Pulse Combustion in a Traveling Wave Thermoacoustic Engine

2004 ◽  
Author(s):  
Nathan T. Weiland ◽  
Ben T. Zinn
Keyword(s):  
Power Output ◽  
Control Strategies ◽  
Combustion Process ◽  
Acoustic Power ◽  
Acoustic Energy ◽  
Cryogenic Temperatures ◽  
Thermoacoustic Engine ◽  
Engine Design ◽  
Pulse Combustion ◽  
Thermoacoustic Refrigeration

This work describes the use of pulse combustion for increasing the acoustic power output of a thermoacoustic engine. Such engines directly convert thermal energy into acoustic energy, which is typically used to drive a thermoacoustic refrigeration process that can achieve cryogenic temperatures without the use of moving parts. After a brief overview of thermoacoustics, the design of the thermoacoustic engine is discussed, and a perturbation analysis of the thermoacoustic energy fluxes and pulse combustion process is presented to quantify the extent to which pulse combustion has the potential to add to the engine’s acoustic power output. Guided by this analysis and the requirements of the engine design, various active and passive combustion control strategies for the reactant injection configuration and combustion chamber design are discussed.

Acoustic Radiation From Thick Laminated Cylindrical Shells With Sparse Cross Stiffeners

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Xiongtao Cao ◽  
Chao Ma ◽  
Hongxing Hua
Keyword(s):  
Cylindrical Shell ◽  
Radial Displacement ◽  
Acoustic Radiation ◽  
Periodic Structures ◽  
Cylindrical Shells ◽  
Acoustic Power ◽  
Acoustic Energy ◽  
Parallel Plates ◽  
Wavenumber Domain ◽  
Laminated Cylindrical Shells

A general method for predicting acoustic radiation from multiple periodic structures is presented and a numerical solution is proposed to find the radial displacement of thick laminated cylindrical shells with sparse cross stiffeners in the wavenumber domain. Although this method aims at the sound radiation from a single stiffened cylindrical shell, it can be easily adapted to analyze the vibrational and sound characteristics of two concentric cylindrical shells or two parallel plates with complicated periodic stiffeners, such as submarine and ship hulls. The sparse cross stiffeners are composed of two sets of parallel rings and one set of longitudinal stringers. The acoustic power of large cylindrical shells above the ring frequency is derived in the wavenumber domain on the basis of the fact that sound power is focused on the acoustic ellipse. It transpires that a great many band gaps of wave propagation in the helical wave spectra of the radial displacement for stiffened cylindrical shells are generated by the rings and stringers. The acoustic power and input power of stiffened antisymmetric laminated cylindrical shells are computed and compared. The acoustic energy conversion efficiency of the cylindrical shells is less than 10%. The axial and circumferential point forces can also produce distinct acoustic power. The radial displacement patterns of the antisymmetric cylindrical shell with fluid loadings are illustrated in the space domain. This study would help to better understand the main mechanism of acoustic radiation from stiffened laminated composite shells, which has not been adequately addressed in its companion paper (Cao et al., 2012, “Acoustic Radiation From Shear Deformable Stiffened Laminated Cylindrical Shells,” J. Sound Vib., 331(3), pp. 651-670).

Simulating Ultrasound Piezoelectric Power Transfer in the Near Field and Experimental Validations

2021 ◽  
Vol 05 ◽  
Author(s):  
Ammar Mohammed ◽  
Changki Mo ◽  
John Miller ◽  
David Lowry ◽  
Jassim Alhamid
Keyword(s):  
Energy Transfer ◽  
Lead Zirconate Titanate ◽  
Near Field ◽  
Acoustic Power ◽  
Acoustic Energy ◽  
Transfer Efficiency ◽  
Ultrasonic Power ◽  
Power Transfer ◽  
Piezoelectric Energy ◽  
Power Transfer Efficiency

Background: Acoustic power transfer is a method for wireless energy transfer to implanted medical devices that permits a greater range of separation between transmitter and receiver than is possible with inductive power transfer. In some cases, short-distance ultrasonic power transfer may be employed; consequently, their operation may be complicated by the near-field aspects of piezoelectric acoustic energy transfer. Methods: A piezoelectric energy transfer system consisting of two lead zirconate titanate (PZT) transducers was analyzed in this work using a combination of experimental measurements and computer simulations. Results: Simulations using the COMSOL Software package showed good agreement with a measured output voltage as a function of the distance between and alignment of the transmitter and receiver with water as a medium. We also simulated how operating frequency affects power transfer efficiency at various distances between the transmitter and receiver and found reasonable agreement with experiments. We report model predictions for power transfer efficiency as a function of the thickness and diameter of the transmitter and receiver. Conclusion: The results show that with proper choice of parameters, piezoelectric systems can provide high power transfer efficiency in the near-field region.

The High Performance Toroidal Engine Concept (HiPerTEC)

2011 ◽  
Author(s):  
Karl V. Hoose ◽  
Eric E. Shorey
Keyword(s):  
High Performance ◽  
Combustion Process ◽  
Thermodynamic Cycle ◽  
Unmanned Vehicles ◽  
Advanced Materials ◽  
Specific Power ◽  
Operating Characteristics ◽  
Free Piston ◽  
Engine Design ◽  
Swept Volume

The traditional reciprocating I.C. engine has evolved to a point where significant improvements in thermal efficiency and specific power are not expected. Modifications to existing engines may prove to be difficult and expensive while resulting in only marginal gains. In addition, most modifications result in added components that often increase cost and decrease reliability of the system as a whole. For applications requiring major advances in performance, such as unmanned vehicles, meeting mission requirements will likely stem from a revolutionary rather than an evolutionary engine design. The slider crank mechanism is a major impediment to the traditional reciprocating I.C. engine. Although this mechanism has been used for the past 100 years, it is very wasteful of the available energy supplied by the combustion process, where piston-liner interactions from this arrangement accounts for 50–70% of the total friction losses in this engine design. Eliminating the slider crank could significantly reduce friction losses and provide additional benefits that can increase fuel conversion efficiency. The HiPerTEC engine is an opposed, free-piston engine arranged in a toroidal configuration with two counter reciprocating sets of pistons. The counter reciprocating masses eliminate the vibration found in linear free-piston engines. The HiPerTEC employs a unique shared volume configuration where the swept volume is twice the physical cylinder volume. This attribute offers a significant increase in specific power, while the free-piston characteristics provide for substantial gains in thermodynamic cycle efficiency. An eight cylinder/chamber arrangement offers balanced operation in both two and four-stroke cycle modes to allow for a wide operating envelope. The final HiPerTEC configuration will require advanced materials to address lubrication and cooling requirements. This paper discusses the HiPerTEC design, operating characteristics, development progress to date, and the challenges that lie ahead.

Modeling of Thermoacoustic Resonators With Nonuniform Medium and Boundary Conditions

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Konstantin I. Matveev ◽  
Sungmin Jung
Keyword(s):  
Boundary Conditions ◽  
Acoustic Power ◽  
Solid Surfaces ◽  
Small Scale ◽  
Nonuniform Medium ◽  
Thermoacoustic Engine ◽  
Efficient Calculation ◽  
Thermoacoustic Engines ◽  
The Subject ◽  
Low Amplitude

The subject of this paper is modeling of low-amplitude acoustic fields in enclosures with nonuniform medium and boundary conditions. An efficient calculation method is developed for this class of problems. Boundary conditions, accounting for the boundary-layer losses and movable walls, are applied near solid surfaces. The lossless acoustic wave equation for a nonuniform medium is solved in the bulk of the resonator by a finite-difference method. One application of this model is for designing small thermoacoustic engines. Thermoacoustic processes in the regular-geometry porous medium inserted in resonators can be modeled analytically. A calculation example is presented for a small-scale thermoacoustic engine coupled with an oscillator on a flexing wall of the resonator. The oscillator can be used for extracting mechanical power from the engine. A nonuniform wall deflection may result in a complicated acoustic field in the resonator. This leads to across-the-stack variations of the generated acoustic power and local efficiency of thermoacoustic energy conversion.

Relationships Between Acoustic Radiation Modes, Complex Acoustic Power, and Radiation Efficiency

1997 ◽  
Author(s):  
Pei-Tai Chen
Keyword(s):  
Acoustic Radiation ◽  
Acoustic Power ◽  
Radiation Efficiency ◽  
Acoustic Energy ◽  
Normal Velocity ◽  
Far Field ◽  
Surface Complex ◽  
Surface Integral ◽  
Complex Power ◽  
Mass Spring

Abstract The paper explores the physical meaning underlying the surface complex acoustic power of a vibrating body, and its relationship to radiation efficiency under mono-frequency oscillations. The vibrating can be the entire wetted surface, or only a part of the surface with the remaining surface being held rigid. The surface complex acoustic power can be computed by the surface integral of pressure multiplying the complex conjugate of normal velocity. Based on the Gaussian Divergence theorem, it is shown that the real part of the complex power is the power radiated into a far field, while that the imaginary part pertains to the volume integral of the difference between the acoustic kinetic energy density with the potential energy density over the volume between the vibrating surface and the far field. The dynamical behavior of the acoustic field can be viewed as an infinite degree of freedom mass/spring/dashpot system, where the mass and spring are the inertia effects and acoustic compression effects of the acoustic particles and the dashpot is due to the plane wave relationship of the pressure waves at the far field that the acoustic energy propagates away from the acoustic field. By the model of the mass /spring/dashpot system, the phase angle of the complex acoustic power is identified as an indication of the ability of the vibrating surface to radiate acoustic power. The phase angle of the complex power depends on the distribution of the surface normal velocity. In order to study the normal velocity profile in relation to the ability to radiate acoustic energy, the previously established radiation mode (Chen and Ginsberg, 1995) is introduced and extended to situations in which a part of the surface is held rigid. An orthogonal condition for the velocity radiation modes is also established such that arbitrary velocity profiles can be decomposed into radiation modes. The acoustic modal radiation efficiency, defined as the radiated modal acoustic power divided by the surface integral of mean square normal velocity, is investigated in terms of the acoustic eigenvalue of that mode. Several different geometries of vibrating bodies are used to demonstrate the correlation of radiation efficiencies to eigenvalues of radiation modes, which include a rectangular baffled vibrating membrane, a box with only one of the six surfaces vibrating, a slender spheroidal body, and a spherical body. This correlation of acoustic radiation characteristics for different geometries is also demonstrated for a spheroidal body vibrating at some areas with other areas being held rigid.

Optimisation of Support Fuel Consumption Burning Low Heat Value Gas Using Controlled Combustion Oscillations

2015 ◽  
Author(s):  
Fabrice Giuliani ◽  
Vanessa Moosbrugger ◽  
Markus Stuetz ◽  
Thomas Leitgeb-Simandl
Keyword(s):  
Landfill Gas ◽  
Combustion Process ◽  
Methane Emissions ◽  
Inlet Temperature ◽  
Technical Solution ◽  
Ambient Conditions ◽  
Pulse Combustion ◽  
Combustion Technology ◽  
Heat Value ◽  
Approach Zero

The purpose of this work is to develop a new combustion technology to reduce the operation costs of thermal systems that burn low heat value gases. Landfill methane emission is a greenhouse gas source which can be defined and reduced. Landfill managing companies in Austria have adapted the latest regulations on methane emissions primarily by collecting and flaring off landfill gas, sometimes with energy recovery. Their concern is related to long-term landfills where the methane concentration by volume falls well below 20%. The costs to flare-off these gases are mostly driven by the use of support fuel to ensure combustion. A technical solution using the programme MethaNull (to approach zero methane emissions) is proposed to extend the combustion domain of gases with low heat value so that the amount of support fuel can be significantly reduced. This solution should fit a large range of LHV gases, for combustion at ambient conditions as well as under pressure at elevated inlet temperature conditions. The process has similarities with pulse combustion, where the combustion process benefits from a higher energy density and better heat transfer rates. As the forced pulsation is generated by a separate module, the methodology can be easily adapted or retrofitted for existing facilities. This paper covers the MethaNull programme, the burner design, the flow pulsation technology and its operation. A systematic comparison between steady state and oscillating combustion is presented.

Pulse Combustion Technology

2006 ◽  
Author(s):  
Gene Plavnik
Keyword(s):  
Combustion Process ◽  
Industrial Applications ◽  
Waste To Energy ◽  
State Variables ◽  
Pulse Combustion ◽  
Combustion Technology

Pulse combustion has been used in a variety of ways since first being discovered in 1877. This a combustion process that occurs under oscillatory conditions with changing state variables, such as pressure, temperature and velocity. This paper looks at the historic uses of pulse combustion, and it provides an overview of this unique process. Pulse combustion has been used to amplify thrust power with the German V-1 rockets. Pulse combustion has been used to optimize flame efficiencies, and it is now reemerging in many new industrial applications including some for Waste to Energy.

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