 20, a photodetector 19, a signal conditioner 18, a data acquisition card 21, and a photodetector signal transmission line 41. The side, facing the external environment, of the first detachable observation window is sequentially provided with an optical fiber coupler 36, an optical fiber 13 and a laser light source array 12; the diffraction grating 20 is arranged on one side of the second detachable observation window facing the external environment; the photoelectric detector 19 is arranged in the reflection path of the diffraction grating 20, the photoelectric detector 19 is connected with the signal conditioner 18, and the signal conditioner 18 is connected with the data acquisition card 21. Preferably, the laser light source array 12 selects and combines light sources with specific wavelengths according to extinction characteristics of a measurement substance, and has certain flexibility.
The optical fiber 13 transmits light with each wavelength in the laser light source array 12 to the optical fiber coupler 36, the light is coupled into one path of light through the optical fiber coupler 36 and emitted, the synthesized one path of light vertically passes through the first observation window glass and is emitted into a sample cell in the experiment section 14, the synthesized one path of light vertically passes through the second observation window glass after passing through the sample cell and is emitted, then the light is split under the action of the diffraction grating 20, and the number of the split light paths is consistent with the number of the light paths before coupling, namely the number of the split light paths.
The photodetector 19 can detect the light intensity of each wavelength light path after light splitting, and convert the light intensity signal into an electrical signal, which is collected by the data acquisition card 21 after passing through the signal conditioner 18, and transmitted to the computer host 24 through the photodetector signal transmission line 41. Under the control of the computer host 24, the change of the light intensity signal can be continuously measured, the change of the particle size and the concentration of the liquid mist in the experimental section 14 can be inverted through an inversion algorithm, and the influence of the shock wave on the evaporation process of the fuel liquid drops at the supersonic speed can be further researched. The extinction method has the advantages of small measurement lower limit, no need of calibration and the like, so that the requirement of measuring the particle size change of the micron-sized liquid drop under the condition of shock wave impact can be met.
As shown in fig. 2, the present embodiment further includes a suction pump 26, and the low pressure section I7 is provided with a hole, which is connected to the suction pump 26 through a suction pipe 27, and the suction pump 26 is used for guiding the air flow in the low pressure section during atomization.
The embodiment also provides a research method for influence of shock waves on the evaporation process of the fuel liquid drops under the supersonic air flow, which comprises the following steps:
step 1, calculating the pressure value of critical gas in the high-pressure section 4: the critical gas pressure value in the high-pressure section 4 is p 4 The pressure value of the gas in the low-pressure section is p 1 ，p 4 And p 1 Is p ratio of 41 (ii) a Determining the Mach number Ma of the required shock wave s Measuring p 1 Through p 41 And Ma s To obtain the pressure value p of the critical gas in the high-pressure section 4 4 ；
Wherein p is 1 The pressure is atmospheric pressure or a preset specific pressure value;
p 41 and Ma s Has the relation of
In the formula a 14 For the sound speed ratio, it can be expressed as:
wherein, γ 1 Specific heat ratio of gas in low-pressure section, gamma 4 Is the specific heat ratio of the gas in the high-pressure section, M 1 Molecular weight of gas in low pressure zone, M 4 Is the molecular weight, T, of the gas in the high pressure section 1 Is the initial temperature, T, of the gas in the low-pressure section 4 Is the initial temperature of the gas in the high pressure section.
The optical paths with multiple wavelengths are coupled into a beam of optical path through the optical fiber coupler 36, the optical path is output to sequentially pass through the first detachable observation window, the experiment section 14 and the second detachable tube wiping window, and then the optical path with the same path number and wavelength number is divided into the optical paths through the diffraction grating 20; the photodetector 19 converts the detected light intensity signals of the split wavelengths into electrical signals, and transmits the electrical signals to the data acquisition card 21 through the signal adjusting circuit, so as to obtain light intensity signals before extinction.
the sealing rod linkage plate 32 is pushed to move towards the direction of the switching section cavity 16 by rotating the cam handle 34, so that the end part of the conical surface structure of the sealing rod 33 is separated from the second blind hole plate 15 with the hole, and the switching section cavity 16 in the ultrasonic atomization system is communicated with the experimental section 14; after the fuel droplets sprayed into the experimental section 14 reach a set concentration, the cam handle 34 is rotated to move the sealing rod linkage plate 32 in the direction away from the switching section cavity 16, so that one end face of the sealing rod 33 which is of a conical surface structure is matched with one end of the boss which is provided with a plurality of conical through holes, and the switching section cavity 16 of the ultrasonic atomization system is sealed with the experimental section 14.
the optical paths with multiple wavelengths are coupled into a beam of optical path through the optical fiber coupler 36 and output to pass through the experimental section 14, and then are divided into optical paths with the same path number and wavelength number through the diffraction grating 20; the photodetector 19 converts the detected light intensity signals of each wavelength after light splitting into electrical signals, and transmits the electrical signals to the data acquisition card 21 through the signal adjusting circuit, so as to obtain the light intensity after extinction by the aerosol, and then the change of the particle size and concentration of the fuel droplets is inverted by combining the initial light intensity before extinction measured in the step 3, so as to obtain the change curve of the particle size distribution of the wavefront fuel droplets along with time.
the actual shock velocity Δ v is calculated as follows:
in the formula:
the installation distance between the low-voltage section I piezoelectric sensor and the low-voltage section II piezoelectric sensor is delta L 1 ，
The response time difference between the low-voltage section I piezoelectric sensor and the low-voltage section II piezoelectric sensor is delta t 1 ，
The installation distance between the low-voltage section I piezoelectric sensor and the low-voltage section III piezoelectric sensor is delta L 2 ，
The response time difference between the low-voltage section I piezoelectric sensor and the low-voltage section III piezoelectric sensor is delta t 2 ，
The installation distance between the low-voltage section II piezoelectric sensor and the low-voltage section III piezoelectric sensor is delta L 3 ，
The response time difference between the low-voltage section II piezoelectric sensor and the low-voltage section III piezoelectric sensor is delta t 3 。
The optical paths with multiple wavelengths are coupled into a beam of optical path through the optical fiber coupler 36 and output to pass through the experimental section 14, and then are divided into optical paths with the same path number and wavelength number through the diffraction grating 20; the photoelectric detector 19 converts the detected light intensity signals of each wavelength after light splitting into electric signals, and transmits the electric signals to the data acquisition card 21 through the signal adjusting circuit, so that the light intensity in the interaction process of the shock wave and the fuel droplets is obtained, and then the change of the particle size and the concentration of the fuel droplets is inverted by combining the initial light intensity before extinction measured in the step 3, so that the change curve of the particle size distribution of the fuel droplets along with the time in the interaction process of the shock wave and the fuel droplets is obtained.
To facilitate the verification of the above-described research methods, this example provides a specific embodiment, which is as follows:
setting of test stripsThe part is formed by driving air at room temperature by nitrogen to obtain shock wave of Mach 1.4 under the initial condition of gamma 1 ＝γ 4 ＝1.4；M 1 ＝29，M 4 ＝28；T 1 ＝T 4 ＝298K。
Step 1, calculating p 41 ：
When the pressure in the low pressure section is atmospheric pressure, the pressure required in the high pressure section 4 is p 4 ＝4.881atm≈0.495MPa。
According to the experimental conditions, step 2: because the particle size of the liquid drops in the liquid mist is small, the evaporation life of the liquid drops is short even under normal temperature and normal pressure, namely the evaporation is finished in a short time, and the pressurization of the high-pressure section 4 needs a long time, so that the needed liquid mist is filled in the low-pressure section of the shock tube and then the high-pressure section 4 is pressurized in the future. In order to pass through the shock wave as soon as possible after the liquid mist is distributed, the high-pressure section can be pre-pressurized, so that the pressure of the high-pressure section 4 is slightly lower than a calculated value p 4 ＝0.495MPa。
And 3, step 3: after the atomization is complete, rapid pressurization of the high pressure section 4 to the desired pressure causes the diaphragm 42 to rupture, thereby generating a shock wave. Since the pressure of the high-pressure section 4 has been close to the desired pressure p before 4 Therefore, the time from the continuation of the pressurization to the rupture of the diaphragm 42 is short. The actual generated shock wave speed can be calculated according to the distance between a plurality of low-voltage section piezoelectric sensors and the response time.
In summary, in the present embodiment, during the experiment, the micron-sized fuel droplets are generated by the ultrasonic atomization system and injected into the experiment section 14, and then the high-pressure section 4 is pressurized to rupture the membrane 42, so as to generate the shock wave in the low-pressure section and the experiment section 14; meanwhile, the particle size of the micron-sized fuel droplets in the experimental section 14 is measured in real time according to a particle size measuring system of a multi-wavelength extinction method.
According to the embodiment, the diaphragms 42 with different strengths can be selected according to experiment requirements to generate shock waves with different strengths, and the inner sections of the shock tubes are all rectangular, so that the generated shock waves do not need to pass through a circular-square section in the conventional design scheme, and the quality of the generated shock waves is better.
According to the embodiment, the time difference of pressure change between each low-voltage section piezoelectric sensor and other low-voltage section piezoelectric sensors is detected through the installed low-voltage section piezoelectric sensors, a plurality of shock wave speeds are calculated according to the time differences and the installation distance between each low-voltage section piezoelectric sensor and other low-voltage section piezoelectric sensors, and then the average value of the shock wave speeds is obtained, so that the error is reduced.
The observation window can be dismantled to first observation window and the second of dismantling of this embodiment can provide the measurement channel for multiple measurement mode, can satisfy the measurement demand under the different experimental conditions.
The selection of the laser light source array 12 in the multi-wavelength extinction method particle size measurement system in the embodiment has flexibility, and light sources with different wavelengths can be selected to be combined according to the extinction characteristics of substances in the experiment section 14; the data acquisition card 21 may be selected as required by the sampling frequency.
The particle size is measured by adopting a multi-wavelength extinction method, when the particle size is measured by means of optics, the interaction between shock waves and liquid mist can affect the scattering of light, and the rise of pressure and temperature after the shock waves can also affect the scattering of light to a certain extent, so that a measuring instrument receiving scattered light signals cannot meet the requirements of experiments. In the extinction method measurement process, the transmitted light passing through the particle system is collected during measurement, but the scattered light of the particles is not collected, so that the optical signal is strong; in addition, the influence of shock waves on light intensity is small, so that the particle size measured by the extinction method can be used in an experiment with shock wave impact. In addition, the extinction method not only needs to collect the light intensity signal after passing through the particle system, but also needs to collect the light intensity signal before passing through the particle system, so that the extinction method is an absolute measurement method and does not need calibration.
In this embodiment, a continuous laser light source is used, so the data acquisition frequency depends on the acquisition frequency of the data acquisition card 21, and the data acquisition card 21 with different acquisition frequencies can be selected according to the experimental requirements. For example, the time of the shock wave passing through the measurement region is microsecond, so that the data acquisition card 21 with the acquisition frequency of 1MHz can be adopted to ensure that reliable data are acquired in the time of the shock wave passing through. In order to acquire more reliable data in a specific time, a data acquisition card 21 with a higher acquisition frequency may be used, and thus the selection of the acquisition frequency has flexibility.
In the present embodiment, the selection of optical wavelengths in the multi-wavelength extinction method has flexibility. Since the selection of the wavelength has an influence on the inversion of the particle size, the particle size distribution range can be measured in advance by a well-established particle size measuring apparatus without shock, and a desired laser light source array 12 can be configured by selecting an appropriate wavelength from the measured particle size range.
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
The meaning of "and/or" in this application is intended to include both the individual and the simultaneous presence of both.
The term "connected" in the present application may mean either a direct connection between the components or an indirect connection between the components through other components.
In the description of the present invention, it is to be understood that the terms "upper side", "lower side", and the like indicate orientations or positional relationships based on those shown in the drawings only for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, "first", "second", and the like do not indicate a degree of importance to the component parts, and thus are not to be construed as limiting the present invention.
In light of the foregoing description of the preferred embodiment of the present invention, many modifications and variations will be apparent to those skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.
Claims (4)
1. A research method for influence of shock waves on a fuel liquid droplet evaporation process under supersonic airflow is characterized by comprising a shock tube, wherein the shock tube comprises a high-pressure section, a low-pressure section and an experimental section which are sequentially arranged along the movement direction of an incident shock wave, and a diaphragm is arranged between the high-pressure section and the low-pressure section; the research method comprises the following steps:
step 1, calculating the pressure value of critical gas in a high-pressure section: critical gas pressure value in the high pressure section is p 4 The pressure value of the gas in the low-pressure section is p 1 ，p 4 And p 1 Has a ratio of p 41 (ii) a Determining the Mach number Ma of the required shock wave s Measuring p 1 Through p 41 And Ma s To obtain the pressure value p of the critical gas in the high-pressure section 4 ；
Step 2, pre-pressurizing a high-pressure section: the high-pressure section is pressurized through a pressure control system, so that the gas pressure value p 'in the current high-pressure section' 4 Close to but less than p 4 ；
Step 3, measuring initial light intensity: measuring initial light intensity before extinction by adopting a multi-wavelength extinction method particle size measurement system;
step 4, atomization: starting an air pump, wherein an ultrasonic atomization system is communicated with an experimental section, and an ultrasonic atomizer in the ultrasonic atomization system sprays atomized fuel droplets into the experimental section through an atomization switching section to form aerosol until the concentration reaches a set concentration;
step 5, measuring the particle size distribution of the fuel droplets in the shock front: during atomization, a multi-wavelength extinction method measurement particle size system is adopted to measure the particle size distribution of the fuel droplets in the experimental section in real time, and a change curve of the particle size distribution of the wavefront fuel droplets along with time is obtained;
step 6, generating shock waves: by pressure controlThe system boosts the high-pressure section to make the gas pressure value in the current high-pressure section reach p 4 (ii) a At the moment, the diaphragm is broken, the gas in the high-pressure section rapidly rushes into the low-pressure section and the experimental section, and shock waves are generated in the low-pressure section and the experimental section;
step 7, measuring the particle size distribution of the fuel droplets in the interaction process of the shock waves and the fuel droplets: when the shock wave moves, the particle size distribution of the fuel droplets in the experimental section is measured in real time by the particle size measuring system by the multi-wavelength extinction method, and a change curve of the particle size distribution of the fuel droplets along with time in the interaction process of the shock wave and the fuel droplets is obtained; meanwhile, a plurality of groups of shock wave speeds are calculated according to the installation distance between the piezoelectric sensors in the low-voltage sections and the response time difference between the piezoelectric sensors in the low-voltage sections during shock wave motion, the average value of the shock wave speeds is used as the actual shock wave speed delta v, and therefore the actual shock wave Mach number Ma is obtained s ；
Actual shock Mach number Ma s Δ v/a, a is the speed of sound;
the low-voltage section piezoelectric sensors are a low-voltage section I piezoelectric sensor, a low-voltage section II piezoelectric sensor and a low-voltage section III piezoelectric sensor which are sequentially arranged along the movement direction of the incident shock wave; the actual shock velocity Δ v is calculated as follows:
in the formula:
the installation distance between the low-voltage section I piezoelectric sensor and the low-voltage section II piezoelectric sensor is delta L 1 ，
The response time difference between the low-voltage section I piezoelectric sensor and the low-voltage section II piezoelectric sensor is delta t 1 ，
The installation distance between the low-voltage section I piezoelectric sensor and the low-voltage section III piezoelectric sensor is delta L 2 ，
The response time difference between the low-voltage section I piezoelectric sensor and the low-voltage section III piezoelectric sensor is delta t 2 ，
Low-voltage section II piezoelectric sensorThe installation distance between the sensor and the low-voltage section III piezoelectric sensor is delta L 2 ，
The response time difference between the low-voltage section II piezoelectric sensor and the low-voltage section III piezoelectric sensor is delta t 3 ；
Step 8, measuring the particle size distribution of fuel liquid drops after shock wave: after the shock wave is passed, the particle size distribution of the fuel droplets in the experimental section is continuously measured in real time by the particle size measuring system by the multi-wavelength extinction method until the fuel droplets are completely evaporated, and the measurement is stopped, so that a change curve of the particle size distribution of the fuel droplets after the shock wave along with the time is obtained;
step 9, pressure relief: removing waste gas in the shock tube through a pressure control system;
step 10, data processing: the host computer measures the change curve of the particle size distribution of the fuel droplets with time and the change curve of the particle size distribution of the fuel droplets with time after the interaction process of the fuel droplets and the actual shock Mach number Ma according to the multi-wavelength extinction method s So as to obtain the evaporation rate of the fuel liquid drops and the shock wave Mach number Ma s The relationship between them.
2. The method for researching the influence of the shock wave under the supersonic air flow on the evaporation process of the liquid droplets is characterized in that: in step 1 p 1 The pressure is atmospheric pressure or a preset specific pressure value; p is a radical of formula 41 And Ma s The relation of (A) is as follows:
in the formula a 14 For the sound speed ratio, it can be expressed as:
wherein, gamma is 1 Specific heat ratio of gas in low-pressure section, gamma 4 Specific heat ratio of gas in high pressure section, M 1 Is lowMolecular weight of the ballast gas, M 4 Is the molecular weight, T, of the gas in the high pressure section 1 Is the initial temperature, T, of the gas in the low-pressure section 4 Is the initial temperature of the gas in the high pressure section.
3. The method for researching the influence of the shock wave under the supersonic air flow on the evaporation process of the liquid droplets is characterized in that: and (4) after the fuel droplets sprayed into the experimental section in the step (4) reach the set concentration, sealing the space between the ultrasonic atomization system and the experimental section.
4. The method for researching the influence of the shock wave under the supersonic air flow on the evaporation process of the liquid droplets is characterized in that: the multi-wavelength extinction method particle size measurement system comprises an optical fiber coupler, a diffraction grating, a photoelectric detector, a signal adjusting circuit and a data acquisition card; in the steps 3, 5, 7 and 8, optical paths with multiple wavelengths are coupled into a beam of optical path through an optical fiber coupler and output to pass through an experimental section, and then the optical path with the same path number and wavelength number is divided into optical paths through a diffraction grating; the photoelectric detector converts detected light intensity signals of various wavelengths after light splitting into electric signals, and the electric signals are transmitted to the data acquisition card through the signal adjusting circuit, so that the change of the particle size and the concentration of the fuel droplets is inverted, and a corresponding change curve of the particle size distribution of the fuel droplets along with time is obtained.
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