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At least 19 records

All sources NASA NTRS DOE OSTI

NASA NTRS2018

Resonant Pulse Combustors: A Reliable Route to Practical Pressure Gain Combustion

Pressure Gain Combustion (PGC) defined: A fundamentally unsteady process whereby gas expansion by heat release is constrained, causing a rise in stagnation pressure and allowing work extraction by expansion to the initial pressure. A particular type of pressure gain combustion (PGC) device is described, which is under investigation at GRC (Glenn Research Center). The Resonant Pulse Combustor (RPC) has been largely overlooked due to its theoretically low performance. However, its practical performance is quite competitive with other PGC systems, and its physical simplicity is unmatched.

combustion↗

NASA NTRSDate not supplied

Resonant Pulse Combustors: A Reliable Route to Practical Pressure Gain Combustion

combustion↗

NASA NTRS2013

The Influence of Unsteadiness on the Analysis of Pressure Gain Combustion Devices

Pressure gain combustion (PGC) has been the object of scientific study for over a century due to its promise of improved thermodynamic efficiency. In many recent application concepts PGC is utilized as a component in an otherwise continuous, normally steady flow system, such as a gas turbine or ram jet engine. However, PGC is inherently unsteady. Failure to account for the effects of this periodic unsteadiness can lead to misunderstanding and errors in performance calculations. This paper seeks to provide some clarity by presenting a consistent method of thermodynamic cycle analysis for a device utilizing PGC technology. The incorporation of the unsteady PGC process into the conservation equations for a continuous flow device is presented. Most importantly, the appropriate method for computing the conservation of momentum is presented. It will be shown that proper, consistent analysis of cyclic conservation principles produces representative performance predictions.

Paxson, Daniel E.↗

NASA NTRS2012

Low Order Modeling Tools for Preliminary Pressure Gain Combustion Benefits Analyses

Pressure gain combustion (PGC) offers the promise of higher thermodynamic cycle efficiency and greater specific power in propulsion and power systems. This presentation describes a model, developed under a cooperative agreement between NASA and AFRL, for preliminarily assessing the performance enhancement and preliminary size requirements of PGC components either as stand-alone thrust producers or coupled with surrounding turbomachinery. The model is implemented in the Numerical Propulsion Simulation System (NPSS) environment allowing various configurations to be examined at numerous operating points. The validated model is simple, yet physics-based. It executes quickly in NPSS, yet produces realistic results.

Paxson, Daniel E.↗

NASA NTRSDate not supplied

Pressure-Gain Combustion for Gas Turbines

Pressure Gain Combustion (PGC) is under investigation as a means to improve the thermal efficiency of gas turbines. PGC is a fundamentally unsteady combustion process which, through some means of confinement, raises the total pressure of the working fluid relative to the initial process state. When implemented as a gas turbine combustor it yields a total pressure gain across the device instead of the typical loss seen in a conventional combustor. This pressure gain can significantly improve gas turbine performance. This presentation is a modified and updated version of a 2018 tutorial of the same name. It is tailored to a graduate student audience that is familiar with the PGC concept, but has focused entirely on a specific type of implementation. It will provide a brief review of the concept of PGC and why it's important. The majority of the presentation will describe the various approaches to implementation that are under investigation by the PGC community. Emphasis will be on strategies other than the one that the students are investigating.

Combustion↗

NASA NTRS2018

Determining the Pressure Gain of Pressure Gain Combustion

Over the past few decades, there has been significant research into propulsion concepts attempting to employ pressure gain combustion. Pressure gain combustion concepts to date have resulted in dynamic, non-uniform gas flows which are difficult to characterize and compare with more conventional forms of propulsion. This paper proposes a technique to derive for the pressure gain combustion device an equivalent, steady, uniform gas pressure that is available to do work or provide thrust, thereby providing a direct comparison with conventional propulsive devices.

combustion↗

NASA NTRS2018

Pressure-Gain Combustion for Gas Turbines

Pressure Gain Combustion (PGC) is under investigation as a means to improve the thermal efficiency of gas turbines. PGC is a fundamentally unsteady combustion process which, through some means of confinement, raises the total pressure of the working fluid relative to the initial process state. When implemented in a combustor it yields a total pressure gain across the device instead of the typical loss seen in a conventional combustor. This pressure gain can significantly improve gas turbine performance. The tutorial will provide an introduction to the concept of PGC. It will begin with a process description in fundamental thermodynamic terms, and will quantify potential benefits. The majority of the presentation will describe the various approaches to implementation that are under investigation by the PGC.

Paxson, Dan↗

NASA NTRS2017

Resonant Pulse Combustors: A Reliable Route to Practical Pressure Gain Combustion

A particular type of pressure gain combustion (PGC) device is described, which is under investigation at GRC. The Resonant Pulse Combustor (RPC) has been largely overlooked due to its theoretically low performance. However, its practical performance is quite competitive with other PGC systems, and its physical simplicity is unmatched.

detonation↗

NASA NTRS2018

Summary of Pressure Gain Combustion Research at NASA

NASA has undertaken a systematic exploration of many different facets of pressure gain combustion over the last 25 years in an effort to exploit the inherent thermodynamic advantage of pressure gain combustion over the constant pressure combustion process used in most aerospace propulsion systems. Applications as varied as small-scale UAV's, rotorcraft, subsonic transports, hypersonics and launch vehicles have been considered. In addition to studying pressure gain combustor concepts such as wave rotors, pulse detonation engines, pulsejets, and rotating detonation engines, NASA has studied inlets, nozzles, ejectors and turbines which must also process unsteady flow in an integrated propulsion system. Other design considerations such as acoustic signature, combustor material life and heat transfer that are unique to pressure gain combustors have also been addressed in NASA research projects. In addition to a wide range of experimental studies, a number of computer codes, from 0-D up through 3-D, have been developed or modified to specifically address the analysis of unsteady flow fields. Loss models have also been developed and incorporated into these codes that improve the accuracy of performance predictions and decrease computational time. These codes have been validated numerous times across a broad range of operating conditions, and it has been found that once validated for one particular pressure gain combustion configuration, these codes are readily adaptable to the others. All in all, the documentation of this work has encompassed approximately 170 NASA technical reports, conference papers and journal articles to date. These publications are very briefly summarized herein, providing a single point of reference for all of NASA's pressure gain combustion research efforts. This documentation does not include the significant contributions made by NASA research staff to the programs of other agencies, universities, industrial partners and professional society committees through serving as technical advisors, technical reviewers and research consultants.

Perkins, H. Douglas↗

NASA NTRS2018

Pressure Gain Combustion 101

This presentation contains notes for a 30 minute lecture that is part of an AIAA Special Session titled, Pressure Gain Combustion Overview: Principles, Operation, and Applications. The presentation covers an introduction to Pressure Gain Combustion (PGC) and the devices used to implement it. The concept of PGC is discussed on a thermodynamic basis, the performance benefits are demonstrated, and methods of implementation are described. These include devices such as Resonant Pulse Combustors, Internal Combustion Wave Rotors, Pulse Detonation Engines, and Rotating Detonation Engines.

pressure gain combustion↗

NASA NTRSDate not supplied

Pressure Gain Combustion Research at NASA

A brief non-technical program summary of NASA efforts in Pressure Gain Combustion research and development for both aeronautics and space applications for a Pressure Gain Combustion Panel session.

Propulsion↗

NASA NTRS2019

Pressure Gain Combustion for High Speed Propulsion

This presentation contains notes for a one-hour lecture that is part of a two-day AIAA Short Course titled, Hypersonic Air-Breathing Propulsion: Emerging Technologies and Cycles. The presentation covers an introduction to Pressure Gain Combustion (PGC) and its applicability to high speed airbreathing propulsion (HSABP). The concept of PGC is discussed on a thermodynamic basis, the performance benefits are demonstrated, and methods of implementation are described. These include devices such as Resonant Pulse Combustors, Internal Combustion Wave Rotors, Pulse Detonation Engines, and Rotating Detonation Engines.

pressure gain combustion↗

NASA NTRS2013

Time Averaged Pressure Measurement in Fundamentally Unsteady Pressure Gain Combustion Systems

Experimental results and analysis are presented on a technique for obtaining time averaged pressure in the harsh and highly unsteady environment of a pressure gain combustor. The technique utilizes a long, narrow, stand-off tube leading from the measurement point to a pressure transducer. The tube damps the fluctuations (which may result from strong shocks and/or detonations) and thermally isolates the transducer. The damping must be sufficient to ensure that net gasdynamic work exchange does not occur on the fluid in the stand-off tube, and it must be linear to insure that the time-averaged pressure at the transducer end is the same as that at the combustor end. The paper presents experimental and analytical results from two rigs which indicate that, using certain stand-off tube dimensions, these criteria are met. Physical rational for the tube dimensions (i.e., guidelines) are also presented.

detonation↗

NASA NTRS2012

Foundational Performance Analyses of Pressure Gain Combustion Thermodynamic Benefits for Gas Turbines

A methodology is described whereby the work extracted by a turbine exposed to the fundamentally nonuniform flowfield from a representative pressure gain combustor (PGC) may be assessed. The method uses an idealized constant volume cycle, often referred to as an Atkinson or Humphrey cycle, to model the PGC. Output from this model is used as input to a scalable turbine efficiency function (i.e., a map), which in turn allows for the calculation of useful work throughout the cycle. Integration over the entire cycle yields mass-averaged work extraction. The unsteady turbine work extraction is compared to steady work extraction calculations based on various averaging techniques for characterizing the combustor exit pressure and temperature. It is found that averages associated with momentum flux (as opposed to entropy or kinetic energy) provide the best match. This result suggests that momentum-based averaging is the most appropriate figure-of-merit to use as a PGC performance metric. Using the mass-averaged work extraction methodology, it is also found that the design turbine pressure ratio for maximum work extraction is significantly higher than that for a turbine fed by a constant pressure combustor with similar inlet conditions and equivalence ratio. Limited results are presented whereby the constant volume cycle is replaced by output from a detonation-based PGC simulation. The results in terms of averaging techniques and design pressure ratio are similar.

Paxson, Daniel E.↗

NASA NTRS2019

Defining and Measuring Pressure Gain

This presentation describes experimental and computational approaches to measuring pressure gain in the various devices currently under investigation wherein the working fluid undergoes a pressure gain combustion (PGC) process. Pressure gain is essentially a measure of the fluid availability for work or thrust production. The devices covered are Resonant Pulse Combustors, Internal Combustion Wave Rotors, Pulse Detonation Engines, and Rotating Detonation Engines. The approaches to pressure gain measurement differ in each device. However, all of the approaches attempt to address the fundamental challenges of PGC system measurement: the extremely harsh environment which makes instrumentation difficult, and the temporal and spatial non-uniformity associated with the exhausting flow which makes assigning a single value to the total pressure difficult. As part of the two-day 2019 International Constant Volume and Detonative Combustion Workshop, held in conjunction with the 2019 AIAA Propulsion and Energy Forum, this presentation is intended to foster discussion and eventual consensus on acceptable measurement methods.

pressure gain combustion↗

NASA NTRS2005

Ejector Enhanced Pulsejet Based Pressure Gain Combustors: An Old Idea With a New Twist

An experimental investigation of pressure-gain combustion for gas turbine application is described. The test article consists of an off-the-shelf valved pulsejet, and an optimized ejector, both housed within a shroud. The combination forms an effective can combustor across which there is a modest total pressure rise rather than the usual loss found in conventional combustors. Although the concept of using a pulsejet to affect semi-constant volume (i.e., pressure-gain) combustion is not new, that of combining it with a well designed ejector to efficiently mix the bypass flow is. The result is a device which to date has demonstrated an overall pressure rise of approximately 3.5 percent at an overall temperature ratio commensurate with modern gas turbines. This pressure ratio is substantially higher than what has been previously reported in pulsejet-based combustion experiments. Flow non-uniformities in the downstream portion of the device are also shown to be substantially reduced compared to those within the pulsejet itself. The standard deviation of total pressure fluctuations, measured just downstream of the ejector was only 5.0 percent of the mean. This smoothing aspect of the device is critical to turbomachinery applications since turbine performance is, in general, negatively affected by flow non-uniformities and unsteadiness. The experimental rig will be described and details of the performance measurements will be presented. Analyses showing the thermodynamic benefits from this level of pressure-gain performance in a gas turbine will also be assessed for several engine types. Issues regarding practical development of such a device are discussed, as are potential emissions reductions resulting from the rich burning nature of the pulsejet and the rapid mixing (quenching) associated with unsteady ejectors.

Paxson, Daniel E.↗

DOE OSTI2024

Experimental Study of Instabilities in Hydrogen-Air Fueled Rotating Detonation Combustion Presentation

Conventional gas turbine engines rely on an idealized constant pressure combustion process that in reality produces a pressure decrease as a result of viscous and other non-reversible losses. An alternative approach is rotating detonation combustion (RDC) which is a form of pressure gain combustion in which one or more detonation waves propagate an annular channel resulting in an increase in pressure across, subsequently providing greater work availability compared to deflagration ultimately leading to opportunities for greater thermodynamic efficiency when used in gas turbine engines that conventionally relies on constant. Modern gas turbine engines often rely on pre-mixed reactants to limit NOx emissions, although this may result in greater susceptibility to instabilities such as flashback and thermoacoustic oscillation, particularly for applications that utilize hydrogen as the fuel. Research in RDC has focused on non-premixed reactants thus limiting the occurrence of flashback, and high frequency detonation wave propagation (kHz) may interfere with the occurrence of thermoacoustic oscillations. Thermal NOx emissions are controlled through rapid combustion and sudden expansion of the working fluid. Although RDC may not be susceptible to instabilities encountered in conventional state of the art gas turbine engine combustion, there may be other mechanisms occurring that support instabilities that could be detrimental to performance.

Weber, Justin↗

DOE OSTI2025

Novel Design and Fabrication of a High Frequency Transient Heat Flux Sensor for Use in an RDE

Rotating detonation engine (RDE) combustion systems have been a topic of interest in the pressure gain combustion community for their benefits over traditional gas turbine engine combustors. However, cooling requirements for these engines are significantly higher and less predictable than non-detonating engines. To understand the high-speed heat transfer dynamics inside an RDE, a novel, high-frequency heat flux gage is presented. This study aims to design a robust, single-sided sensor that can withstand the high temperature and harsh environment of an RDE for extended durations. Sensor bench testing is performed using a hot plate as a heat source, and the sensor response is compared to a finite-element analysis (FEA) model. The sensor response is then tested inside a water-cooled RDE and the wall heat flux is compared to calorimetry data.

rotating detonation engines↗