RU144872U1 - GAS-DYNAMIC ACCELERATOR OF SOLID BODIES - Google Patents

Abstract

The accelerator is designed to accelerate objects (shells) to high, more than 1 km / s speeds, which is important for studying the thermodynamic properties of materials at high pressures, for launching small satellites, for simulating the entry of aircraft into dense atmospheric layers, for simulating meteorites, etc. .

The accelerator contains a pipe of arbitrary profile of constant cross section, on the inner surface of which solid fuel is located. It is a composition containing a mixture of an oxidizing agent and a reducing agent, for example smokeless powder, or only a reducing agent or an oxidizing agent, and the second component of the fuel, an oxidizing agent or a reducing agent, may be contained in the pipe in the gas phase. An important feature of fuel combustion is that it does not go into detonation.

To achieve high speeds, the accelerated projectile has a cone-shaped or wedge-shaped bottom.

The accelerator combustion chamber is formed by the surface of the fuel on the one hand, and the surface of the bottom of the projectile on the other. Solid fuel is distributed on the surface of the pipe, evenly or according to some algorithm along its length, not necessarily completely and continuously. The fuel itself contains pre-formed combustion channels where hot gas penetrates from the combustion chamber in a very short time, which causes ignition of the fuel throughout its thickness. Ignition of fuel on the surface is initiated by:

as a result of its heating during friction of the projectile at high speed on the fuel surface;

or using a tribochemical combustion initiator;

or using an electric spark from a special high-voltage generator on board the projectile;

or with the help of a shock wave generated by the contact of a projectile at high speed with charge fuel;

or by adiabatic heating during compression of the remaining gas or air in the pipe as a result of the movement of the projectile;

or using a flame source on board the projectile.

The advantage of the device is that the projectile accelerates to speeds much higher than the speed of the accelerating gases. In this case, fuel and combustion products protect the pipe surface from erosion during the movement of the projectile. In addition, the distribution of fuel on the surface of the pipe allows the use of fuel, the burning rate of which will be much less than the velocity of the projectile. The principles of operation of this accelerator exclude fuel detonation, sharp (spasmodic) drops in projectile acceleration, temperature and pressure in the pipe. During operation of the device, the values of these parameters are constant. This allows you to create an extremely simple and inexpensive device for cost-effective launch of small-sized satellites into near-Earth orbit.

Description

The device is designed to accelerate solids (shells) to high speeds of more than 1 km / s, which is important for studying the thermodynamic properties of materials at high pressures, for launching small satellites, for simulating the entry of aircraft into dense atmospheric layers, to simulate meteorites and etc.

The traditional method of dispersing shells using a smokeless gun has an upper speed limit of less than 2 km / s. This is due to both the limited energy intensity of the powder and the high molecular weight of the powder gases. In addition, any methods of increasing the powder charge, including the multi-chamber principle (Lyman AS Improvement in accelerating-guns / US Patent 200740) do not allow the gun to work in optimal mode, since the excess of incoming gases does not allow the gun to work in adiabatic expansion mode, and work guns in subcritical mode reduces this limit to 1 km / s.

These limitations are overcome in the so-called light-gas guns, where light gas (usually hydrogen, less often expensive helium) does the work, and energy is pumped into it from the outside, using a powder piston, explosion or heating (WD Crozier and William Hume, ″ High-Velocity, Light-Gas Gun, ″ Journal of Applied Physics, Vol. 28, August 1957, pp. 892-894.) In this way, it is relatively easy to achieve speeds of up to 11 km / s for objects weighing several grams, but technically light gas guns very complex, must use incandescent to high temperature hydrogen at high pressure. For example, here are the parameters for the Quicklaunch small two-stage satellite launch project (http://quicklaunchinc.com):

projectile weight 450-680 kg

weight of protective sheath and carbon plastic 230 kg

rocket engine weight 220 kg

weight of displayed cargo 110 kg

projectile speed 7-8 km / s

initial acceleration 2500 g

average gas pressure 350 atm

gun barrel length 1500 m

gun’s inner diameter 0.6 m

estimated price of $ 1250 per kilogram of displayed cargo

estimated cost of the project $ 500 million

dimensions of the chamber itself with compressed hydrogen:

weight 8,000 tons

volume of 20,000 cubic meters m

initial hydrogen pressure 700 atm

initial hydrogen temperature 1500 K

(12th AIAA / USU Conference on Small Satellites. 1. The Feasibility of Launching Small Satellites with a Light Gas Gun. H. Gilreath, A. Driesman).

Working with such a dangerous gas is extremely problematic due to its flammability, explosiveness and poor compatibility with metals in such extreme conditions. In addition, additional complexity causes:

the presence of two membranes, one of which (outlet) must withstand high pressure, and the other very quickly cut off hydrogen from the projectile flying out of the gun.

the need to place dozens of additional hydrogen injectors along the barrel in order to avoid energy losses during gas acceleration. This creates undesirable strong vibrations both for the projectile itself and for the gun.

It should be noted that in these devices there are two drawbacks associated with the uneven distribution of pressure along the barrel. The first is the extreme mode of operation of the devices at the beginning of acceleration (high temperature and pressure), which leads to their accelerated wear during continuous operation, and the second is a strong non-uniformity of the acceleration of the projectile, which can be inconvenient when starting devices containing complex equipment and electronics. Also, in these devices, a significant part of the fuel energy is spent unproductively on accelerating the gases themselves.

One of the features similar to the proposed method is the so-called Scram Cannon (Charles Ε. Kepler, Raymond L. Deblois, Louis J. Spadaccini, Wake stabilized supersonic combustion ram cannon. / US Patent 4726279), also called Ram Accelerator (Edward B. Fisher, Ram accelerator / US Patent 5121670). Here, the projectile is accelerated by the jet thrust of a ramjet (scramjet) formed by the walls of the gun and the surface of the projectile itself, and gaseous fuel, a mixture of oxidizer and reducing agent, is distributed in the pipe. Fuel enters the combustion chamber in the opposite direction to the movement of the projectile.

A similar project to the launch of small-sized satellites using the Ram Accelerator of The Ballistic Flight Group (http://www.tbfg.org) involves milder modes of operation, has the following characteristics:

projectile weight 300 kg

projectile speed 8 km / s. After passing through the atmosphere, the projectile loses speed up to 6 km / s.

average acceleration 2000 g

gas pressure 50 atm

pressure in the combustion chamber 2000 atm

gun barrel length 1,400 m

gun’s internal diameter 0.5 m

estimated cost of the project $ 50 million

However, the features of the combustion mode of the gas mixture entail the following problems:

1. The device can only work when the velocity of the projectile is greater than the speed of sound of the gas medium, about 1 km / s

2. The need to change the composition of the gas mixture with increasing velocity of the projectile leads to a complication of the design of the accelerator, which in the project consists of sections separated by a membrane

3. The operation of the accelerator leads to the generation of strong acoustic vibrations with a frequency of 2-10 kilohertz and an amplitude of 250 atm.

Also, the presence of compressed gas in the barrel of the accelerator leads to a strong aerodynamic heating of the projectile's motion zone, which sharply increases with an increase in its velocity. (C. Knowlen, B. Joseph, A.R. Bruckner, Ram Accelerator as an Impulsive Space Launcher / International Space Development Conference, May 25-28, 2007, Dallas TX).

It should be noted that a common drawback of all the above methods of acceleration is the friction of the projectile on the surface of the gun, which at high speeds leads to its erosion and energy loss.

The closest in its features to the proposed method is the so-called Blast wave accelerator, a shock-wave accelerator (detonation gun). In such an accelerator, fuel, explosive, is distributed in the barrel’s barrel in the form of rings (Werner K. Kern, Tallahassee, and Fay Ε. Null, Explosive linear acceleration. / US Patent 3031933) or a continuous layer (Charles A. Rodenberger, Propellant ligned high velocity accelerator. / US Patent 3411403). The detonation of fuel here is initiated by the passage of a projectile, which is accelerated by the shock wave acting on its bottom. One of the problems of such accelerators is the high detonation speed, which makes it impossible to use a continuous layer of condensed fuel. Therefore, projects are usually considered where fuel in the form of segments is located in the gun’s barrel, usually rings that can be frustrated (Abraham L. Korr, Evan Harris Walker, Muzzle attachment for accelerating a projectle. / US Patent 3880044) or electric detonators (George T Pinson, Controlled explosive, hypervelocity self-contained round for a large caliber gun. / US Patent 5016537), which fire directly above the conical bottom of the projectile. In the first case, detonation begins directly on the shell of the projectile, which leads to its deformation, in the second, a complex system of electric detonators, controlled by precision tracking sensors, is required. In any case, detonation also leads to deformation of the barrel surface. Therefore, it is necessary to enclose the fuel in a special shell, for example, from foam, the remains of which must be removed each time from the accelerator pipe. On the other hand, fuel segmentation leads to a series of shock waves acting on the projectile itself, which eliminates the use of sophisticated equipment on board. All of the above problems prevented the creation of a reusable accelerator of this type at the moment (Eric W. Davis, Advanced Propulsion Study. / Special Report of AIR FORCE RESEARCH LABORATORY, September 2004).

The utility model is based on the task of creating an accelerator capable of accelerating a projectile at a speed much higher than the speed of its accelerating gases, and the operation of which excludes such extreme operating conditions as uneven acceleration, a surge in temperature and pressure at the beginning of acceleration, and eliminates such harmful phenomena like ripple and detonation.

To solve this problem, fuel combustion is initiated by the movement of the projectile and occurs without detonation, in contrast to the shock-wave accelerator.

In this case, the combustion products press on inclined, wedge-shaped or conical elements of the bottom of the projectile orthogonal to the direction of its movement.

This technique allows you to solve the main problems of the previously considered devices: the dependence of the final velocity of the projectile on the maximum propagation velocity of the combustion products and on the burning rate of the fuel. In order to understand how this works, consider the movement of the element of the bottom of the projectile, a rectangular wedge 1 with a base D and a height of the H axis (Fig. 1) Here, the degree of freedom of movement is fixed by the wall 2 along which the wedge slides. Incident or compressed gas exerts pressure on the surface of the wedge. The corresponding force vector F acting on the surface element can be decomposed into two, one of which F1 is directed to the wall, and the second F2 along the direction of movement. The first is compensated by the elastic force of the wall, and the second leads to an acceleration of the wedge. If we take the velocity of the incident gas as V1, then it is easy to notice that the wedge will accelerate until its velocity V2 reaches the value V2 = V1 * (H / D). That is, if the value (H / D) >> 1, then the interaction will occur at a wedge speed V2 much more than the gas velocity V1. For example, if (H / D) = 10, and the rate of fall of the gas generated during the combustion of the fuel will be 1 km / s, then the wedge can accelerate to a speed of 10 km / s. That is, the speed limit is determined by the angle of the wedge a, where the ratio (H / D) of its cotangent.

The solution to this problem is achieved by the following methods:

1. Solid fuel is located on the inner surface of the pipe 3 of an arbitrary profile and constant cross section 4. The combustion chamber is formed by the fuel surface and the bottom surface of the projectile 5, which form an acute angle so that the distance between them in the plane of the pipe cross section increases in the opposite direction to the movement projectile (Fig. 2, top view). The profile of the pipe can be round 6 (cone-shaped shell bottom 7), rectangular 8 (wedge-shaped shell bottom 9), or another, and not necessarily closed. (Fig. 3 profile view). The bottom of the projectile may be more complex.

2. Solid fuel, unitary or mixed, contains a reducing agent and / or an oxidizing agent (the second component, an oxidizing agent or a reducing agent, if necessary, may be contained in the pipe in the gas phase for complete combustion). It is distributed on the inner surface of the pipe evenly or according to some algorithm along its length, not necessarily completely and continuously. The composition and structure of the fuel may be variable. Fuel can be distributed in the form of a continuous layer of constant or variable thickness. The fuel contains combustion channels through which hot gas can penetrate from the combustion chamber, which ensures its rapid ignition and combustion throughout its thickness. This is a fundamental difference, which allows the use of fuels that do not need detonation.

It can be gunpowder, or even just combustible materials, if an oxidizing agent (for example, air or oxygen) is in the accelerator tube.

From the technical point of view, the simplest is the use of pressed fine-fibrous material (for example, pyroxylin wool), which is placed on the pipe surface in various ways, for example, as a continuous layer. (Fig. 2). This solves the general problem of all stem acceleration systems. A layer of fuel and its combustion products on the surface of the pipe protects it from erosion. The fuel layer is also involved in the obturation of the projectile, although at speeds greater than the velocity of distribution of the combustion products this is not relevant. From burning monolithic material of a similar nature (e.g. nitrocellulose plastic) can be made:

armor of the charge of fuel, which holds it to the barrel,

guides that support the projectile in the bore,

annular obturators, which are placed along the trunk at certain intervals.

The fuel charge itself can be made in the form of cylindrical segments that are inserted sequentially one after another into the accelerator barrel.

In the case of placing solid fuel on the surface in the form of a layer of thickness L, its combustion time t is defined as

t = L / V3,

where v3 is its burning rate. The surface of the combustion front is almost parallel to the surface of the pipe. The fuel must have time to burn out during the passage of a projectile with a length H of the combustion zone at a speed of V2 (projectile velocity):

t = H / V2

From here the relation is derived:

V3 / V2 = L / H

This means that by distributing fuel in a thin layer, where L << H, the velocity of the projectile can be much higher than the rate of combustion of the fuel, which gives another advantage to this method of acceleration. Namely, it allows the projectile to control the combustion of fuel, in contrast to detonation guns.

3. The combustion of fuel, normal or deflagration, is organized in such a way that the combustion products go from the surface of the fuel (pipe) in the direction along its normal. The front of fuel combustion is almost parallel to the surface of the pipe (Fig. 2), which provides the desired direction of the flow of combustion products. It can be noted that the following operating modes are possible here. During normal fuel combustion, the gas pressure in the combustion chamber remains almost constant for the entire duration of the accelerator operation (mode 1). In this case, with an increase in the velocity of the projectile, the rate of entry of combustion products increases proportionally. In this case, the gas pressure at the bottom of the projectile will be determined by the average kinetic velocity of the gas molecules. It determines the limiting velocity of gas outflow to the bottom of the projectile. With the rapid combustion of fuel at the very beginning of the combustion chamber, or before it, the adiabatic expansion of the combustion products will occur already in the combustion chamber, as occurs in the Laval nozzle (mode 2). During deflagration combustion, the combustion products accelerate to the maximum possible speeds as a result of adiabatic expansion (mode 3). Preliminary calculations show that modes 2 and 3 are approximately 2-4 times more efficient in terms of fuel consumption for dispersing a projectile. However, in this case, in the zone of passage of the projectile, strong changes in temperature and pressure will be observed, which of course is less favorable for the wear resistance of the accelerator. Nevertheless, the projectile itself, even under these operating conditions, does not experience sudden changes in acceleration, shocks, and pressure pulsations.

4. Fuel combustion is initiated in contact with a moving projectile:

using thermomechanical heating during friction of the projectile at high speed on the fuel surface,

using a tribochemical combustion initiator, for example, a combination of potassium chlorate and phosphorus, applied as a mixture to the surface of the fuel, or used separately according to the “match + match box” scheme

using an electric spark from a special high-voltage generator on board the projectile,

using a shock wave generated by the contact of a projectile at high speed with fuel,

using adiabatic heating of gas or air residues in a pipe during compression as a result of drag,

using a flame source on board the projectile.

The latter method has been described previously. The flame source may be a special chamber of the projectile 12, in which the hot gas of high pressure is accumulated, as proposed in the scheme of gas-static centering of the projectile

(E.M. Macks. Fluid supported device / US Patent 3001609), or which contains a powder gas generator (Mamaev O.A., Edigarov V.R., Bolshtyansky A.P. Shell with gas suspension. / RF Patent RU 2285226 C1 ) (Fig. 4). In this case, the hot gas exiting from the openings of the chamber not only initiates fuel combustion, but also prevents friction between the projectile and the barrel.

Based on the proposed accelerator, one can evaluate a possible project to launch small-sized satellites. For him, options are offered that are close to the previously mentioned projects. The accelerator itself is made in the form of a steel pipe of a round profile, inside of which charges of ballistic powder are placed in the form of cylindrical elements. Typical parameters for such a fuel are: an energy consumption of 4 MJ / kg, a volume of 1000 liters per kilogram emitted during gas combustion (normal conditions). We assume that the fuel burns in the mode when a constant pressure is maintained in the accelerator’s combustion chamber. The fuel material can be made:

from pressed fibers

in the form of a monolithic layer that contains combustion channels orthogonal to its surface.

The thickness of the fibers, the wall thickness of the channels, as well as the diameter of the channels themselves are on average 10 microns. The operating pressure in the combustion chamber is proposed at about 500 atm. In this case, the typical burning rate of nitrocellulose powder is 50 mm / s (Serebryakov M.E. Internal ballistics of barrel systems and powder rockets. (Ed. 3e), Oborongiz 1962, p. 137), which ensures the combustion of the fuel material in 0.1 ms. Preliminary calculations show that for channels or open pores with a diameter of 10 microns and a length of 1-2 cm, the diffusion of hot gases over a period of about 0.01 ms is ensured. (Golubev I.F., Gnezdilov N.E. Viscosity of gas mixtures. Goskomstandart M .: 1971 p. 316) For this case, let us assume a fuel density of 500 kg / m3. The cylindrical element of the fuel charge is reinforced (armored) on the outer surface with a layer of dense and hard, burning nitrocellulose plastic. The charge is also reinforced with a honeycomb structure of the same material. This is necessary to give it mechanical rigidity, ease of loading cylindrical elements into the barrel of the accelerator, to protect the pipe surface from the high temperature of the powder gases. In addition, the longitudinal elements of the reinforcement are simultaneously guide rails for the projectile. The bottom of the projectile is a cone, the diameter of the base of which is about 0.46 meters, height 2.3 meters, H / D = 10. We also take the characteristic steel tensile strength of 1 GPa, which allows us to estimate the thickness of the steel pipe with a double safety margin and its weight. From this data, you can evaluate the parameters of the entire device:

projectile weight 500 kg

fuel mass (ballistic powder) 27 600 kg

final velocity of the projectile 8 km / s

constant acceleration 2130 g

average pressure 530 atm

powder gas temperature 3700 K

gun barrel length 1500 m

accelerator tube inner diameter 0.5 m

accelerator steel pipe thickness 0.2 m

thickness of cylindrical fuel element 0.02 m

length of cylindrical fuel element 1-5 m

outer diameter of the cylindrical fuel element 0.5 m

the number of fuel elements 300-1500

accelerator (gun) weight about 5000 tons

Taking the lower price limit for large-diameter pipes of $ 2000 per ton, we can estimate the minimum project cost of $ 10 million. It is more difficult to estimate the cost of launch due to the lack of data on the cost of production of gunpowder. But it can be considered less than $ 1 / kg for typical nitro compounds as products of large-scale production. Then you can estimate the cost of launching a kilogram of projectile cargo as fuel at $ 55 / kg. Following the previously discussed estimates (C. Knowlen, W. Joseph, A.R. Bruckner, Ram Accelerator as an Impulsive Space Launcher / International Space Development Conference, May 25-28, 2007, Dallas TX), a projectile launched on one side during passage dense layers of the atmosphere loses speed from 8 to 6 km / s. In order to achieve the first space velocity of 8 km / s (i.e., to obtain an additional speed of 2 km / s), as well as to carry out movement correction in order to enter low Earth orbit, the projectile must have a simple solid propellant jet engine (it is more resistant to overloads). Assuming a jet stream outflow rate of about 2 km / s, characteristic of it, we obtain, with the help of the jet propulsion formula (Tsiolkovsky equation), an increase in the cost of cargo removal by approximately 2.7 times. That is, the cost of launching in near-Earth orbit will be $ 150 / kg, and the actual output of this accelerator will be approximately 116 kg. You can also estimate the number of launches per year. Taking charge loading into the pipe at a speed of 1 m / s, it turns out 2 starts per hour, or 17520 per year, or 2030 tons per year. The lower threshold for self-sufficiency of such a system can also be estimated on the basis of the accelerator cost estimate discussed earlier. This is 575 launches at a commercial cost of cargo withdrawal of 300 $ / kg. The efficiency of the device, in principle, can be increased in comparison with rocket systems when launching cargo into high-lying orbits due to a decrease in the mass of the rocket engine.

In addition to the mentioned methods for the output of small-sized satellites, there are also promising electromagnetic accelerators (Glinov A.P. Relsotron. / RF Patent RU 2094934 C1). But they require the use of superconductors, which increases the cost of creating such devices by at least an order of magnitude. On the other hand, the necessary energy storage devices for this task, of the order of 10 GJ or more, have not yet been created. The problem of controlling a giant current (of the order of 10 MA) for a short time characteristic of such systems for 2-3 seconds also remains a problem. In addition, for railguns, of course, there remains the problem of erosion of accelerating rails and plasma instability in the event of a discharge between the contacts, which fundamentally limits the upper limit of the projectile velocity to 3 km / s.

It can be concluded that, based on existing technologies, it is possible to create an extremely simple and inexpensive device that can bring small-sized satellites into low Earth orbit at a low price. At the same time, it is devoid of such drawbacks as mechanical erosion of the accelerating surface, sharp (spasmodic) drops in projectile acceleration, temperature and pressure in the barrel. In addition, it can work in different modes, which gives ample opportunities for optimal engineering design.

Claims (1)

The accelerator of solids, which is a pipe of arbitrary profile of constant cross section, on the inner surface of which is solid fuel, characterized in that the fuel contains pre-formed combustion channels, its ignition is initiated by the movement of the projectile, and its combustion does not go into detonation.