RU2744308C1 - Method for generation of high-speed shock wave in impact pipe - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: claimed invention relates to physics of strong shock waves, physics of combustion and explosion and can be used for initiation of shock waves propagating at a speed of more than 11 km/s. Method for generating a high-speed shock wave in an impact tube comprising a high-pressure (HPC) chamber, from one end is equipped with a forechamber with a perforated end facing in direction of wave propagation, and from the other end through the diaphragm connected to the low pressure (LPC) chamber, includes supply of helium and propellant in the HPC, supply and ignition of the explosive mixture in the prechamber, combustion of which provides injection of hot gas jets from antechamber through holes of perforation into HPC cavity, which at a distance of not more than 3 gages from the end of HPC lead to formation of a flat incident shock wave, which destroys the diaphragm with formation of a reflected Chapman-Jouguet detonation wave and passing to LPC shock wave at a speed of more than 11 km/s, pushing gas for which are combustion products of explosive mixture with helium.

EFFECT: technical result consists in the possibility of generation of the shock wave propagating in the low-pressure chamber of the shock tube with the second space (and more) speed, and reducing energy costs for high-speed and shock waves ofmaking best use of energy combustion helium diluted oxygen-hydrogen mixture in high-pressure chamber (HPC).

5 cl, 4 dwg

Description

Technology area

The claimed invention relates to the physics of strong shock waves, the physics of combustion and explosion and can be used to initiate shock waves propagating at a speed of more than 11 km / s. Measurement of the spectral and kinetic characteristics of gases obtained at such shock wave velocities is necessary for solving scientific and technical problems, and can be used, for example, in the creation of thermal protection required when various bodies enter the atmosphere of the Earth and other planets, in particular, space descent devices. In addition, the claimed invention can be used to verify physicochemical models of nonequilibrium dissociation and ionization processes of various gases under extreme conditions.

State of the art

In classical devices for initiating detonation, either direct initiation of detonation is used - a short-term release of energy much greater than the specified value (Zeldovich Ya.B., Kogarko S.M., Simonov N.N. // ZhTF, 1956, volume 26, No. 8, p. . 1744-1752), or the transition of combustion to detonation: the combustible mixture is ignited with a weak ignition source in a pipe with regular annular obstacles and provides a progressive acceleration of the flame with a transition to detonation at distances (pre-detonation distance) and for a time (pre-detonation time) significantly exceeding the indicated meanings, see, for example, O. Peraldi, R. Knystautas and JH Lee "Criteria for transition to detonation in tubes". Twenty-First Symposium (International) on Combustion / The Combustion Institute, 1986, pp. 1629-1637. However, all of them are characterized by significant energy consumption, while the speed of propagation of the shock wave does not exceed 10 km / s.

From the prior art, there is a known method for initiating detonation in a pipe with a combustible mixture (RF patent No. 2672244), including the formation of a turbulent flame front, its acceleration and amplification of the formed shock wave, while the formation of a turbulent flame front is carried out in a high-speed turbulent flow of a combustible mixture formed by turbulent mixing of cross supersonic jets of fuel and oxidizer, using a prechamber-torch ignition, while the prechamber is filled with a combustible mixture coming from the detonation tube, and the ignition of the combustible mixture in the prechamber is carried out using a weak ignition source.

However, the known method is also characterized by a low velocity of propagation of the shock wave. So, the speed of the reaction front at a distance of ~ 300 mm is about 2300-2400 m / s, and increases to 2500 m / s depending on the average composition of the mixture.

There is also known a method of initiating a pulsed detonation of a fuel-air mixture (RF patent No. 2659415), which consists in generating a primary shock wave and then exerting a small energetic effect on the fuel-air mixture in front of the leading shock wave. As a small energy impact, the effect of selective laser radiation is used, upon absorption of which the oxygen molecules of the mixture pass into the state of singlet-delta O ₂ (a ¹ Δg) and accelerate the chemical reactions of fuel combustion, and the laser radiation is applied to the fuel-air mixture in local regions before by the front of the leading shock wave with a time advance less than the relaxation time of oxygen in the singlet-delta O ₂ state (a ¹ Δg), at the moment when the velocity of the leading shock wave is less than the detonation velocity in the Chapman - Jouguet regime in the fuel-air mixture, and the energy of laser radiation is set from the condition of sufficiency to increase the speed of the leading shock wave with the transition to a non-stationary oscillatory detonation mode. The technical result is a decrease in the subcritical energy of initiation of pulsed detonation in the fuel-air mixture is lower than in the case of sequential ignition of the combustible mixture by electric discharges.

In this source, it was found that the maximum decrease in the energy of initiation of detonation in the mixture under consideration is achieved when exposed to selective laser radiation at the moment when the wave speed is about 1700 m / s, which is a rather low indicator to make it possible to use this method to initiate strong shock waves.

From the publication "EXPERIMENTAL STUDY OF RADIATION OF SHOCK-HEATED AIR ON A DOUBLE-DIAPHRAGM IMPACT TUBE" P.V. Kozlov, Yu.V. Romanenko, Research Institute of Mechanics, Moscow State University. M.V. Lomonosov Moscow State University (http://chemphys.edu.ru/media/published/011_5whp3ut.pdf) a shock tube is known that includes a high-pressure chamber connected by means of flanges, with a perforated prechamber located at its end, an intermediate pressure chamber and a low-pressure chamber. Between the flanges of the sections of the high-pressure chamber (HPC) and the intermediate-pressure chamber (efficiency) filled with helium, as well as the sections of the efficiency factor and the low-pressure chamber (LPC), there are cassettes with type-setting diaphragms made of mylar film with a thickness of 20 μm.

When the detonation wave was formed in accordance with the data of the sources, it was possible to achieve speeds of 4-7 km / s, however, the method disclosed in the publication materials, as well as its modes, do not allow achieving higher speeds, in particular, due to the fact that during the generation of a shock wave lavsan (polyethylene terephthalate) diaphragms were used, which, when ruptured, significantly limit the flow, fly into the pipe, create hydrocarbon impurities and settle on the walls.

It has been experimentally confirmed that the detonation velocity is constant for a specific combustible gas mixture. The Chapman-Jouguet state is the most stable detonation state.

The closest in technical essence to the claimed invention is a method for initiating high-speed shock waves, disclosed in (Yuan CK, Zhou K., Liu YF, Hu ZM, Jiang, ZL (2018). Spectral measurements of hypervelocity flow in an expansion tunnel. Acta Mechanica Sinica.doi: 10.1007 / s10409-018-0806-8). In the JF16 double-diaphragm detonation tube, a high-speed shock wave is formed as a result of detonation combustion of a hydrogen-oxygen mixture in a high-pressure chamber. To obtain a shock wave velocity of 7.9 km / s at an initial air pressure of 0.15 Torr, the energy consumption per unit area is about 74 kJ / cm2.

However, the maximum speed achieved using the known method is not 10.2 km / s, while to obtain such a speed, an energy of 4 MJ is expended, which is an extremely high indicator for the successful application of the method.

The technical problem solved by the claimed invention consists in the need to overcome the disadvantages inherent in analogues and the prototype by creating a method for generating high-speed shock waves, providing increased efficiency of the shock tube.

Brief disclosure of the essence of the claimed invention

The technical result achieved thanks to the claimed invention consists in the possibility of generating a shock wave propagating in the low-pressure chamber of the shock tube at a second cosmic (or more) speed and reducing energy costs to obtain high-speed shock waves due to the most complete use of the combustion energy diluted with helium oxygen hydrogen mixture in a high-pressure chamber (HPC) by ensuring the combustion of its main mass in the Chapman-Jouguet detonation wave, which provides the energetically most efficient combustion mode in a limited volume (see, for example, Ya.B. Zeldovich. On the energy use of detonation combustion // Journal of technical physics. - 1940. - T.10, No. 17. - S. 1453-1461).

The claimed technical result is achieved by the fact that the method for generating a high-speed shock wave in a shock tube containing a high-pressure chamber (HPC), from one end is equipped with a prechamber with a perforated end facing in the direction of wave propagation, and from the other end through a diaphragm connected to the low-pressure chamber (LPC), includes the supply of helium and an explosive mixture to the HPC, the supply and ignition of an explosive mixture in the prechamber, as a result of its combustion, hot gas jets are injected from the prechamber through the perforation holes into the HPC cavity, which are at a distance of no more than 3 calibers from the end HPC leads to the formation of a plane incident shock wave, which destroys the diaphragm with the formation of a reflected Chapman - Jouguet detonation wave and a shock wave passing through the LPC at a speed of more than 11 km / s, the propelling gas for which is the combustion products of an explosive mixture with helium. The diaphragm is made of a copper sheet with a thickness of 0.3 to 0.7 mm, equipped with cruciform notches with a size of 0.2 to 0.3 mm, which prevent the scattering of its particles during destruction. The initial pressure in the HPC is in the range from 8 to 10 atm, and the partial pressure of helium in the HPC is from 50 to 65%. After the supply of helium and the explosive mixture to the HPC, the components of the mixture are mixed by holding for 30-80 minutes. The length of the HPC does not exceed 1.5 m.

Ignition and combustion of an explosive mixture in the prechamber provides injection of hot jets of combustion products into the HPC cavity through the perforation holes, which leads to the formation of a plane incident shock wave in the HPC at a distance of no more than 3 calibers from the HPC end wall. The incident shock wave ignites the gas in the HPC. The resulting flame maintains the intensity of the incident shock wave, but quickly lags behind the shock front.

The claimed invention is illustrated by the following drawings, where

in fig. 1 shows a diagram of a high-pressure chamber with pressure sensors and a prechamber located in it,

in fig. 2 shows a drawing of the prechamber,

in fig. 3 shows a sample oscillogram of signals from pressure sensors (the distance between sensors P9 and P10, which register the speed of the shock wave in the low-pressure chamber of the shock tube, is 100 mm),

in fig. 4 shows a diagram of the installation by means of which the inventive method is implemented (shock tube).

Positions in the drawings indicate:

1 - prechamber,

2 - diaphragm,

3 - high pressure chamber,

4 - pressure sensors

5 - a candle that initiates the ignition of an explosive mixture in the prechamber,

6 - perforated end of the prechamber.

When describing the device by means of which the claimed method is implemented, the following conventions are used:

CHP - shock tube high pressure chamber;

CIP - intermediate chamber (intermediate pressure chamber) of the shock tube;

CLP - shock tube low pressure chamber;

CV1 - vacuum chamber for gas mixture preparation;

CV2 - vacuum chamber of the damper volume;

CV3 - vacuum chamber for helium preparation in the intermediate chamber of the shock tube;

NI - rotary vane pump 2НВР-5ДМ;

NR - oil-free pumping station DRYTEL-1025;

PD1 ÷ PD6 - deformation vacuum gauges and manometers;

PM - vacuum gauge VMB-14 with a magnetic electric discharge sensor PMM-32-1;

V1 ÷ V10 - straight-through shut-off valves;

VT - damper;

VF1 ÷ VF7 regulating valves;

VM - shut-off valve with electromagnetic drive.

Implementation of the invention

The inventive method is implemented using a device that is a shock tube (UT), generally consisting of three sections: a high-pressure chamber (HPC) with a length of not more than 1.55 m, an intermediate chamber (efficiency) with a length of not more than 3.5 m and a low-pressure chamber ( KND) with a length of not more than 3 m. The listed chambers are made of solid sections of seamless hot-deformed steel pipe GOST 9940-81 (made of steel 12X18H10T), with an outer diameter of about 60 mm, wall thickness of at least 5 mm. At the ends, collar flanges are welded to the sections, made, for example, from steel 12X18H9T by hot pressing. The length of the sections was chosen taking into account the availability of free space in the laboratory room, the thickness of the tube walls was chosen from considerations of the possibility of manual installation and maintenance of the shock tube by two laboratory employees. Each section is housed on two adjusting tables fixed to steel legs fixed to the floor. Cassettes with diaphragms are located between the flanges of adjacent sections. The flanges are tightened with four 20mm bolts. The claimed invention can be implemented in its absence, with the direct connection of HPC and LPC. The efficiency has an auxiliary function, is not an obligatory element of the shock tube and is intended mainly to exclude the effect of the pushing gas (hydrogen) during kinetic studies. Nevertheless, it was found that the presence of efficiency in the composition of the shock tube leads to an increase in the speed of the recorded shock wave by 10-20%.

Each chamber is equipped with a gas admission and evacuation system.

The LPC inlet system consists of three cylinders 1-3 with a volume of 40 liters, a standard PD1 vacuum gauge, three VF1-VF3 leaks connected to the measuring volume CV1, and a bypass valve V1 (DN 10 mm). The filling system is evacuated through the overflow valve V1 and the valve V2 by an oil-free pumping station NR.

The helium filling system in efficiency, when used, consists of a 40-liter cylinder, a VF4 leak, a CV3 measuring volume, a PD2 vacuum gauge and a V8 bypass valve. The helium filling system is evacuated through bypass valve V8, intermediate chamber CIP and valve V7 with an NI backing pump.

The HPC filling system includes three 40-liter cylinders containing hydrogen, oxygen and helium. The cylinders are connected to the high-pressure chamber by leak valves VF5-VF7 and bypass valve V5. The push gas pressure in the high pressure chamber is monitored with PD4 and PD5 pressure gauges. The PD6 pressure gauge monitors the pressure in the hydrogen cylinder. Valve V10 provides an emergency release of hydrogen from the high-pressure chamber.

The distribution of the inlet systems is carried out with a stainless steel pipe ∅3x0.5 mm. The tube is soldered with PSR-40 silver solder to the corresponding valve and pressure gauge nipples. All seals of the venting systems are made of fluoroplastic.

FIG. 4 shows a schematic diagram of the filling and pumping of the shock tube. With the help of an NI pump connected by a VM solenoid valve (DN 30 mm) to a vacuum line laid along the entire pipe, and valves V3, V5, and V7, all sections of the shock pipe are evacuated. With the help of valve V6, atmospheric air or neutral gas is injected into the pipe when changing diaphragms. The vacuum line is made of 18 mm diameter stainless pipe sections joined by quick-release flanges welded to the pipe through bellows. The forevacuum pressure in the pipe is controlled by a PD3 exemplary vacuum gauge. On the side of the low-pressure chamber, a 47-liter CV2 damper tank made of stainless steel is connected to the pipe through the VT damper valve, bellows and L-shaped branch pipe. The VT damper valve has a flow area of 60 mm. An oil-free pumping station NR is connected to the damper tank via valve V2 (DN 60 mm). To control the degree of pumping out of the shock tube, a PM vacuum gauge with a magnetic electric discharge sensor is also connected to the damper tank. The VT valve makes it possible to change the diaphragms in the shock tube without letting atmospheric pressure into the damper tank, thereby significantly reducing the time for final pumping of the shock tube. All connections of the vacuum system are made by quick disconnect flange connections. As seals for the vacuum system of pipe sections, tanks, valves, etc. standard seals made of high vacuum rubber are used.

The high-pressure chamber (inner diameter 50 mm, length 30-60 calibers) and the low-pressure chamber are separated by a diaphragm. If used as part of an efficiency unit, the diaphragm is located at the interface between HPC and efficiency. In general, the diaphragm is a copper sheet (foil) with a thickness of 0.2 to 0.7 mm. Copper foil with a thickness of 0.3-0.4 mm is used as a diaphragm between the chambers. The use of this type of diaphragm has made it possible to attain shock wave velocities of 11.4 km / s at an initial air pressure in the low-pressure chamber of 0.25 Torr. On the area of the diaphragm, special cross-shaped notches are made to facilitate its rupture, full disclosure and prevention of entrainment of the torn off "petals" of copper into the flow, that is, there is practically no entrainment of scraps of diaphragm material into the flow. For each mode, a specific diaphragm thickness and notch depth are selected. The diaphragm is designed to reflect a plane shock wave formed as a result of the ignition of an explosive mixture, simultaneously with its opening without destruction and detachment of the petals, which leads to the combustion of the bulk of the gas stored in the high-pressure chamber in a mode close to Chapman-Jouguet detonation.

At the end of the HPC, located on the side opposite to the diaphragm, there is a prechamber intended for igniting the explosive mixture. The prechamber can be formed by the end and walls of the HPC and bounded by a perforated stainless steel sheet. In another embodiment, the prechamber is formed by inserting a steel "cup" with a perforated bottom into the HPC end. Thus, the prechamber has a diameter that coincides with the inner diameter of the pressure build-up and has a length of about 20 mm. The perforation is made uniform, with each hole made in the form of an analogue of the Laval nozzle. The ratio of the perforated areas to the cross-sectional area of the UT is in the range: 20-100. Perforation in the wall of the prechamber provides the outflow of uniform hot jets and the formation of a plane shock wave at a distance of several calibers (3 calibers) from the end of the pressure build-up pump, near which the prechamber is formed.

At the end of the HPC, there is also a means for igniting an explosive mixture, made, for example, in the form of a car candle. A certain pressure is maintained in each chamber of the shock tube. Thus, the pressure range in the HPC is 8-10 atm.

Measurement of the shock wave velocity in the measuring section is carried out by piezoelectric sensors. Signals from piezoelectric sensors are recorded by digital storage oscilloscopes with a bandwidth of 100 MHz.

In the low-pressure chamber, at a distance of 50 and 60 calibers from the diaphragm, pairs of optical windows with a diameter of 10 mm are located opposite each other for observing the emission of the studied gas. Through the windows in each experiment, measurements were made of both the spectral composition of the radiation and the time variation of the radiation intensity.

At the first stage of the method implementation, gases are fed into the high-pressure chamber to form the initial gas mixture. A helium / oxygen / hydrogen mixture in the stoichiometric concentration of oxygen and hydrogen can be used as the initial gas mixture. In this case, the concentration of helium is from 50 to 65%. Gases for the formation of the initial gas mixture are fed into the high-pressure chamber (HPC), while the HPC is first filled with helium, after which oxygen and hydrogen are fed in succession. For faster mixing, gases in the HPC can be fed from two opposite ends of the chamber. The chamber is then left to mix the gases. Mixing time for 150 cm HPC is at least 60 minutes to ensure good repeatability. It is possible to pre-prepare a mixture of helium with oxygen in a separate tank and supply a ready-made mixture of helium / oxygen and hydrogen separately to the HPC. In this case, the time is somewhat reduced and, for example, for a pressure build-up with a length of 150 cm, it will be about 40 minutes.

The explosive mixture for ignition is fed into the prechamber. Using a car spark plug, the explosive mixture is ignited in the prechamber, the spark ignition of which leads to the formation of transverse compression waves, which equalize the pressure in the prechamber. With an increase in pressure, a jet outflow of combustion products begins through the perforation of the end of the prechamber into the main part of the high-pressure chamber filled with an explosive mixture with helium. The jets, which are close in intensity and composition (coming from the prechamber and located in the HPC), ensure homogeneous ignition of the gas in the high-pressure chamber in the transverse direction. The resulting flame front generates an almost plane shock wave, which, by the time it approaches the diaphragm separating the high-pressure chamber and the low-pressure chamber, has time to move a relatively large distance from the flame front. Empirically selected values of pressure (8-10 atm. In HPC) and gas composition (combination of an explosive mixture and helium in almost equal ratio), as well as material (copper foil) and diaphragm thickness (0.3-0.7 mm) lead to the fact that the intensity of the reflected shock wave is not enough to rupture the diaphragm, but enough to explosively ignite the gas at the diaphragm. The explosive release of energy increases the pressure behind the shock wave reflected from the diaphragm, which causes over-compressed detonation and rupture of the diaphragm, which quickly approaches the Chapman-Jouguet detonation mode and ensures complete combustion of the gas in the high-pressure chamber. The intensity of the shock wave that forms in the low-pressure chamber is determined by the work that the combustion products of the gas stored in the high-pressure chamber can do. It should be noted that even with complete combustion of the gas, the products of deflagration (slow) combustion perform less work than during combustion in the Chapman-Jouguet detonation mode [2].

To study the received shock wave in the LPC, two measuring sections are provided at a distance of 50 and 60 calibers from the diaphragm. Each measuring section has two optical windows with a diameter of 10 mm, located opposite each other. The windows in the measuring section are located between two piezoelectric sensors ∅4 mm, which measure the average velocity of the shock wave at the moment of its passage past the corresponding optical window. Piezoelectric pressure sensors have a rise rate of 0.9 μs, the sensitivity of the sensors is ~ 0.3 V / atm. The signal from the pressure sensors is recorded with a digital oscilloscope and recorded in the computer memory. The efficiency (if used) is equipped with two similar piezoelectric pressure sensors located on the side facing the low-pressure chamber at a distance of 11 and 21 cm from the diaphragm. Efficiency pressure sensors allow monitoring the shock wave velocity in the buffer gas and obtaining information about the process of opening the diaphragm between the efficiency and LPC. The information from the sensors is recorded by a digital oscilloscope and transferred to a computer for recording.

An example of a specific implementation

The claimed method in the framework of trial operation is implemented on the experimental complex "Shock tube" laboratory "Kinetic processes in gases" (lab. 109) Research Institute of Mechanics, Moscow State University. Pressure sensors are installed in the high-pressure chamber, the signal from which was recorded on a computer using an L-20-10 ADC. The gas filling of the high-pressure chamber is a mixture of an explosive mixture (stoichiometric oxygen-hydrogen mixture and an inert diluent gas helium in the proportions He: H2: O2 = 3: 2: 1). The working pressure in the high-pressure chamber (HPC) is 9 atm, the gas filling it consists of 50% explosive mixture and 50% helium, a spark plug with a discharge energy of 100 mJ was used to ignite the explosive mixture in the prechamber, the perforated disk is located 20 mm from the end the HPC walls and has 19 micro-nozzle holes with an inlet diameter of 1 mm and an outlet diameter of 2 mm; the copper diaphragm has a thickness of 0.5 mm. The low pressure chamber has the following characteristics: p ₁ = 0.25 Torr; 100% air. The mixture of the specified composition is fed to the HPC through the fuel mixture supply system. A pure explosive mixture is fed into the prechamber and ignited, after which the explosive mixture ignites, the hot gas enters the HPC cavity through the perforation holes, where a plane shock wave is formed, which reaches the diaphragm, is reflected from it, as a result of which the Chapman-Jouguet regime is achieved and a shock wave with a speed of 11.4 km / s. The experiments carried out confirm the claimed invention. In this case, the energy costs are 84.4 kJ, which is significantly lower than the energy costs for obtaining high-speed shock waves in accordance with the prototype (more than forty times).

FIG. 3 shows a sample oscillogram of pressure sensor signals (the distance between sensors P9 and P10, which register the speed of the shock wave in the low-pressure chamber of the shock tube, is 100 mm).

Thus, the claimed method allows, in a traditional shock tube with a pressure build-up pressure not exceeding 1.5 m, during the combustion of virtually any combustible mixture, in particular, an oxygen / hydrogen / helium mixture, to obtain a shock wave velocity equal to the 2nd cosmic one and higher, at initial pressures equal to 0.25 Torr, which corresponds to the most important site of the descent of spacecraft.

Claims (5)

1. A method of generating a high-speed shock wave in a shock tube containing a high-pressure chamber (HPC), from one end is equipped with a prechamber with a perforated end facing in the direction of wave propagation, and from the other end through a diaphragm connected to a low-pressure chamber (LPC), including the supply of helium and an explosive mixture to the HPC, the supply and ignition of an explosive mixture in the prechamber, as a result of its combustion, hot gas jets are injected from the prechamber through the perforation holes into the HPC cavity, which, at a distance of no more than 3 calibers from the HPC end, lead to the formation of a flat an incident shock wave that destroys the diaphragm with the formation of a reflected Chapman - Jouguet detonation wave and a shock wave passing through the LPC at a speed of more than 11 km / s, the propelling gas for which is the combustion products of an explosive mixture with helium. 2. The method according to claim 1, characterized in that the diaphragm is made of a copper sheet with a thickness of 0.3 to 0.7 mm, equipped with cruciform notches with a size of 0.2 to 0.3 mm, which prevent the dispersion of its particles upon destruction. 3. The method according to claim 1, characterized in that the initial pressure in the HPC is in the range from 8 to 10 atm, and the partial pressure of helium in the HPC is from 50 to 65%. 4. The method according to claim 1, characterized in that after the supply of helium and the explosive mixture to the HPC, the components of the mixture are mixed by holding for 30-80 minutes. 5. The method according to claim 1, characterized in that the length of the HPC does not exceed 1.5 m.

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