Air-augmented rockets have specific thermodynamic limits on bypass ratio
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INSUFFICIENT LEANING
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The retrieved evidence mentions physical limits and design concepts associated with air-augmented rocket propulsion and bypass ratios, but it lacks specific quantitative or theoretical findings regarding thermodynamic limits on bypass ratios.
Development of a 12-Thrust Chamber Kerosene /Oxygen Primary Rocket Sub-System for an Early (1964) Air-Augmented Rocket Ground-Test System - NASA Technical Reports Server (NTRS) NTRS NTRS - NASA Technical Reports Server Search more_vert Collections About News Help Login Press Enter or click the Search button to begin your search. Back to Results Development of a 12-Thrust Chamber Kerosene /Oxygen Primary Rocket Sub-System for an Early (1964) Air-Augmented Rocket Ground-Test System Airbreathing/Rocket combined-cycle, and specifically rocket-based combined- cycle (RBCC), propulsion systems, typically employ an internal engine flow-path installed primary rocket subsystem.
To achieve acceptably short mixing lengths in effecting the "air augmentation" process, a large rocket-exhaust/air interfacial mixing surface is needed. This leads, in some engine design concepts, to a "cluster" of small rocket units, suitably arrayed in the flowpath. To support an early (1964) subscale ground-test of a specific RBCC concept, such a 12-rocket cluster was developed by NASA's Marshall Space Flight Center (MSFC). The small primary rockets used in the cluster assembly were modified versions of an existing small kerosene/oxygen water-cooled rocket engine unit routinely tested at MSFC.
Following individual thrust-chamber tests and overall subsystem qualification testing, the cluster assembly was installed at the U. S. Air Force's Arnold Engineering Development Center (AEDC) for RBCC systems testing. (The results of the special air-augmented rocket testing are not covered here.) While this project was eventually successfully completed, a number of hardware integration problems were met, leading to catastrophic thrust chamber failures. The principal "lessons learned" in conducting this early primary rocket subsystem experimental effort are documented here as a basic knowledge-base contribution for the benefit of today's RBCC research and development community.
Document ID 19990103941 Acquisition Source Marshall Space Flight Center Document Type Abstract Authors Pryor, D. (NASA Marshall Space Flight Center Huntsville, AL United States) Hyde, E. H. (NASA Marshall Space Flight Center Huntsville, AL United States) Escher, W. J. D. (Science Applications International Corp. Huntsville, AL United States) Date Acquired August 19, 2013 Publication Date January 1, 1999 Subject Category Spacecraft Propulsion And Power Report/Patent Number AIAA Paper 99-4896 Report Number: AIAA Paper 99-4896 Distribution Limits Public Copyright Work of the US Gov. Public Use Permitted. Available Downloads There are no available downloads for this record.
# Limits of bypass ratio in air-augmented (ejector-jet/ducted) rocket
Tags: rockets, atmosphere, design
- Score: 10
- Views: 2065
- Answers: 1
- Answered: yes
- Asked by: sevenperforce (431 rep)
- Asked: 2016-01-27
- Site: space
## Question
Air-augmented rockets have not historically been very successful. In most cases, adding a shroud around the outside of an existing rocket was a large weight cost in exchange for only a modest increase in thrust specific fuel consumption. Because they weren't optimized for using the air as reaction mass, most of the added thrust was the result of secondary combustion between the fuel-rich rocket exhaust and the atmospheric air, making them essentially very inefficient ramjets.
If, however, an air-augmented rocket engine were designed in an inside-out configuration with a central bypass rather than an external bypass, you'd could end up with a simpler, lower-drag design which could be scaled up and would likely be pretty high in efficiency.
Such a design could allow a really, really high bypass ratio, causing thrust specific fuel consumption to drop ridiculously low. The combination of really high thrust and really high specific impulse is p
Augmentation of Rocket Propulsion: Physical Limits - NASA Technical Reports Server (NTRS)
NTRS NTRS - NASA Technical Reports Server Search more_vert Collections About News Help Login Press Enter or click the Search button to begin your search. Back to Results Augmentation of Rocket Propulsion: Physical Limits Rocket propulsion is not ideal when the propellant is not ejected at a unique velocity in an inertial frame. An ideal velocity distribution requires that the exhaust velocity vary linearly with the velocity of the vehicle in an inertial frame. It also requires that the velocity distribution variance as a thermodynamic quantity be minimized. A rocket vehicle with an inert propellant is not optimal, because it does not take advantage of the propellant mass for energy storage. Nor is it logical to provide another energy storage device in order to realize variable exhaust velocity, because it would have to be partly unfilled at the beginning of the mission. Performance is enhanced by pushing on the surrounding because it increases the reaction mass and decreases the reaction jet velocity. This decreases the fraction of the energy taken away by the propellant and increases the share taken by the payload. For an optimal model with the propellant used as fuel, the augmentation realized by pushing on air is greatest for vehicles with a low initial/final mass ratio. For a typical vehicle in the Earth's atmosphere, the augmentation is seen mainly at altitudes below about 80 km. When drag is taken into account, there is a well-defined optimum size for the air intake. Pushing on air has the potential to increase the performance of rockets which pass through the atmosphere. This is apart from benefits derived from "air breathing", or using the oxygen in the atmosphere to reduce the mass of an on-board oxidizer. Because of the potential of these measures, it is vital to model these effects more carefully and explore technology that may realize their advantages. Document ID 1
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