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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 ...

Wave rotors are periodic-flow devices that provide dynamic pressure exchange and efficient energy transfer through internal pressure waves generated due to fast opening and closing of ports. Wave turbines are wave rotors with curved channels that can produce shaft work through change of angular momentum from inlet to exit. In the present work, conservation equations with averaging in the transverse directions are derived for wave turbines, and quasi-one-dimensional model for axial-channel non-steady flow is extended to account for blade curvature effects. The importance of inlet incidence is explained and the duct angle is optimized to minimize incidence loss for a particular boundary condition. Two different techniques are presented for estimating the work transfer between the gas and rotor due to flow turning, based on conservation of angular momentum and of energy. The use of two different methods to estimate the shaft work provides confidence in reporting of work output and confirms internal consistency of the model while it awaits experimental data for validation. The extended wave turbine model is used to simulate the flow in a three-port wave rotor. The work output is calculated for blades with varying curvature, including the straight axial channel as a reference case. The dimensional shaft work is reported for the idealized situation where all loss-generating mechanisms except flow incidence are absent, thus excluding leakage, heat transfer, friction, port opening time, and windage losses. The model developed in the current work can be used to determine the optimal wave turbine designs for experimental investment.

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.

Combustion and evaporation processes occurring in a closed chamber can result in signie cant pressurerise and direct work transfer. The pressure and volumetric changes that accompany such processes allow substantial work potential to be achieved in cyclic nonsteady devices, such as internal combustion engines and pulsed combustion or detonation engines. The ideal pressure gain or work production is a function of the prescribed ine ow and oute ow conditions, volumetric cone nement, e uid properties, and other parameters. The generalized thermodynamic limits of pressure gain and work production in such devices are investigated. Analytic and iterative methods are provided to evaluate cyclic combustion and evaporation processes for enhancing airbreathing combustion engine performance.

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.

Hot-jet ignition of a combustible mixture has application in internal combustion engines, detonation initiation, and wave rotor combustion. Numerical predictions are made for ignition of combustible mixtures using a traversing jet of chemically active gas at one end of a long constant-volume combustor (CVC) with an aspect ratio similar to a wave rotor channel. The CVC initially contains a stoichiometric mixture of ethylene or methane at atmospheric conditions. The traversing jet issues from a rotating prechamber that generates gaseous combustion products, assumed at chemical equilibrium for estimating major species. Turbulent combustion uses a hybrid eddy-breakup model with detailed finite-rate kinetics and a two-equation k-ω model. The confined jet is observed to behave initially as a wall jet and later as a wall-impinging jet. The jet evolution, vortex structure, and mixing behavior are significantly different for traversing jets, stationary centered jets, and near-wall jets. Pressure waves in the CVC chamber affect ignition through flame vorticity generation and compression. The jet and ignition behavior are compared with high-speed video images from a prior experiment. Production of unstable intermediate species like C2H4 and CH3 appears to depend significantly on the initial jet location while relatively stable species like OH are less sensitive.

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.

Ignitability and the ignition delay time of ethylene-air mixtures, ignited by a hot gas jet generated from combustion in a pre-chamber were investigated experimentally. The jet enters one end of a long combustion chamber, consistent with seeking a viable igniter method for wave rotor combustors. A numerical simulation of jet penetration and mixing in the main chamber provided guidance in testing and interpretation. The ignitability limits were established and ignition delay times were measured for a range of equivalence ratios. Chemical kinetics and mixing between the combustion torch jet and the combustible mixture both appear to be important in determining ignition delay times. This is in contrast with chemical ignition delay studies using shock-heated ignition techniques. Ethylene-air mixtures proved to be ignitable for initial premixed equivalence ratios ranging from 0.4 to 2.4, with the shortest ignition delay times of about one millisecond occurring for lean nearstoichiometric mixtures. The ethylene-air ratio of the combustion torch jet affected the ignition delay time in the main chamber combustible mixture, with the slightly rich prechamber mixtures providing the lowest delay times in igniting the main chamber ethyleneair mixtures.

High-fidelity unsteady, three-dimensional simulations were used to understand the mixing characteristics of gas from an injector that traverses the end of a narrow long chamber. Such a translating jet has applications in a Wave Rotor Constant Volume Combustor (WRCVC) for fueling and ignition. The simulations help visualize the jet in 3D injected through a hole and illuminate the possible mixing mechanisms responsible for gas mixing. Comparisons are made with previous 2D simulations, which represent injection through a slot. A method to quantify the amount of mixing between injected gas and the chamber gas is also proposed. The simulations discussed here do not model combustion and only analyzes gas mixing. To allow relative motion, a moderate clearance gap between a hot gas injector and multiple combustion chambers is assumed. The simulations indicate that pressure differences cause hot gas flow between chambers in the form of a ‘wall jet’ that precedes injector arrival. This hot gas tends to stay in the vicinity of the end wall, and may be a potential source of ignition, but only if an ignitable combustible mixture exists at that location. The 2D slot jet is seen to have higher penetration in the axial direction compared to the 3D hole jet for the same velocity, density and temperature boundary conditions at the injector inlet. As expected for injection through a hole, there are regions near the end wall that are bypassed by the jet and remain near chamber conditions, whereas the slot jet sweeps away all chamber gas near the wall.

Shear-dominated flows generated by compressible turbulent confined jets were simulated using two-equation turbulence models. A representative test problem was selected for which reliable experimental data was available for comparison. For validation of the improved models used for this study, a confined steady round turbulent jet interacting isothermally with co-flowing air was analyzed. The method was implemented in a widely used code using a pressure-based implicit solver. Three variations of two-equation models were considered: (i) a ‘high-Reynolds-number’ k-e equations with corrections for compressibility effects and non-linearity of the governing equations, (ii) standard k-e model with correction for round jets due to vortex stretching in three dimensions, and (iii) shear stress transport (SST) k-ω model.

A numerical method is developed with the capability to predict transient thermal boundary layer response under various flow and thermal conditions. The transient thermal boundary layer variation due to a moving compressible turbulent fluid of varying temperature was numerically studied on a two-dimensional semi-infinite flat plate. The compressible Reynolds-averaged boundary layer equations are transformed into incompressible form through the Dorodnitsyn–Howarth transformation and then solved with similarity transformations. Turbulence is modeled using a two-layer eddy viscosity model developed by Cebeci and Smith, and the turbulent Prandtl number formulation originally developed by Kays and Crawford. The governing differential equations are discretized with the Keller-box method. The numerical accuracy is validated through grid-independence studies and comparison with the steady state solution. In turbulent flow as in laminar, the transient heat transfer rates are very different from that obtained from quasi-steady analysis. It is found that the time scale for response of the turbulent boundary layer to far-field temperature changes is 40% less than for laminar flow, and the turbulent local Nusselt number is approximately 4 times that of laminar flow at the final steady state.

Gas flows of varying temperature occur in heat exchangers, nuclear reactors, non-steady flow devices, and combustion engines, among other applications with heat transfer processes that influence energy conversion efficiency. A general numerical method is developed for predicting the transient laminar thermal boundary layer response to arbitrarily prescribed changes in the bulk far-field fluid temperature. The method is tested for the step change of the far-field flow temperature of a two-dimensional semi-infinite flat plate with steady hydrodynamic boundary layer and constant wall temperature assumptions. Changes of the fluid-wall temperature difference in magnitude and sign are considered, including flow with no initial temperature difference and built-up thermal boundary layer. The governing differential equations for momentum and energy are solved based on the Keller-Box finite difference method. The accuracy of the solutions is verified through comparing with the steady state solution. Transient heat transfer coefficients are presented, which indicate that both magnitude and direction of heat transfer can be significantly different from quasi-steady models commonly used.

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

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

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.

This study concerns the dynamic performance of passive and active wax-actuator driven thermostats. The study is extended to wax actuator driven thermostats that have been fitted with a heating device, such that the thermostat can be actuated electrically. The thermostat valve type chosen for this study is a balanced, sleeve-type thermostat typically used in large over-the-road and industrial diesel engines. The valve operates like a spool valve to direct the flow of the engine coolant to the bypass, the heat exchanger, or partially to each. Since conventional thermostats are passive devices they lag in response to dynamic engine conditions, and under certain circumstances overheating can occur as a result of the device’s inability to respond quickly. Also, conventional thermostats are designed to protect an engine against overheating year round. Therefore, a thermostat designed to protect against overheating in the summer will often result in an overcooling condition in the winter. One possible solution to the problem is to control the thermostat electrically through the electronic engine control system, or other system, making the thermostat an active control device instead of a passive one. In this study, a mathematical model is developed to determine wax temperature, and thereby predict the thermostat operation and response. The wax temperature depends on the heat transfer from the engine coolant through the brass cup that encapsulates the wax, as well as heat transfer from the heater. The simulations are compared with measurements of temperature, thermostat position and flow at several locations around the thermostat in an experimental set-up. The outcome is used to analyze the accuracy of the methods used in the thermodynamic calculations.

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.

Combustion within the channels of a wave rotor is examined as a means of obtaining pressure gain during heat addition in a gas turbine engine. Several modes of combustion are considered and the factors that determine the applicability of three modes are evaluated in detail; premixed autoignition/detonation, premixed deflagration, and non-premixed compression ignition. The last two will require strong turbulence for completion of combustion in a reasonable time in the wave rotor. The compression/autoignition modes will require inlet temperatures in excess of 1500 R for reliable ignition with most hydrocarbon fuels; otherwise, a supplementary ignition method must be provided. Examples of combustion mode selection are presented for two core engine applications that had been previously designed with equivalent 4-port wave rotor topping cycles using external combustion.

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.