07-05-2011, 12:17 PM
Presented By
Deepak S V Gowda
Arjun S
[attachment=13406]
SCRAMJET TECHNOLOGY
Abstract:
Hypersonic aircraft having a lateral arrangement of turbojet and Scramjet engines are disclosed. The Scramjet engines may be positioned laterally outboard of the turbojet engines. In one embodiment, the turbojet inlet and outlet openings may be covered during use of the Scramjet in order to provide compression and expansion ramps for the laterally adjacent Scramjet engines. The side-by-side arrangement of the turbojet and Scramjet engines reduces the vertical thickness of the aircraft, thereby reducing drag and potentially increasing performance.
Introduction:
A scramjet (supersonic combustion ramjet) is a variation of a ramjet. A pure scramjet remains supersonic throughout the combustion process and does not require a choking mechanism. Modern scramjet engines are able to seamlessly make the transition between ramjet and scramjet operation. A scramjet propulsion system is a hypersonic air breathing engine in which heat addition, due to combustion of fuel and air, occurs in the flow that is supersonic relative to the engine. In a conventional ramjet, engine the incoming supersonic airflow is decelerated to subsonic speeds by means of a multi-shock intake system and diffusion process. Fuel is added to the subsonic airflow, the mixture combusts and then re-accelerates through a mechanical choke to supersonic speeds. By contrast, the airflow in a pure scramjet remains supersonic throughout the combustion process and does not require a choking mechanism. Modern scramjet engines are able to seamlessly make the transition between ramjet and scramjet operation.
Historical Overview:
Scramjets have a long development history in the United States. In the 1940s, fundamental theoretical studies provided an understanding of high-velocity flow in ducts with heat addition. In the late 1950s, the first efforts to develop and demonstrate scramjet engines took place with Air Force, Navy and NASA laboratory experiments, which provided a foundation for the many development programs that followed. From the 1960s through today, many programs have had the objective of developing and demonstrating hydrogen and hydrocarbon-fueled scramjet engines. McClinton1 explored these developments and examined each generation along with its unique contributions to the understanding of supersonic combustion. Fry R. S2 provided a comprehensive look into advances in ramjet propulsion technology from subsonic to hypersonic flight speeds since the early 1900s. The following references provide insight into some of the key programs that have helped to evolve scramjet technology to its current state.
The most influential program in modern scramjet development was National Aero-Space Plane (NASP) program, which was established in 1986 to develop and fly a synergistically integrated low speed accelerator, ramjet and scramjet propulsion system. Designed to operate on hydrogen fuel, the X-30 (shown in Figure 1) was developed intensively over the years of the NASP program.
The original engine design from the NASP program, while significantly modified by NASA, was used as the foundation for power plant of the successful X-43A vehicle that flew at Mach 7 (5,000 miles/hour) in March 2004 3 as part of the Hyper-X program. The data collected during the flight of X-43A (Figure 2) is an important step in the validation of hypersonic air-breathing vehicle and engine design methods.
The United States Government has been furthering the development of hydrogen and hydrocarbon scramjets. The U.S. Air Force/NASA and Pratt & Whitney ground tested the first uncooled hydrocarbon-fueled scramjet engine at simulated flight Mach numbers of 4.5 and 6.5, as reported in Aviation Week & Space Technology/March 20014. Further development of this engine led to the ground demonstration of liquid JP7 hydrocarbon-fueled scramjet constructed from flight-weight (nickel-based alloys) fuel-cooled structures with the potential for satisfying requirements of future operational engines capable of powering missiles, aircraft, and access to space vehicles at sustained hypersonic speeds, as reported in Aviation Week & Space Technology/June 20035. This program was marked by the first successful test of a flight-weight scramjet operating on storable JP-7 fuel. The Defense Advanced Research Projects (DARPA)/U.S. Navy and Boeing/Aerojet/JHU have also ground demonstrated a JP10 hydrocarbon-fueled dual combustion ramjet, which was constructed from non-flight weight materials (primarily nickel alloys) and intended exclusively for hypersonic missiles, as reported in Aviation Week & Space Technology/September 20036.
What is a SCRAMJET?
A scramjet propulsion system is a hypersonic air breathing engine in which heat addition, due to combustion of fuel and air, occurs in the flow that is supersonic relative to the engine. In a conventional ramjet, engine the incoming supersonic airflow is decelerated to subsonic speeds by means of a multi-shock intake system and diffusion process. Fuel is added to the subsonic airflow, the mixture combusts and then re-accelerates through a mechanical choke to supersonic speeds. By contrast, the airflow in a pure scramjet remains supersonic throughout the combustion process and does not require a choking mechanism. Modern scramjet engines are able to seamlessly make the transition between ramjet and scramjet operation.
Why supersonic combustion?
As flight Mach numbers increase beyond Mach 5, the use of supersonic combustion can provides higher performance (i.e. specific impulse) due to inlet efficiency offset by higher Rayleigh losses associated with combustion (Figure 3). Crossover points between ramjet and scramjet operation indicate the benefits of operating in ramjet until Mach 5-6. The process of decelerating airflow at flight Mach 6 to subsonic speeds for combustion results in near-stagnation conditions, with attendant high pressures and heat transfer rates. The engine structural integrity dictates supersonic combustion past Mach 6. Somewhere between Mach 5 and 6, the combination of these factors indicates a switch to scramjet operation. The physics beyond Mach 8 dictates supersonic combustion.
Engine Description:
The description of geometrical configuration and design consideration are the most important requirements for understanding the aerophysics of hypersonic air-breathing engines. The most closely integrated engine/vehicle integration is observed in the case of a propulsion system with a scramjet engine. The scramjet engine occupies the entire lower surface of the vehicle body. Scramjet propulsion system consists of five major engine and two vehicle components: internal inlet, isolator, combustor, internal nozzle and the fuel supply subsystem. The vehicle forebody is an essential part of the air induction system while the vehicle aftbody is a critical part of the nozzle component. These are described schematically in Figure 4.
The primary purpose of the high-speed air induction system, comprised of the vehicle forebody and internal inlet, is to capture and compress air for processing by the remaining components of the engine. In a conventional jet engine, the inlet works in combination with the mechanical compressor to provide the necessary high pressure for the entire engine. For vehicles flying at high supersonic or hypersonic speeds, adequate compression can be achieved without a mechanical compressor. The forebody provides the initial external compression and contributes to the drag and moments of the vehicle. The internal inlet compression provides the final compression of the propulsion cycle. The forebody along with the internal inlet is designed to provide the required mass capture and aerodynamic contraction ratio at maximum inlet efficiency. The air in the captured stream tube undergoes a reduction in Mach number with an attendant increase in pressure and temperature as it passes through the system of shock waves in the forebody and internal inlet. It typically contains non-uniformities, due to oblique reflecting shock waves, which can influence the combustion process. Scramjet air induction phenomena include vehicle bow shock and isentropic turning Mach waves, shock-boundary layer interaction, non-uniform flow conditions, and three-dimensional effects.
Fuel Choice:
Fuel choice, between hydrocarbon and hydrogen, is typically driven by heat-sink requirements and vehicle system-level requirements (Figure 5). Missiles and short-range aircraft may use hydrocarbon fuels for their storability and volumetric energy density. Long cruise range aircraft or space access systems tend toward hydrogen because it has superior energy release per pound of fuel, and heat absorption capability, critical to actively cooled structures exposed to scramjet environment.
Deepak S V Gowda
Arjun S
[attachment=13406]
SCRAMJET TECHNOLOGY
Abstract:
Hypersonic aircraft having a lateral arrangement of turbojet and Scramjet engines are disclosed. The Scramjet engines may be positioned laterally outboard of the turbojet engines. In one embodiment, the turbojet inlet and outlet openings may be covered during use of the Scramjet in order to provide compression and expansion ramps for the laterally adjacent Scramjet engines. The side-by-side arrangement of the turbojet and Scramjet engines reduces the vertical thickness of the aircraft, thereby reducing drag and potentially increasing performance.
Introduction:
A scramjet (supersonic combustion ramjet) is a variation of a ramjet. A pure scramjet remains supersonic throughout the combustion process and does not require a choking mechanism. Modern scramjet engines are able to seamlessly make the transition between ramjet and scramjet operation. A scramjet propulsion system is a hypersonic air breathing engine in which heat addition, due to combustion of fuel and air, occurs in the flow that is supersonic relative to the engine. In a conventional ramjet, engine the incoming supersonic airflow is decelerated to subsonic speeds by means of a multi-shock intake system and diffusion process. Fuel is added to the subsonic airflow, the mixture combusts and then re-accelerates through a mechanical choke to supersonic speeds. By contrast, the airflow in a pure scramjet remains supersonic throughout the combustion process and does not require a choking mechanism. Modern scramjet engines are able to seamlessly make the transition between ramjet and scramjet operation.
Historical Overview:
Scramjets have a long development history in the United States. In the 1940s, fundamental theoretical studies provided an understanding of high-velocity flow in ducts with heat addition. In the late 1950s, the first efforts to develop and demonstrate scramjet engines took place with Air Force, Navy and NASA laboratory experiments, which provided a foundation for the many development programs that followed. From the 1960s through today, many programs have had the objective of developing and demonstrating hydrogen and hydrocarbon-fueled scramjet engines. McClinton1 explored these developments and examined each generation along with its unique contributions to the understanding of supersonic combustion. Fry R. S2 provided a comprehensive look into advances in ramjet propulsion technology from subsonic to hypersonic flight speeds since the early 1900s. The following references provide insight into some of the key programs that have helped to evolve scramjet technology to its current state.
The most influential program in modern scramjet development was National Aero-Space Plane (NASP) program, which was established in 1986 to develop and fly a synergistically integrated low speed accelerator, ramjet and scramjet propulsion system. Designed to operate on hydrogen fuel, the X-30 (shown in Figure 1) was developed intensively over the years of the NASP program.
The original engine design from the NASP program, while significantly modified by NASA, was used as the foundation for power plant of the successful X-43A vehicle that flew at Mach 7 (5,000 miles/hour) in March 2004 3 as part of the Hyper-X program. The data collected during the flight of X-43A (Figure 2) is an important step in the validation of hypersonic air-breathing vehicle and engine design methods.
The United States Government has been furthering the development of hydrogen and hydrocarbon scramjets. The U.S. Air Force/NASA and Pratt & Whitney ground tested the first uncooled hydrocarbon-fueled scramjet engine at simulated flight Mach numbers of 4.5 and 6.5, as reported in Aviation Week & Space Technology/March 20014. Further development of this engine led to the ground demonstration of liquid JP7 hydrocarbon-fueled scramjet constructed from flight-weight (nickel-based alloys) fuel-cooled structures with the potential for satisfying requirements of future operational engines capable of powering missiles, aircraft, and access to space vehicles at sustained hypersonic speeds, as reported in Aviation Week & Space Technology/June 20035. This program was marked by the first successful test of a flight-weight scramjet operating on storable JP-7 fuel. The Defense Advanced Research Projects (DARPA)/U.S. Navy and Boeing/Aerojet/JHU have also ground demonstrated a JP10 hydrocarbon-fueled dual combustion ramjet, which was constructed from non-flight weight materials (primarily nickel alloys) and intended exclusively for hypersonic missiles, as reported in Aviation Week & Space Technology/September 20036.
What is a SCRAMJET?
A scramjet propulsion system is a hypersonic air breathing engine in which heat addition, due to combustion of fuel and air, occurs in the flow that is supersonic relative to the engine. In a conventional ramjet, engine the incoming supersonic airflow is decelerated to subsonic speeds by means of a multi-shock intake system and diffusion process. Fuel is added to the subsonic airflow, the mixture combusts and then re-accelerates through a mechanical choke to supersonic speeds. By contrast, the airflow in a pure scramjet remains supersonic throughout the combustion process and does not require a choking mechanism. Modern scramjet engines are able to seamlessly make the transition between ramjet and scramjet operation.
Why supersonic combustion?
As flight Mach numbers increase beyond Mach 5, the use of supersonic combustion can provides higher performance (i.e. specific impulse) due to inlet efficiency offset by higher Rayleigh losses associated with combustion (Figure 3). Crossover points between ramjet and scramjet operation indicate the benefits of operating in ramjet until Mach 5-6. The process of decelerating airflow at flight Mach 6 to subsonic speeds for combustion results in near-stagnation conditions, with attendant high pressures and heat transfer rates. The engine structural integrity dictates supersonic combustion past Mach 6. Somewhere between Mach 5 and 6, the combination of these factors indicates a switch to scramjet operation. The physics beyond Mach 8 dictates supersonic combustion.
Engine Description:
The description of geometrical configuration and design consideration are the most important requirements for understanding the aerophysics of hypersonic air-breathing engines. The most closely integrated engine/vehicle integration is observed in the case of a propulsion system with a scramjet engine. The scramjet engine occupies the entire lower surface of the vehicle body. Scramjet propulsion system consists of five major engine and two vehicle components: internal inlet, isolator, combustor, internal nozzle and the fuel supply subsystem. The vehicle forebody is an essential part of the air induction system while the vehicle aftbody is a critical part of the nozzle component. These are described schematically in Figure 4.
The primary purpose of the high-speed air induction system, comprised of the vehicle forebody and internal inlet, is to capture and compress air for processing by the remaining components of the engine. In a conventional jet engine, the inlet works in combination with the mechanical compressor to provide the necessary high pressure for the entire engine. For vehicles flying at high supersonic or hypersonic speeds, adequate compression can be achieved without a mechanical compressor. The forebody provides the initial external compression and contributes to the drag and moments of the vehicle. The internal inlet compression provides the final compression of the propulsion cycle. The forebody along with the internal inlet is designed to provide the required mass capture and aerodynamic contraction ratio at maximum inlet efficiency. The air in the captured stream tube undergoes a reduction in Mach number with an attendant increase in pressure and temperature as it passes through the system of shock waves in the forebody and internal inlet. It typically contains non-uniformities, due to oblique reflecting shock waves, which can influence the combustion process. Scramjet air induction phenomena include vehicle bow shock and isentropic turning Mach waves, shock-boundary layer interaction, non-uniform flow conditions, and three-dimensional effects.
Fuel Choice:
Fuel choice, between hydrocarbon and hydrogen, is typically driven by heat-sink requirements and vehicle system-level requirements (Figure 5). Missiles and short-range aircraft may use hydrocarbon fuels for their storability and volumetric energy density. Long cruise range aircraft or space access systems tend toward hydrogen because it has superior energy release per pound of fuel, and heat absorption capability, critical to actively cooled structures exposed to scramjet environment.
