Gleb Kulev, Candidate of Technical Sciences
Abstract
The rapid exploration of outer space has faced a problem related to the insufficient efficiency of modern rocket engines. As a solution to this problem, the concept of a jet engine based on new operating principles is proposed, using a combination of known physical laws and having advantages over known types of jet engines.The article presents the results of testing three modifications of jet engines based on new operating principles and their analysis. The article discusses the physical principles of operation of a jet engine based on new principles, its advantages and problems arising during its creation.
Nomenclature
Cf = trust coefficient
Dcn = critical nozzle cross section, mm
Dicc = combustion chamber diameter, mm
F = thrust, N
Isp = specific impulse, s
Lcc = combustion chamber length, mm
Mf = oxidizer and fuel mass flow, g/s
Pcc = combustion chamber pressure, kPa
Pp = fuel supple pressure in front of the engine, kPa
Rf = frequency of gases rotation in the combustion chamber, Hz
t = time, s
V = outflow velocity, m/s
Vcc = velocity of the gaz jet in the combustion chamber, m/s
I. Introduction
This work is the result of a five-year study with numerous experiments (more than a hundred). Some of the results of these studies are presented in this article.
Currently, there are two main types of rocket engines: chemical (liquid, or solid fuel) rocket engines and electric rocket engines (ion, or plasma). The chemical ones have greater thrust and low specific impulse, the second ones have low thrust and high specific impulse (Isp). The idea is to combine these two types of rocket engines into one hybrid version. The goal in this case is to obtain high traction characteristics, with a significantly higher specific impulse. The method of achieving this goal was to create a scheme for the operation of a jet engine based on new principles. This study was conducted over a period of four years, with a large number of experiments. A part of the results of these studies are presented in this article in the form of a test report on three modifications of rocket engines (RE) operating according to the scheme on new principles.
Let's briefly look at the existing schemes of a RE operation. Let’s analyze the work of chemical rocket engines using the example of liquid rocket engines. A mixture of fuel and an oxidizer is fed into the combustion chamber (CС) (mainly axially, along the axis of the engine), where it burns with the formation of a large amount of gases. The speed of movement of this amount of gases in the combustion chamber of the RE is insignificant and is usually not used in calculations. The increase in the velocity of the gas jet occurs in the Laval nozzle, consisting of subsonic and supersonic parts (the existing scheme of a rocket engine operation). [1] At the same time, it should be taken into account that any rocket engine ejects weakly ionized plasma from the nozzle. Charged particles are present in the hydrocarbon fuel flame. It has been experimentally found that the concentration of ions (positively charged particles, or protons) and electrons (negatively charged particles) in a flame can be 4-6 orders of magnitude higher than the concentration that would be observed with a purely thermal ionization mechanism, and in fact the flame can behave like a weakly ionized plasma. However, the flame temperature is insufficient for the components of the mixture to be ionized as a result of collisions of molecules with each other. [5] The charged particles themselves move chaotically in the flame and have no effect on the operation of the liquid RE. The principle of operation of ion or plasma rocket engines uses charged particles. First, the working fluid (usually a gas) is ionized, then accelerated in a magnetic field and ejected from the engine, with or without the nozzle part, at a jet stream velocity significantly higher than that of liquid engines. However, the thrust of such engines is not great, and the consumption of electrical energy is large. There is also a problem of separation of opposite charges in order to disperse the charges of one sign, while the charges of the other sign must be removed from the zones of the accelerating field. However, it is extremely difficult to effectively separate the charges. This is prevented by powerful Coulomb attraction forces arising between differently charged plasma clumps, which immediately restore electrical equilibrium. [2] Liquid RE and plasma RE are now rapidly developing, there are more and more of their varieties and modifications, but we should not expect any significant improvements in the characteristics of their work.
Let's look at what is proposed in this research. In the engine working on new principles, it is proposed to use charged particles arising during the combustion of fuel in order to transition from deflagration turbulent combustion to plasma combustion, allowing to significantly improve the characteristics of the RE.
The possibility of charged particles to influence the combustion characteristics has been studied quite well. For example, if a candle flame is placed in an electrostatic field, the so-called "butterfly effect" will occur (see Fig. 1), or the separation and deflection of the candle flame into two horizontal oppositely directed parts. This is due to the positively charged ions and negatively charged electrons in the candle flame of the candle. It should be noted that the right part of the flame containing positively charged ions is significantly larger than the left part of the flame containing negatively charged electrons. This is explained by the fact that the mass of an ion is about 1800 times greater than the mass of an electron and, accordingly, the ability to influence combustion processes in the electrostatic field of ions is significantly greater. [3] From this it can be concluded that the number of ions and electrons in the flame is sufficient to significantly influence the processes occurring during the combustion of hydrocarbon fuel, under certain conditions.
How do charged particles behave in plasma? The answer to this question is given by a research conducted on the ISS called "Plasma Crystal". Briefly, the study can be described as follows: dust particles are introduced into a low-temperature plasma under microgravity conditions with video recording of the processes taking place. Let's analyze one of the conclusions of this work: when clouds of microparticles of different diameters interpenetrate, the spontaneous formation of stable spatial structures in plasma (see Fig. 2) lines, chains, or passages is possible. [4] From this it can be concluded that plasma, under certain conditions, can create a spatial structure and interact within this structure at large distances.
The interaction of particles in plasma is, strictly speaking, not paired, but collective, this is to say a large number of particles interact with each other simultaneously. [6] It must be taken into account that at temperatures of more than 2000 degrees in the combustion chamber of the RE, some changes in the type of chemical bonds are already taking place. Therefore, to a corresponding increase in the chemical energy reserve, at even higher temperatures which have not yet been reached in existing liquid rocket engines, thermal ionization may occur, accompanied by energy consumption and changing the internal gas energy, increasing its reserve. [7]
The existing methods of increasing ionization are associated with a sharp increase in the temperature in the combustion chamber (CC), or a strong electromagnetic effect associated with a large consumption of electricity, which is difficult to implement in aircraft engines.
A brief description of the rocket engine design based on new principles
The concept of an engine based on new principles uses a combination of these factors to increase its efficiency: temperature and pressure.
In the engine there is a centrifugal force, which occurs when the gas and combustion products rotate, giving the gas particles the most ordered motion (tangential motion along the circumference of the gas in the combustion chamber). In a combustion chamber of this type, the average kinetic energy of the particles (caused by the centrifugal force and the speed of rotation of the gas) can be greater than the potential energy of their interaction, and such a gaseous medium can be called a plasma. As the pressure in the combustion chamber increases, the plasma properties of the particles will increase, which will lead to an increase in the efficiency of the engine.
The combustion chamber is a cylinder with an internal diameter of: Dc-50 mm and a length of: Lc-300 mm, ending with a conical nozzle, without a supersonic part. The critical section of the nozzle diameter: Dcn-30 mm. A stoichiometric mixture of methane (CH4) and oxygen (O2) in a gaseous state is used as fuel. The fuel mixture in the combustion chamber is supplied tangentially (along the circumference of the combustion chamber). In total, three series of tests were carried out (engines RE1, RE2, RE3), with the same geometry of the combustion chamber and nozzle, but with a different design of nozzles in the combustion chamber (see Fig. 3).
The rest of the article is presented in the sections II, III, IV which describe the tests of three engine modifications based on new principles, analyze the results of their testing, and draw conclusions based on the results of which the design was finalized. The section V summarizes the results of all tests, analyzes the plasma properties identified in the operation of the engines and presents a physical diagram of the engine operation on new principles using the example of RE3 operation. The section VI (conclusion) lists the advantages and disadvantages of running the engine on new principles in comparison with engines with the existing scheme of operation.
II. RE1 test
A. Purpose, devices used during the test, description
The purpose of the rocket engine 1 (RE1) test is to test the possibility of its operation on a cycle based on new principles. The design of the RE1 is a hybrid of the existing scheme of operation (a scheme with axial fuel supply, along the axis of the engine), and a scheme based on new principles of operation (a scheme with tangential fuel supply, along the circumference of the CS). RD1 is designed so that the first part of the time to work according to a scheme close to the existing one, and from a certain time to switch to the new principle of operation (this is achieved with the help of injectors located in a special way in the combustion chamber and their sequential inclusion). In the Fig. 4 you will see the appearance of the RE1 and the layout of the injectors in a cross section.
The order of operation of RE1 is as follows: in the first second of operation, the first two injectors are turned on (numbered from the bottom of the combustion chamber) and 26 grams of the gas mixture per second is supplied. Then one injector is turned on every subsequent second (the gas mixture flow rate is 13 grams per second per injector) and so on up to 10 seconds inclusive, with the measurement of thrust (F) in newtons, every second. You will see the RE1 tests with frame-by-frame shooting (1 frame per second) in the Fig. 5
B. Test results, analysis, conclusions
The results of the RE1 test are summarized in a general graph and are shown in the Fig. 6.
From the 1st to the 5th second, the RE1 operates according to a scheme close to the existing one (fuel is supplied along the axis of the engine), the number of injectors involved is not enough for tangential diffusion of the gas mixture. This work area is shown in Fig. 6-yellow sector (1).
From the 5th to the 6th seconds, the RE1 automatically switched from the existing operating scheme (axial fuel supply, along the axis of the engine) to the mode based on new operating principles (tangential fuel mixture supply). Fig. 6. Seconds 5-6. The number of connected injectors is sufficient for tangential diffusion of the fuel mixture.
From the 6th to the 10th second, the RE1 works according to the scheme based on new principles. The fuel mixture is constantly supplied tangentially to the combustion chamber, see Fig. 3.
The characteristics of the RE1 operation based on the new principles are shown below in the Fig. 6-green sector (2). X—Mass flow, fuel mixture consumption in grams per second (g/s), X-time (S), Y—F, thrust newtons (N). Yellow sector (1)—RE1 operation from the 1st to the 5th second. Green sector (2)—RE1 operation from the 6th to the 10th second.
Analyzing the RE1 operation from the 5th to the 6th second, it can be seen that:
The jet stream of the engine has changed, it has become brighter, denser and shorter.
The mass consumption of the fuel mixture (Mf) increased from 78 to 91 grams per second, so by 1.17 times.
The thrust (F) increased from 40 N to 145 N, so by 3.6 times.
The outflow velocity of the jet stream (V) has increased from 512 m/s to 1593 m/s, more than by 3 times.
Schemes of the engine operation at the 5th second – Fig. 7, at the 6th second – Fig. 8.
The engine operates according to the scheme close to the existing one (fuel is supplied along the axis of the engine). Data: the velocity of the gas mixture and combustion products in the combustion chamber is close to zero, thrust F-40 N, mass flow Mf-78 grams per second, outflow velocity V-512 m/s.
The engine operates according to the scheme based on new principles (fuel is supplied tangentially). Data: combustion products velocity the combustion chamber is not equal to zero, thrust F-145 N, mass flow Mf-91 grams per second, outflow velocity V-1593 m/s.
During the RE1 test, a transition was made during the operation of the engine from one cycle to another. There were no serious remarks on the test results.
It is known from physical laws that the velocity of the gas jet outflow from the diffuser cannot be higher than the local speed of sound, and the local speed of sound itself is proportional to the square root of the temperature in combustion chamber (for a methane-oxygen pair when burning in the combustion chamber it is approximately 900 m/s). From the 1st to the 5th second of the test, the outflow velocity is subsonic - up to 512 m/s, which corresponds to the local speed of sound and engine operation according to the scheme close to the existing one. However, from the 6th to the 10th second, the outflow velocity becomes 1593 m/s and, accordingly, the outflow velocity of the jet stream becomes supersonic. In this case, it should be taken into account that the supersonic part of the nozzle of the RE1 is absent.
So, what happened? From the 1st to the 5th seconds everything happens according to the operation of the engine with the existing scheme, but it should be taken into account that the rate of the combustion products in the combustion chamber is close to zero.
In fact, in the combustion chamber of the RE1 there is only potential energy (it is characterized by temperature and pressure in the combustion chamber). The kinetic energy in the combustion chamber of the engine is practically zero, and the conversion of potential energy into kinetic energy occurs only in the nozzle part. But from the 6th to the 10th second everything is different. In an engine based on new principles, the fuel is initially supplied tangentially from the injectors to the combustion chamber and has a significant speed, respectively, accordingly, the share of the kinetic energy in the combustion chamber is already large. An additional step appears to increase the speed of the jet flow rate in addition to the nozzle part.
Based on the results of the RE1 test, it can be concluded that the cycle based on new principles in the studied range is more efficient (see Fig. 8), compared to the existing scheme of work (see Fig. 7), and the scheme itself based on new principles is of practical interest.
The next version of the rocket engine based on the new principles was the RE2 test with a modified design of the combustion chamber.
III. RE2 test
А. Purpose, devices used during the test, description
The purpose of the rocket engine 2 test is to study its operation on new principles and to obtain the throttle characteristics of the engine. The thrust (F) and the fuel supply pressure at the inlet in front of the engine (Pp) were measured. You can see below the position of the injectors and the direction of the gas rotation in the combustion chamber, cross section (from the nozzle side).
The procedure for conducting the experiments for the RE2 is as follows:
Four separate experiments are carried out with a sequential increase in the fuel supply pressure at the inlet in front of the engine and with measuring the engine thrust. In each experiment, all the injectors in the combustion chamber are involved at once. The RE2 showed a maximum thrust of F-420 N, at a fuel mixture supply pressure of Pp-700 kPa. During the operation of the first RE2 sample (three RE2 samples were tested in total), at a fuel supply pressure of Pp-700 kPa, a rapid (1-2 seconds) burnout effect of the engine nozzle occurred due to the displacement of the gas jet from the central axis. The opposite side of the burnout nozzle side was not damaged. According to the damage (burnout effect) of the nozzle, it is clearly visible how the gas jet turns from transverse rotation into the longitudinal movement of the jet. These effects of burnout and reversal of the gas jet you will see in the Fig. 10. At the same time, another effect was observed.
In the combustion chamber of the RE2, the fuel mixture in the combustion chamber is supplied in the clockwise direction (see Fig. 9), at the exit of the jet from the engine in addition to the main longitudinal movement of the jet, there is a slow rotational effect of the entire volume of gas of the jet. The rotation of the reactive jet occurs in the opposite direction (counterclockwise) to the rotation of gas in the combustion chamber (clockwise), the direction of which is set by the injectors.
This rotational jet effect appears immediately when the engine is started, even at the lowest fuel supply pressures. You will see the schematic movement of the gas jet in the RE2 in the Fig. 11.
To prevent the nozzle damage during testing of the second RE2 engine, cooling of the nozzle part was applied, and the injectors connection scheme was changed. However, the damage to the nozzle was repeated in the same place.
When testing the third RE2 engine, the connection scheme of the injectors was changed once again, and the engine itself was turned 180 degrees, but the burnout effect occurred in this case too, in the same place, only from the opposite side. It was not possible to eliminate the burnout effect by the methods listed above.
B. Test results, analysis, conclusions
The RE2 worked stably and showed thrust (F) in the range of 0-420 N at the supply pressure (Pp) of the gas mixture from 0-700 kPa. At a higher Pp, the nozzle burnout effect occurred. The data obtained in this range up to 700 kPa are sufficient to build the throttle characteristic of the RE2 (Pp - thrust). The throttle response is a quadratic relationship (see Fig. 12). All engines with a standard operating scheme have a linear throttle characteristic. With a quadratic characteristic, unlike a linear characteristic, the dynamics of the specific impulse (Isp) will be higher.
Let’s analyze the listed effects and data. The effect of nozzle burnout and the effect of slow rotation of the jet at the exit from the engine were described in sufficient detail above. Both of these effects should be considered together and are explained by the transition of deflagration combustion to plasma combustion in the combustion chamber and in the nozzle of the RE2. The jet leaving the engine has cohesion and collective effects which are characteristics of plasma. The process of increasing plasma properties occurs smoothly, as the pressure in the combustion chamber increases. The slow rotation of the jet as it exits the engine is known in physics and is called drift. The drift itself is characteristic of plasma (see Fig.13).
Based on the plasma properties of the jet stream, we can simulate the processes occurring in the RE2. Taking into account the collective properties and cohesion in the gas (jet) stream during plasma combustion, we can explain the nozzle burnout effect. And the jet stream itself can be represented as a spring (taking into account its cohesion and collective properties). In this case, the jet stream coming out of the nozzle, due to its turning in the opposite direction relative to the jet stream in the combustion chamber, is pressed against the nozzle diffuser section resulting in the burnout effect (Fig. 14).
Accordingly, considering the operation scheme of the RE2 and the processes occurring during its operation, we can conclude that this process can be controlled by changing the design of the combustion chamber. By changing the direction of the gas jet to the opposite one in the combustion chamber, it is possible to eliminate the effect of nozzle burnout. See the modified scheme in the Fig. 15.
The modified scheme (Fig, 15) has been implemented and tested in the RE3.
IV. RE3 test
А. Purpose, devices used during the test, description
The purpose of the RE3 test is to investigate the operating modes of the rocket engine, taking into account the changes in the design of the combustion chamber according to the Fig. 15 (direction of the gas rotation in the combustion chamber is counterclockwise). The thrust (F), pressure in the combustion chamber (Pcc), fuel supply pressure in front of the engine (Pp) were measured. The spectra of sound during engine operation were also recorded.
See Fig. 16 the RE3 injectors layout and the direction of gas rotation in a cross section (from the side of the nozzle) in the combustion chamber.
See Fig.17 for the appearance of the RE3.
The RE2 and RE3 do not differ externally, all their constructive difference is in the combustion chamber, as in the RD2 the gas rotation in the combustion chamber is clockwise, while in the RE3 it is counterclockwise. Geometric parameters of injectors and their number are the same, the nozzle part of the engines is also identical.
The order of experiments for the RE3 is as follows. Three separate experiments are conducted with successive increases in the fuel supply pressure at the inlet in front of the engine (Pp), with a thrust measurement (F), and with a pressure measurement in the combustion chamber (Pcc). In each experiment, all the injectors in the combustion chamber are involved at once.
The RE3 showed a maximum thrust (F) of 2340 N, with fuel mixture supply pressure (Pp) of 2900 kPa and the pressure in the combustion chamber (Pcc) of 2027 kPa. In addition, two more points were obtained during tests: F-876 N, Pp-1350 kPa, Pcc-709 kPa and F-1297 N, Pp-2000 kPa, Pcc-1267 kPa.
The revision of the RE3 operation scheme according to the Fig. 15 completely eliminated the effect of nozzle burnout, the phenomenon of jet drift during engine operation was preserved. The rotation (drift) of the jet stream when
exiting the engine and the movement of the gas jet in the combustion chamber are unidirectional (see Fig. 18). The engine worked steadily throughout the studied range. The same RE3 engine was used for all three tests.
B. Test results, analysis, conclusions
The RE3 worked steadily in all the studied ranges. No remarks on the operation of the engine were found. Based on the test results, three graphs were built. The first two are the throttle characteristics, the relationship between the fuel supply pressure in front of the engine (Pp), or pressure in the combustion chamber (Pcc) and thrust (F). These results are shown in the combined graph in the Fig. 19. The third graph is the relationship between the fuel supply pressure in front of the engine (Pp) and the pressure in the combustion chamber (Pcc) (Fig. 21).
Throttle characteristics
After having analyzed the throttle characteristics (Fig. 19), we can conclude that both curves have a quadratic dependence and correspond to each other on the dynamics of their change, which is actually logical. And the graphs themselves just like in the case with the throttle characteristics of the RE2 have a quadratic and not linear dependence like the engines with the standard operating scheme, which is better. Since the RE3 and the RE2 have identical dimensions of the combustion chamber and of the nozzle, and also injectors cross-section and their quantity that are the same, the only difference is the direction of rotation of the gas mixture in combustion chamber. So, we combine their throttle characteristics (Fig. 12 and Fig. 19) on fuel supply (Pp) and thrust (F) in one graph of combined throttle characteristics of the RE2 and the RE3 (Fig. 20).
In the Graph 1 you will see the relationship between the pressure in the combustion chamber (Pcc) and the thrust (F). The Graph 2 is the relationship between the fuel pressure in front of the engine (Pp) and the thrust (F). X - Pcc pressure, Pp (kPa), Y - thrust F (N).
In the yellow sector (1) is the RE2 operation, in the green sector (2) is the RE3 operation. X-Pp (kPa), Y -thrust (N). In general, the characteristics of both engines are harmonized, the quadratic dependence remains, but the sector 2 (RE3) looks preferable to the sector 1 (RE2). In the sector 2, the possibility of growth of the quadratic dependence is higher.
Analysis of the fuel supply pressure (Pp), and the pressure in the combustion chamber (Pcc)
Having analyzed the graph for the RE3 of interdependence (Fig. 21) of the fuel mixture supply pressure in front of the engine (Pp) and the pressure in the combustion chamber (Pcc), we can conclude that with increasing the fuel supply pressure to the engine, the pressure difference is decreases, which is a positive moment in the process of engine operation.
Energy costs for fuel supply to the engine are reduced, the operating modes of the engine turbocharger become more sparing and economical. It is possible to achieve higher pressures in the combustion chamber at lower turbocharger pressure. Let's analyze why this happens: for the engines with the existing scheme of operation (Fig. 22), when the gas mixture is fed into the combustion chamber, it has to overcome the counter resistance of expanding gases during its combustion (partially with counter vector of acting forces).
In the scheme based on the new principles of RE operation (Fig. 23), the gas mixture is fed around the circumference, which creates an injection effect. Accordingly, the vectors of the acting forces become unidirectional, the resistance when the gas mixture is supplied decreases.
Sound spectrum analysis
During the RE3 tests, in addition to measuring the traction (F) characteristics, the combustion chamber pressure (Pc) and the fuel supply pressure (Pc), the RE3 sound spectrum was recorded in real time (through a microphone). Let's analyze this data.
The velocity of the gas jet during its rotation in the combustion chamber is clearly traced in the sound spectrum of the RE3. When the gas mixture is switched off in the combustion chamber, a smooth decrease in the gas jet rotation frequency from the maximum frequency to zero values is traced. The analyzed sound spectra are shown in the Fig. 24, 25, 26.
Knowing the gas rotation frequency and the diameter of the combustion chamber (Dic- 50mm), it is possible to determine the velocity of the gas jet in combustion chamber.
The analysis of the Fig. 24, 25, 26 showed that the velocity of the gas jet in the combustion chamber with increasing pressure varies from 314 m/s to 353 m/s, the velocity tends to increase. In addition to determining the velocity of the gas jet, the spectrum analysis shows the absence of low-frequency oscillations dangerous for all types of engines.
The thrust coefficient (Cf)
The data obtained as a result of the tests is sufficient to calculate the thrust coefficient (Cf). To do this, we need to know the thrust (F), the nozzle area (calculated from Dice) and the pressure in combustion chamber (Pc). The higher the thrust coefficient (Cf), the more efficient the nozzle part and, accordingly, the more efficient the engine itself. The thrust coefficient (Cf) is equal to the thrust (F) of a RE divided by the pressure in combustion chamber (Pc) and the area of the critical section of the nozzle (from Dick).
The thrust coefficient (Cf) consists of the sum of two values: the subsonic part of the nozzle (its value up to 1.2) and the supersonic part (range of 0.5-0.8). At the ground surface the total value is up to 2 (the sum of subsonic and supersonic parts).
For the RE3, the thrust coefficient was obtained according to the data of the first test with F-867 N thrust and had the thrust coefficient Cf of 1.8. For comparison, the RD-180 at the maximum pressure and thrust with a nozzle consisting of subsonic and supersonic parts, the thrust coefficient Cf = 1.73. But it should be taken into account that the RE3 has no supersonic part of the nozzle. In the case of an engine working on new principles, this is explained by the plasma properties of the gas jet, and as a result, the possibility to eliminate the limitations related to overcoming supersonic speed when the gas jet flows out of the diffuser. This is basically impossible in the standard rocket engine operation scheme as when exceeding the local supersonic velocity, there is a locking effect of the diffuser or the nozzle, with all the negative consequences that follow from this. For more details, see the RE1 test. Also, we should not forget that already in the combustion chamber the gas has a high velocity, and it grows in the nozzle part.
RE3 thrust control and its range
During the tests, the RE3 tested the operating mode at minimum pressure in the combustion chamber and, as a result, at minimum thrust. The tests have shown that the thrust is regulated uniformly in the range from zero to the maximum values. Immediately after starting, the jet stream has a supersonic velocity (Fig. 27), at low thrust and pressure values. Accordingly, there will be no loud clap when the engine is turned to the maximum power.
The thrust control in the RE3 is possible at 100% of the operating range, in engines with the existing scheme only about 50% of the range are operational. The phenomenon of instability of the combustion process, including pressure surges in the combustion chamber and dangerous low-frequency vibrations, is completely absent.
Analysis of the jet stream of the RE3 engine
The jet stream coming out of the engine with the existing operation scheme (Fig. 28) looks like a series of compaction jumps (shock diamonds) representing a periodic change in velocity and pressure. Naturally, this has a negative effect on the jet stream, reducing its effectiveness.
When starting the engine based on the new principles of the RE3 (Fig. 27), we can observe the maximum number of shock diamonds located evenly along the jet stream. As the pressure in the combustion chamber increases, the shock diamonds shift almost completely to the nozzle and begin to disappear (Fig. 29 a, b). At the maximum pressure tested in the combustion chamber of the RE3 (Fig. 29 c), the shock diamonds completely disappeared (except for the first supersonic shock diamonds).
The jet stream looks optimal: its transition layer is sharply outlined; it is uniform in structure and generally resembles the jet of plasma engines. The degree of expansion of the jet stream is optimal.
V. Analysis of plasma properties of the RE1, RE2, RE3, engine scheme based on new operating principles
Immediately after the start of the RE2 and the RD3 at low pressure in the combustion chamber, the gas jet coming out of the nozzle behaves like a plasma. Why does this happen in the engine on new principles? Let's look into it. In an engine based on existing principles, the combustion in the engine's combustion chamber is turbulent. The appearance of the turbulent combustion is shown in the Fig. 30 from SpaceX.
As already written above in a normal flame there are already enough charged particles, and they are able to affect the combustion process under certain conditions. But, at a turbulent combustion of the gas in the combustion chamber (which is typical for engine based on existing principles), the movement of elementary particles is chaotic. Any impact on these particles, including electromagnetic field, will not lead to any significantly positive effects in the operation of the engine with the existing operating scheme. In the engine based on new principles everything is different.
In the engine working on new principles there has initially been worked out the processes of ordered movement of gas particles, both fuel and combustion products in the combustion chamber. Let's analyze the main ones.The fuel in the engine combustion chamber is supplied tangentially (along the circumference of the combustion chamber), over its entire area. The fuel is supplied to the combustion chamber with the help of slot nozzles (Fig. 31), in order to create the most laminar (orderly) movement of the fuel. The rotational movement with high velocity of the fuel and the combustion products creates a significant centrifugal force, reinforcing the laminar effect due to a more uniform distribution of gas and combustion products along the walls of the combustion chamber.
Already at a low pressure in the combustion chamber, when the engine is started, the gas jet coming out of the nozzle behaves like a weakly ionized plasma, the number of ionized particles is really small. However, plasma properties appear immediately and can be defined as stationary, constantly acting. Each particle interacts with many other surrounding particles, due to which plasma particles, in addition to chaotic thermal motion, can participate in various ordered motions. The manifestation of plasma properties at the first moment after launch is a change in the direction the gas jet rotation when exiting the RE2 nozzle (see Fig. 32). More details are described in the section about the RE2 test.
Due to the collective interactions, plasma behaves as a kind of elastic medium in which various kinds of oscillations and waves are easily appeared and propagated. As an example, it is possible to measure the frequency characteristics in the combustion chamber (see Fig. 33).
For comparison, the Fig. 34 shows the sound spectrum of the RE operation with the existing operation scheme. The frequency characteristics are almost evenly distributed over the entire spectrum.
Let's briefly list some more manifestations of plasma properties revealed during tests of the RE1, RE2, RE3. During the RE1 tests, a sharp surge of thrust was detected in the throttle characteristics of the engine with an almost constant level of fuel consumption, which is impossible for the engine with the existing operation scheme.
Drift. Slow counterclockwise rotation of the gas jet (when viewed from the nozzle side of the engine)
Possibility to control the plasma jet in order to prevent the nozzle burnout effect (see the RE2 and RE3 tests). In deflagration combustion this is not possible.
Change of throttle characteristics (Pcc - thrust) from linear to quadratic function.
Smooth disappearance of diamond shocks in the jet as the pressure in the combustion chamber increases and the plasma properties increase.
The thrust coefficient of the RE with a nozzle without a supersonic part, at low pressure in the combustion chamber, is anomalously high Cf=1.8.
Based on the results of the tests of the engines working on new principles, let’s analyze the physical scheme of the RE3 and describe the process occurring in the engine.
As written in the introduction, during the combustion, the flame already has a significant amount of positively and negatively charged particles, capable of influencing the combustion process (butterfly effect) and manifesting plasma properties under certain external influences. When the fuel is supplied tangentially and burned, the gas begins to rotate at high speed (V=353 m/s) in the combustion chamber. This creates a significant centrifugal force.
The centrifugal force equation = V² (353 m/s) * m (1 kg/s) / r (25 mm). Naturally, this force is redistributed over the whole surface area of the combustion chamber (combustion chamber: radius R-25 mm, length h-300 mm). Accordingly, taking into account the above data, the centrifugal force is equal to 1000 N per 1 mm^2. Which is a significant force affecting processes taking place in the combustion chamber.
Once again, during a normal combustion, a sufficient number of free charged particles are already formed, and in the case of centrifugal force impact on the combustion, their number significantly increases. Considering that the combustion process occurs at high speed, and when the centrifugal force is applied, the mass of positively charged protons is 1800 times greater than that of negatively charged electrons, there is a process of their separation. Heavier protons begin to rotate at high speed along the maximum diameter in the combustion chamber, and the light electrons remain in its central part. It is clear that the problem of separation of dissimilar charges in the scheme with the new principles occurs naturally, without any energy consumption. Separation of charged particles and rotation (motion) of positively charged particles at high-speed leads to appearance of a magnetic field in the engine based on the new principles. Naturally, if there is a moving magnetic field, an electric current also arises. This explains the formation of the plasma jet in the engine. Regarding the appearance of the jet drift at its exit from the engine (during its operation, the gas jet coming out of the engine begins to rotate counterclockwise, when viewed from the nozzle side of the engine), this phenomenon coincides with the right-hand screw rule, and is explained by the electrical properties of the plasma. The diagram of the motion of charged particles in the RE3 is shown in the Fig. 35.
Based on the information mentioned above, the acceleration of the gas jet occurs all the way from the combustion chamber and the nozzle, to the jet coming out of the nozzle.
In conclusion I would add one assumption, if an external corresponding electric field is applied to the electrical processes taking place in a RE working on new principles, then it is possible to gain an amplification of all processes in the engine by accelerating the jet stream.
VI.Conclusion
The conducted tests of the 3 engines working on new operating principles and their results show that the presented scheme is promising and has a number of significant advantages compared to the existing scheme of a rocket engine operation.
Let's list some of the advantages of the engine based on new principles, as well as the problems identified as a result of tests. Advantages of an engine based on new principles:
It is possible to obtain a higher value of the RE impulse at a lower pressure in combustion chamber. It is also possible to achieve record values on impulse for liquid rocket engines.
Uniform and stable engine operation in all ranges (in thrust from zero to maximum values) in a safe mode, the absence of unstable combustion in the combustion chamber, the absence of low-frequency vibrations and oscillations.
There is no, or significantly reduced supersonic part of the Laval nozzle. This is especially important for vacuum rocket engines as their size will be reduced, so the problem of under-expanded jet stream in a vacuum is eliminated due to its plasma properties.
Significantly lower energy costs for supplying the fuel mixture to the combustion chamber than for the engines with the existing operating scheme.
Abnormally high dimensionless thrust coefficient (Cf=1.8) in the absence of supersonic part of the nozzle, which indicates the high efficiency of the RE scheme based on new principles. Realistically achievable Cf>3 at ground level.
There is no supersonic clap when starting the engine. The supersonic clap of a RE working on the new principles occurs immediately after the start of the engine at low thrust, and as a consequence it is practically not audible. And all further operation of the engine takes place in the supersonic mode of the jet stream flow.
Unlike the existing plasma engines, where the thrust of the engine is usually up to one newton, the engine operation scheme with new principles allows to get thrust from one newton to hundreds of tons of thrust in plasma mode.
One of the disadvantages is a very high load on the walls of the combustion chamber because of the large centrifugal force that occurs when the fuel mixture rotates in the combustion chamber, and, as a result, a more complex design of the combustion chamber due to the lack of experience in creating engines and combustion chambers based on new principles of operation using cryogenic components.
There is one remark related to the RE1 test (Fig. 6) regarding the thrust surge in the engine from the fifth to the sixth second of operation. It is known that the throttle response of a jet engine is an unbroken line. However, this is not the case this time, and there is a thrust surge. The explanation is simple. If we test separately an engine with a standard operating scheme and an engine based on new operating principles, then in the first and in the second case the principle of continuity (the law of conservation of energy) will be strictly observed, although in the first case the dependence will be linear, and in the second quadratic (Fig. 19,20). In the case of the RE1 test (Fig. 6), there is a transition from the deflagration combustion to the plasma burning mode, and as a consequence, there is a thrust surge in the engine associated with greater energy efficiency of the engine working on new principles compared to the existing scheme. At the same time, it should be taken into account that the engine uses additional gravitational energy (centrifugal force) on new principles, which is not used in the engine with a standard working scheme.
The tests of the three engines provided a sufficiently large amount of information for further work to be carried out in the shortest possible time. And its design can be implemented in the project to create an engine based on new principles in the near future.
This review of testing three engine modifications on new operating principles conveys the main part of the tests and principles of operation. If you are interested in this work from a practical point of view (design, manufacture, testing, and so on), I am ready to discuss working together to create a jet engine demonstrator using cryogenic methane-oxygen fuel pair and a thrust of 5-10 tons of force.
My email address: kulevsp@gmail.com
This work was carried out on my own initiative, by myself, at my own expenses.
Tables
Table 1 RE1 test |
Time t,s Mf, g/s F,N |
1 26 5 |
2 39 10 |
3 52 15 |
4 65 25 |
5 78 40 |
6 91 145 |
7 104 155 |
8 117 165 |
9 130 190 |
10 143 230 |
Table 2 RE2 test |
Test number Pp,kPa F,N |
1 420 235 |
2 560 307 |
3 640 371 |
4 700 420 |
Table 3 RE3 test |
Test number Pp, kPa Pcc, kPa F, N Cf |
1 1350 709 876 1.8 |
2 2000 1267 1297 1.6 |
3 2900 2027 2340 1.7 |
References
Periodicals
[1] Dieter K. Huzel, “Modern Engineering for Design of Liquid-Propellant Rocket Engines”, Ingenieria de transportes y aeronautica Progress in astronautics and aeronautics, AIAA, Vol.147, 1992, p.7.
[2] Juk B. E. Juk C. B. “Electric hydrogen rocket engine concept”, Innovative science, Vol.62, 2016, Pp 65-67.
[3] Graff, G., Kalinowsky, H. & Traut, J. “A direct determination of the proton electron mass ratio.” Z Physik, Vol. 297, 1980, Pp. 35-39.
doi: 10.1007/BF01414243
[4] Pustylnik M. Y., Fink M. A., Nosenko V., Antonova T., Hagl T., Thomas H. M., Zoblin A.V., Lipaev A. M., Usachev A. D., Molotkov V. I., “Plasmakristall-4: New complex (dusty) plasma laboratory on board the International Space Station.”,Review of Scientific Instruments, Vol.87, 2016.
doi: 10.1063/1.4962696
Books
[5] Lawton James, Weinberg F., “Electrical aspects of combustion “, Oxford: Clarendon press, 1969, p.183.
[6] Artsimovitch L. A., “Elementary Plasma Physics”, Atomizdat, 1969, Pp 200.
[7] Dobrovolskii M. B., “Liquid rocket engines: design basics”, Bauman Moscow State University, 2005, Pp 487.
Used photos
Fig.1 - Video channel Vertasium,” What’s In A Candle Flame?”
Fig.2 - @KUDSVERCHKOV. ISS., “Plasma Kristall experiment.”
Fig.30 - SpaceX, “Structure in Turbulence.”