Mechanical and Energy Engineering Works

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    Analytic Design Methods for Wave Rotor Cycles
    (1994-09) Resler, Edwin L.; Moscari, Jeffrey C.; Nalim, M. Razi
    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 one-dimensional 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.
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    Wave Cycle Design for Wave Rotor Gas Turbine Engines with Low NOx emissions
    (1996-07) Nalim, M. Razi; Resler, Edwin L.
    The wave rotor is a promising means of pressure-gain for gas turbine engines. This paper examines novel wave rotor topping cycles that 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.
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    A Numerical Investigation of Premixed Combustion in Wave Rotors
    (1997-07) Nalim, M. Razi; Paxson, Daniel E.
    Wave rotor cycles that 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 that 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.
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    Assessment of Combustion Modes for Internal Combustion Wave Rotors
    (1999-04) Nalim, M. Razi
    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. Three modes of combustion are assessed: premixed autoignition (detonation), premixed deflagration, and non-premixed autoignition. The last two will require strong turbulence for completion of combustion in a reasonable time in the wave rotor. The autoignition modes will require inlet temperatures in excess of 800 K for reliable ignition with most hydrocarbon fuels. Examples of combustion mode selection are presented for two engine applications.
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    Modified Through-Flow Wave-Rotor Cycle with Combustor-Bypass Ducts
    (1999-05) Paxson, Daniel E.; Nalim, M. Razi
    A wave-rotor cycle is described that avoids the inherent problem of combustor exhaust gas recirculation (EGR) found in four-port, through-flow (uniflow) pressure-gain wave-rotor cycles currently under consideration for topping gas-turbine engines. The recirculated hot gas is eliminated by the judicious placement of a bypass duct that transfers gas from one end of the rotor to the other. The resulting cycle, when analyzed numerically, yields a mean absolute temperature for the rotor that is 18% below the already impressive value (approximately the turbine inlet temperature) predicted for the conventional four-port cycle. The absolute temperature of the gas leading to the combustor is also reduced from the conventional design by 17%. The overall design-point pressure ratio of this new bypass cycle is approximately the same as the conventional cycle. This paper will describe the EGR problem and the bypass-cycle solution, including relevant wave diagrams. Performance estimates of design and off-design operation of a specific wave rotor will be presented. The results were obtained using a one-dimensional numerical simulation and design code.
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    Longitudinally Stratified Combustion in Wave Rotors
    (2000-11) Nalim, M. Razi
    A wave rotor may be used as a pressure-gain combustor, effecting wave compression and expansion, and intermittent confined 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 subftammable values, premixed stratification techniques are necessary to burn hydrocarbon fuels in small engines with compressor discharge temperatures well below autoignition conditions. One-dimensional, nonsteady numerical simulations of stratified-charge combustion are performed using an eddy-diffusivity turbulence model and a simple reaction model incorporating a flammability limit temperature. For good combustion efficiency, a stratification strategy is developed that concentrates fuel at the leading and trailing edges of the inlet port. Rotor and exhaust temperature profiles and performance predictions are presented at three representative operating conditions of the engine: full design load, 40% load, and idle. The results indicate that peak local gas temperatures will cause excessive temperatures in the rotor housing unless additional cooling methods are used. The rotor temperature will be acceptable, but the pattern factor presented to the turbine may be of concern, depending on exhaust duct design and duct-rotor interaction.
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    Thermodynamic Limits of Work and Pressure Gain in Combustion and Evaporation Processes
    (2002-11) Nalim, M. Razi
    Combustion and evaporation processes occurring in a closed chamber can result in significant pressure rise 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 inflow and outflow conditions, volumetric confinement, fluid 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.
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    Expression and Activities of Matrix Metalloproteinases under Oscillatory Shear in IL-1-Stimulated Synovial Cells
    (2003) Sun, Hui Bin; Nalim, M. Razi; Yokota, Hiroki
    Matrix metalloproteinases (MMPs) are known to play a critical role in tissue disintegration, and an elevated level of MMPs is observed in synovium and synovial fluid of joints with rheumatoid arthritis. During joint movement, synovial tissue receives various mechanical stimuli, but effects of mechanical challenges on regulation of MMPs in rheumatic synovium are poorly understood. Focusing on cellular responses to oscillatory fluid shear in human synovial cells, we determined the expression of MMP-1 and MMP-13 by polymerase chain reaction and immunoblotting as well as proteolytic activities of total MMPs by a fibril degradation assay and zymography. The results revealed that ~0.5 dyn/cm 2 oscillatory shear at 1 Hz not only reduced an mRNA level and a protein level of MMP-1 and MMP-13, but it also decreased collagenase and gelatinase activities of total MMPs. Furthermore, the induction of the MMP expression and activities by interleukin-1 was suppressed by the oscillatory shear. Interestingly, the oscillatory shear upregulated the mRNA expression of TIMP-1 and TIMP-2. Our results support a potential role of oscillatory shear in regulating expression and activities of MMPs in the presence and the absence of proinflammatory cytokine.
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    Two-Dimensional Flow and NOx Emissions in Deflagrative Internal Combustion Wave Rotor Configurations
    (2003-07) Pekkan, K; Nalim, M. Razi
    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.
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    Performance Enhancement of Microturbine Engines Topped With Wave Rotors
    (2006-01) Akbari, Pezhman; Nalim, M. Razi; Mueller, Norbert
    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.