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Design and testing of a wave-rotor constant-volume combustor achieved stable combustion at near-atmospheric inlet conditions and demonstrated the potential of pressure-gain combustion using a wave ...

This work presents implementation of numerical analysis and topology optimization techniques for redesigning traditional injection molding tools. Traditional injection molding tools have straight cooling channels, drilled into a solid body of the core and cavity. The cooling time constitutes a large portion of the total production cycle that needs to be reduced as much as possible in order to bring in a significant improvement in the overall business of injection molding industry. Incorporating conformal cooling channels in the traditional dies is a highly competent solution to lower the cooling time as well as improve the plastic part quality. In this paper, the thermal and mechanical behavior of cavity and core with conformal cooling channels are analyzed to find an optimum design for molding tools. The proposed design with conformal cooling channels provides a better alternative than traditional die designs with straight channels. This design is further optimized using thermo-mechanical topology optimization based on a multiscale approach for generating sound porous structures. The implemented topology optimization results in a light-weight yet highly effective die cavity and core. The reduction in weight achieved through the design of dies with porous structures is meant to facilitate the adoption of additive manufacturing for die making by the tooling industry.

This paper describes best practice and effective techniques in international administration (IA) within the Globally Engaged University. The Globally Engaged University is one that continually promotes, communicates, initiates, controls, monitors, and evaluates international activity in at least one of its major academic units [5]. Emphasis is IA within engineering and technology higher education. Nonetheless, the description of best practice in IA is also applicable to various other academic disciplines at the Globally Engaged University. In describing best practice in IA, the paper adds the perspective of the authors' applied experience. The combined IA experience among the coauthors includes successful international programs in South and Southeast Asia, the European Union, and the USA. Three of the co-authors are senior administrators within one and the same university in the USA. Another co-author is a senior administrator at a university in Malaysia. Broadening the perspective yet further, another team member is an IA specialist at a Globally Engaged University in Poland. The authors compare and contrast techniques and organizational structure common to IA at three differing locations: USA, Malaysia, and Poland as a central member state of the European Union.

Natural gas substitution for diesel can result in significant reductions in pollutant emissions. In addition, with a high ignition temperature and relatively low reactivity, natural gas can enable promising approaches to combustion engine design. In particular, the combination of low-reactivity natural gas and high-reactivity diesel may allow for optimal operation as a reactivity-controlled compression ignition (RCCI) engine, which has potential for high efficiency and low emissions. In this computational study, a lean mixture of natural gas is ignited by direct injection of diesel fuel in part-load operating condition in a model of the heavy-duty CAT3401 diesel engine. A multi-dimensional simulation was performed using a finite-volume computational code for fuel spray and combustion processes in the Reynolds-averaged Navier-Stokes (RANS) framework. Adaptive mesh refinement (AMR) and multi-zone reaction modeling enables simulation in a reasonable time. The latter approach avoids expensive kinetic calculations in every computational cell, with considerable speedup. The model produces encouraging agreement between the simulation and experimental data. For reasonable accuracy and computation cost, a minimum cell size of 0.2 millimeters is suggested for the natural gas-diesel (NGD) dual-fuel engine. The results reveal that in part-load operating condition, much of the CH4, which is used as surrogate fuel for natural gas, cannot burn. The main goal of this research work is to assess the possibility to improve the performance of Caterpillar-3401 engine in NGD dual-fuel operation by in-cylinder modification strategies. The results reveal that among different strategies, double injection of diesel fuel with an early main injection can reduce the unburned hydrocarbon (UHC) emission significantly.

For some decades, efforts have been made to exploit nonsteady combustion and gas dynamic phenomenon. The theoretical potential of nonsteady-flow machines has led to the investigation of various oscillatory flow devices such as pulse detonation engines, wave rotors, pulse jets, and nonsteady ejectors. This paper aims to provide a progress review of past and current research in developing a particular combustion concept: the wave rotor combustor. This pressure-gain combustor appears to have considerable potential to enhance the performance and operating characteristics of gas turbine and jet engines. After attempts in the mid-twentieth century were thwarted by mechanical problems and technical challenges identified herein, recent successes in Switzerland and efforts in the United States benefited from design expertise developed with pressure-exchange wave rotors. The history, potential benefits, past setbacks, and existing challenges and obstacles in developing these nonsteady combustors are reviewed. This review focuses on recent efforts that seek to improve the performance and costs of future propulsion and power-generation systems.

A simultaneous consideration of the thermodynamic, economic and emission criteria regarding both CO 2 and NO x emissions of a distributed combined heating, cooling and power generation (tri-generation) system in an urban residential area in Beijing has been realized through thermo-economic optimization. Technologies such as gas turbine, internal combustion engine, absorption chiller and gas boiler are considered as options of the plant optimum configuration. System Net Present Value (NPV) is taken as the objective to be maximized. The presented mixed integer and non-linear programming (MINLP) problem is solved by a Genetic Algorithms (GAs) optimizer. The optimal plant configurations are found with the consideration of system configuration, design and operation under different economic and environmental legislation contexts.

Significant performance enhancement of microturbines is predicted by implementing various wave-rotor-topping cycles. Five different advantageous cases are considered for implementation of a four-port wave rotor into two given baseline engines. In these thermodynamic analyses, the compressor and turbine pressure ratios and the turbine inlet temperatures are varied, according to the anticipated design objectives of the cases. Advantages and disadvantages are discussed. Comparison between the theoretic performance of wave-rotor-topped and baseline engines shows a performance enhancement up to 34%. General design maps are generated for the small gas turbines, showing the design space and optima for baseline and topped engines. Also, the impact of ambient temperature on the performance of both baseline and topped engines is investigated. It is shown that the wave-rotor-topped engines are less prone to performance degradation under hot-weather conditions than the baseline engines.

Synovial joints are loaded by weight bearing, stretching, and fluid-driven shear. To simulate in vitro fluid-driven shear, we developed an "oscillating Couette flow mechanical shear loader". Oscillating Couette flow mimics relative motion of articular surfaces; hence, characterizing flow-induced shear by the loader enhances understanding of mechanotransduction in the joint tissue. Here, the analytical and computational models for an oscillating Couette flow were used to predict time-varying shear distribution on a plate surface, applying numerical simulation to evaluate the effects of finite plate dimension in a 2D flow. Shear stress on the plate was significantly different from that in simpler models (unbounded plates and viscous low-frequency flow). High-stress spots appeared near the leading and trailing edges of a moving plate, and a relatively uniform shear region was restricted to the interior area. Stress prediction in an example experimental geometry is presented, where the frequency and finite width effects are feasibly accounted.

A wave rotor may be used as a pressure-gain combustor, effecting wave compression and expansion, and intermittent cone ned combustion, to enhance gas-turbine engine performance. It will be more compact than an equivalent pressure-exchange wave-rotor system, but will have similar thermodynamic and mechanical characteristics. Because the allowable turbine blade temperature limits overall fuel ‐air ratio to sube ammable values, premixed stratie cation techniques are necessary to burn hydrocarbon fuels in small engines with compressor discharge temperatures well below autoignition conditions. One-dimensional, nonsteady numerical simulations of stratie ed-charge combustion are performed using an eddy-diffusivity turbulence model and a simple reaction model incorporating a e ammability limit temperature. For good combustion efe ciency, a stratie cation strategy is developed that concentrates fuel at the leading and trailing edges of the inlet port. Rotor and exhaust temperature proe les and performance predictions are presented at three representative operating conditions of the engine: full design load, 40% load, and idle. Theresults indicate thatpeak local gas temperatures will causeexcessivetemperaturesintherotorhousingunlessadditionalcoolingmethodsareused. Therotortemperaturewillbeacceptable,but the pattern factor presented to the turbine may be of concern, depending on exhaust duct design and duct ‐rotor interaction.

A wave-rotor pressure-gain combustor (WRPGC) ideally provides constant-volume combustion and enables a gas turbine engine to operate on the Humphrey-Atkinson cycle. It exploits pressure (both compression and expansion) waves and confined propagating combustion to achieve pressure rise inside the combustor. This study first presents thermodynamic cycle analysis to illustrate the improvements of a gas turbine engine possible with a wave rotor combustor. Thereafter, non-steady reacting simulations are used to examine features and characteristics of a combustor rig that reproduces key features of a WRPGC. In the thermodynamic analysis, performance parameters such as thermal efficiency and specific power are estimated for different operating conditions (compressor pressure ratio and turbine inlet temperature). The performance of the WRPGC is compared with the conventional unrecuperated and recuperated engines that operates on the Brayton cycle. Fuel consumption may be reduced substantially with WRPGC introduction, while concomitantly boosting power. Simulations have been performed of the ignition of propane by a hot gas jet and subsequent turbulent flame propagation and shock-flame interaction.

Early drop out and poor retention rates are a major challenge to engineering education, which in many institutions have prompted a focus on improved first-year experiences. Retention and contributing learning challenges persists into the middle years, particularly when students confront the first engineering science courses in their major field. Students often perceive these courses as too abstract, intended to weed them out, and not meaningfully connected to their professional aspirations. A proven approach to improve student learning, self-efficacy, motivation, and retention is the use of active learning, including problems and projects [1–4]. Despite evidence of the benefits of active learning, engineering schools and faculty members have inadequate incentives to experiment with non-traditional approaches [5].

The application of problem-based learning (PBL) to undergraduate engineering education has emerged as an area of research interest over the past few decades, although it does not appear to be the dominant pedagogy for most engineering programs. A related form of active learning is project-enhanced learning (PEL), specifically designed to enhance but not replace traditional teaching methods in engineering science courses. The perceptions of instructors who attempt PEL were examined using extended-term mixed-method approaches, seeking to examine perceived benefits and barriers to PEL as an intervention for improved student learning. Instructors expressed satisfaction with improved student motivation, interaction, and socialization, which may help with student success and retention in engineering. Instructors also expressed concern about losing focus on the challenging analytical course topics, but were able to achieve appropriate balance by designing project tasks to align well with the topics and limiting non-aligned project activity.

Renewed interest in pressure gain combustion applied as a replacement of conventional combustors within gas turbine engines creates the potential for greatly increased capability engines in the marine power market segment. A limited analysis has been conducted to estimate the degree of improvements possible in engine thermal efficiency and specific work for a type of wave rotor device utilizing these principles. The analysis considers a realistic level of component losses. The features of this innovative technology are compared with those of more common incremental improvement types of technology for the purpose of assessing potentials for initial market entry within the marine gas turbine market. Both recuperation and non-recuperation cycles are analyzed. Specific fuel consumption improvements in excess of 35% over those of a Brayton cycle are indicated. The technology exhibits the greatest percentage potential in improving efficiency for engines utilizing relatively low or moderate mechanical compression pressure ratios. Specific work increases are indicated to be of an equally dramatic magnitude. The advantages of the pressure gain combustion approach are reviewed as well as its technology development status.

A procedure to design a preliminary wave rotor cycle for any application is presented. To complete a cycle with heat addition there are two separate—but related—design steps that must be performed. Selection of a wave configuration determines the allowable amount of heat added in any case, and the ensuing wave pattern requires associated pressure discharge conditions to allow the process to be made cyclic. This procedure, when applied, gives a first estimate of the cycle performance and the necessary information for proceeding to the next step in the design process, namely, the application of a characteristic-based or other appropriate detailed onedimensional wave calculation that locates more precisely the proper porting around the periphery of the wave rotor. Examples of the design procedure are given to demonstrate its utility and generality. These examples also illustrate the large gains in performance that might be realized with the use of wave rotor enhanced propulsion cycles.

A review of recent testing has been performed to assess the viability of a wave-rotorbased pressure-gain combustor. Tests accomplished in 2009 at the Purdue Zucrow lab on the Wave Rotor Combustor Rig (WRCR) provide basic information on the combustion processes achievable in a wave rotor passage. During a 30 day test period, 34 successful tests were completed, the longest of which was a 3-second firing was completed which totaled nearly 2,000 individual combustion events. Analysis of the results indicated stable combustor operation. The operability of the device is assessed regarding stability and combustion speeds. Agreement with predicted operation is examined. Potential for successful integration into a gas turbine as a replacement of a conventional combustor is addressed.

The wave rotor combustor can significantly improve gas turbine engine performance by implementing constant-volume combustion. The periodically open and closed combustor complicates thermodynamic analysis, and key cycle parameters depend on complex gas dynamics. In this study, a consistent air-standard aerothermodynamic model with variable specific heat is established. An algebraic model of the dominant gas dynamics estimates fill fraction and internal wave compression for typical port designs, using a relevant flow Mach number to represent wave amplitudes of compression and expansion. Nonlinear equations for thermodynamic state variables are solved numerically by Newton-Raphson iteration. Performance measures and key operating conditions are predicted, and a quasi-one-dimensional computational model is used to evaluate the usefulness of the algebraic model.

Design and evaluation of the wave rotor as a combustion device requires estimates of the performance as a function of operating conditions and gasdynamic processes occurring inside the rotor channels. An analytical model based on a combination of thermodynamic and gasdynamic approaches is established for assessing quantitatively the influence of various design parameters and operating conditions on the wave rotor performance. Performance results expressed by specific cycle work, thermal efficiency, and specific fuel consumption are calculated as functions of several design parameters. The results indicate that significant performance improvements are possible using combustion wave rotors, making this technology desirable for next generation of gas turbines and propulsion systems.

This study is aimed to make a systematic comparison between performance of pulse detonation engines (PDE) and detonative wave rotors, using a quasi-one dimensional numerical model. The model incorporates almost all major losses including viscous, heat transfer, port mixing, gradual opening and closing of channels losses. Two scenarios of (a) instantaneous detonation and (b) deflagration to detonation transition (DDT) for each engine are considered and flow field of these cases are compared with each other. To make flow field comparisons, the same rotor length, fuel distribution, inlet port size, and frequency are used for both engines. As expected, the outlet flow of the detonative wave rotor is shown to be more uniform than of the PDE, due to its fast rotation and large number of channels. This is more acceptable to turbine blades for gas turbine applications and may provide the combustor for new generation of aircraft engines. Higher pressure gain is produced in the detonative wave rotor configuration due to the mixture pre-compression by a hammer shock. Other advantages of the wave rotor approach are discussed.

This work is aimed to investigate the fundamental combustion and reignition process in semi-intermittent pressure-gain combustors for gas turbine applications. A combustion-torch ignition method is used to simulate reignition in one tube of a pressure-gain combustor by employing burned gas produced in a pre-chamber combustor. Numerical flow and combustion simulations are performed to understand and guide preliminary experimental results. The computational fluid dynamics code StarCD® is used to predict internal flow and combustion upon attempted ignition by a hot gas jet. This study provides improved understanding of the complex, sub-millisecond processes involved: transient supersonic jet mixing, ignition, highly turbulent flame propagation, and shock-flame interaction in near-wall region. The results are useful for successful design of rotary pressure gain combustors or internal combustion wave rotors under various operating conditions.Copyright © 2006 by ASME

Efficient cooling system designs are required for the modern diesel truck engine to meet new standards of increased efficiency and reduced emissions. Often, emissions reduction requires substantial cooled exhaust gas recirculation (EGR) to decrease peak combustion temperatures. This extra heat rejection imposes additional costs on the cooling system, and may not comply with application space constraints. Space and cost constraints require minimization of EGR cooler size and the risks from coolant boiling and exhaust condensation, while restraining growth in radiator frontal area, pumping power, and fan power. These objectives are usually contradictory, and a careful optimization is needed. This paper examines the effect of a coolant flow rate and peak temperature on these objectives, in parallel-flow and counter-flow arrangements of EGR cooler systems. It is concluded that these systems are likely to be inadequate, and alternative configurations may be necessary.Copyright © 2005 by ASME

Pressure gain combustion in a wave rotor approaching the thermodynamic ideal of constant volume combustion has been proposed to significantly enhance the performance of gas turbine engines. A computational and experimental program is currently being conducted to investigate the combustion process and performance of a wave rotor with detonative and near-detonative internal combustion. An innovative and flexible preliminary design of the test rig is presented to demonstrate the operation and performance of the system. A preliminary design method based on a sequence of computational models is used to design wave processes for testing in the rig and to define rig geometry and operating conditions. The operating cycle allows for propagation of the combustion front from the exit end of the combustion channel to the inlet end. This is similar to and motivated by the Constant Volume Combustor (CVC) concept that seeks to produce a relatively uniform set of outflow conditions in both spatial and time coordinates.Copyright © 2004 by ASME

The objective of this paper is to provide a succinct review of past and current research in developing wave rotor technology. This technology has shown unique capabilities to enhance the performance and operating characteristics of a variety of engines and machinery utilizing thermodynamic cycles. Although there have been numerous efforts in the past dealing with this novel concept, this technology is not yet widely used and barely known to engineers. Here, an attempt is made to summarize both the previously reported work in the literature and ongoing efforts around the world. The paper covers a wide range of wave rotor applications including the early attempts to use wave rotors, its successful commercialization as supercharges for car engines, research and development for gas turbine topping, and other developments. The review also pays close attention to more recent efforts: utilization of such devices in pressure-gain combustors, ultra-micro gas turbines, and water refrigeration systems, highlighting possible further efforts on this topic. Observations and lessons learnt from experimental studies, numerical simulations, analytical approaches, and other design and analysis tools are presented.Copyright © 2004 by ASME

In the last two decades, jet engines and gas turbines attempting constant-volume combustion without positive–displacement mechanisms have regained attention, mainly due to their theoretical high efficiency, potential low emissions, and compact design features. The idea can be traced back to experiments in the 1930’s and production of devices like the V1 missile motor and the Comprex® supercharger. Both for power generation and for aerospace applications, specific hardware and ingenious cycle designs are being developed to address known technological challenges. Different thermodynamic approaches and design methods are proposed to predict the performance potential of these periodic-unsteady wave machines. There have been experimental studies and successfully operated test-rigs that were sometimes shelved due to immediate economic concerns. These “lost” previous studies and experiences are worth reviewing amidst the increased attention to pulse detonation engine and wave-rotor applications proposed for gas turbine cycles by engine makers and government laboratories. In this review paper, our aim is to summarize the status and important efforts in this field. Recent research is highlighted by specific research groups worldwide attempting diverse applications. A compilation of promising applications is presented, to help focus efforts on future work needed.Copyright © 2003 by ASME

Emission controls in stationary gas engines have required significant modifications to the fuel injection and combustion processes. One approach has been the use of high-pressure fuel injection to improve fuel-air mixing. The objective of this study is to simulate numerically the injection of gaseous fuel at high pressure in a large-bore two-stroke engine. Existing combustion chamber geometry is modeled together with proposed valve geometry. The StarCD® fluid dynamics code is used for the simulations, using appropriate turbulence models. High-pressure injection of up to 500 psig methane into cylinder air initially at 25 psig is simulated with the valve opened instantaneously and piston position frozen at the 60 degrees ABDC position. Fuel flow rate across the valve throat varies with the instantaneous pressure but attains a steady state in approximately 22 ms. As expected with the throat shape and pressures, the flow becomes supersonic past the choked valve gap, but returns to a subsonic state upon deflection by a shroud that successfully directs the flow more centrally. This indicates the need for careful shroud design to direct the flow without significant deceleration. Pressures below 300 psig were not effective with the proposed valve geometry. A persistent re-circulation zone is observed immediately below the valve, where it does not help promote mixing.Copyright © 2003 by ASME

A novel version of a type of Pulse Detonation Engine (PDE) cycle has been developed using detonation combustion within the passages of a wave rotor. The innovation uses an internal stationary duct to supply a premixed fuel -air to the tubes whil e also eliminating the feedback of unsteady gas -dynamic interactions through the inlet and nozzle. Although believed to be broad in its potential application, initial steps in applying analytical modeling are aimed at developing the concept into a high pre ssure gain device suitable for use in a gas turbine engine. Termed the Constant Volume Combustor (CVC), the device is currently studied as a replacement for conventional constant pressure combustion systems and able to achieve a step improvement in engine performance. Gas dynamic predictions have been made using the NASA one dimensional non -steady code for simulation and analysis of wave rotors including combustion. Initial modeling results for the CVC confirm the cycle’s ability to deliver a downstream gas flow of high pressure gain. Results also predicted an inlet and outlet flowstream vastly more uniform in time and space than conventional PDE approaches. Furthermore, a range of design parameters is examined for the CVC’s ability to deliver exit temperatu re levels relevant to a turbine engine. Pressure gain performance increases realized with systematic design parameter examination are presented. A very limited examination of the inclusion of further loss mechanisms has been briefly addressed. A comparison of overall operating performance is made to pressure gain estimates obtained using a simple thermodynamic combustor model.

A wave rotor is proposed for use as a constant volume combustor. A novel design feature is investigated as a remedy for hot gas leakage, premature ignition and pollutant emissions that are possible in this class of unsteady machines. The base geometry involves fuel injection partitions that allow stratification of fuel/oxidizer mixtures in the wave rotor channel radially, enabling pilot ignition of overall lean mixture for low NOx combustion. In this study, available turbulent combustion models are applied to simulate approximately constant volume combustion of propane and resulting transient compressible flow. Thermal NO production histories are predicted by simulations of the STAR-CD code. Passage inlet/outlet/wall boundary conditions are time-dependent, enabling the representation of a typical deflagrative internal combustor wave rotor cycle. Some practical design improvements are anticipated from the computational results. For a large number of derivative design configurations, fuel burn rate, two-dimensional flow and emission levels are evaluated. The sensitivity of channel combustion to initial turbulence levels is evaluated.Copyright © 2002 by ASME

This paper reports on a new methodology for detecting surface cracks in metallic structures by combining a microwave resonant cavity with infrared imaging. The underlying principle is based on crack induced disruptions of microwave wall currents creating localized concentrations of microwave energy. These regions of concentrated energy may, in turn, produce a localized heating in a thin layer of dielectric material placed adjacent to the surface being inspected. Detection of local hot spots via infrared imaging may then be used to infer the presence of a crack or other discontinuity in the surface. This study utilized a numerical simulation of electromagnetic fields within the resonant cavity and the resulting dielectric heating. The objective of the numerical study was to gain insight into fundamental electromagnetic and thermophysical processes on which this NDT scheme was based. The transient 3D Maxwell's equations were solved numerically using the method of Finite Difference-Time Domain to determine electromagnetic field distributions. The energy equation was then solved in order to determine thermal energy deposition and temperature fields in the dielectric layer. The sample numerical simulations indicate that combining microwave heating with thermographic imaging could lead to a viable non- destructive testing instrument for crack detection.

Wave rotor cycles which utilize premixed combustion processes within the passages are examined numerically using a one-dimensional CFD-based simulation. Internal-combustion wave rotors are envisioned for use as pressure-gain combustors in gas turbine engines. The simulation methodology is described, including a presentation of the assumed governing equations for the flow and reaction in the channels, the numerical integration method used, and the modeling of external components such as recirculation ducts. A number of cycle simulations are then presented which illustrate both turbulent-deflagration and detonation modes of combustion. Estimates of performance and rotor wall temperatures for the various cycles are made, and the advantages and disadvantages of each are discussed.

The wave rotor is a promising means of pressure-gain for gas turbine engines. This paper examines novel wave rotor topping cycles which incorporate low-NOx combustion strategies. This approach combines two-stage ‘rich-quench-lean’ (RQL) combustion with intermediate expansion in the wave rotor to extract energy and reduce the peak stoichiometric temperature substantially. The thermodynamic cycle is a type of reheat cycle, with the rich-zone air undergoing a high pressure stage. Rich-stage combustion could occur external to or within the wave rotor. An approximate analytical design method and CFD/combustion codes are used to develop and simulate wave rotor flow cycles. Engine cycles designed with a bypass turbine and external combustion demonstrate a performance enhancement equivalent to a 200–400°R (110–220°K) increase in turbine inlet temperature. The stoichiometric combustion temperature is reduced by 300–450°R (170–250°K) relative to an equivalent simple cycle, implying substantially reduced NOx formation.

Direct work and pressure exchange between gases can be accomplished by cyclic wave processes in the channels of a wave-rotor, circumventing the limitations of turbo-compressors. A wave-rotor cycle is presented for use as the high-pressure core in a high speed aircraft engine with turbine bypass. The products of a “low-NOx” combustor undergo a large immediate wave-expansion to reach a permissible turbine blade temperature. The wave rotor provides a substantial increase in pressure ratio and peak cycle temperature resulting in high specific power and efficiency. Approximate analytical methods are employed for initial design and optimization of the cycle. The method of characteristics is then used to compute the detailed time evolution of the flow-field in a wave channel.