CA2834478A1

CA2834478A1 - A method of operating a scramjet engine

Info

Publication number: CA2834478A1
Application number: CA2834478A
Authority: CA
Inventors: Vladimir Ponomarev
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-11-26
Filing date: 2013-11-26
Publication date: 2015-05-26

Abstract

Method of operation of a scramjet engine provides a higher thrust and greater specific impulse by 30%
to 110% depending on the selected mode and velocity of an aircraft with the same fuel consumption.
Sequence of combustible and non-combustible zones is generated by modulating the fuel injection rate with sequential ignition and energy transfer between combustible and non-combustible zones.
Invention is based on a pressure-gain combustion being implemented without valves and can be used at supersonic and hypersonic speeds.

Description

A Method of Operating a Scramjet Engine TECHNICAL FIELD OF INVENTION
The present invention relates to engines that utilize air moving at supersonic speeds for combustion and expansion. Engines that use combustion at supersonic speed of air in a combustor are known as scramjets. More specifically, the present invention relates to the engines for supersonic and hypersonic aircrafts.
BACKGROUND OF THE INVENTION AND PRIOR ART
A ramjet engine uses the momentum of the airstream to compress air within an inlet, without the use of moving parts such as rotating compressors or fans. The airstream is slowed down to subsonic speeds for burning a fuel in the combustor. A scramjet engine is similar to a ramjet engine except that the flow is not slowed to subsonic speeds and in the combustor remains at supersonic speeds. A dual mode scramjet engine is an engine that can operate in both ramjet and scramjet modes.
In the prior art various methods of operating a scramjet engine are described as shown in the following patent applications and patents granted in Canada.
Patent application CA2034466, George A. Coffinberry, discloses a method of operating a scramjet engine. The method includes the steps of providing supersonic compressed airflow to a combustor and supplying fuel to the combustor for generating a fuel/air mixture having a predetermined temperature less than a temperature required for spontaneous ignition of the fuel/air mixture. The method also includes igniting the fuel/air mixture and generating combustion gases.
Unites States patent US 5255513 A, John C. Blanton, Paul H. Kutschenreuter, Jr., discloses a method of operating a scramjet engine that includes injecting fuel into the inlet-combustor for mixing fuel with supersonic airflow for generating supersonic combustion gases in the inlet-combustor. In the preferred embodiment of the invention, the fuel is injected to create a fluid boundary defining a subsonic fuel zone and a supersonic fluid zone. The fluid boundary is variable and eliminates start and unstart problems requiring variable inlet geometry in a conventional scramjet engine.
It is known that at relatively low supersonic speeds the thrust is limited due to low ram pressure.
At hypersonic speeds the thrust is limited due to less efficient use of energy of combustion process due to high temperature of the exhaust gases and relatively slow recombination of ionized gases. Another issue that is not effectively addressed is very high temperature in a combustor.

SUMMARY OF THE INVENTION
An objective of the invention is to provide a method of operating of the scramjet engine (or a dual mode engine that incorporates operation in a scramjet mode) having higher thrust and specific impulse at supersonic and hypersonic speeds. Sequence of combustible and non-combustible zones is generated by modulating the fuel injection rate with sequential ignition and energy transfer between combustible and non-combustible zones. Invention is based on a pressure-gain combustion being implemented without valves and can be used at supersonic and hypersonic speeds.
The proposed method of operating a scramjet engine includes providing supersonic (or hypersonic) airstream from the inlet of the engine to a combustor, injection of fuel in the airstream, mixing the injected fuel with the air, igniting and burning the injected fuel generating heat. The hot products of combustion are discharged through the nozzles producing thrust. Fuel is being injected with periodically varying flow rate forming a continuous series of zones in the airstream with subsequently higher and lower concentration of fuel in the fuel/air mixture. At the maximum fuel flow rate the injection of fuel produces stoichiometric (or substantially stoichiometric) mixture ratio in the airstream, thus forming a gaseous combustion zone (CZ) that moves with the airstream along the axis of the combustor towards the nozzle.
At the minimum (or zero) fuel flow rate the injection of fuel produces gaseous non-combustion zones (NCZ) in the airstream being devoid or substantially devoid of fuel.
Heat being produced by burning the fuel increases temperature and pressure in the moving CZ.
The CZ expands into the adjacent NCZs at the speed of sound while moving towards the nozzle.
Pressure in the NCZ increases until pressures in the adjacent CZ and NCZ are equalized. Full equalization of pressure is not necessary for implementation of this invention. Gases from CZs and NCZs are discharged through the nozzle generating thrust. Due to energy transfer between CZs and NCZs, the average velocity of gases being discharged through the nozzle reduces but overall thrust increases due to increased mass flow.
Thrust and specific impulse will increase due to pressure gain, associated higher discharge speed, and increased mass flow being discharged through the nozzle while having the same fuel flow rate as compared with the known methods of operation of the scramjet engine.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG.1 illustrates a method of operating a scramjet engine at the moment of beginning of formation of a new CZ and combustion and expansion of previously formed CZs.
FIG.2 through FIG.6 illustrate subsequent phases of combustion and expansion of CZs and compression of NCZs.

2 FIG.7 illustrates a method of operating a scramjet engine by forming a continuous combustion zone, specifically at the moment of beginning of formation of a new CZ and combastion and expansion of previously formed CZs.
= FIG.7 through FIG.12 illustrate subsequent phases of combustiont and expansion of CZs and compression of NCZs for the method of operating a scramjet engine comprising a process of forming a continuous combustion zone.
FIG. 13 shows distribution of pressure along the axis of a scramjet engine at the moment of the combustion and expansion process shown on FIG. 4.
FIG. 14 shows the change of pressure in the individual CZ and NCZ during movement from the inlet 40 to the nozzle 50 along the axis of a scramjet engine.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with a first embodiment of the invention, the proposed method of operating a scramjet engine includes providing supersonic (or hypersonic) airstream from the inlet of the engine to a combustor, injection of fuel in the airstream downstream of the inlet, mixing the injected fuel with the air, igniting by the ignition means, and burning the injected fuel generating heat. The hot products of combustion are discharged through the nozzles producing thrust. Fuel is being injected with periodically varying flow rate within predetermined minimum and maximum values and forming a continuous series of zones in the airstream with subsequently higher and lower concentration of fuel in the fuel/air mixture. At the maximum fuel flow rate the injection of fuel produces stoichiometric (or substantially stoichiometric) mixture ratio in the airstream, thus forming a gaseous combustion zone (CZ) that moves with the airstream along the axis of the combustor towards the nozzle. At the minimum (or zero) fuel flow rate the injection of fuel produces gaseous non-combustion zones (NCZ) in the airstream being devoid or substantially devoid of fuel. The NCZ moves with the airstream along the axis of the combustor towards the nozzle. Subsequently, the fuel flow rate increases to a maximum predetermined value forming a next CZ followed by the next NCZ, and the process continues.
The CZs and NCZs have common boundaries allowing mass and energy transfer between the CZs and NCZs.
Heat being produced by burning the fuel increases temperature and pressure in the moving CZ.
Combustion takes place as a detonation or a deflagration process. Due to increasing temperature, pressure of the combustion products in the CZ starts increasing and the CZ
expands into the adjacent NCZs at the speed of sound for deflagration combustion while moving towards the nozzle. Pressure in the NCZ increases until pressures in the adjacent CZ and NCZ are equalized.
Gases from CZs and NCZs are discharged through the nozzle generating thrust.
The speed of the airstream and the CZ in the combustor is supersonic (moving from the inlet to the nozzle). The pressure boundary of the CZ propagates towards the inlet of the engine at the speed of sound

3 =
against the flow of the supersonic airstream. Therefore, the higher pressure generated in the CZ
never reaches the inlet of the engine.
The process of operation of the engine according to the present invention is represented by two = processes: combustion in the CZs with temperature and pressure increase, partial expansion in the combustor and further expansion in the nozzle, and compression of the NCZ
with associated pressure increase in the combustor and expansion in the nozzle. If total mass flow of the airstream is divided equally between the CZs and NCZs, and assumed instantaneous pressure increase ratio in the CZs (for hydrogen fuel) is equal to 6, the overall pressure gain ratio will be equal to 3 when the pressure is equalized between the CZs and NCZs. Thrust and specific impulse will increase due to pressure gain, associated higher discharge speed, and increased by 100% mass flow being discharged through the nozzle while having the same fuel flow rate as compared with the known methods of operation of the scramjet engine. If total mass flow of the airstream is divided between the CZs and NCZs in a ratio of 1:2, and assumed instantaneous pressure increase ratio in the CZs (for hydrogen fuel) is equal to 6, the overall pressure gain ratio will be equal to 2 when the pressure is equalized between the CZs and NCZs.
Thrust and specific impulse will increase due to pressure gain, associated higher discharge speed, and increased by 200% mass flow being discharged through the nozzle while having the same fuel flow rate as compared with the known methods of operation of the scramjet engine.
FIG.1 through FIG. 6 illustrate sequence of forming the CZs and NCZs by injection of a fuel by a fuel injection means (a group of fuel injection nozzles 60) and their movement from the inlet 30 to the nozzle 50. FIG.1 shows initiation of forming of the CZ 1 downstream of the inlet 30.
The CZ 2 and CZ 3 are shown at different stages of combustion (the moment of ignition is not shown) and expansion in the combustor 40, and the NCZ 10, NCZ 11, and NCZ 12 at different stages of compression. The CZ 4 is shown at the stage of expansion in the nozzle 50. FIG. 2 and FIG.3 also show as the CZs and NCZs move along the engine axis in the combustor 40 towards the nozzle 50. FIG. 3 shows formation of a new NCZ 13 immediately downstream of the inlet 30. FIG.4, FIG.5, and FIG.6 sequentially show combustion and expansion of CZ
1, CZ 2, and CZ
3 and compression of NCZ 10, NCZ 11, and NCZ 12 with subsequent expansion in the nozzle 50 of CZ 4 (FIG. 4), compressed NCZ 12 (FIG. 4 and FIG. 5), and CZ 3 (FIG. 5 and FIG. 6). Each of the newly formed CZs is ignited during an expansion phase of the combustible zone formed immediately prior to said newly formed CZ allowing better pressure stability in the combustor 40 and better overall efficiency of the scramjet engine.
For better stability of the combustion process (flame stability) at least one continuous CZ is formed along the axis of the combustor filling part of the cross-sectional area of the combustor by continuous injection of fuel through one nozzle (or a group of the nozzles) in the range of 10% to 20% of the total fuel flow rate.
FIG. 7 through FIG. 12 illustrate a method of operation of a scramjet engine comprising formation of a continuous CZ along the axis of the combustor 40 that occupies part of the cross-sectional area of the combustor 40. FIG. 7 through FIG. 12 also illustrate sequence of forming the CZs and NCZs and their movement from the inlet 30 to the nozzle 50. FIG.7 shows initiation of forming of the CZ 1 downstream of the inlet 30. The CZ 2 and CZ 3 are shown at different

4 stages of combustion and expansion in the combustor 40, and the NCZ 10, NCZ
11, and NCZ 12 at different stages of compression. The CZ 4 is shown at the stage of expansion in the nozzle 50.
FIG. 8 and FIG.9 also show as the CZs and NCZs move along the engine axis in the combustor 40 towards the nozzle 50. FIG. 9 shows formation of a new NCZ 13 immediately downstream of the inlet 30. FIG. 10, FIG. 11, and FIG. 12 sequentially show combustion and expansion of CZ 1, CZ 2, and CZ 3 and compression of NCZ 10, NCZ 11, and NCZ 12 with subsequent expansion in the nozzle 50 of CZ 4 (FIG. 10), NCZ 12 (FIG.10 and FIG. 11), and CZ 3 (FIG. 11 and FIG.
12).
Depending on the speed of the aircraft, a ratio of the masses (mass flows) of CZs and NCZs, and the speed of airstream in the combustor, the overall improvement of the thrust and specific impulse varies between 30% and 110% for hydrogen or or hydrocarbons used as a fuel. These numbers indicate that the scramjet engine operated in accordance with this invention will have a specific impulse values similar to the specific impulse values of a turbojet engine.
The engine thrust can be controlled by changing the average fuel injection flow rate and frequency of modulation of the fuel injection flow rate, thus changing the ratio of mass flows of CZs and NCZs and average pressure in the combustor 40 before the nozzle 50.
Additional advantage of the present invention is lower average temperature in the combustor. Partial expansion of CZs in the combustor reduces potential for efficiency losses due to incomplete recombination of free radicals in the nozzle.
Distribution of pressure (not to scale) in the scramj et engine is shown on FIG. 13, at the moment of the CZs expansion shown on FIG.4. FIG. 14 shows the change of pressure in the individual CZ and NCZ during movement from the inlet 40 to the nozzle 50 along the axis of a scramjet engine.
Area between the inlet 30 and a combustion zone in the combustor 40 can also perform functions of an isolator (not shown on the drawings). Different design of the inlet can be used, including a diffuser, a Buseman type inlet, a conical inlet, an inlet using a magnetic field for deceleration of the airstream, or other types known in the art. The thermodynamic cycle used in this method of operation of the scramjet engine differs from the Brayton cycle because the heat addition process is not isobaric.
Supersonic airstream is defined as having speed greater than the speed of sound (above Mach 1) that includes hypersonic speeds (above Mach 5). Speed of airstream in the combustor is supersonic in the scramjet mode of operation.
The invention improves the performance of a scramjet engine and provides a higher thrust and greater specific impulse. Several embodiments of the present invention have been described and further details are understood by any person knowledgeable in this art and area of knowledge. It is understood that various modifications may be made without departing from the principles and scope of the present invention.

Claims

What is claimed is:

1. A method of operating a scramjet engine, said engine comprising a fuel injection means for injection of a fuel in an supersonic airstream, an ignition means, and in series of flow communication an inlet, a combustor, and an exhaust nozzle, comprising the steps of:
- providing said supersonic airstream from said inlet to said combustor;
- controllably injecting said fuel in said airstream generating a fuel/air mixture and forming a gaseous combustible zone in said airstream;
- forming a gaseous non-combustible zone being devoid or substantially devoid of said fuel and having a common boundary with said gaseous combustible zone;
- continuously repeating formation of said gaseous combustible zones and said gaseous non-combustible zones in said airstream;
- igniting said fuel/air mixture in said gaseous combustible zones generating a gaseous product of combustion and increasing temperature and pressure in said gaseous combustible zones;
- expanding said gaseous product of combustion in said gaseous combustible zones by compressing adjacent said gaseous combustible zones;
- expanding compressed said gaseous non-combustible zones and said gazeous product of combustion in said gaseous combustible zones in said exhaust nozzle.

2. The method of claim 1 including a further step of generating and positioning said gaseous combustible zones predominantly along an axis of said combustor.

3. The method of claim 1 including a further step of forming said gaseous combustible zones and said gaseous non-combustible zones by modulating a flow rate of injection of said fuel from a minimum predetermined value to a maximum predetermined value.

4. The method of claim 1 including a further step of injecting part of the total flow of said fuel continuously forming a continuous gaseous combustible zone along the axis of said combustor wherein said continuous gaseous combustible zone occupies part of cross-sectional area of said combustor.

5. The method of claim 1 wherein said inlet comprises a means for compression of said airstream.

6. The method of claim 5 wherein said means for compression of said airstream comprises a diffuser.

7. The method of claim 1 including a further step of sequentially forming said gaseous combustible zones and sequentially igniting a latest formed said gaseous combustible zone during an expansion phase of the combustible zone formed immediately prior to forming the latest formed gaseous combustible zone.