Department of Mechanical Engineering

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Natural Gas/Diesel Dual Fueling of a Prechamber Type Diesel Engine
(University of Alabama Libraries, 1990) Ramsey, Charles Burton Jr; University of Alabama Tuscaloosa
The diesel engine, or the compression ignition engine, was invented by Dr. Rudolph Diesel, who patented the device in 1892. Diesel's patent covered the use of coal dust as a fuel, but also included other solid, liquid, or gaseous duels. Some of the fuels tried during the initial development of this engine included coal-tar mixtures, blends of coal dust and oil, and petroleum-based products.
Kinetic Model of a Collisional Admixture in Dusty Gas and its Application to Calculating Flow Past Bodies
(2000) Volkov, Alexey N.; Tsirkunov, Yury M.; University of Alabama Tuscaloosa
Using the methods of statistical physics, the basic kinetic equation describing the dynamics of a polydisperse admixture of solid particles in a dilute dusty-gas flow is derived. Particle rotation, inelastic collisions, and interaction with the carrier gas are taken into account. The basic kinetic equation is used to obtain a Boltzmann-type equation for the one-particle distribution function, for which the boundary conditions for the problem of dusty-gas flow past a body are formulated. On the basis of the kinetic model developed, using direct statistical modeling, the flow patterns and the fields of the dispersed-phase macroparameters in a uniform crosswise dusty-gas flow past a cylinder are obtained for various free-stream particle sizes and concentrations.
Characterization and comparison of white layer by hard turning versus grinding
(University of Alabama Libraries, 2004) Sahani, Jasdeep Singh; University of Alabama Tuscaloosa
Compared with grinding, hard turning has the potential to make a variety of precision components of superior surface integrity, such as bearings, gears, cams, shafts, tools, dies, etc., while reducing investment, increasing production rate, and eliminating environmental pollution. Despite its spectrum of advantages over cost intensive grinding process, industrial realization of hard turning still remains in incipient stage. The low industrial acceptance of hard turning may be attributed to uncertainty related to surface quality especially for the white layer which is a key factor of surface integrity and thus product performance.
Numerical Modelling of the Magnus Force and the Aerodynamic Torque on a Spinning Sphere in Transitional Flow
(2007) Volkov, Alexey N.; University of Alabama Tuscaloosa
Three dimensional transitional flow over a spinning sphere is studied numerically by the direct simulation Monte Carlo method. The flow is assumed to be steady-state, gas molecules interact with each other as hard spheres and the speculardiffuse scattering model describes the interaction between molecules and the sphere surface. The translational and rotational velocities of the sphere is assumed to be perpendicular to each other. The drag coefficient, the Magnus force coefficient and the torque coefficient are found as functions of the Mach and Reynolds numbers and the dimensionless rotation parameter for subsonic and supersonic flows. Computational results are compared with the analytical solution for a spinning sphere in free molecular flow and with available semi-empirical data. The "critical" Knudsen number when the Magnus force is equal to zero is found as a function of the Mach number.
3D Numerical Modelling of a Rarefied Gas Flow in the Nearby Atmosphere around a Rotating Cometary Nucleus
(2007) Volkov, Alexey N.; Lukyanov, German A.; University of Alabama Tuscaloosa
A combined 3D model of a nearby atmosphere around an arbitrary rotating spherical cometary nucleus is developed. The model includes a 3D unsteady model of solar radiation absorption and heating of the nucleus material (water ice), its evaporation and condensation and a 3D quasi-stationary kinetic model of flow inside the near nucleus coma. This model can be used to predict the coma flow in conditions typical for rendezvous projects such as ESA project Rossetta. Calculations are carried out with the help of this model to reveal the influence of nucleus rotation on its temperature field and the flow field in the nearby atmosphere. It was found that the nucleus rotation influences significantly the nucleus temperature field and the coma flow. Vapor flow around a rotating nucleus is essentially three dimensional and differs qualitatively from the coma flow around a non-rotating nucleus.
A study of heat fluxes in oblique cutting of A390 using infrared imaging and inverse heat conduction
(University of Alabama Libraries, 2009) McCarty, Sean Christopher; Woodbury, Keith A.; University of Alabama Tuscaloosa
The energy released during mechanical cutting is carried away by the metal chips and conduction into the tool. This report focuses on determination of the heat fluxes into the tool during orthogonal cutting using Beck's method. An infrared camera is used to measure the temperature rise on the surface of a cutting tool during turning of aluminum A390 cylinders. A detailed model of the tool in FLUENT is used to compute the sensitivity coefficients for the temperature response at specified sensor locations due to a unit heat flux disturbance at the cutting zone. These sensitivity coefficients are used in Beck's method along with the measured temperature history, to determine the heat flux history at the cutting zone.
Computational fluid dynamic analysis of the purification process of the neutrino detector KamLAND
(University of Alabama Libraries, 2009) Cossey, Aaron Mitchell; Woodbury, Keith A.; University of Alabama Tuscaloosa
A simplified two-dimensional finite volume axisymmetric mesh was constructed that represented the geometry of the Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND) experiment in order to perform a computational fluid dynamics (CFD) analysis of the purification process of the liquid scintillator (LS). 1,000 tons of the LS, contained within a 13 meter-diameter spherical balloon in the center of the detector, is purified in a continuous process where the LS is simultaneously withdrawn from the bottom and replaced at the top of the detector. During this purification process, the interface between the newly purified and unpurified LS is not stratified horizontally as expected, but instead mixing is observed, reducing the efficiency of the process and preventing the desired level of purification throughout the LS. Using the commercial CFD software FLUENT, the purification process of the experiment was simulated based on the conditions and data previously recorded during the purification phase. The CFD analysis of the experiment was modeled as a transient problem, with flow and heat transfer solved. The phenomenon of natural convection was modeled using the Boussinesq approximation. The volume of fraction (VOF) method was used to track the interaction between the purified and unpurified liquids in the simulation. The CFD simulation will be used to test proposed improvements to the purification process for future purification programs of KamLAND. The CFD simulation will serve as a guide to test these improvements and improve the efficiency of the process.
Statistical tomography for scalar turbulence measurements using line of sight optical techniques
(University of Alabama Libraries, 2009) Kolhe, Pankaj Sharadchandra; Agrawal, Ajay K.; University of Alabama Tuscaloosa
Turbulence has been an intriguing subject for several decades with past studies focusing on understanding the transition to turbulence and characterizing turbulence using statistical tools. In present research rainbow schlieren deflectometry (RSD), a line of sight optical technique, is used and its high spatio-temporal resolution measurement capability is demonstrated through transitional hydrogen gas jet diffusion flame experiments wherein hitherto unknown secondary instability in flame surface is captured by employing 23 microseconds exposure time and 400 micro-meter/pixel resolution at 2000 Hz image sampling rate. Significant effects of buoyancy previously thought unimportant are identified and a conceptual view of transitional jet diffusion flames illustrating various instabilities is developed. The quantitative characterization of turbulent flow requires local scalar field statistics. However, RSD provides path integrated measurements that must be deconvoluted to obtain the local field statistics. For round turbulent jets, Abel inverse transform can be used to deconvolute time averaged local field quantities such as mean refractive index difference. Based on critical evaluation of four techniques two point formula, a semi-analytical approach, is recommended to evaluate the improper integral in Abel inverse transform with best accuracy and minimum error propagation. For deconvolution of second moment statistics (scalar fluctuation intensity) from path integrated measurements cross beam correlation (CBC) algorithm is presented and analyzed using noise free synthetic scalar turbulent data. CBC algorithm is found to yield accurate reconstruction only in fully developed turbulent flows and it required knowledge of statistics at inlet boundary that are generally unknown. To overcome limitations of CBC algorithm, a novel spectral analysis algorithm is developed and verified using synthetic scalar turbulent data. The algorithm provided local field statistics (mean and variance) at high accuracy using path integrated data in only one line of sight. Present implementation was limited to time averaged axisymmetric turbulent flow although its extension to asymmetric flow is feasible. Spectral analysis algorithm was applied for measurements in a turbulent helium jet with diameter, d = 2.96 mm at Reynolds number, Re = 3500 and Richardson's number, Ri =0.0000102335. Mean, variance, autocorrelation function, and power spectra of local scalar properties are presented to characterize the turbulent flow.
Study of a cold start fuel produced by an active vapor utilization system for use in gasoline powered vehicles
(University of Alabama Libraries, 2009) Crawford, John William; Ashford, Marcus D.; University of Alabama Tuscaloosa
This research focuses on the continuous development of the Active Vapor Recovery System (AVUS) which has the potential to reduce unburned hydrocarbon emissions from automobiles. The AVUS collects, condenses and stores hydrocarbon vapors from the fuel tank and saves them in a pressurized storage tank for later use as a cold starting fuel. This highly volatile starting fuel has the capability to reduce tailpipe emissions that occur during cold starts, as well as evaporative emissions that occur while the vehicle is at rest. Instead of commercial gasoline, the bench top AVUS was run using a five component fuel composed of 25% iso-pentane, 17.5% hexane, 17.5% heptanes, 17.5% toluene, and 22.5% isooctane; as well as an E85 mixture composed of 15% five component fuel and 85% ethanol. The condensate produced from AVUS was then analyzed using simple gas chromatograph techniques and found to have as much as 75% iso-pentane. Such a mixture would be an excellent starting fuel. Successive tests on the same batch of fuel proved that AVUS can produce this starting fuel without depleting the parent fuel of the species needed for non-AVUS starts. Index of refraction and infrared tests were also used in an attempt to establish reliable correlations between the condensate composition, refractive index, and infrared absorption that could be used for onboard analysis of the starting fuel. However, index of refraction results were found to be inconclusive while infrared testing proved to have great potential for determining alcohol concentration.
Spray characteristics and combustion performance of unheated and preheated liquid biofuels
(University of Alabama Libraries, 2010) Panchasara, Heena V.; Agrawal, Ajay K.; University of Alabama Tuscaloosa
Recent increases in fuel costs, concerns for global warming, and limited supplies of fossil fuels have prompted wide spread research on renewable liquid biofuels produced domestically from agricultural feedstock. In the present research diesel, Vegetable Oil (VO), two types of biodiesel produced from VO and animal fat are investigated as potential fuels for gas turbines to generate power. Experiments are performed using a laboratory scale burner simulating gas turbine combustor operated at atmospheric pressure. A commercially available air blast (AB) atomizer is used to create the fuel spray. A parametric study of combustion performance (CO and NOx emissions) and spray characteristics (droplet diameter, drop size distribution, and mean and RMS axial velocities) is carried out by varying air to liquid mass ratio (ALR),and fuel inlet temperature in cold spray and spray flame with/without swirl air and without/with enclosure. The problems of high viscosity and poor volatility of VO (soybean oil) were addressed by using diesel-VO blends with up to 30% VO by volume. Gas chromatography/mass spectrometry, thermogravimetric analysis, and density, kinematic viscosity, surface tension and water content measurements are used to characterize the fuel properties. Characteristics of the resulting spray are measured using a laser sheet visualization system and a Phase Doppler Particle Analyzer system (PDPA). However, several operational and durability problems of using straight VO's for direct combustion occur because of their higher viscosity and low volatility compared to diesel fuel. The high kinematic viscosity of vegetable oil (VO) makes it unsuitable for direct combustion using conventional fuel preparation systems. Thus, we preheat the fuel to reduce its kinematic viscosity and to improve fuel atomization. Measurements are obtained for fuel inlet temperature varying from 40 to 100°C and for ALR varying from 2 to 4. Results show that an increase in the fuel inlet temperature decreases NOx and CO emissions, which can be attributed to improved fuel atomization resulting from decreased kinematic viscosity at higher fuel temperatures. Results also show a decrease in Sauter Mean Diameter (SMD) with an increase in VO temperature, regardless of the ALR at any given axial location in the spray. A significant difference in the distributions of mean and root mean square (RMS) axial velocity occurs with an increase in VO inlet temperature for a fixed ALR, presence of swirling air, and presence of flame. In general, the radial profiles show larger droplets distributed towards the edge of the spray and smaller droplets in the interior spray region. Higher VO inlet temperature and higher ALR produced a narrower spray with smaller diameter droplets and higher peak axial velocities. Swirling air flow and of high temperatures in flames facilitates secondary breakup of larger droplets to significantly reduce the SMD. Finally the effect of enclosure is also studied since it represents a more realistic combustor design for any continuous flow system. The insulated enclosure eliminated the ambient air entrainment and minimized hear loss to the ambient air to create a fine spray flame with characteristics similar to those of an open flame.
Vibration absorber implementation for space launch vehicle vibration reduction
(University of Alabama Libraries, 2010) Lozes, Brian Andrew; Williams, Keith A.; University of Alabama Tuscaloosa
Vibration is a major problem in space launch vehicles during burning sequences. These vehicles are vulnerable to impulsive and pulsed vibrations like those produced by rocket engines. The Ares I launch vehicle is anticipated to produce vibration in the organ pipe mode. The problems may be particularly severe if the pulses occur at the natural frequencies of the vehicle structure. In the case of the Ares, as the rocket burns, the excitation frequency drifts through the frequency corresponding to a longitudinal mode of the vehicle. Although it is not certain, there is concern that the corresponding vibrations are potentially severe enough as to be lethal to crew members and thus some consideration of vibration mitigation is warranted. Common approaches to dealing with vibration problems - structural redesign, addition of mass or damping materials - are not thought to be viable solutions; structural redesign through addition of mass and/or damping would result in excessive weights with corresponding performance limitations in terms of payload. The alternative approach is to retrofit the aft skirt with one or more tuned vibration absorbers (TVA). Application of an undamped TVA to a primary system introduces a zero in the frequency response of the primary system that is located at the TVA natural frequency. In the case of the Ares, however, the excitation frequency, while easily measured, is not fixed, but varies as the rocket burns. The effect of a TVA on the vibration of a primary system experiencing such an excitation is not known. The main objective of this research was to predict and simulate the behavior of a two degree of freedom (two-mass) system experiencing sinusoidal excitation with a linearly-varying frequency. In doing so, a framework for analyzing a primary system with a TVA implemented was realized. The resulting software was then used to model implementation of a specific TVA solution. Through analytical and simulated solutions, it was confirmed that a specific TVA could be used to effectively absorb the response at target frequencies when acted upon by a linearly changing oscillatory input.
Background UV in the 300 to 400 nm region affecting the extended range detection of radioactive material
(University of Alabama Libraries, 2010) West, William Carey; Fonseca, Daniel J.; University of Alabama Tuscaloosa
The desire to find alternative methods for the detection of radioactive material at extended ranges has resulted in an increased interest in the detection of the air fluorescence resulting from the alpha or beta radioactive particle's interaction with molecules of air. Air fluorescence photons travel further than the radioactive particles, allowing for detections at longer distances. However, any detection of the ultraviolet (UV) air fluorescence is dependent on overcoming natural and man-made background UV to achieve favorable signal to noise ratios. This research describes laboratory and field experiments conducted to determine the background UV in the 300 to 400 nm region of the electromagnetic spectrum for certain detection scenarios, and number of UV air fluorescence photons required to achieve detections with a certain confidence limit. The reflective, scintillation, and transmissive UV characteristics of some common materials are discussed and their contribution to a successful detection explored. Additionally, the contributions to the UV background from natural and man-made light sources are investigated. The successful outside optical detection of alpha and beta radioactive isotopes in the 300 to 400 nm region is possible in the lower part of the spectral region (i.e., near 316 nm), when there is no UV light from man-made sources in that band and only natural light exists. Alpha sources (i.e., ^241 Am) equal to or larger than 1.017 curies, theoretically can be detected with 95% confidence during nighttime scenarios with moonless overcast skies at a distances of 20 meters at 316 nm with the optical system assumed for these calculations. Additionally, where scintillators are available that can be employed near ^90 Sr radioactive sources, the detectable activities can be reduced by factors as high as 250. This allows for detections of sources in the millicuries. Tests results are presented for several common materials (e.g., polypropylene, high density polyethylene, low density polyethylene, etc.) that scintillate in the presence of ^90 Sr and can be used to achieve gains in the 100s in the air fluorescence bands centered on 316 nm and 337 nm.
Design of a powered above knee prosthesis using pneumatic artificial muscles
(University of Alabama Libraries, 2010) Waycaster, Garrett Clinton; Shen, Xiangrong; University of Alabama Tuscaloosa
This paper describes the mechanical design for both a one and two degree of freedom above-knee (AK) prosthesis actuated by pneumatic artificial muscles. Powered prosthetics aim to improve the quality of life of the 50% of AK amputees who never regain the ability to walk. Pneumatic artificial muscle (PAM) provides great potential in prosthetics, since this type of actuator features a high power density and similar characteristics to human muscles. Currently, commercially available AK prosthetics are largely passive devices, and no research has been conducted on PAM actuators in AK prosthetics. In this thesis, the design requirements of an above knee prosthesis using PAM are discussed and a prototype one degree of freedom prosthesis with a PAM actuated knee joint is constructed. This prototype is then tested, and based on the results a new actuator is developed. This new actuator uses a flexible tendon and an elliptical pulley to improve torque, adding more functionality and increasing the maximum mass of a user by 25 kilograms. This actuator is also tested and compared to the initial prototype design. Finally, this new actuator is incorporated into the design of a two degree of freedom prosthesis with an actuated ankle as well as the knee joint.
The effects of drive cycle accessory load and degree of hybridization on fuel economy and emissions for hybrid electric buses
(University of Alabama Libraries, 2010) Chen, Dennis; Midkiff, K. Clark; University of Alabama Tuscaloosa
Hybrid Electric Vehicles (HEVs) have gained much attention in recent years. This is mainly due to rising fuel prices and increasing environmental awareness. By implementing electricity as one of the power sources, a HEV can not only reduce fuel consumption but can also decrease tailpipe emissions. In this thesis, the software package Powertrain Systems Analysis Toolkit (PSAT) was chosen as the simulation tool to model several bus powertrain configurations - conventional, three different degrees of hybridization parallel hybrid electric (PHEB), and a series hybrid electric (SHEB) to predict fuel economy and emissions level. The simulations were run with a typical accessory load, 15 kW, for a 40-foot transit bus as well as for no accessory load. The effect of accessory load on fuel economy was identified. Four different drive cycles - Manhattan, UDDS, CBD, and WVU City cycles - that covered a wide range of driving conditions were chosen as the testing cycles for the simulations. For no accessory load, it was found that the PHEB1, which had the highest degree of hybridization, yielded the best fuel economy improvement on all four drive cycles. The highest fuel economy improvement without accessory load, 121.9%, was found for the Manhattan cycle. The maximum fuel economy improvement, 51.8%, for a 15 kW accessory load also occurred running the Manhattan cycle, and was achieved by the PHEB1 as well. The maximum fuel economy reduction with a 15 kW accessory load was 48.9%. The largest emissions reductions with a 15 kW of accessory load were achieved by the PHEB1 operated in the Manhattan cycle, with NOx and PM emissions reductions of 73.4% and 45.9% over the conventional bus, respectively. Based on the emissions analysis, a bus with better fuel economy tends to have lower emissions and a bus with lower gas mileage usually produces more emissions, although there were some exceptions in the inverse relationship between gas mileage and emissions level.
Dynamic behavior and degradation of a fuel cell system
(University of Alabama Libraries, 2010) Jung, Minjae; Williams, Keith A.; University of Alabama Tuscaloosa
In this dissertation, the effect of dynamic operation of a Ballard Nexa 1.2kw fuel cell system is investigated. Three specific topics are considered: the first is an analysis of the dynamic behavior of the fuel cell system, the second is an evaluation and examination of fuel cell membrane degradation during dynamic operation and the last is numerical simulation to predict the transient response in the cell voltage. To enable the analysis of the fuel cell system's dynamic behavior, a simple method for analyzing the system's voltage response to a step change in load resistance is presented. A modified Randles model is used as the system model, where two resistors and two capacitors are implemented for the Warburg impedance. Using that model, the response is fitted with three exponential curves. Six independent equations corresponding to six parameters of the model can be solved using the fitted values, under a specific assumption for the initial state. The impedance is also simulated using the estimated parameters. Cyclic operation is thought to have a negative impact on fuel cell lifetime. The frequency effect of the cyclic operation on chemical degradation is investigated. After calculating each parameter value through exponential curve fitting, the dynamic behaviors of the three resistor-capacitor pairs are simulated using MATLAB Simulink®. In addition, fluoride release as the change of the frequency of cyclic operation is evaluated by measuring the concentration of fluoride ion in effluent of a fuel cell. The frequency effect on chemical degradation is explained by comparing the simulated result and the fluoride release result. Finally, a single-phase numerical model to predict the transients in voltage of a PEMFC is presented. A new approach is developed by classifying the current density by two groups; charging currents which are accumulated in the interfaces where the reaction occurs, and faradaic currents which are charge transfer currents. The successive change of the activation overpotential is calculated by using the charging currents and the element law for an ideal linear capacitor, and then the transient voltage response to a step load change is shown in results.
Development of a low density jet flow apparatus
(University of Alabama Libraries, 2010) Smith, Nicholas Edward; Baker, John; University of Alabama Tuscaloosa
An apparatus was designed and constructed to study supersonic fluid flow in a low temperature and low pressure environment similar to the same conditions associated with near space. The apparatus allows the visualization of supersonic flows through an annular nozzle using a shadowgraph system. The flow system that creates supersonic flows is capable of producing pulsating jets at virtually any frequency. This thesis includes details of design of a near space jet flow apparatus that is capable of producing low temperature and low pressure environment for studying annular jets. The annular jets are produced from a nozzle that may be later incorporated on near space vehicle. After testing, it was discovered that the apparatus was capable of producing low temperatures and low pressures, but the results were inconsistent with a near space environment. The nozzle being studied has a blocking ratio of 0, 0.5 and 0.75. For each blocking ratio, the flow is choked, producing a constant mass flow rate. The theoretical and actual thrust were calculated using propulsion equations. The experimental results were compared to the theoretical, isentropic results. The jet length was also measured as a reference for vehicle design limitations. It was found that the maximum experimental thrust coefficients for a nozzle with blocking ratios of zero, 0.5 and 0.75 were calculated to be 0.430, 0.439, and 0.537 respectively. All maximum thrust coefficients occur at an ambient pressure of 0.5 kPa.
Fabrication, characterization, and tribological performance of micro dent arrays produced by laser shock peening on Ti-6Al-4V alloy
(University of Alabama Libraries, 2010) Caslaru, Roberto; Guo, Yuebin B.; University of Alabama Tuscaloosa
Ti-6AL-4V is a widely used structural material in aerospace, biomedical, and power generation industries due to its low density, good corrosion resistance and high strength properties. However, Ti-6Al-4V is not a suitable material for wear applications due to its tendency to gall. Improving the tribological performance by reducing frictional coefficient and decreasing wear rate may result in significant savings. Laser shock peening (LSP) is a surface treatment designed to induce compressive residual stress and improve fatigue performance. This study presents a novel micro LSP based surface patterning technique to fabricate micro dent arrays. Comprehensive 3D dent topography was measured to evaluate the effect of laser intensity on dent geometry, process repeatability, and pile-up. Surface integrity has been characterized with respect to dent profile, surface residual stress, surface hardness, and microstructure. Post-peening polishing process has been conducted to eliminate the potential pile-up. Tribological performance of dented arrays with and without pile-up and two peening densities was tested at low and high viscosity lubrication conditions using pin-on-disk setup. Real time measurements of the coefficient of friction (CoF) and acoustic emissions were made. Finally, correlations between dent density, CoF, wear rate, and AE signal were investigated. 2D dent profile showed an increase in dent depth and diameter with laser power. 3D surface topography revealed good process repeatability. Pile-up region develops around the dent containing about 40% of the total material volume displaced from the peened region. Consequently, the remaining 60% is compressed within the dented region. Peened surfaces with micro-dent arrays have high compressive residual stress and increased hardness by 37% in the peened zone. Pin-on-disc tribology tests have shown a CoF reduction by 18% on peened surfaces with 10% dent density and pile-up when compared to polished smooth surface under high viscosity conditions. An increase in CoF was found for a surface with 20% dent density and pile-up when compared to the smooth surface. It was found that removing pile-up reduces CoF with only 2% to 3% for both peening densities. Correlations between wear rate, absolute energy, amplitude, and counts was established. RMS signal has a weak correlation with frictional coefficient.
Lean burn and stratified combustion strategies for small utility engines
(University of Alabama Libraries, 2010) Mahato, Chandan; Midkiff, K. Clark; Puzinauskas, P.; University of Alabama Tuscaloosa
The research presented in this thesis is an effort to improve small engine combustion through the application of lean combustion. The first part of the research is focused on conducting an experimental investigation into the application of lean burn strategy on a single cylinder OHV utility engine to reduce engine-out emissions and at the same time maintain acceptable cyclic variability in combustion. The parameters of interest to investigate cyclic variability in combustion were spark plug variations, load control and charge stratification. The main findings showed that the spark discharge energy had a major influence on engine performance. It was also found that the engine can be operated at a high volumetric efficiency and very lean AFR at 75% and 50% load by the use of fuel injection. This is especially helpful for small engines operating on the EPA B-cycle. The second part of the research deals with the study of a Flat head, also known as side valve (SV) engine platform. A novel approach to lean combustion in a flat head engine is proposed by directly injecting gasoline fuel into the combustion chamber. The main advantage of the direct injection flat head (DIFH) engine over the conventional OHV GDI engine is its simplicity in design, low cost and, greater flexibility in placement of key engine performance hardware in the cylinder head. To first understand the behavior of the in-cylinder air motion, the air-flow structure developing within the combustion chamber was investigated using PIV techniques. The results show that squish is the dominant turbulence generating mean flow structure in the combustion chamber of the DIFH engine. Although the DIFH engine produced about 8 times more UHC emissions as compared to the conventional spark ignited OHV engines, it produced about 5 times less CO emissions as compared to the OHV engine and showed a 16% improvement in brake specific fuel consumption. The current combustion chamber has a dual chamber design exhibiting different combustion mechanisms in both the chambers, causing complex undesirable interactions between key engine performance parameters. Based on these fundamental studies a new combustion chamber design is presented for better performance.
Analytical modeling and design optimization of piezoelectric bimorph energy harvester
(University of Alabama Libraries, 2010) Zhang, Long; Williams, Keith A.; University of Alabama Tuscaloosa
As wireless sensor networks continue to grow in size and scope, the limited life span of batteries produces an increasingly challenging economic problem, in terms of not only the capital cost of replacing so many batteries, but also the labor costs incurred in performing battery replacement, particularly with sensor nodes in remote or limited-access locations. This growing problem has motivated the development of new technologies for harvesting energy from the ambient environment. Piezoelectric energy harvesters (PEH) are under consideration as a means for converting mechanical energy, specifically vibration energy, to electrical energy, with the goal of realizing completely self-powered sensor systems. There are three primary goals with regards to this study. The first goal is to develop an analytical model for the resonant frequency of a piezoelectric cantilever bimorph (PCB) energy harvester, aiming to study the geometric effects of both the piezoelectric bimorph and the proof mass on the resonant frequency of a PEH. The analytical model is developed using the Rayleigh-Ritz method and Lagrange's equation of motion and is validated by finite element analysis (FEA) and laboratory experiments. It is shown that this analytical model is better at predicting resonant frequencies than a model currently available in the literature. The second goal is the development of an enhanced analytical model for the voltage and power output of the PCB. The modified analytical model is realized using the conservation of energy method and Euler-Bernoulli beam theory. It is compared with a general equivalent spring-mass-damper model and an equivalent electrical circuit model, and validated by the laboratory prototype experiments. The results show that the modified model provides improved prediction of PCB voltage and power output. Simultaneously, finite element analysis on piezoelectric structures using the commercially available software package ANSYS® Multiphysics is also carried out to study the dynamic response of the PCB in terms of both tip displacements and the electrical potentials of the top and bottom electrodes. It is shown that the simulations are quite close to the experimental results, in terms of both peak frequencies and peak amplitudes. The third goal is the design optimization of the PCB energy harvester in order to maximize the power harvesting from the ambient vibration. Three design optimization approaches are carried out, including multi-parameter optimization of the single PCB generator using a genetic algorithm (GA), a band-pass generator design with a group of the PCB generators based on the system transfer function, and the new design features of the PCB generator for consideration of the improvements of the strain energy and the lifetime. The results of the optimized designs are validated through FEA, and the discrepancies between the theoretical derivation and FEA are also analyzed. Other optimal design considerations are also discussed.
Fabrication and characterization of bulk nanostructured materials of steel and aluminum alloys by air blast shot peening
(University of Alabama Libraries, 2010) Waikar, Rahul; Guo, Yuebin B.; University of Alabama Tuscaloosa
In recent years, bulk nanostructured materials processed by methods of severe plastic deformation (SPD) have attracted the growing interest in academia and industry. This interest is caused not only by unique physical and mechanical properties inherent to various nanostructured materials, e.g., higher hardness and Young's modulus, etc, but also by the ability of SPD process to create bulk nanostructures. In this dissertation work, air blast shot peening (ABSP) a SPD process using very high shot velocities was used to achieve high strain rates of surface material causing bulk surface nanocrystallization. ABSP process parameters has been extensively investigated to understand their effects on bulk nanostructures formed on steel (AISI 1018, AISI 1045, AISI 1075) and aluminum (Al 6061, Al 7075) components. Finite element simulations have also been carried out to study the effect of peening parameters on stress/strains and temperatures in the peened component. The peened samples have been characterized using optical microscope and scanning electron microscope (SEM) and the grain size shows a gradual reduction from the subsurface to the surface. The grain size of the steel and aluminum peened samples based on the TEM images was less than 50 nm. The nanocrystalline (NC) zone showed a considerably higher hardness as compared to the unpeened material. Lastly a study of corrosion characteristics of the NC layers fabricated on steel and aluminum alloys indicated a higher corrosion potential of the NC layers as compared to the bulk material.

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