RU2633730C1 - Method of working process organizing in direct-flow air jet engine - Google Patents

Abstract

FIELD: engines and pumps.

SUBSTANCE: method includes supplying a powder of metal fuel to the combustion chamber, igniting it and burning it in a stream of air from the air inlet. The powder in the form of a uniformly mixed suspension in a liquefied fuel gas placed in a fuel tank is preloaded with a displacement pressure, heated and supplied to the combustion chamber through a nozzle. The maximum diameter of the powder particles, the extrusion pressure and the heating temperature of the slurry are determined from the protected ratios.

EFFECT: increased power characteristics and reliability of the direct-flow air-jet engine.

2 cl, 2 tbl, 2 dwg

Description

The invention relates to the field of aircraft engine manufacturing and can be used in the development of ramjet engines.

There is a method of organizing a workflow in a combined ramjet of a gas generator circuit (ramjet engine), which is a combination of ramjet and rocket engines [1, 2]. The principle of operation of this ramjet engine is that the products of incomplete combustion of solid, liquid or gaseous fuels formed in the combustion chamber of a rocket engine (gas generator) are used as fuel for the direct-flow circuit. This fuel is burned in a stream of air entering through the air intakes into the afterburner. The products of complete combustion expire through the nozzle block, creating thrust ramjet.

A promising direction for increasing the energy characteristics of ramjet engines is the use of metal powders as combustible components of the fuel mixture of a gas generator. The use of metals (primarily aluminum) is due to their high activity, significant heat release and high combustion temperature [3].

There is a method of increasing the energy characteristics of ramjet by introducing powders of metals (aluminum, boron, beryllium, magnesium) with a dispersion of particles (1 ÷ 100) microns in liquid rocket fuel [4]. A significant drawback of such suspensions is their separation during storage with the precipitation of metal. To reduce this effect, thickeners are used - substances whose addition in small quantities increases the viscosity of the fuel. However, there are difficulties associated with the supply of fuel to the combustion chamber and its atomization.

A known method of organizing a working process in a hybrid rocket-ramjet air-propelled aerospace engine [5], which includes a rocket engine on fuel in the form of a suspension of aluminum nanopowder with a particle size of not more than 25 nm in the liquid aqueous phase. The engine is designed to create traction at launch and at the initial stage of the flight, as well as to produce fuel consumed by the combined molecular-hydrogen cruise ramjet produced during the combustion of aluminum nanopowder. Aluminum nanopowder is burned in water vapor in a combustion chamber, which is also a chemical reactor for producing hydrogen.

The disadvantage of this method is the difficulty of implementing a stable combustion mode, including multi-stage mutually affecting processes of diffusion, heat and mass transfer, chemical kinetics and gas dynamics.

The closest in technical essence to the claimed method is the organization of the working process in a ramjet engine on a metal powder fuel [6]. The engine comprises a start system, a fuel supply system including a fuel tank with metal powder fuel and a perforated piston, and a combustion chamber. An additional gas generator is installed in the engine housing, which enables the start-up of a powder metal fuel supply system. The combustion chamber consists of a prechamber, with a fuel dispenser located at its inlet and a chamber for the final afterburning of fuel. The prechamber and afterburner have air ducts.

The disadvantage of this method is the difficulty of ensuring a uniform and metered supply of powder into the prechamber. Existing dispensers have, as a rule, large dimensions and weight and do not provide reliable operation in conditions of high temperature and pressure drops.

The technical result of the present invention is to increase the energy characteristics and reliability of the ramjet.

The technical result of the invention is achieved by the fact that a method for organizing a working process in a ramjet engine has been developed, including supplying metal fuel powder to the combustion chamber, igniting it and burning in the air stream from the air intake. The powder in the form of a uniformly mixed suspension in a liquefied combustible gas, placed in the fuel tank, is pre-loaded with displacement pressure, heated and fed into the combustion chamber through the nozzle. The maximum particle diameter of the powder, displacement pressure and heating temperature of the suspension are determined from the relations

where D _max - the maximum diameter of the powder particles, microns;

μ is the dynamic viscosity coefficient of liquefied gas, Pa⋅s;

L is the characteristic size of the fuel tank, m;

ρ _p - the density of the metal powder, kg / m ³ ;

ρ ₁ - density of liquefied gas, kg / m ³ ;

g is the acceleration of gravity, m / s ² ;

t is the time guaranteed to maintain a uniform distribution of powder particles in suspension, year;

p _Kam - pressure in the combustion chamber, Pa;

p _tank is the pressure of the displacement of the suspension, Pa;

p _cr - the critical pressure of saturated steam for a combustible gas, Pa;

T _bale (p _Kam ) - the boiling point of a liquefied combustible gas at a pressure equal to the pressure in the combustion chamber, ° C;

T is the heating temperature of the suspension, ° C;

T _bale (p _tank ) is the boiling point of the liquefied combustible gas at a pressure equal to the pressure of the displacement of the suspension, ° C.

Powders of aluminum, boron, beryllium, magnesium, zirconium or lithium are used as metal fuel, and hydrocarbons C _n H _2n , C _n H _{2n + 2} , C _n H _2n-2 are used as liquefied fuel.

The invention is illustrated by the diagram (Fig. 1), which shows a method of organizing a work process in a ramjet engine. The numbers indicate: 1 - air intake; 2 - elastic membrane; 3 - a fuel tank; 4 - suspension of metal powder in a liquefied gas; 5 - exhaust ducts for supplying air to the combustion chamber; 6 - combustion chamber; 7 - cylinder with compressed gas; 8 - gear; 9, 11 - electro-pneumatic valves; 10 - heater; 12 - nozzle; 13 - igniter; 14 - nozzle.

The implementation of the method is as follows. The ramjet is previously accelerated by an external carrier — a solid-fuel accelerator or an airplane (not shown in FIG. 1) —to a speed greater than 0.6 M, where M is the Mach number providing stable ramjet operation [4]. Open the valve 9, and the compressed gas from the cylinder 7 through the reducer 8 enters the fuel tank 3 and through an elastic membrane 2 loads a suspension of metal powder in the liquefied gas 4, creating a predetermined pressure p _tank in it. The pressure level p _tank exceeds the working pressure in the combustion chamber p _kam , but less than the critical pressure for liquefied gas p _kr . Then it includes heater 10, and the suspension is heated to a temperature of 4 T, at the boiling point of the liquefied gas at a pressure in the fuel tank T _heated (P _tub).

After heating a suspension of 4 open valve 11 and the suspension was heated 4 through the nozzle 12 is supplied into the combustion chamber 6. As the pressure in the combustion chamber pressure p _Cams less fuel tank p _tank, liquified gas is superheated relative to the pressure in the combustion chamber. This will lead to its "explosive" boiling and evaporation. Evaporated gas and metal powder particles are mixed with air coming from the exhaust ducts 5 and ignited using a pyrotechnic igniter 13. The combustion products expire through the nozzle 14, creating an engine thrust.

The achievement of the positive effect of the invention is provided by the following factors.

1. The use of metal fuel powder in the form of a uniformly mixed suspension in liquefied gas provides a uniform and reliable supply of combustible components to the ramjet combustion chamber through a nozzle (for example, centrifugal or jet).

2. Preloading the suspension placed in the fuel tank, the displacement pressure p _tank , determined from the ratio p _kam <p _tank <p _kr , and heating the suspension to a temperature T determined by the ratio of T _bale (p _kam ) <T <T _bale (p _tank ), allows you to enter the suspension into the combustion chamber of the ramjet in an overheated state. This intensifies the processes of evaporation of liquefied combustible gas and the mixing of combustible components (vapors of combustible gas and metal powder particles) with an oxidizing component (air oxygen). Ultimately, the completeness of combustion increases and, as a result, the specific impulse of thrust of the ramjet.

The superheated state of the suspension is illustrated by the PT diagram of the phase transitions shown in FIG. 2 [7]. In the initial state, the suspension has an ambient temperature at atmospheric pressure (point 0 in Fig. 2). Then, the pressure in the fuel tank is set equal to the displacement pressure p _tank (point 1 in Fig. 2). At this pressure, the suspension is heated to a temperature T ₂ that is lower than the boiling point of the liquefied gas T ₅ at a pressure p _tank (point 2 in FIG. 2). When applying compressed liquefied gas into the combustion chamber pressure dramatically decreases the pressure value P in the tank to _{the tank} chamber pressure p _cam (point 3 in FIG. 2) and does not change temperature T ₃ = T _2. The state of the liquefied gas at point 3 will be unstable, since at this pressure the liquefied gas is superheated by ΔT = T ₃ -T ₄ (the boiling point of the liquefied gas at a pressure of p _cams is T ₄ , with T ₄ <T ₃ ). There is an “explosive” boiling and evaporation of liquefied gas, which goes into a gaseous state, and its temperature decreases due to evaporation to a temperature of T ₄ (point 4 in Fig. 2). The greater the pressure difference between the p _tank and p _chamber , the greater the superheat of the liquefied gas can be realized and the more intense its boiling and evaporation (Fig. 2). During evaporation, the volume of gas increases many times, it is mixed with air and the distribution of particles of metal powder in the volume of the combustion chamber. It does not require the use of nozzles or nozzles with nozzles of small diameter (to ensure crushing of liquefied gas) and virtually eliminates the possibility of clogging them with metal powder particles, which increases the reliability of the ramjet.

3. The use of metal fuel powder with a maximum particle diameter D _max determined from relation (1) provides a guaranteed time for maintaining a uniform distribution of powder particles in suspension. This ensures reliable operation of the ramjet when it is launched in a period of time no later than the specified warranty period.

To justify relation (1), we consider the equation of particle deposition in a gravitational field [8]:

where u is the deposition rate of the powder particles; D is the particle diameter. It follows from (4) that the larger the particle size, the faster their separation in suspension. Therefore, for a long period of time to maintain uniform distribution of particles in the suspension, it is necessary to introduce a restriction on the maximum particle diameter D _max . From relation (4) it follows:

In stationary particle deposition, the deposition rate is u = const and can be represented as

where l is the distance traveled by the particle in time t.

For time t, we take the time to guarantee the uniform distribution of powder particles in the suspension, and for the distance l , the distance equal to l = 0.1L, where L is the characteristic size of the fuel tank (for example, its diameter or height). Substituting (6) into (5), we obtain the relation

For the convenience of calculations, we take the following dimensions: [D _max ] = μm = 10 ^-6 m, [ρ _p ] = [ρ ₁ ] = kg / m ³ , [L] = m, [μ] = Pa⋅s, g = 9.80665 m / s, [t] = year = 31.536⋅10 ⁶ s. In this case, formula (7) will take the form (1):

Relation (1) determines the maximum size of particles that will travel 0.1L in time t. Smaller particles with a diameter of D <D _max will shift to a smaller distance, which will ensure the preservation of the equilibrium distribution of particles.

4. The use of metal powders of metals (aluminum, beryllium, magnesium, zirconium or lithium) or metalloid (boron) as a metal fuel provides a high energy release during the combustion reaction and, therefore, high energy characteristics of ramjet. The main characteristics of these substances are given in table 1 [3].

When choosing metallic fuel, it is necessary, along with the calorific value of a unit mass Q _m [kJ / g], to evaluate the calorific value of a unit volume Q _v [kJ / cm ³ ], which is determined by the ratio Q _v = ρ _p Q _m .

This is due to the fact that in the ramjet engine it is important not only the amount of heat released per unit mass of fuel, but also the volume occupied by it.

The use of hydrocarbons C _n H _2n , C _n H _{2n + 2} , C _n H _2n-2 as liquefied combustible gas provides additional heat during combustion in the air stream in the ramjet combustion chamber. The main characteristics of some combustible gases are given in table 2 [9].

Implementation example

As an example of the implementation of the proposed method of organizing the working process in a ramjet engine, consider a ramjet (Fig. 1), which uses a suspension of aluminum powder in liquefied cyclohexane C ₆ H ₁₂ .

Characteristics of cyclohexane [9]:

T _cr = 281 ° C is the critical temperature;

p _cr = 4.1 MPa - critical pressure;

T _PL = 6.6 ° C is the melting temperature at atmospheric pressure;

Т _bale = 80.7 ° С - boiling point at atmospheric pressure;

With _p = 1.86 kJ / (kg⋅K) - specific isobaric heat capacity;

ρ ₁ = 779 kg / m ³ - density at 20 ° C;

μ = 1.06⋅10 ^-3 Pa⋅s - dynamic viscosity coefficient at 20 ° С;

Q _vap = 366 kJ / kg - specific heat of evaporation.

Characteristics of aluminum:

ρ _p = 2700 kg / m ³ - density;

Q _m = 30.98 kJ / g - calorific value per unit mass;

Q _v = 83.6 kJ / cm ³ is the heat of combustion per unit volume;

Let us take the pressure values in the combustion chamber, typical for ramjet engine, p _cam = 0.5 MPa and the characteristic size of the fuel tank L = 1 m [4].

The value of D _{max is} calculated by the relation (1). For a fuel tank L = 1 m and a warranty storage time of 1 year, the maximum particle diameter of the powder should be no more than D _max ≤57 nm. For a warranty period of storage of 1 month - D _max ≤0.2 microns.

Under normal conditions (T = 20 ° C, p = 0.1 MPa), cyclohexane is a liquid in which aluminum powder is uniformly mixed with a given ratio of powder to liquid mass (determined from thermodynamic calculations). The resulting suspension is poured into the ramjet fuel tank.

Before starting the engine, the suspension 4 in the fuel tank 3 is loaded through the membrane 2 with the displacement pressure p _tank by supplying compressed gas from the cylinder 7 through the gearbox 8 and the electro-pneumatic _valve 9. The gearbox 8 provides the pressure p _tank in accordance with the relation (2), for example, p _tank = 3.5 MPa:

0.5 MPa <3.5 MPa <4.1 MPa.

Then the suspension 4 in the fuel tank 3 is heated at this pressure from an external heat source 10 (for example, an electric heater) to a temperature T in accordance with relation (3).

From the p-T diagram for cyclohexane [9] determine the value of the boiling point for a given p _kam and p _tank :

T _bale (p _tank ) = T _bale (3.5 MPa) ≈ 260 ° С.

In view of (8), the temperature of the suspension heating is chosen, for example, T = 220 ° C.

The engine is accelerated by an external solid fuel accelerator or aircraft to a speed greater than 0.6 M. Then, valve 11 is opened, and the flow of the heated suspension into the combustion chamber begins. When entering the combustion chamber 6, the pressure in the suspension stream sharply decreases from p _tank = 3.5 MPa to p _cam = 0.5 MPa. The liquefied gas turns out to be superheated for a pressure p _kam = 0.5 MPa by ΔT = (220-120) ° С = 100 ° С, which will lead to its “explosive” boiling and evaporation.

The amount of excess heat stored in the superheated liquefied gas and spent on its evaporation is ΔQ = C _P ⋅ΔT == 186.3 kJ / kg. Therefore, the amount of excess heat in the superheated liquefied gas (ΔQ / Q _vap ) ⋅100 ~ 50% is sufficient for instant evaporation of the liquefied gas entering the combustion chamber. Since the boiling of the liquid occurs “explosively” in the volume of the jet, the non-evaporated part of the liquefied gas will be dispersed throughout the volume of the combustion chamber and mixed with air. When the pyrotechnic igniter is triggered, combustion of the gas-air mixture with metal powder particles and its outflow through the nozzle are initiated.

The given example proves that when implementing the proposed method of organizing the work process in ramjet, a positive effect is achieved, which consists in the following.

1. The method allows to increase the energy characteristics of ramjet by using powders of metallic fuel with high values of volumetric heat of combustion in combination with high-calorie hydrocarbons.

2. The method improves the reliability of the ramjet due to the supply of metal fuel powder in the form of a suspension in a liquefied combustible gas, which ensures uniform and reliable atomization of the combustible components by a centrifugal or jet nozzle.

3. The method improves the efficiency of the ramjet by feeding the suspension into the combustion chamber in an overheated state, which increases the efficiency of its crushing and mixing with air.

LITERATURE

1. Bondaryuk M.M., Ilyashenko S.M. Ramjet engines. - M .: Oborongiz, 1958.- 392 p.

2. Integrated ramjet engines for solid fuels: Fundamentals of theory and calculation / Ed. L.S. Yanovsky - M: IKC "Akademkniga", 2006. - 343 p.

3. Pokhil P.F., Belyaev A.F., Vrolov Yu.V. et al. Combustion of powdered metals in active media. - M: Nauka, 1972.- 294 p.

4. Orlov B.V., Masing G.Yu., Reidel A.L., Stepanov M.N., Topcheev Yu.I. Fundamentals of designing ramjet engines. - M: Mechanical Engineering, 1967 .-- 424 p.

5. RF patent No. 2563641, IPC F02K 7/18, B81C 99/00. Hybrid rocket-propelled air-propelled aerospace engine / A.M. Old Man, P.S. Kuleshov, A.M. Saveliev - Publ. 09/20/2015.

6. RF patent No. 2439358, F02K 7/18. Ramjet engine on powder metal fuel / V.I. Malinin, S.M. Vinogradov, O.M. Ivanov, V.V. Gureev, A.I. Marchenko - Publ. 01/10/2012

7. Stanley G. Phase transitions and critical phenomena. - M .: Mir, 1973.- 425 p.

8. Arkhipov V.A., Usanina A.S. The motion of particles of the dispersed phase in a carrier medium: textbook. allowance. - Tomsk: Publishing House of Tomsk State University, 2014. - 252 p.

9. Dubovkin N.F. Handbook of the thermophysical properties of hydrocarbon fuels and their combustion products. - M.-L.: Gosenergoizdat, 1962 .-- 288 p.

Claims (19)

1. The method of organizing a working process in a ramjet engine, including the supply of metal fuel powder to the combustion chamber, its ignition and combustion in the air stream from the air intake, characterized in that the powder is in the form of a uniformly mixed suspension in a liquefied combustible gas placed in the fuel tank, pre-loaded with displacement pressure, heated and fed into the combustion chamber through the nozzle, and the maximum diameter of the powder particles, displacement pressure and heating temperature of the suspension limit from the relations

p _cam <p _tank <p _cr T _bales (p _cam ) <T <T _bales (p _tank ), where D _max - the maximum diameter of the powder particles, microns; μ is the dynamic viscosity coefficient of liquefied gas, Pa⋅s; L is the characteristic size of the fuel tank, m; ρ _p is the density of the metal powder, kg / m ³ ; ρ ₁ - density of liquefied gas, kg / m ³ ; g is the acceleration of gravity, m / s ² ; t is the time guaranteed to maintain a uniform distribution of powder particles in suspension, year; p _cam - pressure in the combustion chamber, Pa; p _tank is the pressure of the displacement of the suspension, Pa; p _cr - critical pressure of saturated steam for combustible gas, Pa; T _bales (p _Kam ) is the boiling point of the liquefied combustible gas at a pressure equal to the pressure in the combustion chamber, ° C; T is the suspension heating temperature, ° C; T _bale (p _tank ) is the boiling point of the liquefied combustible gas at a pressure equal to the pressure of the displacement of the suspension, ° C. 2. The method according to p. 1, characterized in that as a metal fuel use powders of aluminum, boron, beryllium, magnesium, zirconium or lithium. 3. The method according to p. 1, characterized in that the hydrocarbons C _n H _2n , C _n H _{2n + 2} , C _n H _2n-2 are used as liquefied combustible gas.

Images