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The Pulse Detonation Engine Technology (PDET) Project within the Propulsion and Power R&T Base Program will evaluate the application of pulse detonation combustion technology to hybrid subsonic and supersonic gas turbine engines for commercial and military applications and combined cycle propulsion systems for access to space applications. This will be accomplished through the conceptual design of a number of possible system configurations followed by the "breadboard" demonstration of the critical sub-system(s) of the best candidate system(s). This propulsion system development process will be supported by the development of and demonstration of advanced detonative and non-detonative components required for system operation.
High frequency (>60 Hz) pulse detonation combustors have been developed over the past 5 years by several commercial firms and government laboratories in configurations consistent with aerospace propulsion applications. These combustors have an advantage over traditional near-constant pressure combustors in being more thermodynamically efficient by approximating constant volume (pressure gain) combustion. At the same time, engine systems based on these combustors are expected to be significantly simpler than current engine designs due to reduced air and fuel inlet pressure requirements.
Pulse detonation based propulsion systems can be broadly classified into three categories. "Pure" PDE's are the simplest systems consisting of an array of detonation tubes, an inlet, and a nozzle. Combined-cycle PDE systems consist of a PDE combined with a ramjet/scramjet flowpath or other propulsion cycle where each cycle operates in a different speed range to optimize overall system performance. Hybrid PDE's make use of detonative combustion in place of constant pressure combustion, usually in combination with turbomachinery. For any of these systems, the requirements for the components external to the detonation tubes are not well understood. The use of an unsteady detonative combustor will have major impacts on those components which need to be evaluated. The overall system performance is by the same token poorly characterized because of the unknown component performances. The PDET project will address these issues for combined-cycle and hybrid engine concepts, while the GRC/DFRC PDE Flight Research Project will be addressing these issues for the pure PDE intended for primarily military applications.
The development of pulse detonation based propulsion supports the following AT goals.
Revolutionize Aviation (Goal One)
Hybrid pulse detonation systems are thermodynamically more efficient than standard gas turbine systems as well as being more light weight, thus reducing CO2 emissions. Pulse detonation also offers new solution space in which to pursue reduced NO emissions.
Hybrid and combined cycle pulse detonation systems are expected to be efficiently operable to Mach numbers as high as 5 at a significantly lower cost than gas turbine engines due to simplified designs, lower part count, and reduced engineering material requirements.
Advance Space Transportation (Goal Two)
The potential for increased performance at reduced weight will provide additional vehicle weight fraction available for increasing health monitoring and more robust structural designs.
The combination of pulse detonation cycles with other air-breathing and rocket cycles offers increased overall system performance at lower weight and cost for access to space applications.
Pioneer Technology Innovation (Goal Three)
The mechanical simplicity of pulse detonation propulsion systems will enable shortened design cycle times. The system and cycle analysis tools being developed under this project will also aid in the design of new systems employing pulse detonation.
Pulse detonation engines operate on a different thermodynamic cycle than conventional gas turbine engines, offering different operational modes and performance levels at various flight conditions. Mission-specific PDE designs could enable new aerospace missions, depending on requirements.
Support of DOD Goals
The technology developed within PDET will be broadly applicable to single cycle "pure" PDE systems under consideration for a variety of DOD missions including missiles and tactical aircraft.
The development of pulse detonation based propulsion systems presents a series of difficult technical challenges due to the unsteady nature of the flow processes and the severe pressure/thermal environment created. Current design and analysis methodologies need to be significantly modified, or discarded altogether. The PDET project will look at those technologies critical to the successful design and demonstration of a viable PDE-based propulsion system consistent with NASA's aerospace propulsion goals.
The major deliverables at the end of the 3-year project duration are as follows.