Search Results (1 - 25 of 128 Results)

Sort By  
Sort Dir
 
Results per page  

Janes, NigelSIMPLIFIED MODELING OF STRATIFIED-CHARGE COMBUSTION IN A CONSTANT VOLUME CHAMBER
Doctor of Philosophy, The Ohio State University, 2002, Mechanical Engineering
The value of combustion models cannot be overstated. As a major component of engine models they are widely used as research tools in the continuing effort to improve existing combustion systems and to develop completely new concepts. Models also find use in the classroom where they allow students to manipulate control parameters and study the effect on performance, efficiency and pollutant formation without ever visiting an engine test cell. Models of varying complexity are available for premixed combustion but there is a lack of published work on simplified modeling of the more complex case of stratified-charge combustion. In this investigation, such a model is developed and validated against experimental data for stratified combustion in a constant volume chamber. This first iteration is intended as an oversimplified foundation to which additional complexity can be added in subsequent iterations after weaknesses are identified. Data are obtained for a range of test cases from a purpose-built test stand. Each of the experimental cases is simulated and the results compared. Simulation results for pressure and flame radius match well with the experimental data. The timing of key events is also predicted with relative accuracy. Significant errors are observed only in the period where the model is predicted to break down. The overall positive result shows that it should be possible to capture the essential characteristics of stratified-charge combustion in a simple model, given adequate development time.

Committee:

Yann Guezennec (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

stratified-charge; stratified-charge model; stratified-charge combustion; stratified combustion model; stratified combustion; combustion modeling; simplified combustion modeling

Cornwell, MichaelCauses of Combustion Instabilities with Passive and Active Methods of Control for practical application to Gas Turbine Engines
PhD, University of Cincinnati, 2011, Engineering and Applied Science: Aerospace Engineering
Combustion at high pressure in applications such as rocket engines and gas turbine engines commonly experience destructive combustion instabilities. These instabilities results from interactions between combustion heat release, fluid mechanics and acoustics. This research explores the significant affect of unstable fluid mechanics processes in augmenting unstable periodic combustion heat release. The frequency of the unstable heat release may shift to match one of the combustors natural acoustic frequencies which then can result in significant energy exchange from chemical to acoustic energy resulting in thermoacoustic instability. The mechanisms of the fluid mechanics in coupling combustion to acoustics are very broad with many varying mechanisms explained in detail in the first chapter. Significant effort is made in understanding these mechanisms in this research in order to find commonalities, useful for mitigating multiple instability mechanisms. The complexity of combustion instabilities makes mitigation of combustion instabilities very difficult as few mitigation methods have historically proven to be very effective for broad ranges of combustion instabilities. This research identifies turbulence intensity near the forward stagnation point and movement of the forward stagnation point as a common link in what would otherwise appear to be very different instabilities. The most common method of stabilization of both premixed and diffusion flame combustion is through the introduction of swirl. Reverse flow along the centerline is introduced to transport heat and chemically active combustion products back upstream to sustain combustion. This research develops methods to suppress the movement of the forward stagnation point without suppressing the development of the vortex breakdown process which is critical to the transport of heat and reactive species necessary for flame stabilization. These methods are useful in suppressing the local turbulence at the forward stagnation point, limiting dissipation of heat and reactive species significantly improving stability. Combustion hardware is developed and tested to demonstrate the stability principles developed as part of this research. In order to more completely understand combustion instability a very unique method of combustion was researched where there are no discrete points of combustion initiation such as the forward stagnation point typical in many combustion systems including swirl and jet wake stabilized combustion. This class of combustion which has empirical evidence of great stability and efficient combustion with low CO, NOx and UHC emissions is described as high oxidization temperature distributed combustion. This mechanism of combustion is shown to be stable largely because there are no stagnations points susceptible to fluid mechanic perturbations. The final topic of research is active combustion control by fuel modulation. This may be the only practical method of controlling most instabilities with a single technique. As there are many papers reporting active combustion control algorithms this research focused on the complexities of the physics of fuel modulation at frequencies up to 1000 Hz with proportionally controlled flow amplitude. This research into the physics of high speed fluid movement, oscillation mechanical mechanisms and electromagnetics are demonstrated by development and testing of a High Speed Latching Oscillator Valve.

Committee:

Ephraim Gutmark, PhDDSc (Committee Chair); Shaaban Abdallah, PhD (Committee Member); Jeffrey Kastner, PhD (Committee Member); Prem Khosla, PhD (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Combustion Instability;Thermoacoustic Instability;Active Combustion Control;Flameless Combustion;Swirl Stabilized Combustion;Vortex Breakdown

Yi, TongxunReduced-Order Modeling and Active Control of Dry-Low-Emission Combustion
PhD, University of Cincinnati, 2007, Engineering : Aerospace Engineering

This dissertation is a complementary experimental and theoretical investigation of combustion instability and lean blowout (LBO) in dry-low-emission (DLE) gas turbine engines, aiming to understand the fundamental mechanisms and shed light on active combustion control.

Combustion instability involves complicated physicochemical processes, and many of the underlying mechanisms remain unknown, despite extensive research in the past several decades. A practical control system must be able to achieve satisfactory control performances in the presence of large uncertainties, large variations, and even unknown system dynamics. Toward this goal, an observer-based controller, capable of attenuating multiple unstable modes with unknown characteristics, is developed. A mechanism suitable for online prediction of the safety margin to the onset of combustion instability is presented, which does not require knowing the unstable frequencies. The shortage of a reliable, high-frequency, proportional fuel actuator is a major technical challenge for active combustion control. A complementary theoretical and experimental study is performed on a pump-style, high-frequency, magnetostrictive fuel actuator. Improvements to the fuel setup have been made according to the model predictions, which have been experimentally shown to be beneficial to combustion instability control.

The second part of this dissertation is about modeling, prediction, and control of lean blowout. The experimentally observed, “intensified”, low frequency, near-LBO combustion oscillations have been used as incipient LBO precursors, and are characterized as low-dimension chaotic behavior in the present study. The normalized chemiluminescence RMS and the normalized cumulative duration of LBO precursor events are recommended for LBO prediction in generic gas turbine engines. Linear stability analysis shows that, with decreasing equivalence ratios, a complex conjugate pair of eigenvalues emerges from three negative real ones, moves left toward the right half phase plane, and finally crosses the imaginary axis. Model predictions qualitatively and even quantitatively match the experiments. Simulation of the nonlinear WSR models shows the “triggered instability” which is similar to that in rocket motors. It is numerically demonstrated that zero-mean small-amplitude fuel modulations based on modern feedback control principles, can be very effective in strengthening the flame’s robustness to external disturbances without exacerbating the overall emissions. Experimental demonstrations are suggested for future research.

Committee:

Dr. Ephraim Gutmark (Advisor)

Keywords:

dry-low-emission combustion; combustion instability; lean blowout; active combustion control; observer-based control

Milligan, Ryan TimothyDUAL MODE SCRAMJET: A COMPUTATIONAL INVESTIGATION ON COMBUSTOR DESIGN AND OPERATION
Master of Science in Engineering (MSEgr), Wright State University, 2009, Mechanical Engineering
Numerical analysis was performed on a Dual-Mode Scramjet isolator-combustor. Preliminary analysis was performed to form a baseline geometry. Another study validated the results of a 2D model compared to a 3D model. Stable combustion was shown at two different flight conditions, M=3.0 and M=2.5. A marginal 5% decrease in stream thrust was shown by introducing a 50/50 mix of methane and ethylene. Based on the results of the preliminary analysis, detailed geometry analysis was performed on the 3D baseline geometry. Adding a new set of cavity feeding injectors increased the overall stream thrust and the equivalence ratio in the cavity. Using less fuel than the baseline configuration, revealed a 6.4% increase in stream thrust and an 11% increase in combustion efficiency by placing the second stage injector further upstream. Future analysis includes combining the cavity feeding with closer injector placement, which is expected to yield even better results.

Committee:

J. Mitch Wolff, PhD (Advisor); J. Mitch Wolff, PhD (Committee Co-Chair); Dean Eklund, PhD (Committee Co-Chair); Chung-Jen Tam, PhD (Committee Member)

Subjects:

Chemical Engineering; Chemistry; Design; Engineering; Fluid Dynamics; Mechanical Engineering; Physics

Keywords:

dual mode combustion; scramjet combustion; high speed chemical kinetics; dual mode; combustion

Knadler, MichaelValidation of a Physics-Based Low-Order Thermo-Acoustic Model of a Liquid-Fueled Gas Turbine Combustor and its Application for Predicting Combustion Driven Oscillations
PhD, University of Cincinnati, 2017, Engineering and Applied Science: Aerospace Engineering
This research validates a physics based model for the thermo-acoustic behavior of a liquid-fueled gas turbine combustor as a tool for diagnosing the cause of combustion oscillations. A single nozzle, acoustically tunable gas turbine combustion rig fueled with Jet-A was built capable of operating in the unsteady combustion regime. A parametric study was performed with the experimental rig to determine the operating conditions resulting in thermoacoustic instabilities. The flame transfer function has been determined for varying fuel injection and flame stabilization arrangements to better understand the feedback loop concerning the heat release and acoustics. The acoustic impedance of the boundaries of the combustion system was experimentally determined. The results were implemented in a COMSOL Multiphysics model as complex impedance boundary conditions at the inlet and exit and a source term to model the flame and heat release. The validity of that model was determined based on an eigenvalue study comparing both the frequency and growth rate of the eigenvalues with the experimentally measured frequencies and pressures of the stable and unstable operating conditions. The model demonstrated that it can accurately predict the instability of the examined operating conditions. The model also closely predicted the frequency of instability and demonstrated the usefulness of including the experimentally determined acoustic boundary conditions over idealized sound hard boundaries.

Committee:

Jongguen Lee, Ph.D. (Committee Chair); Jay Kim, Ph.D. (Committee Member); Kwanwoo Kim, Ph.D. (Committee Member); Mark Turner, Sc.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Combustion;Combustion Instabilities;Thermoacoustics;Gas Turbine Combustion

Long, Brandon ScottEffect of Rayleigh-Taylor Instability on Fuel Consumption Rate: A Numerical Investigation
Master of Science (M.S.), University of Dayton, 2017, Aerospace Engineering
An extensive numerical investigation is conducted in order to assess the effect of Rayleigh-Taylor instability on fuel consumption rate (or flame speed). Two geometries are used for this investigation, viz., a high pressure high-g (HPHG) cavity stabilized combustor and a curved duct with a backward facing step. The former geometry is a more practical combustion system that contains liquid fuel injectors with operating conditions that mimic gas turbine cycles, whereas the latter is a canonical combustor used to study turbulent premixed flames. Reynolds averaged Navier-Stokes (RANS) and large eddy simulations (LES) are used. RANS is used for the practical combustor, and both RANS and LES are used for the canonical combustor. The combustion models used are the flamelet generated manifold (FGM) and the two-step species transport for the practical and canonical combustor, respectively. The HPHG combustor is designed to induce bulk rotational flow in the cavity, inducing centrifugal acceleration. The centrifugal force acts from the high-density reactants towards the low-density products creating a Rayleigh-Taylor instability (RTI). Rayleigh-Taylor instabilities are expected to increase the turbulent flame speed and reduce the size of the combustor by increasing the flame wrinkling and/or corrugation. Simulations at two different levels of centrifugal acceleration, and, consequently, dissimilar Rayleigh-Taylor instability were performed. It was found that the nominal g-loads are overestimating the local g-loads from the simulation because thermal expansion is not taken into account. From these simulations it was not possible to discern the effect of RTI on fuel consumption rate due to the complex physical-chemical process inherent to this combustor such as fuel vaporization, molecular mixing, spray-turbulence interaction, turbulence-chemistry interaction, and partial premixing. Therefore, gaseous premixed turbulent flames were simulated in a curved duct with a backward facing step. Two radius of curvature were used, viz., an infinite (straight duct) and a finite radius of curvature (curved duct). These combustors were operated at low and high Reynolds number (3,200 and 32,000). The computational results are compared with broadband chemiluminescence and shadowgraph images reported in the literature for similar conditions and geometries. Both RANS and LES results are in general agreement with measurements. Both experiments and simulations show that increasing the Reynolds number in both straight and curved canonical combustor the flame cannot withstand the Karlovitz number effects and the flame is positioned behind the backward-facing step. In addition, the LES results indicate that at high Reynolds number the flame blows out for the straight channel while it remains stabilized for the curved channel. This result is in agreement with the blowout data reported in the literature. On the other hand, RANS over predict the flame stabilization for the straight channel. Consequently, RANS should not be used in research involving RTI-induced blowout. In conclusion, RTI interacts with a turbulent premixed flame and its overall effect is to extend the conditions under which turbulent premixed flames can be stabilized. This improved flame stabilization is a direct manifestation that the fuel consumption rate (or flame speed) has been enhanced in order for the flame to withstand higher Karlovitz number effects induced by high Reynolds number. However, the mechanism through which RTI works on the turbulent premixed flame is not clear. A new hypothesis is proposed. The increase in RTI should increase the turbulent length scale as well as increase the Karlovitz number. The corrugated flame would withstand the higher Karlovitz number because RTI temporarily and periodically reverses the turbulent energy cascade by minimizing the potential energy of the stratified flow.

Committee:

Scott Stouffer, Ph.D. (Committee Chair); Alejandro Briones, Ph.D. (Committee Member); Brent Rankin, Ph.D. (Committee Member); Jamie Ervin, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Rayleigh-Taylor Instabilities; Fuel Consumption Rate; High Swirl Combustion; High-G Combustion; Backward Facing Step Combustion

Gross, Justin TylerExperiments with a High Pressure Well Stirred Reactor
Master of Science (M.S.), University of Dayton, 2014, Aerospace Engineering
The existing WSR has been successfully used to evaluate pollutant emissions, soot formation, combustion stability and alternative fuel performance at atmospheric pressure. The HPWSR project extends the capabilities of this laboratory tool, allowing the generation of benchmark quality data over a range of operating pressures. Lean blow out data collected is correlated against loading parameter, forming fuel stability loops. Combustion stability of JP-8 will be evaluated over a range of operating pressures from 4 psia to 5 atm. A new, internal vaporization technique is applied to allow operation at higher pressures than with previous hardware. Lean emissions will be collected simultaneously and used to further characterize the HPWSR operability and lean combustion performance. This work will validate nitrogen dilution using true low pressure testing compared to dilution in the same configuration, and further extend WSR capabilities by operating at elevated pressures up to 20 atm.

Committee:

Scott Stouffer, Ph.D (Advisor); Alejandro Briones, Ph.D (Committee Chair); Jamie Ervin, Ph.D (Committee Chair)

Subjects:

Aerospace Engineering

Keywords:

combustion;WSR;well stirred reactor;lean blowout;combustion stability;nitrogen dilution;low pressure simulation;chemical kinetics;high pressure combustion;lean emissions

Pinchak, Matthew D.Enhanced Flame Stability and Control: The Reacting Jet in Vitiated Cross-Flow and Ozone-Assisted Combustion
PhD, University of Cincinnati, 2018, Engineering and Applied Science: Aerospace Engineering
The operation of gas turbine engines in increasingly harsh environments while constrained by stringent emissions regulations requires multiple advances in combustion technology. This dissertation addresses two different ways to enhance the stability and control of the combustion process under such conditions: the reacting jet in vitiated cross-flow (Part I) and ozone-assisted combustion (Part II). The first chapter of original research (Chapter 4) examines several fundamental aspects of the reacting jet in cross-flow (RJICF). A circular nozzle and high aspect ratio slotted nozzle of identical area were investigated for jet to cross-flow momentum flux ratios ranging from J = 5 to 65 for jet equivalence ratios of up to φj = 5.0. Particle image velocimetry was utilized to study the flow-field and OH* chemiluminescence was used to capture features of the flame behavior. The nozzle geometry was determined to have a significant effect on RJICF flame stability, with substantially expanded blow-out limits for the high aspect ratio slotted nozzle. Enhanced operability of the slotted nozzle is attributed to the substantially larger and stronger recirculation zone on the leeward side of the jet when compared to the circular nozzle. This area is characterized by a more disperse region of elevated vorticity levels, resulting in the entrainment of more hot combustion products with a longer residence time in the recirculation zone, which in turn provides a stronger and more stable ignition source to the oncoming, unburned reactants. The RJICF is a highly dynamic phenomenon, and its unsteady characteristics are discussed in Chapter 5. It is shown that both the non-reacting and reacting flow-fields are characterized by a peak oscillation frequency present in both the streamwise and transverse velocity components. The wake Strouhal numbers (Stw) of the isothermal slotted jet match values of Stw ≈ 0.13 reported in previous studies, whereas under combusting conditions Stw increases from 0.152 to 0.173 as J is increased from 10 to 35. Proper-orthogonal decomposition (POD) was performed on the data to extract the primary coherent structures present in the flow-field. It was shown that the strongest modes correspond to structures associated with the fluctuating wake vortices. Chapter 6 investigates the effects of cross-flow fueling on the RJICF. It is demonstrated that as the cross-flow equivalence ratio, φ, is increased, less fuel is required in the jet fluid to stabilize a flame. For φ = 0.7, no fuel is required in the jet and a flame can be stabilized by a pure air jet. Part II is an investigation comprised of detailed experiments and numerical simulations on the effects of the addition of ozone on the combustion process for gaseous ethylene (C2H4) and liquid n-heptane (C7H16) and toluene (C7H8) mixtures. The experimental results show increases in the laminar flame speed when 7.8% of the O2 in the air is converted to 11,000 ppm O3. Simulations showed that most of the O3 is consumed through two dominant pathways: decomposition through collision with N2 and the direct reaction with H. Significantly, it was demonstrated that flow conditions influence the amount of flame speed enhancement for a constant amount of O3 addition. It was found that as the stretch rate is increased, the H that is produced at higher temperatures later in the flame does not have to diffuse as far upstream to react with O3. Increased flux through this pathway results in elevated levels of heat release earlier in the flame and, depending on the fuel, diverts H from detrimental pathways, resulting in increased flame propagation rates.

Committee:

Ephraim Gutmark, Ph.D. (Committee Chair); Shaaban Abdallah, Ph.D. (Committee Member); Prashant Khare, Ph.D. (Committee Member); Timothy Ombrello, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Reacting jet in cross flow;Plasma-assisted combustion;Ozone-Assisted Combustion;Particle image velocimetry;Fluidic flame stabilization

Horning, MarcusFeedback Control for Maximizing Combustion Efficiency of a Combustion Burner System
Master of Science in Engineering, University of Akron, 2016, Electrical Engineering
An observer-controller pair was designed to regulate the fuel flow rate and the flue-gas oxygen ratio of a combustion boiler. The structure of the observer was a proportional-integral state estimator. The designed controller was composed of a combination of two common controller structures: state-feedback with reference tracking and proportional-integral-derivative(PID). A discrete-time, linear state-space model of the combustion system was developed such that the linear controller and observer could be designed. This required establishing separate models pertaining to the combustion process, actuators, and sensors. The complete model of the combustion system incorporated all three models. The combustion model, which related the flue-gas oxygen ratio to the fuel and oxygen flow rates, was obtained using the mathematical formulas corresponding to combustion of natural gas. The actuators were modeled using measured fuel and oxygen flow rate data for various actuator signals, and fitting the data to a parametric model. The established nonlinear models for the combustion process and actuators required linearization about a specified operating point. The sensors model was then obtained using the predictive error identification technique based on batch input-output data. For the acquired model of the combustion system, a linear quadratic regulator was used to calculate the optimal state feedback gain. The classical controller gains were determined by tuning the gains and evaluating the simulation of the closed-loop response. Computer-aided simulations provided evidence that the controller and state estimator could regulate the desired set point in the presence of moderate disturbances. The observer-controller pair was implemented and verified on an experimental boiler system by means of an embedded system. Even in the presence of a disturbance resulting from a 50% blockage of the surface area of the air intake duct, the closed-loop system was capable of regulating the desired set point for slow-varying reference signal changes.

Committee:

Nathan Ida, Dr. (Advisor); Robert Veillette, Dr. (Committee Member); Kye-Shin Lee, Dr. (Committee Member)

Subjects:

Electrical Engineering; Engineering

Keywords:

PID control; combustion burner system; state-feedback control; combustion efficiency; kalman filter; PI state estimation; system identification; prediction error identification

Hoffmeister, Kathryn Nicole GabetDevelopment and Application of High-Speed Raman/Rayleigh Scattering in Turbulent Nonpremixed Flames
Doctor of Philosophy, The Ohio State University, 2015, Mechanical Engineering
In this dissertation, a new, high-speed, combined 1D Raman-Rayleigh scattering imaging approach was developed for quantitative temporally-correlated (10-kHz) measurements of temperature, major combustion species (O2, N2, H2O, and H2), and mixture fraction in the turbulent DLR H3 nonpremixed jet flame. The new high-speed measurements presented here were facilitated through the development of a custom high-speed imaging spectrometer, implementation of a robust data reduction methodology, and the use of the High-Energy Pulse Burst Laser System (HEPBLS) at Ohio State, which produces ultra-high pulse energies at multi-kHz repetition rates. Detailed measurements in near-adiabatic, laminar calibration flames were used to assess the accuracy and precision of the kHz-rate measurements using the high-speed Raman/Rayleigh scattering imaging system. In general, good agreement was found as compared to adiabatic flame calculations over a broad range of temperature and equivalence ratios. Current 10-kHz measurements and derived statistics within the turbulent H3 flames were compared to previously-measured, low-repetition-rate scalar data available through the Turbulent Nonpremixed Flame (TNF) workshop database. In general, good agreement between the mean values and RMS fluctuations of the temperature and major species were found between the current and previous data, indicating sufficient accuracy in single-shot measurements in turbulent environments. Following technique development, a series of 10-kHz measurements were used to visualize the highly intermittent dynamics of the scalar fields. In addition to flow visualization, time-dependent measurements were used to deduce the temporal autocorrelation function and the associated integral time-scales of the major species, mixture fraction, and temperature in the DLR H3 flames. This research presents the first measurements of the integral timescales of the major combustion species and mixture fraction in turbulent flames as well as the first reporting of integral timescales of multiple scalars simultaneously. While the integral timescales of all scalars (O2, H2O, and H2, ξ, and T) generally increase with both axial and radial position, the individual integral timescales are significantly different, displaying a factor of three spread across all of the measured scalars. The integral timescales for temperature and water are highly correlated to one another at all spatial locations, while the integral timescale for mixture fraction closely tracks that of hydrogen between the jet centerline and the stoichiometric contour and tracks that of oxygen between the stoichiometric contour and the co-flowing oxidizer stream. Results indicate that in regions of high chemical activity and heat release, the use of single characteristic (integral) timescale to describe the large-scale behavior is not appropriate; that is, each scalar has its own unique spatially-dependent integral timescale. For spatial positions beyond the flame tip, the integral timescales for all scalars collapse upon one another meaning that the system can be described adequately as a pure mixing situation with a single characteristic timescale. Finally, new, temporal cross-correlations of various scalar pairs are presented along with a discussion of the derived scalar interaction times. In general, the scalar interaction times are bound by the individual scalar integral timescales, although unique characteristics are observed near the stoichiometric contour, which varies amongst the various scalar pairs. It is expected that the newly developed high-speed 1D Raman/Rayleigh imaging approach will provide new physical insight into the intermittent behavior of turbulent nonpremixed combustion and the subsequent turbulence-chemistry interaction, as well as providing new, time-resolved data for assessment and validation of time-dependent combustion models.

Committee:

Jeffrey Sutton (Advisor); Walter Lempert (Committee Member); Mohammad Samimy (Committee Member); Shaurya Prakash (Committee Member)

Subjects:

Aerospace Engineering; Chemistry; Experiments; Fluid Dynamics; Mechanical Engineering

Keywords:

Laser Diagnostics; High-Speed Laser Diagnostics; Combustion; Turbulent Combustion; Raman Scattering; Rayleigh Scattering; Turbulence-Chemistry Interaction; H3 Flame

Li, TingExperimental Study of the Effects of Nanosecond-Pulsed Non-equilibrium Plasmas on Low-Pressure, Laminar, Premixed Flames
Doctor of Philosophy, The Ohio State University, 2014, Aero/Astro Engineering
In this dissertation, the effects of nanosecond, repetitively-pulsed, non-equilibrium plasma discharges on laminar, low-pressure, premixed burner-stabilized hydrogen/O2/N2 and hydrocarbon/O2/N2 flames is investigated using optical and laser-based diagnostics and kinetic modeling. Two different plasma sources, both of which generate uniform, low-temperature, volumetric, non-equilibrium plasma discharges, are used to study changes in temperature and radical species concentrations when non-equilibrium plasmas are directly coupled to conventional hydrogen/hydrocarbon oxidation and combustion chemistry. Emission spectroscopy measurements demonstrate number densities of excited state species such as OH*, CH*, and C2* increase considerably in the presence of the plasma, especially under lean flame conditions. Direct imaging indicates that during plasma discharge, lean hydrocarbon flames “move” upstream towards burner surface as indicated by a shift in the flame chemiluminescence. In addition, the flame chemiluminescence zones broaden. For the same plasma discharge and flame conditions, quantitative results using spatially-resolved OH laser-induced fluorescence (LIF), multi-line, OH LIF-thermometry, and O-atom two-photon laser-induced fluorescence (TALIF) show significant increases in ground-state OH and O concentrations in the preheating zones of the flame. More specifically, for a particular axial position downstream of the burner surface, the OH and O concentrations increase, which can be viewed as an effective “shift” of the OH and O profiles towards the burner surface. Conceivably, the increase in OH and O concentration is due to an enhancement of the lower-temperature kinetics including O-atom, H-atom and OH formation kinetics and temperature increase due to the presence of the low-temperature, non-equilibrium plasma. High-fidelity kinetic modeling demonstrates that the electric discharge generates significant amounts of O and possibly H atoms via direct electron impact, as well as quenching of excited species rather than pure thermal effect which is caused by Joule heating within the plasma. These processes accelerate chain-initiation and chain-branching reactions at low temperatures (i.e. in the preheat region upstream of the primary reaction zone in the present burner-stabilized flames) yielding increased levels of O, H, and OH. The effects of the plasma become more pronounced as the equivalence ratio is reduced which strongly suggest that the observed effect is due to plasma chemical processes (i.e. enhanced radical production) rather than Joule heating supports the kinetic modeling.

Committee:

Jeffrey Sutton (Advisor); Igor Adamovich (Advisor); Walter Lempert (Committee Member); Joseph Rich (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Plasma-Assisted Combustion, Combustion Chemical Kinetics, Laser Diagnostics

Jones, MatthewIgnition and Combustion Characteristics of Nanoscale Metal and Metal Oxide Additives in Biofuel (Ethanol) and Hydrocarbons
Master of Science, University of Toledo, 2011, Mechanical Engineering

Metal energetic additives are added to propellants and explosives to improve ignition and combustion performance. In particular, aluminum has been used as an energetic material in solid-based propellant rockets and explosives for many years due to its high combustion enthalpy and low cost. Recently, the introduction of nanotechnology has led to significant developments in the field of energetic materials. Nanoscale energetic materials, due to their surface area and unique thermal properties, are known to exhibit many advantages over conventional micron sized particles. However, the current mechanisms of nanoaluminum ignition and combustion are not fully understood. Furthermore, studies involving suspensions of energetic nanomaterials in a liquid medium (nanofluids) are very limited. A fundamental understanding of micron and nanoscale aluminum combustion is critical to the design and implementation of practical propulsion systems that use aluminum additives. Therefore, a comprehensive review on the ignition and combustion of energetic nanoparticles was performed, with a primary focus on aluminum, and two novel experimental studies were performed to investigate the combustion characteristics of nanoscale aluminum (n-Al) and aluminum oxide (n-Al2O3) in liquid fuels, namely, ethanol (C2H5OH).

The first experimental study examined the heating values of several nanofluid suspensions of n-Al (50 nm) and n-Al2O3 (36 nm) in ethanol. The primary objective of this experimental study was to characterize the combustion reaction and gain a better understanding of nanoaluminum oxidation in a multi-component heterogeneous system. The heat of combustion was studied using a modified static bomb calorimeter system. Combustion experiments were performed with volume fractions of 1%, 3%, 5%, 7%, and 10% for n-Al, and 0.5 %, 1%, 3%, and 5% for n-Al2O3. Combustion element composition and surface morphology were evaluated using a scanning electron microscope and energy dispersive spectroscopy system. The results indicate that the amount of heat released volumetrically from ethanol combustion increases almost linearly with n-Al concentration. Nanoaluminum volume fractions of 1% and 3% did not show enhancement in the average volumetric heat of combustion, however, higher volume fractions of 5%, 7%, and 10% increased the volumetric heat of combustion by 5.82%, 8.65%, and 15.31%, respectively. Aluminum oxide and heavily passivated n-Al additives did not participate in combustion reactively, and there was no contribution from Al2O3 to the combustion enthalpy in the tests. A combustion model that utilized Chemical Equilibrium with Applications (CEA) was conducted as well and was shown to be in good agreement with the experimental results.

Along with energy density enhancement, achieving precise control over the reactivity of nanofluids is an opportunity for future nanoenergetic fuel applications. A second experimental study involved the study in ignition probability of n-Al (50 nm) and n-Al2O3 (36 nm) in ethanol and the commonly used No. 2 fuel oil (diesel). The primary aims in this study were to study the effect of nanoenergetic additives on the ignition probability of ethanol with a hot-plate setup, and to explore the underlying mechanisms of ignition. Aluminum and Al2O3 were suspended in ethanol and diesel fuels from 0.1% to 3% volume fractions, and dropped onto a hot plate at temperatures varying from approximately 300 °C to 600 °C. The experimental probability was calculated and a logistic regression approach was used to determine the 50% ignition threshold. Nanoaluminum in ethanol was found to significantly increase the ignition probability: ethanol suspensions with 1%, 2%, and 3% aluminum volume fractions ignited as much as 100 °C lower than pure ethanol, and exhibited burning regimes similar to disruptive combustion in slurry droplets, while ethanol suspensions with n-Al2O3 volume fractions ignited at higher temperatures than pure ethanol. In addition, diesel mixtures with n-Al and n-Al2O3 additives demonstrated relatively the same hot plate ignition probability as pure diesel. Therefore, the likelihood of nanofluid ignition was strongly correlated with volume fraction concentration, metal additive material, and surface tension (contact angle).

Committee:

Calvin Li, PhD (Advisor); Matthew Franchetti, PhD (Committee Member); Yong Gan, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Biofuel; Calorimetry; Combustion; Energetics; Ethanol; Fuels; Fuel additives; Heat of combustion; Ignition; Ignition probability; Nanoaluminum; Nanoenergetics; Nanofluids; Nanoparticles; Nanotechnology

Hicks, Michael CMICROGRAVITY DROPLET COMBUSTION IN CARBON DIOXIDE ENRICHED ENVIRONMENTS
Doctor of Philosophy, Case Western Reserve University, 2016, EMC - Mechanical Engineering
Microgravity droplet combustion experiments were performed in atmospheres with elevated concentrations of CO2 at pressures of 1.0 atm, 3.0 atm, and 5.0 atm to examine the effects of a radiatively participating gas commonly used as a fire suppressant in space applications. Results were obtained from two unique experimental platforms, NASA Glenn Research Center’s 5.2 second drop tower (i.e., the Zero Gravity Facility “ZGF”) and the International Space Station (ISS). Tests performed in the ZGF deployed methanol and n-heptane droplets, with initial diameters ranging from 1.25 mm to 2.0 mm, onto a 120 micron quartz fiber. Tests performed on the ISS deployed n-heptane droplets with initial diameters ranging from 2.0 mm to 4.0 mm and were were either freely deployed or tethered with an 80 micron SiC fiber. Ambient atmospheres comprised 21% O2 with various concentrations of CO2 ranging from 0% to a maximum of 70% by volume with a balance of N2 . Results are reported showing the effects of a thermally participating gas at atmospheric and elevated pressures on the fuel droplet’s average burning rates, sooting propensity and, in the case of methanol at 1 atm, on its unique extinction mechanism.

Committee:

James Tien, PhD (Advisor)

Subjects:

Aerospace Engineering; Mechanical Engineering; Physical Chemistry; Physics; Radiation

Keywords:

microgravity; droplet combustion; combustion science; molecular gas radiation

Menapace, Henry RobertThe gas chromatographic study of the cool flame and motored engine combustion of some hydrocarbons /
Doctor of Philosophy, The Ohio State University, 1958, Graduate School

Committee:

Not Provided (Other)

Subjects:

Chemistry

Keywords:

Internal combustion engines;Combustion;Gas chromatography;Hydrocarbons

Denton, Michael JExperimental Investigation into the High Altitude Relight Characteristics of a Three-Cup Combustor Sector
MS, University of Cincinnati, 2017, Engineering and Applied Science: Aerospace Engineering
The altitude relight of a gas turbine combustor is an FAA and EASA regulation which dictates the successful re-ignition of an engine and its proper spool-up after an engine malfunction during flight. At cruising altitudes, this becomes problematic, as the ignition energy required is proportional to the inverse of the squared ambient pressure, and the ignition sources are limited operationally. Additionally, current trends in gas turbine combustor for the reduction of harmful emissions such as NOx, CO, and UHC are resulting in designs that are leaner, quicker, and smaller. A comparison of combustor designs across generations yields that the stability margin during a high altitude relight has narrowed, and the combustion efficiency upon ignition decreases as the volume becomes smaller, all else being constant. The goal of this research is then to study the relight process of the currently operational generation of RQL combustors, which have shown proven reliability. Pressure drop, ambient pressure, ambient temperature, and equivalence ratio were all studied on a 3-cup single-annular combustor sector to create an ignition map. The flame development process was studied through the implementation of high-speed video. The three swirlers were each a radial-jet design with pressure atomizing fuel nozzles of the same flow number. Nozzles were inserted such that the face was flush with the base of the swirler, and the fuel pre-filmed on the swirler venturi during normal operation. Sets of dilution holes on the upper and lower radius of the combustor walls lined the combustor liner. Testing was conducted by placing the three-cup sector horizontally upstream of an air jet ejector in a high altitude relight testing facility. Air was maintained at room temperature for varying pressure, and then liquid nitrogen was introduced to chill the air down to a limit of -50 deg F, corresponding with an altitude of 30,000 feet. Fuel was injected at consistent equivalence ratios across multiple operating conditions, giving insight into the ignition map of the combustor sector.

Committee:

San-Mou Jeng, Ph.D. (Committee Chair); Awatef Hamed, Ph.D. (Committee Member); Samir Tambe, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

altitude relight;gas turbine combustion;flame development;applied combustion;RQL combustor;ignition

Estefanos, WessamEffects of the Fuel-Air Mixing on Combustion Instabilities and NOx Emissions in Lean Premixed Combustion
PhD, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering
An experimental study was conducted to investigate the effects of the fuel-air mixing on combustion instabilities and NOx emissions in lean premixed combustion. High speed PIV measurements in water were conducted to capture the mean and dynamic behavior of the cold flow generated by a 3X model of the tested premixer. High speed PLIF in water measurements were conducted to quantify the mean and unsteady fuel-air mixing at different momentum flux ratios. Atmospheric combustion tests using the original premixer, were conducted using natural gas and propane at the same momentum flux ratios of the PLIF mixing tests. An emissions analyzer was used to measure the emissions from combustion tests. Dynamic pressure transducers were used to measure the amplitude and the frequency of the dynamic pressure oscillations associated with the combustion instabilities. CHEMKIN-PRO was used to model the atmospheric combustion and predict NOx emissions at different conditions. Results showed that unsteady fuel-air mixing was concentrated at the center and near the outer edges of the premixer. These regions were characterized by high fuel concentration gradients. With the increase in the momentum flux ratio, the concentration gradient and the level of unsteady mixing increased, indicating that the fuel-air spatial unmixedness was the source of the unsteady mixing. It was found that local flow turbulence tended to decrease the concentration gradient through enhancing the fuel-air mixing, which resulted in decreasing the level of unsteady mixing. NOx emissions from atmospheric combustion increased with the increase in the momentum flux ratio due to the increase in the flame temperature and the fuel-air spatial and temporal unmixedness. The intensity of the combustion dynamics increased with the increase in the level of unsteady mixing. Axial injection of the fuel into the regions of strong unsteady mixing eliminated the combustion dynamics through damping the unsteady mixing. Results of CHEMKIN-PRO agreed very well with the experimental results and showed that the spatial and temporal unmixedness have a significant effect on NOx emissions for very lean combustion (F = 0.4). With the increase in the equivalence ratio, their relative contribution decreased.

Committee:

San-Mou Jeng, Ph.D. (Committee Chair); Anne Geraldine Mouis, Ph.D. (Committee Member); Awatef Hamed, Ph.D. (Committee Member); Samir Tambe, Ph.D. (Committee Member)

Subjects:

Engineering

Keywords:

Lean premixed combustion;Fuel-air mixing;NOx emissions;Combustion instabilities;Unsteady flow behavior

Parajuli, BikashLaminar Flame Speeds and Autoignition of Dimethyl Ether at Elevated Pressures and Temperature using Novel Combustion Technique
Doctor of Philosophy, University of Akron, 2016, Mechanical Engineering
Dimethyl Ether (DME) is a candidate fuel that has potential to be renewable and advantageous over diesel in terms of combustion and emission characteristics as well as suitable for use in stationary gas turbines. Further, it can be used neat as well as blended with diesel, gasoline or other fuels in conventional and advanced CI engines. The design of various types of engines that use DME as a fuel is greatly dependent on computational simulations which require validated chemical kinetic mechanisms that can reliably mimic the combustion and pollutant formation behavior of DME at physical conditions that are relevant to engines. The objective of this work is to contribute to a better understanding and validation of chemical kinetics of DME, particularly at elevated pressures. This is done by obtaining data for auto-ignition and laminar flame speed of DME, which is subsequently used to assess and refine existing chemical kinetic mechanisms. To this effect, a novel optically accessible experimental facility, called DCF (Dynamic Combustion Facility), is first designed, fabricated, characterized and validated for laminar flame propagation studies. In this facility, the combustible mixture in the reactor cylinder is compressed to elevated pressures and temperatures by controlled motion of the reactor piston through a custom-designed hybrid cylinder arrangement. Spark is initiated after compression in the constant volume spherical chamber, yielding an outward propagating flame which is observed by Schlieren imaging technique. The procedures for data interpretation are developed and the experimental conditions under which piston motion induced temperature non-homogeneity is avoided are delineated. The facility is validated by obtaining data for methane/air flame speed at atmospheric and elevated pressures and comparing with the literature data. Subsequently, flame speed data for DME is obtained over a range of pressures and compared with predictions from recent chemical kinetic mechanism. The phenomenon of autoignition in the low-to-intermediate temperature region is of great practical importance in engines. Advanced combustion engines are based on low temperature combustion regime. Operation at these low temperature strategies is significantly kinetically-influenced by the complex low temperature chemistry of fuels. Therefore, autoignition of DME is investigated at low temperatures (630-785 K) and high pressures (8-38 bar) over a range of equivalence ratios (1-6) using a Rapid Compression Machine (RCM). In addition, the effect of CO2 addition on ignition is investigated to gauge the effect of exhaust gas recirculation. Results show that DME is very reactive and there is significant kinetic activity during the compression stroke. Experiments using CO2 show that there is no kinetic effect of CO2 on ignition delay. The experimental data are compared with simulations from available detailed and skeletal chemical kinetic models. In general, there is good overall agreement and discrepancies are noted at low temperatures. The key reactions are identified through flux and sensitivity analysis. The designed facility (DCF) is a novel approach and will be a substantial contribution to the existing arsenal of experimental facilities in combustion. The innovation can extend the range of experimental studies to higher pressures and temperatures, conditions beyond those attainable in existing facilities.

Committee:

Gaurav Mittal, Dr. (Advisor)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

Novel Combustion Technique, Laminar Flame Speed, Dimethyl Ether, DME, Elevated Pressure, Elevated Temperature, Rapid Compression Machine, RCM, Dynamic Combustion facility, DCF

Wang, XionghuiExperimental Investigation of Self-Excited Instabilities in Liquid-Fueled Swirl Combustion
PhD, University of Cincinnati, 2017, Engineering and Applied Science: Aerospace Engineering
A self-excited instability of liquid-fueled swirling combustion in a laboratory scale combustor is investigated in this study.Liquid fuel is injected through a simplex nozzle and mixed with a swirling air flow generated by an in-house designed, radial-radial, counter-rotating swirler. Air is preheated to 400F (477K). Air flow rate is maintained constant during tests while fuel flow rate is varied to achieve different global equivalence ratios. Pressure perturbations were monitored and recorded by two dynamic pressure transducers (Model PCB 116B) located at 4 and 9.5 inches downstream of a dome plate. Global chemiluminescence filtered by a CH* filter is recorded by a photomultiplier tube (PMT). The data of perturbed pressure and instant chemiluminescence emission are saved simultaneously through a high-response-data-acquisition board. Instant flame image indicating spatial chemiluminescence fluctuations is recorded by a high-speed camera. Acoustic boundaries of the combustion chamber’s inlet and outlet were first characterized. For the no bias flow case, the swirler impedance exhibits classical compact-element characteristics. When bias flow is presented, the swirler impedance greatly depends on flow Mach number. The temperature dependence of the impedance is captured in the wavenumber. The chamber exit impedances were measured and curve-fitted into correlations. Then the flame response to air modulation is studied at four equivalence ratios. A loudspeaker is used to perturb plenum air in a 22.5 inches (0.5715m) long combustion chamber. The flame dynamics are expressed as flame transfer functions which are defined as the ratio of relative global heat release rate oscillations to the relative velocity fluctuations at the base of the flame, and calculated within the range of tested equivalence ratio. The behavior of the flame dynamics indicates that the combustion system is similar to a damped high-order system. At last, the instability map of the studied swirler is established. Pressure and flame chemiluminescence emission oscillations were recorded. Velocity oscillations are computed from pressure perturbations using a two-microphone method. The measurements recovered Rayleigh’s criterion which states that when pressure perturbation and unsteady heat input are in phase, combustion instability tends to occur. During tests, a sudden increase of static pressure was observed while air mass flow rates remained the same when combustion instabilities occurred, indicating the air flow temperature at the exit of the swirler increased. Meanwhile, the intensity of chemiluminescence emissions inside the swirler venturi observed from the top view of the combustion chamber became stronger at the occurrence of combustion instability. A possible theory of burning inside the venturi or burning on the fuel nozzle tip is proposed. The possible relation of burning inside the venturi and the occurrence of combustion instability is investigated. The variation of air mass distribution between the primary swirler and secondary swirler due to burning inside the venturi is checked using a numerical simulation. The increased flow Mach number at the chamber inlet altered the inlet acoustic impedance. The outcomes of burning inside the venturi are in favor of combustion instabilities. The universality of the relationship between burning inside the venturi and combustion instability requires further investigations.

Committee:

San-Mou Jeng, Ph.D. (Committee Chair); Jongguen Lee, Ph.D. (Committee Member); Asif Syed, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Combustion Instability;Swirling Flow;Heat release rate oscillation;Liquid-fueled swirling combustion

Abd El-Nabi, BassamSingle Annular Combustor: Experimental investigations of Aerodynamics, Dynamics and Emissions
PhD, University of Cincinnati, 2010, Engineering : Aerospace Engineering
The present work investigates the aerodynamics, dynamics and emissions of a Single Cup Combustor Sector. The Combustor resembles a real Gas Turbine Combustor with primary, secondary and dilution zones (also known as fuel rich dome combustor). The primary jets considerably contribute to the heat release process at high power conditions. Also, the primary jets drastically impact the flow field structure. Therefore, the parameters influencing the primary jets are studied using PIV (pressure drop, jets size, off-centering, interaction with convective cooling air, jet blockage and fuel injection). This study is referred to as a jet sensitivity study. The results indicate that the primary jets can be used effectively in controlling the flow field structure. A pressure drop of 4.3% and 7.6% result in similar flows with no noticeable effect on the size of the CRZ and the four jets wake regions. On the other hand, the results show that the primary jets are very sensitive to perturbations. The cooling air interacts with the primary jet and influences the flow field although the momentum ratio has an order of magnitude of 100:1. The results also show that the big primary jets dictate the flow field in the primary zone as well as the secondary zone. However, relatively smaller jets mainly impact the primary zone. Also, the results point to the presence of a critical jet diameter beyond which the dilution jets have minimum impact on the secondary region. The jet off-centering shows significant effect on the flow field though it is on the order of 1.0 mm. The jet sensitivity study provides the combustion engineers with useful methods to control the flow field structure, an explanation for observed flow structure under different conditions and predictable flow field behavior with engine aging. All results obtained from the jet sensitivity study could be explained in terms of jet opposition. Hence, similar results are expected under reacting conditions. The combustion instabilities are studied using a microphone, high speed camera and regular cameras. The frequency spectrum for the sector is established at different pressure drops (2, 4 and 6%) as well as different pre-heat temperatures (200, 400 and 600F). The acoustic spectrum suggests that there are three frequencies of concern (280, 400 and 600 HZ). The high frequency appears to be related to the combustor ¼ longitudinal wave. The 280 Hz is due to a rotating instability while the 400 Hz is related to the primary jets. The emissions emanating from the combustor are studied using FTIR at pressure drop of 4% and different power conditions. The sector emissions characteristics are determined. Water injection is also used to control the pollutant emissions. Water fuel ratio of 100% and 50% results in a corresponding reduction in the NOx concentration with 50% and 22%. No noticeable effects are observed on the NOx and CO at low power conditions. A high degree of homogeneity in the emissions contours is observed at the combustor exit at low power conditions. However, this homogeneity is noticeably reduced at high power conditions.

Committee:

San-Mou Jeng, PhD (Committee Chair); Milind Jog, PhD (Committee Member); Mustafa Andac, PhD (Committee Member); Shaaban Abdallah, PhD (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Primary jets senstivity;Swirling flow;Combustion Aerodynamics;Combustion Dynamics;Emissions control;Engine Aging effects

Ahmed, AbdelallahInvestigation of High Pressure Combustion and Emissions Characteristics of a Lean Direct Injection Combustor Concept
MS, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering
The present work investigates emission characteristics and flame behavior of a Lean Direct Injection (LDI) combustor at elevated inlet air temperatures and pressures. The LDI consisted of a 9-point fuel injection system setup in a 3 by 3 array, where each point is made of a fuel nozzle fitted into a counter-rotating radial-radial swirler.To optimize flame anchoring and low NOx potential, two swirlers with varying intensities were used. Swirler #1 has a swirl number of 1.03 and is considered the high strength swirler. The larger recirculation zone created by this swirler is desirable for the increased turbulence and residence time, which will allow for more complete combustion and flame anchoring. Swirler #2 has a swirl number of 0.6, and is considered the low strength swirler. The higher axial velocities of this swirler allowed for a decreased residence time, which will lessen NOx production. To balance flame anchoring with lower NOx potential, 3 high strength swirlers were used in the central row of the array and 6 low strength swirlers were placed in the first and third row. To allow for a wide range of operating conditions, three fuel stages were employed with this combustor. The three stages consist of the pilot flame, which is the central cup operating solely, the 5 cup-staged flame, which is the central circuit operating with the 4 side circuit, and the 9 cup-staged flame, which is all active injection points. Three emission probes collected localized combustion byproducts, which were used to measure the molar fractions of nitric oxide, nitrogen dioxide, carbon monoxide, oxygen, and unburned hydrocarbons. Tests were undertaken with inlet air temperatures and pressures varying from 400°F (478-K) to 515°F (541-K) and 1-atm to 7-atm, respectively. Test results indicate that NOx formation is highly dependent on the fuel staging. The emission index of NOx (g-NOx/Kg-Fuel) were similar for just the central circuit lit (pilot) to all circuits lit (9-cup). For example, with 400°F inlet air temperature at 4atm, the EINOx for the pilot (φ=0.16), 5-cup (φ=0.35), and the 9-cup (φ=0.60) flames were 1.4 g/Kg, 1.35 g/Kg, and 1.56 g/Kg, respectively. However, the EINOx becomes exponentially proportional to the equivalence ratio when considering the three injection circuits independently. Correlations of the EINOx were developed for the three circuits with independent variables being equivalence ratio, inlet pressure and inlet air temperature. The experimental results indicate that this combustor generates NOx at similar rates as lean premixed combustors. However, the benefits of the LDI is its inherent ability of avoid unwarranted flashback and auto-ignition.

Committee:

San-Mou Jeng, Ph.D. (Committee Chair); Ahmed M. ElKady, Ph.D. (Committee Member); Shaaban Abdallah, Ph.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Lean Direct Injection;Low NOx;High Pressure Combustion;Aviation Combustion

Hossain, Abu NomanCombustion of solid fuel in a fluidized bed combustor
Master of Science (MS), Ohio University, 1998, Mechanical Engineering (Engineering)

The emissions of pollutants from power plants have become the subject of increasing public concern. Legislation limiting the amount of emitted pollutants has made control of pollutants such SOx, NOx, CO, and particulates a major concern in designing and operating coal fired power plants. Another important environmental issue addressed here is the recent surge in landfill closure. Environmental concern, cost, and availability of new land are major causes for the recent escalation of landfill costs. An alternative to the waste disposal in landfill is the solid waste incineration. Disposal of solid waste through incineration, while offering numerous advantages, produces numerous pollutants. Operating and initial costs associated with the control of these emissions are high. As a result of both engineering and regulatory concerns, researchers are looking for combustion processes with higher efficiency and improved pollutant control. Fluidized Bed Combustion (FBC), which utilizes the phenomenon of fluidization for the purpose of more efficient combustion, has shown the potential to meet these demands at lower costs. FBC is studied in this thesis for the possible reduction of air emissions from coal and solid waste combustion.

The evaluation of design, development of a fluidized bed combustor, the analysis of the fluidizing phenomena, and the combustion process for an unspecified fuel are discussed in this work. In general, the fuel must be fed into a heated bed for combustion. The entrained particles need to be separated from the exhaust gas and unburned particles have to be returned to the bed for complete combustion. The whole system must be integrated to perform the desired operations. However, the prediction of the particle's behavior, the rates of mass and heat transfer, combustion reactions, and distribution of fuel and sorbent within the bed is difficult to predict accurately. Therefore, the design process requires the modeling of the bed in finding the key design parameters. Analytical models are needed to simulate the behavior of the bed in the desired operating conditions and be solved by computer codes to find the design parameters. An acrylic prototype model is also needed to verify analytical data. Agreement between experimental data and analytical predictions would indicate that the corresponding data would be suitable for design. Actual construction and equipment specifications necessary to meet constraints, both engineering and economic, are also needed to complete the design description.

Committee:

David Bayless (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Pollutants; Fluidized Bed Combustion; Combustion Process

Ichihashi, FumitakaInvestigation of Combustion Instability in a Single Annular Combustor
MS, University of Cincinnati, 2011, Engineering and Applied Science: Aerospace Engineering
The well known criterion for combustion instability is called the Rayleigh’s criterion. It indicates that, for combustion instability to occur, the heat release rate (q’) and pressure oscillation (p’) must be in phase. This thesis describes measurement techniques and study methods for combustion instabilities that occurred in the prototype single annular sector Rich-Burn Quick-Mix Lean-Burn (RQL) combustor on the original (short) and new (long) experimental rig configuration with a focus on q’ and p’ measurements. A change in the configuration of the combustor rig was necessary in order to acquire more precise measurements of forward- and backward-moving acoustic pressure waves within the rig by mounting pressure transducers on preselected locations of the upstream duct, downstream duct and combustion area. Pressure transducers provided such local pressure behaviors as amplitude and frequency per location, also in addition to transfer functions that allow for the calculation of the acoustic impedance at any location within the combustor rig. A high-speed camera was capable of filming a chemiluminescene image, i.e., the rate of heat release through a quartz window that is mounted on the side of the combustor. Two imaging analysis techniques, Proper Orthogonal Decomposition and Fourier Transformation, were applied to the chemiluminescene image obtained by a high-speed video device. Two different test cases were investigated. Both a high and low fuel-to-air ratio were used for the investigation of the Rayleigh’s criterion, which was confirmed by the corresponding q’ and p’ data sets. Finally, the resonance frequency that agrees with combustion instability was well predicted by utilizing the one-dimensional wave propagation theory and the known geometry of the combustor rig, temperature of fluid, and boundary conditions.

Committee:

San-Mou Jeng, PhD (Committee Chair); Shanwu Wang, PhD (Committee Member); Kelly Cohen, PhD (Committee Member); Asif Syed, PhD (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Combustion Instability;POD;RQL;Proper Orthogonal Decomposition;Combustion Acoustic;Rayleigh's Criterion

Stalcup, Erik JamesNumerical Modeling of Upward Flame Spread and Burning of Wavy Thin Solids
Master of Sciences, Case Western Reserve University, EMC - Aerospace Engineering
Flame spread over solid fuels with simple geometries has been extensively studied in the past, but few have investigated the effects of complex fuel geometry. This study uses numerical modeling to analyze the flame spread and burning of wavy (corrugated) thin solids and the effect of varying the wave amplitude. Sensitivity to gas phase chemical kinetics is also analyzed. Fire Dynamics Simulator is utilized for modeling. The simulations are two-dimensional Direct Numerical Simulations including finite-rate combustion, first-order pyrolysis, and gray gas radiation. Changing the fuel structure configuration has a significant effect on all stages of flame spread. Corrugated samples exhibit flame shrinkage and break-up into flamelets, behavior not seen for flat samples. Increasing the corrugation amplitude increases the flame growth rate, decreases the burnout rate, and can suppress flamelet propagation after shrinkage. Faster kinetics result in slightly faster growth and more surviving flamelets. These results qualitatively agreement with experiments.

Committee:

James T'ien (Committee Chair); Joseph Prahl (Committee Member); Yasuhiro Kamotani (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

modeling;simulation;numerical modeling;combustion;computational combustion;direct numerical simulation;flame spread;burning;wavy;corrugated;fire dynamics simulator;FDS;fuel structure;fuel geometry;complex geometry;cardboard;

Zhu, Yonry RApplications and Modeling of Non-Thermal Plasmas
Bachelor of Science (BS), Ohio University, 2018, Engineering Physics
This thesis focuses on validation of a 0D plasma kinetic model and its subsequent use as an explanatory tool to support the results of hot-fire tests of a plasma assisted rotating detonation combustor. The plasma model predictions showed good agreement with experimentally measured values of various ground state species number densities, vibrationally excited N2 number densities, plasma temperatures, and ignition delay times. Once validated, the plasma model was combined with a ZND detonation model and semi-empirical correlation to determine the effects of a non-thermal plasma on the reduction of the detonation cell size for an H2 - air mixture. The modeling results showed that non-thermal plasma significantly reduces the detonation cell size. This effect is most pronounced at lean conditions, where the model predicted a reduction in cell size by a factor of more than 100. For stoichiometric and rich conditions, the cell size reduction was around a factor of 5. An investigation was conducted to determine the viability of using a non-thermal plasma to expand the operating regime of a rotating detonation combustor. The plasma was produced with a nanosecond pulse generator connected to a ceramic and metal centerbody electrode. Hot-fire testing results showed that the plasma causes detonation onset in conditions that would otherwise not support detonation. This effect was most prominent at near-stoichiometric conditions, with a reduced effect for richer or leaner mixtures.

Committee:

David Burnette (Advisor)

Subjects:

Aerospace Engineering; Mechanical Engineering; Plasma Physics

Keywords:

non-thermal plasma; plasma assisted combustion; nanosecond pulsed plasma; plasma modeling; detonation combustion; rotating detonation combustor; detonation;

Perkins, Hugh DouglasDevelopment and Demonstration of a Computational Tool for the Analysis of Particle Vitiation Effects in Hypersonic Propulsion Test Facilities
Doctor of Philosophy, Case Western Reserve University, 2009, EMC - Mechanical Engineering

In order to improve the understanding of particle vitiation effects in hypersonic propulsion test facilities, a quasi-one dimensional numerical tool was developed to efficiently model reacting particle-gas flows over a wide range of conditions. Features of this code include gas-phase finite-rate kinetics, a global porous-particle combustion model, mass, momentum and energy interactions between phases, and subsonic and supersonic particle drag and heat transfer models. The basic capabilities of this tool were validated against available data or other validated codes.

To demonstrate the capabilities of the code, and to provide initial insight into the effects of various particle laden flows on ignition, a series of computations were performed for a model hypersonic propulsion test facility and scramjet. Parameters studied were simulated flight Mach number (Mach 5, 6, and 7), particle size (10, 100, and 1000 micron diameters), particle mass fraction (single particle and 1%) and particle material (alumina and graphite). For the alumina particles, it was found that the presence of particles up to 1% mass fraction had very little effect on the gas phase, even though only the 10 micron particles closely followed the gas flow velocity and temperature. With the graphite particles, the 10 micron particles were either quickly quenched, or were quickly consumed, depending on the gas temperature. As the particle size was increased to 100 microns, the particles did not quench, but were still typically consumed within the model test facility. For the 1000 micron particles, combustion was diffusion limited, so particle and gas temperature had little effect on the combustion rate. When the particle mass fraction was increased to 1%, the main change was the addition of significant heat release. In those cases where low graphite reaction rates were observed for single particles, the increase to 1% mass fraction had very little impact.

Hydrogen/vitiated air ignition delay calculations for the 1% mass fraction of graphite particles cases showed significant decreases in ignition delay in cases where higher graphite combustion rates were observed. Further calculations showed that this was due primarily to increased combustor inlet temperature, not the gaseous or solid vitiate species present in the flow.

Committee:

Chih-Jen Sung, PhD (Advisor); James Tien, PhD (Committee Member); Yasuhiro Kamotani, PhD (Committee Member); Steven Izen, PhD (Committee Member)

Subjects:

Engineering; Mechanical Engineering

Keywords:

Gas-Particulate Flows; Hypersonic Wind Tunnel; Graphite Combustion; Flow Vitiation; Scramjet Testing; Hypersonic Propulsion; Particle Combustion

Next Page