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Energy

2006;():3-14. doi:10.1115/IMECE2006-13021.

Retarded injection is used to control NOx emissions. Exhaust Gas Recirculation (EGR) is also an effective means of reducing NOx emissions from compression ignition engines. Higher fuel injection pressure may improve the combustion. EGR can be combined advantageously with other emission reducing measure such as retarded injection timing and performance improvement measures such as higher fuel injection pressure to have a good effect. The methyl ester of jatropha oil, known as biodiesel, is receiving increasing attention as an alternative fuel for diesel engines. Biodiesel is a non-toxic, biodegradable and renewable fuel with the potential to reduce engine exhaust emissions. The jatropha oil methyl ester was obtained through transesterification process. Various properties of the biodiesel thus developed were evaluated and compared in relation to that of conventional diesel oil. In the present investigation neat jatropha oil methyl ester (JME) as well as the blends of varying proportions of JME and diesel were used to run a CI engine with standard conditions (No EGR, No Injection Retard and 20 MPa Fuel Injection Pressure) and with combination of 20 % EGR, 4° retarded injection timing and 30 MPa fuel injection pressure. The addition of jatropha oil methyl ester (JME) to diesel fuel has significantly reduced HC, CO and smoke emissions but it increases the NOx emissions slightly with standard conditions. The NOx emission was drastically decreased with modified conditions. Further the smoke and unburned hydrocarbon emissions were decreased with modified conditions as compared to standard conditions. The brake thermal efficiency was improved with modified conditions at various loads. Exhaust gas temperatures were similar. The maximum cylinder gas pressure and heat release rate were lowered.

Commentary by Dr. Valentin Fuster
2006;():15-27. doi:10.1115/IMECE2006-13048.

An overall stoichiometric mixture of air, gaseous ammonia and gasoline was metered into a single cylinder, variable compression ratio, supercharged CFR engine at varying ratios of gasoline to ammonia. The engine was operated such that the combustion was knock-free with minimal roughness for all loads ranging from idle up to a maximum load in the supercharge regime. For a given load, speed, and compression ratio there was a range of ratios of gasoline to ammonia for which knock-free, smooth firing was obtained. This range was investigated at its roughness limit and also at its knock limit. If too much ammonia was used, then the engine fired with an excessive roughness. If too much gasoline was used, then knock-free combustion could not be obtained while the maximum brake torque spark advance was maintained. Stoichiometric operation on gasoline alone was also investigated, for comparison. It was found that a significant fraction of the gasoline used in spark ignition engines could be replaced with ammonia. Operation on mostly gasoline was required near idle. However, mostly ammonia could be used at high load. Operation on ammonia alone was possible at some of the supercharged load points. Generally, the use of ammonia or ammonia with gasoline allowed knock-free operation at higher compression ratios and higher loads than could be obtained with the use of gasoline alone. The use of ammonia/gasoline allowed practical operation at a compression ratio of 12:1 whereas the limit for gasoline alone was 9:1. When running on ammonia/gasoline the engine could be operated at brake mean effective pressures that were more than 50% higher than those achieved with the use of gasoline alone. The maximum brake thermal efficiency achieved with the use of ammonia/gasoline was 32.0% at 10:1 compression ratio and BMEP = 1025 kPa. The maximum brake thermal efficiency possible for gasoline was 24.6% at 9:1 and BMEP = 570 kPa.

Commentary by Dr. Valentin Fuster
2006;():29-36. doi:10.1115/IMECE2006-13338.

In the recent wake of escalating crude oil prices due to depletion of fossil fuel, biodiesel has generated a significant interest as an alternative fuel for the future. The use of biodiesel to fuel microturbines or gas turbine application is envisaged to solve problems of diminishing supplies of fossil fuel reserves and environmental concerns. This paper examines the combustion of biodiesel derived from Malaysian Waste Cooking Oil (WCO) in a combustion test facility to study the feasibility of using the designated fuel at five various volumetric ratios for gas turbine application. Biodiesel was produced from waste cooking oil in Malaysia, mainly from palm oil sources and animal fats. The oil burner was able to fire the five blends of fuel without any modification or pretreatment. The combustion performance of Malaysian WCO biodiesel and distillate blends was examined with respect to the combustion efficiency. The results indicated biodiesel combustion required less air for stoichiometric combustion due to presence of oxygen in the fuel. Indeed biodiesel stand as a potential alternative fuel for power generation application with the best efficiency at blended ratio of 20% biodiesel and 80% distillate.

Commentary by Dr. Valentin Fuster
2006;():37-50. doi:10.1115/IMECE2006-13874.

The current interest in power generation industry with more efficient and clean, and more environmentally friendly ways has attracted the research and development in solid oxide fuel cell (SOFC). In SOFC, the chemical energy is converted into electric energy and heat as the by-product. In order to make a thermally self-sustained fuel cell stack, the understanding and management of the heat generation and electric power is a critical issue. Infrared thermography provides a non-destructive way to measure surface temperature. It was used to measure the instantaneous cathode surface temperature response to the current in an operating electrolyte supported planar solid oxide fuel cell (LSCF-6ScSZ-NiO). A numerical model was built to study the coupled electric current and temperature relation by incorporating the temperature dependent material properties, i.e. ohmic resistance and activation resistance, as global functions in the model. The thermal and electric fields were solved simultaneously. The measured and the predicted results agree to each other reasonably well. The cathode polarization overpotential tends to increase with the current at low current densities, but the simulated polarization-current curve exhibited a decreased slope under higher current densities that is ascribed to the local temperature increases due to the high current energy losses.

Commentary by Dr. Valentin Fuster
2006;():51-57. doi:10.1115/IMECE2006-14671.

Fuel cell hybrid technology has the potential to significantly change our current energy infrastructure. Past studies have shown that the combination of fuel cells and turbines can produce power at remarkably high efficiencies with low levels of pollution. The work presented in this paper is an initial step to further development of a hybrid system model. The fuel cell model discussed is used to perform parametric studies to aid in the optimization of a hybrid system. This paper provides an overview of fuel cell hybrid systems and distributive generation. A fuel cell model is implemented in SIMULINK using basic balance equations. Key issues of modeling specifically high temperature fuel cells are discussed along with their transient response and how it may affect the performance of a distributive generation system.

Commentary by Dr. Valentin Fuster
2006;():59-68. doi:10.1115/IMECE2006-14686.

Thermal storage plays a major role in a wide variety of industrial, commercial and residential application when there is a mismatch between the supply and demand of energy. Several promising developments are taking place in the field of thermal storage using phase change materials (PCM) in buildings. In the present paper, a detailed study of the thermal performance of a phase change material system for energy conservation in building is analyzed and discussed. An experiment consisting of two identical test houses has been constructed to study the effect of having PCM panel on the roof of the building. One house is constructed without PCM on the room in order to provide a reference case for comparison with the experimental house that includes the phase change material. The PCM is an inorganic eutectic mixture, which has melting temperature in the range of 26 - 28°C. A mathematical model has been developed in which finite volume method is used to predict the thermal behavior of the ceiling system incorporating PCMs. A comparison with the experimental results is also made.

Commentary by Dr. Valentin Fuster

Environmental Engineering

2006;():71-77. doi:10.1115/IMECE2006-14484.

Testing of catalytic converter with exhaust gas recirculation system for diesel engine to reduce pollute gases is chosen for present work. The emphasis is given on hydrocarbon (HC), carbon monoxide (CO) and oxides of nitrogen. The catalytic converter was developed with variations of catalyst plates. Perforated plates of copper and combination of copper oxide and cerium oxide (CeO2 +CuO) were used as the catalyst. Copper spacer was used in between plates to vary the distance. Secondary air was injected into the converter to aid oxidization of HC and CO. Experimental study was carried out on computerized kirloskar single cylinder four stroke (10 B.H.P, 7.4 KW) diesel engine test rig with an eddy current dynamometer. The converter was tested with various combination with exhaust gas re-circulation (EGR) system. There are some improvements in the reduction and conversion efficiency of HC & CO. Exhaust gas re-circulation has proved to be effective in reducing NOx .

Commentary by Dr. Valentin Fuster
2006;():79-94. doi:10.1115/IMECE2006-15343.

This study considers the toxicity and flammability of emitted fuel vapor from un-ignited pools of spilled chemicals on land. It also estimates the thermal radiation levels emitted from such pools in case they catch fire. A software based on EPA dispersion models was utilized to estimate the size and location of the dangerous clouds. The 3D dangerous clouds were presented in downwind, crosswind, and vertical directions from the source of the spill. The growth and decay of the formed dangerous zones with time were also investigated. Among other input data required by the above-mentioned software, the transient evaporation rate from the spilled fuel pool and its area were determined by considering the equations of conservation of mass and energy. The study also considered the situation when the spill is followed by ignition causing a pool fire. In such a case, the main concern for impact assessment was the US EPA-specified limiting radiation levels to which humans or facilities can be exposed. Exposure to 5.1 kW/m2 for more than 30 seconds can cause 2nd degree burns while exposure to the wood charring radiation level of 12.6 kW/m2 for more than one minute can cause fatality for humans. To facilitate this analysis a fire model developed by the US Gas Research Institute was used to find out safe distances from which fire fighting personnel can work towards extinguishing the fire. The application of such techniqus to a case study of an instantaneous accidental spill from a typical mobile gasoline tanker supplying fuel to local petrol stations showed that the toxic and flammable zones may extend to downwind distances of 561m and 399m, respectively. For ignited pools, on the other hand, the dangerous zones corresponding to radiation levels of 5.1 and 12.6 kW/m2 were 199 and 120 meters, respectively. For the case study of gasoline spill from a typical storage tank in a refinery resulted in the possible formation of toxic clouds extending to about 40,000 m and 48 m in the downwind and vertical directions, respectively. The flammability zone, however, was restricted to the pool area only. For most cases considered, parametric studies were performed to investigate the effects of wind speed, atmospheric stability, and vertical height on the size of dangerous zones. An interface between the dynamic results of the dispersion software and the static data of the Doha Geographical Information System (GIS) allowed the immediate identification of the major landmarks affected by the considered accidents. This data would be of a great help in developing an emergency evacuation plan for such accidents.

Topics: Fuels
Commentary by Dr. Valentin Fuster

Nuclear Engineering

2006;():97-99. doi:10.1115/IMECE2006-13625.

The experimental investigation was performed to find the associated changes in characteristics of fretting wear with various water temperatures. Fretting can be defined as the oscillatory motion with very small amplitudes, which usually occur between two contacting surfaces. The fretting wear, which occurs between cladding tubes of nuclear fuel rod and grids, causes in damages the cladding tubes by flow induced vibration in a nuclear reactor. In this paper, the fretting wear tests were carried out using the zirconium alloy tubes and the grids with increasing the water temperature. The tube materials in water of 20°C, 50°C and 80°C were tested with the applied loads from 5N up to 25N and the relative amplitude of 200μm. The worn surfaces were observed by SEM, EDX analysis and 2D surface profiler. As the water temperature increased, the wear volume was decreased, but oxide layer was increased on the worn surface. The abrasive wear mechanism was observed at water temperature of 20°C and adhesive wear mechanism occurred at water temperature of 50°C, 80°C. As the water temperature increased, surface micro-hardness was decreased, but wear depth and wear width were decreased due to increasing stick phenomenon. Stick regime occurred due to the formation of oxide layer on the worn surface with increasing water temperatures.

Commentary by Dr. Valentin Fuster
2006;():101-109. doi:10.1115/IMECE2006-14060.

A wavy annular flow model in a packed-bed is developed by introducing the shape of waves in a thin liquid film to predict the local interfacial area. The trickling flow regime in a packed-bed is often approximated by an annular flow through a narrow circular channel in which the continuous gas and liquid are completely separated by a smooth and stable interface. Most of the existing models for the trickling flow utilize balance equations for each phase to predict hydrodynamics parameters: liquid hold-up, interstitial velocities, pressure drop, or void fraction. However, the smooth and stable annular flow may not result in an accurate prediction of the interfacial area between gas-liquid phases in a packed-bed. Therefore, a wavy annular flow model is introduced to predict the more accurate interfacial area. This is important because the transport of mass, momentum, and energy is proportional to the interfacial area between gas and liquid phase. Because of the annular flow model, the ratio of film thickness to the equivalent channel diameter can be expressed as a function of only void fraction. The two-parallel wire probe allowed to measure the local film thickness has been used to obtain the shape of the interface. By integrating the local interfacial areas over a certain time period, the local interfacial area is evaluated. The interfacial areas predicted by the presented model are comparable with the empirical correlations developed in the past decades.

Commentary by Dr. Valentin Fuster
2006;():111-118. doi:10.1115/IMECE2006-14566.

In the Sulfur-Iodine (SI) water splitting cycle hydrogen is produced via the decomposition of Hydrogen-Iodide (HI) and sulfuric acid (H2 SO4 ). These reactions proceed at around 400 °C and 850 °C respectively. A high temperature heat source, such as nuclear reactor heat, is required for the SI cycle. Since both the nuclear plant and the SI cycle plant are coupled through heat exchangers, any transients for either plant will affect the entire system. For a nuclear reactor system, it is especially important to understand the transient behavior of the SI cycle during a reactor startup or an emergency shutdown. A simplified transient model of the SI cycle, which can be coupled to heat from a nuclear plant, has been developed. Preliminary results from both steady state and transient calculations are presented in this paper.

Commentary by Dr. Valentin Fuster
2006;():119-128. doi:10.1115/IMECE2006-14917.

A kinetic model was developed to investigate the corrosion and precipitation in non-isothermal lead alloy coolant systems. By considering a turbulent core region and a laminar sub-layer, analytical solutions of the mass transfer equations in both regions were obtained. The analytical expressions of both the local corrosion/ precipitation rate and the bulk concentration were obtained from the present kinetic model. Numerical models were also developed for simulating the corrosion and precipitation in non-isothermal Lead alloy pipe/loop systems and the results were compared with the analytical solutions. By applying this model to a test loop named "DELTA" set up at the Los Alamos National Laboratory the present study illustrates systematically dependence of the corrosion/precipitation rate and bulk concentration on the axial temperature profile and other hydraulic factors. The results were compared with the available experimental data.

Commentary by Dr. Valentin Fuster
2006;():129-135. doi:10.1115/IMECE2006-15312.

A set of steam condensation experiments is conducted to evaluate the heat removal capacity of a vertical passive condenser. A condensing tube is submerged in a water pool where condensation heat is transferred by secondary boiling heat transfer. Condensation heat transfer coefficients (HTC) are obtained under various test conditions, such as different primary pressure (150 - 450 kPa), inlet steam flow rate (1 - 5 g/s), air mass fraction (0 - 20%) and tube size (26.6 mm and 52.5 mm ID). The effects of these parameters to condensation performance are evaluated in this paper. Experimental data are compared with code predictions from RELAP5 with 2 condensation models. The comparison result shows that an improved condensation model is needed in RELAP5.

Commentary by Dr. Valentin Fuster
2006;():137-151. doi:10.1115/IMECE2006-15735.

Phenomena associated with jet-plume condensation of steam-air mixtures in a large subcooled pool of water have implications in predicting global system parameters, such as the containment pressure, in light water reactors. A scaled down, reduced pressure suppression pool was designed to study condensation and mixing phenomena using scaled test conditions obtained from RELAP5 code results of a loss of coolant accident in a simplified boiling water reactor. Results from the experiments were compared with the TRACE code predictions which reveal deficiencies in the code to predict the pool thermal stratification as TRACE was not initially developed for predicting such phenomena. A dimensionless boundary map was plotted from several experimental runs of pure steam injection to determine conditions when the pool transits from being a homogeneously mixed volume to being a thermally stratified one. Steam-air mixture injection cases for single horizontal venting indicated that above a pool temperature of 40 °C with air mass flow rates below 0.1 g/s the pool can attain thermal stratification.

Commentary by Dr. Valentin Fuster
2006;():153-158. doi:10.1115/IMECE2006-15885.

The mission of the Transmutation Research Program (TRP) at University of Nevada, Las Vegas (UNLV) is to establish a nuclear engineering test bed that can carry out effective transmutation and advanced reactor research and development effort. TRPSEMPro package, developed from previous project period, integrated a chemical separation code from the Argonne National Laboratories (ANL). Current research focus has two folds: development of simulation system processes applied to Spent Fuel Treatment Facility (SFTF) using ASPEN-plus and further interaction of ASPEN+ program from TRPSEMPro interface. More details will be discussed below. ANL has identified three processes simulations using their separation technologies. The first process is to separate aqueous acid streams of acetic acid, nitric acid, water and a variety of fission product nitric salts. Distillation separation method is used to remove the desired components from the streams. The second simulation is to convert plutonium nitrate to plutonium metal. Steps used for the process simulation are precipitation, calcinations, fluorination and reduction. The third process currently under development is vitrification of fission product of raffinate streams. During the process, various waste streams from the plant are mixed and fed to a process that converts them to a solid state glass phase. The vitrification process used by the Hanford and Savannah River facilities was selected as a guideline to develop the prototype simulation process using ASPEN-Plus. Current research is focusing on identifying unit operations required to perform the vitrification of the waste streams. The first two processes are near completion stage. Microsoft Visual Basic (MS VB) has been used to develop the entire system engineering model package, TRPSEMPro. Currently a user friendly interface is under development to facilitate direct execution of ASPEN-plus within TRPSEMPro. The major purpose for the implementation is to create iterative interaction among system engineering modeling, ANL separation model and ASPEN-Plus process that outputs optimized separation/process simulation results. The ASPEN-plus access interface from TRPSEMPro allows users to modify and execute process parameters derived from the ASPEN Plus simulations without navigating through ASPEN-Plus. All ASPEN-plus simulation results can be also accessible by the interface. Such integration provide a single interaction gateway for researchers interested in SFTF process simulation without struggling with complicate data manipulation and joggling among various software packages.

Commentary by Dr. Valentin Fuster
2006;():159-166. doi:10.1115/IMECE2006-16177.

Water-vapor two-phase flow structure in a fuel bundle of an advanced light water reactor was analyzed numerically by large-scale direct simulations. A newly developed two-phase flow analysis code was used. It can precisely predict the interface behavior between the liquid and gas phase by using the interface tracking method. The present analytical geometry simulates a tight-lattice fuel bundle with 37 fuel rods and four spacers. The fuel rod outer diameter is 13 mm and gap spacing between each rod is 1.3 mm. Each spacer is installed in an arbitrary axial position in order to keeping the gap width. Water flows upward from the bottom of the fuel bundle. The inlet conditions of water are as follows: temperature 283°C, pressure 7.2 MPa, flow rate 400 kg/m2 s, and the Reynolds number 40,000. In the present study three-dimensional computations were carried out under the non-heated isothermal flow condition in order to remove the effect of heat transfer by the fuel rods. The average mesh size in the present numerical study was 0.15 mm. From results of a series of the numerical simulations, the following consideration was derived: 1)The fuel rod surface is encircled with thin water film; 2)The bridge phenomenon by the water film appears in the region where the spacing between fuel rods is narrow; 3)Vapor flows downward the triangular region where the spacing between fuel rods is large; and, 4)A flow configuration of vapor shows the streak structure in the vertical direction.

Commentary by Dr. Valentin Fuster

Power

2006;():169-178. doi:10.1115/IMECE2006-13109.

In this paper, partially premixed flames of propane-hydrogen blends from elliptic burner geometries in coflow environment have been experimentally studied. Two different elliptic burner geometries with aspect ratios (AR) of 3:1 and 4:1 were used. A circular burner with the same discharge area as that of the elliptic burner was employed for comparison. Measurements were taken at stoichiometric and three other equivalence ratios. Global flame characteristics such as visible height, emission indices, and flame radiation were measured. Flame structure data such as transverse profiles of inflame concentrations of combustion products and local flame temperature were also measured at three axial locations in the flame. Results indicate that elliptic burner flames were shorter, more radiating, and produced lower NO and CO emissions than the corresponding circular burner flames. Results from the inflame measurements of NO and CO were in good agreement with the corresponding global data. Further, the 4:1 AR elliptic burners exhibited a twin-jet flame structure at fuel-rich conditions. The twin-flame structure was evident from the inflame measurements of temperature and combustion species. This study suggests that the combination of elliptic burner geometry and coflow reduces NO and CO emissions from combustion systems, which could potentially lead to cleaner environment.

Topics: Flames
Commentary by Dr. Valentin Fuster
2006;():179-187. doi:10.1115/IMECE2006-13162.

An experimental study of a propylene diffusion flame at its smoke point in a cross-flow with velocities ranging from 2 to 4 m/s and a series of diluted conditions was conducted. A gas jet flame from a circular tube burner (ID = 3.2 mm) with a range of exit velocities (4.2 to 34 m/s) corresponding to a Reynolds number range of 520 to 6065 was studied. Nitrogen was added to the fuel stream to eliminate smoking when the fuel flow rate was lower than the flow rate of pure fuel at smoke point condition (which is defined as the Critical Fuel Mass Flow Rate, CFMFR). The curve of N2 flow rate with fuel flow rate at the smoke point showed a skewed bell shape with two distinct regions. In the first region, the diluent flow rate increased with the fuel flow rate, and in the subsequent region the trend was reversed. These two regions were separated by a transition region. Our previous studies on flames in quiescent conditions concluded that these two regions were controlled by jet momentum and chemical kinetics, respectively. This study presents flame structure details such as transverse temperature and concentration profiles in typical flames representing these two regimes. Most of the temperature profiles show a dual peak structure, where the peak nearer to the burner was higher than the other. Furthermore, the peaks in the transition region flame were more distinct than those in the momentum dominated flame. Most of the flames in the 2 m/s cross-flow had lower O2 concentrations than the flames in the 3 and 4 m/s cross-flow. The temperature profiles, and the concentration profiles of O2 and soot change significantly when cross-flow velocity was changed from 2 to 4 m/s. Findings from this study enable us to understand industrial flares that are commonly used in petroleum refineries and chemical plants.

Commentary by Dr. Valentin Fuster
2006;():189-195. doi:10.1115/IMECE2006-13191.

The challenges in designing high performance combustion systems have not changed significantly over the years, but the approach has shifted towards a more sophisticated analysis process. A technical discussion on combustion technology status and needs will show that the classic impediments that have hampered progress towards near stoichiometric combustion still exist. Temperature rise, mixing, liner cooling, stability, fuel effects, temperature profile control and emissions continue to confront the aerodynamic and mechanical designers with a plethora of engineering dilemmas and trade-offs. The process of combustion chamber design has taken a new meaning over the past several years as three dimensional codes and other advanced design and validation tools have finally changed the approach from a "cut and burn" technique to a much more analytical process. All of these new aspects are now integral elements of the new equation for advanced combustor design that must be fully understood and utilized. Only then will the operable, high temperature capable or low emission combustor systems needed for future military and civil aircraft as well as for stationary gas turbines can be developed. The present paper is an attempt to analyze the flow patterns within the combustion chamber of a 20 kW gas turbine engine using a CFD code CFX. It summarize the CFD simulation of the complete combustion chamber including primary zone, intermediate zone and dilution zone and finally attempts to achieve temperature distribution in the entire combustion chamber. These CFD results are then compared with experimental readings which not only validates analytical results but leads towards improved design.

Commentary by Dr. Valentin Fuster
2006;():197-205. doi:10.1115/IMECE2006-13195.

The increasing awareness towards environment protection and peak load response is accredited in the development of gas turbine system. Many such system preliminary utilizes liquid fuels like kerosene. The emission level with such liquid fuel may be reduced by addition of oxygenated fuel like ethanol. Hence, the basic objective of present paper is to investigate analytically the influence of ethanol addition on emission levels of the kerosene fired small laboratory gas turbine unit. This paper discusses about the theoretical investigation on emission levels with kerosene-ethanol blended fuel using thermodynamic equilibrium model. The theoretical investigations have been carried out on Gilkes GT 85/2 twin shaft Gas Turbine Engine with ethanol blended kerosene fuel to a concentration level of 25% ethanol in the step of 5% increment. The investigations of the emission levels were carried out for CO2 , CO, O2 , H2 , N2 , H2 O, OH and NO with respect to equilibrium temperature at different overall equivalence ratios ranging from 0.1 to 1.1. It is worth to mention that the equilibrium thermodynamic model clearly indicates that in narrow operative range of equivalence ratio (0.1 to 0.2) and the ethanol addition to an extent of 10% to 15% clearly offers reduced emission levels.

Commentary by Dr. Valentin Fuster
2006;():207-213. doi:10.1115/IMECE2006-13203.

An experimental investigation was conducted to study the effects of increased ambient pressure (up to 6.89 MPa) and increased nozzle pressure drop (up to 2.8 MPa) on the cone angles for sprays produced by pressure-swirl atomizers having varying amounts of initial swirl. This study extends the classical results of DeCorso and Kemeny [1]. Shadow photography was used to measure cone angles at x/D0 =10, 20, 40, and 60. Our lower pressure results for atomizer swirl numbers of 0.50 and 0.25 are consistent with those of DeCorso and Kemeny [1], who observed a decrease in cone angle with an increase in a pressure drop-ambient density product until a minimum cone angle was reached at ΔPρair 1.6 ~200. Results for atomizers having higher swirl numbers do not match the DeCorso and Kemeny [1] results as well, suggesting that their correlation be used with caution. Another key finding is that an increase in ΔPρair 1.6 to a value of 1000 leads to continued decreases in cone angle, but that a subsequent increase to 4000 has little effect on cone angle. Finally, there was little influence of atomizer pressure drop on cone angle, in contrast to findings of previous workers. These effects are hypothesized to be due to gas entrainment.

Topics: Pressure
Commentary by Dr. Valentin Fuster
2006;():215-223. doi:10.1115/IMECE2006-13360.

An experimental study was conducted to characterize the performance of a hybrid atomizer used in emission control devices. Characterization included drop size distribution, measured using a forward light-scattering instrument, the air flow field (axial and radial velocities), measured using 2-D PIV, and turbulence characteristics of the air flow field, measured using LDA. The air flow field showed characteristics common to turbulent free round jets beyond approximately 8 exit orifice diameters from the atomizer exit plane. The centerline velocity increased with an increase in mass flow rate, while radial velocities were two orders of magnitude smaller than centerline values. The jet spreading factor initially increased with an increase in axial distance from the exit; however, it stabilized at a value of 0.09 at z/Do=11.8. Turbulence intensity along the jet centerline stabilized at 25% at z/Do=7.9. Drop size data showed complex dependencies on liquid and air mass flow rates, and on internal geometry. The influence of liquid mass flow rate on drop size was significantly smaller for the hybrid atomizer than for the pressure swirl atomizer component housed inside the hybrid unit, thus indicating a higher turndown ratio for the hybrid device. Drop size distributions produced by the hybrid atomizer showed multiple peaks, indicating there is more than one important atomizing mechanism. Finally, reducing the gap between the pressure-swirl atomizer and the exit plane of the outer casing resulted in a reduction in drop size.

Commentary by Dr. Valentin Fuster
2006;():225-234. doi:10.1115/IMECE2006-13456.

Heat release and burn rate analysis in Internal Combustion Engines (ICEs) are usually based on a zero-dimensional application of First-Law of thermodynamics. In order to evaluate the heat release models available in literature use the differential form of the energy conservation equation, generally neglecting specific heats derivative terms. In this work the effects of specific heats derivative terms on a two-zone heat release model, for a Spark Ignition (SI) engine, have been evaluated. Results obtained with and without considering specific heats derivative terms have been compared. These comparisons show that proposed modifications allow to obtain more regular curves especially for mass fraction burned and heat release according to the combustion phenomenology. Besides, taking into account the specific heats derivative terms, the model's calibration constants do not need to be tuned, and the combustion efficiency can be evaluated directly by the mathematical model (otherwise experimentally measured).

Topics: Heat
Commentary by Dr. Valentin Fuster
2006;():235-240. doi:10.1115/IMECE2006-13503.

Nitrous oxide can be used for internal combustion engines as a supplemental oxidizer. In a nitrous oxide system the nitrous is stored in a pressurized container or bottle. Under dynamic use, as the nitrous oxide is being spent the mass in the bottle decreases. This decrease in mass leads to a decrease in pressure. The pressure is the source of delivery of the nitrous oxide to the system. Typically nitrous oxide systems do not have a way to maintain a constant oxidizer deliver flow that can adjust to the pressure drop in the bottle as the nitrous oxide is spent. By not having a way to maintain the oxidizer deliver as the bottle pressure drops it becomes hard to stay consistent interms of the Air (Oxidizer) to Fuel ratio (A/F). The net effect of this pressure drop is that the A/F changes. When this happens the performance of the engine may be compromised as well as the health of the engine. One way to maintain the A/F by regulating the pressure the fuel pressure with respect to the nitrous oxide bottle pressure. This regulator is the focus of this project. A pressure regulator would insure that a constant pressure after the regulator could be maintained. The theory behind the regulator has been previously established but the want of a design of a regulator for a certain application has been brought to the design teams attention. A dynamometer test lab based in Milwaukee has offered testing support for the design of a pressure regulator that would maintain a constant A/F mixture delivery. Motorcycles, due to the need for small components, need to have small nitrous oxide bottles when they are set up with nitrous oxide systems. This small bottle empties faster than a large bottle so the need to maintain the A/F is even more applicable for use on a motorcycle.

Topics: Pressure , Fuels , Governors , Design
Commentary by Dr. Valentin Fuster
2006;():241-246. doi:10.1115/IMECE2006-13838.

The combustion zone in a process heater can be treated as an agglomeration or series of confined jet-flame systems that emanate from burner tiles and expand to an allocated fire box crosssectional area. Possible failure of the tubes containing the process fluid due to local over heating requires the ability to predict detailed radiative heat flux and temperature distribution from the knowledge of the inlet and boundary condition and the system geometry. An analytical model has been developed which is capable of determining the heat transferred by radiation. The variation of the dimensionless heat flux number with varying firebox to burner area ration, length to clearance ratio and a dimensionless distance along the combustion zone is studied. A C-program is developed which displays these results for various single-side-gas-fired tubes in floor-fired box furnace geometry. Results were also displayed for the variation of heat flux along the length of the vertical tube carrying the process fluid for single side fired tubes in a two-burner floor-fired box. The results of the analytical model developed are in good agreement with the published data.

Topics: Combustion , Furnaces
Commentary by Dr. Valentin Fuster
2006;():247-257. doi:10.1115/IMECE2006-13908.

The largest source of human-caused mercury air emissions in the U.S principle is from combustion coal, a dominant fuel used for power generation. The coal chlorine content and ash composition, gas temperature, residence time and presence of different gases will decide the speciation of Hg into Hg° (elemental form) and HgCl2 (oxidized form). The extent of oxidation depends on the concentration of chlorine in flue gases. In order to predict the % of oxidized Hg, a transient model for combustion of a coal particle is formulated including Hg reactions. The model assumes that mercury and chlorine are released as a part of volatiles in the form of elemental mercury and HCl. A three step reaction is implemented for the oxidation of mercury. The model investigates the effect of coal blend with feedlot biomass (FB or Cattle manure), ambient temperature, and particle size on the extent of mercury oxidization. Mercury oxidation (HgCl2 ) increased with increase in diameter of particle and FB % in blended fuel.

Commentary by Dr. Valentin Fuster
2006;():259-265. doi:10.1115/IMECE2006-15032.

Alkali metals, mainly sodium and potassium, together with other ash forming inorganic components in biomass increases fouling, slagging, and high temperature corrosion during biomass combustion or gasification. To reduce the amount of alkali vapor to an acceptable level, which may be affected by Si, Al, Ca, S, Mg, and P, the information on the speciation of alkali metals is essential. In this study, thermodynamic equilibrium calculations were performed to determine the distribution and mode of occurrence of gaseous chlorine and alkali metals of three types of biomass (corn stover, switch grass, and wheat straw) in combustion and gasification processes. The influence of temperature, pressure, and air-fuel ratio was also evaluated. Results show that the excess air has limited influence on the speciation of chlorine and potassium during combustion. However, the influence of the excess air is significant during gasification. Increasing excess air enhances the formation of vapor HCl and KOH as well as reduction in vapor KCl and K2 Cl2. In biomass combustion and gasification, increasing pressure increases vapor HCl and K2 Cl2 and reduces the amount of vapor KCl and KOH. At higher temperatures (>1100K), the gaseous alkali species increased greatly. The results will be useful in the better development of hot gas clean-up technologies.

Commentary by Dr. Valentin Fuster
2006;():267-273. doi:10.1115/IMECE2006-15055.

A three-dimensional multiphase CFD model using an Eulerian approach is developed to simulate the process of pulverized coal injection into a blast furnace. The model provides the detailed fields of fluid flow velocity, temperatures, and compositions, as well as coal mass distributions during the devolatilization and combustion of the coal. This paper focuses on coal devolatilization and combustion in the space before entering the raceway of the blast furnace. Parametric studies have been conducted to investigate the effect of coal properties and injection operations.

Commentary by Dr. Valentin Fuster
2006;():275-276. doi:10.1115/IMECE2006-15061.

Miniaturization of solid-propellant thrusters is an area of active research that has been motivated by the reduction in size of aerospace systems and the advancement of micromachining techniques. Though this micro-propulsion problem seems simplistic compared to the macro-scale counterpart, an efficient and reliable device has yet to be produced. A millimeter-scale novel composite solid-propellant thruster design that builds on pervious work [1] and increases efficiency is here presented. Current designs made primarily out of silicon suffer from high thermal losses and, in extreme cases, flame quenching due to the augmented surface area to volume ratio associated with miniaturization. Moreover, the reduced device dimensions drive the combustion reaction to complete outside of the thruster, misemploying the majority of the chemical energy. This occurs because the propellant mixing and chemical time do not scale with size, while the residence time does decrease as the size of the thruster decreases [2]. A novel thruster design that increases the propellant residence time is being characterized using ammonium perchlorate/binder composite propellant. The thruster geometry recycles thermal energy to the unburned propellant grain increasing its temperature and, therefore, burning rate and combustion efficiency. In addition, propellant formulation has been optimized for the thruster minimization.

Topics: Propellants
Commentary by Dr. Valentin Fuster
2006;():277-285. doi:10.1115/IMECE2006-15502.

This study is a part of a comprehensive investigation, to conduct bench-, pilot-, and full-scale experiments and theoretical studies to elucidate the fundamental mechanisms associated with mercury oxidation and capture in coal-fired power plants. The objective was to quantitatively describe the mechanisms governing adsorption, desorption, and oxidation of mercury in coal-fired flue gas carbon, and establish reaction-rate constants based on experimental data. A chemical-kinetic model was developed which consists of homogeneous mercury oxidation reactions as well as heterogeneous mercury adsorption reactions on carbon surfaces. The homogeneous mercury oxidation mechanism has eight reactions for mercury oxidation. The homogeneous mercury oxidation mechanism quantitatively predicts the extent of mercury oxidation for some of datasets obtained from synthetic flue gases. However, the homogeneous mechanism alone consistently under predicts the extent of mercury oxidation in full scale and pilot scale units containing actual flue gas. Heterogeneous reaction mechanisms describe how unburned carbon or activated carbon can effectively remove mercury by adsorbing hydrochloric acid (HCI) to form chlorinated carbon sites, releasing the hydrogen. The elemental mercury may react with chlorinated carbon sites to form sorbed HgCl. Thus mercury is removed from the gas-phase and stays adsorbed on the carbon surface. Predictions using this model have very good agreement with experimental results.

Topics: Combustion , Coal
Commentary by Dr. Valentin Fuster
2006;():287-296. doi:10.1115/IMECE2006-15505.

The fuel used as energy source for aluminum melting is of extreme importance for a better performance of the process. However, the type of oxidant can also lead to better performance, leading to a greater preservation of the equipments. Air is more abundant and cheaper, however due to the presence of nitrogen, there is undesirable NOx formation. An alternative is to employ pure oxygen. Although it is more expensive, it can lead to a cleaner and much more efficient combustion process, by significantly altering the combustion aspects inside the furnace, such as the shape of the flame and the distribution of temperature and heat flux. In the present work, numerical simulations were carried out using the commercial package FLUENT, analyzing different cases with pure oxygen and air as the oxidant for the combustion of natural gas. The results showed the possible damages caused by the process if long or too intense and concentrated flames are present.

Commentary by Dr. Valentin Fuster
2006;():297-303. doi:10.1115/IMECE2006-15573.

In a blast furnace, preheated air and fuel (gas, oil or pulverized coal) are often injected into the lower part of the furnace through tuyeres, forming a raceway in which the injected fuel and some of the coke descending from the top of the furnace are combusted and gasified. The shape and size of the raceway greatly affect the combustion of, the coke and the injected fuel in the blast furnace. In this paper, a three-dimensional (3-D) computational fluid dynamics (CFD) model is developed to investigate the raceway evolution. The furnace geometry and operating conditions are based on the Mittal Steel IH7 blast furnace. The effects of Tuyere-velocity, coke particle size and burden properties are computed. It is found that the raceway depth increases with an increase in the tuyere velocity and a decrease in the coke particle size in the active coke zone. The CFD results are validated using experimental correlations and actual observations. The computational results provide useful insight into the raceway formation and the factors that influence its size and shape.

Topics: Blast furnaces
Commentary by Dr. Valentin Fuster
2006;():305-314. doi:10.1115/IMECE2006-15667.

The Rate-Controlled Constrained-Equilibrium method (RCCE) is a powerful technique for simplifying the treatment of chemical reactions in complex systems. The method is based on the assumption that slow chemical reactions impose constraints on the allowed composition of such systems. Since the number of constraints can be very much smaller than the number of species, the number of rate equations to be integrated can be considerably reduced. In the present work, a kinetic scheme with 55 species and 366 reactions has been used to investigate stoichiometric Ethanol-oxygen mixture in a constant energy constant volume chamber. The state of the system was determined by three fixed elemental constraints: elemental carbon, elemental oxygen and elemental hydrogen and six variable constraints: moles of fuel, moles of fuel radicals, total number of moles, moles of free valence, moles of free oxygen, moles of OH+O+H. The 9 rate equations for the constraint potentials (LaGrange multipliers associated with the constraints) were integrated over a range of 1400 K-1700 K for initial temperature and 1atm-10atm for initial pressure. The RCCE calculations were in good agreement with detailed calculations and were faster than detailed calculations, which required integration of 55 species rate equations.

Commentary by Dr. Valentin Fuster
2006;():315-322. doi:10.1115/IMECE2006-15690.

During the melting/production of aluminum, dross forms on the surface of the molten aluminum. Dross is a contaminant and an insulator so the aluminum industry regularly removes this dross from the aluminum surface. This is done by opening a door on the side of the furnace while the burners are still in operation and manually raking off the dross. As a result, a lot of heat is lost while the door is open. This lost heat depends upon the length of time the door is open and on the firing rate of the burners. This paper will present computational results on how much heat is lost while the door is open, the effect of this heat loss on the combustion space flow field, and the length of time needed to return to equilibrium conditions once the door is closed again.

Commentary by Dr. Valentin Fuster
2006;():323-333. doi:10.1115/IMECE2006-15693.

For many aluminum melting furnaces, natural gas is mixed with air. The ensuing heat from combustion is then used to melt the solid aluminum and heat the liquid metal. Of increasing concern to the industry are the more stringent regulations in regard to NOx emissions from these plants. The formation of NOx mainly depends on the concentration of nitrogen and the temperature of the gas. One problem that affects this formation that has not been adequately addressed is the variability of the local natural gas supply. Natural gas has molecular nitrogen as a portion of its composition. This percentage ranges from approximately one to seven percent of the total mass fraction. In addition, the aluminum industry is investigating methods to reduce NOx emissions. One method is to replace some of the combustion air with pure oxygen. This reduces the amount of nitrogen coming into the furnace, but also raises the combustion temperature which could promote NOx production. This paper details a systematic computational fluid dynamics study on how the variability of the nitrogen concentration coupled with the partial replacement of air with pure oxygen affects heat transfer and pollutant formation in an aluminum furnace. Trends will be discussed as will the ideal oxygen concentration for a given nitrogen mass fraction.

Commentary by Dr. Valentin Fuster
2006;():335-340. doi:10.1115/IMECE2006-15711.

The testing of gas turbine combustors requires large flow rates at high pressures and elevated temperatures. In order to control the flow and pressure inside the combustor, some type of control valve is required in the exhaust section of the testing system. This backpressure valve is exposed to severe operating conditions. To understand the complex flow features in the exhaust section and provide relevant information for selecting suitable low-cost valves for new large test cells, a numerical study was carried out on a backpressure valve that has been used in a number of testing programs. The flow fields in the vicinity of the valve and the piping sections ending at the exhaust stack were resolved for three practical operating conditions. The results indicate that because of the presence of the valve with a V-shape opening, the flow field behind experiences a series of three-dimensional expansion and shock waves. The strong interactions exist between the flow behind the blockage and the flow passing through the opening area. More importantly, it is found that most of the pressure drop occurs immediately downstream of the valve, and its values are much larger than those provided by suppliers based on shock-free flow calculation. This may explain why the valve lost its function during testing and its stainless-steel seat had to be removed in order to maintain its rotational function. Based on this study, it is recommended that a second pressure-drop element be installed in the exhaust section in order to keep the expected lifetime of valves and reduce noise level. This suggestion has been implemented in the new large test cell at the Gas Turbine Laboratory.

Commentary by Dr. Valentin Fuster
2006;():341-346. doi:10.1115/IMECE2006-15864.

The focus of this study is the calculation of the laminar burning speed of JP-8, oxygen, and helium mixtures at high temperatures and pressures. Two constant volume combustion vessels were used for the analysis. The spherical vessel was primarily used for the collection of pressure data from which the burning speed was calculated. A cylindrical vessel was also used in conjunction with a shadowgraph system to observe the flame structure and the onset of instability. Observations of JP-8 with both nitrogen and helium as diluents were made in the cylindrical vessel and it was seen that at a temperature of 200° C over the range of 1-8 atmospheres pressure and equivalence ratios of 0.7-1.0 with helium as the diluent, the flame was laminar throughout its combustion. Pressure measurements of JP-8 and oxygen with helium as the diluent were then made in the spherical vessel. Laminar burning speed of JP-8 with oxygen and helium has been calculated using the spherical vessel pressure data for this range of temperatures, pressures and equivalence ratios. Power law correlations for burning speeds have been developed for these results.

Commentary by Dr. Valentin Fuster
2006;():347-351. doi:10.1115/IMECE2006-15867.

Laser-Induced Incandescence (LII) is used in this study to measure soot volume fractions in steady and flickering ethylene diffusion flames burning at atmospheric pressure. Better understanding of flickering flame behavior also promises to improve understanding of turbulent combustion systems. A very-high-speed solenoid valve is used to force the fuel flow rate with frequencies between 10 Hz and 200 Hz with the same mean fuel flow rate of steady flame. Periodic flame flickers are captured by two-dimensional phase-locked emission and LII images for eight phases (0° - 360°) covering each period. LII spectra scan for minimizing C2 swan band emission and broadband molecular florescence, a calibration procedure using extinction measurements, and corrections for laser extinction and LII signal trapping are carried out towards developing reliable LII for quantitative applications. A comparison between the steady and pulsed flames results and the effect of the oscillation frequency on soot volume fraction for the pulsed flames are presented.

Commentary by Dr. Valentin Fuster
2006;():353-361. doi:10.1115/IMECE2006-15907.

Combustion air systems are an important aspect of any combustion system. With the complexity of modern combustion systems, numerical modeling has become a valuable tool for design and analysis. Two examples of the use of numerical modeling for combustion air systems on pulverized coal utility boilers are presented: first, a combustion analysis to evaluate air system design on combustion performance, and second, the design of a secondary air system windbox. These examples demonstrate the usefulness and value of modeling as a design and analysis tool.

Commentary by Dr. Valentin Fuster
2006;():363-364. doi:10.1115/IMECE2006-15911.

Unsteady flames within alumina combustors with one submillimeter dimension are evaluated and discussed in this extended abstract. The flame dynamics within the combustors are characterized by non-stabilized and transient flame structures accompanied by acoustic emissions. These flames are studied experimentally and are discussed here. The experimental observations are carried out via two imaging techniques, high-speed and still-frame imaging. The acoustic emission and external wall temperature measurements are also recorded.

Topics: Flames
Commentary by Dr. Valentin Fuster
2006;():365-371. doi:10.1115/IMECE2006-16287.

In this paper, an emission control technology for a gas turbine engine is studied. When an aero gas turbine engine WJ5A is modified to drive ground electrical generator, some pollutant emission problems, such as black smoke and excessive NOx, have arisen from the substitution of diesel fuel for aero fuel. In order to reduce these emissions, the original pressure-swirl atomizers are replaced by the air-assist atomizers, which can enhance the atomization quality, to expand the combusting zone, and to improve air to fuel ratio in primary zone of the combustor. Experimental studies on the atomization, combustion and the engine tests with the atomizers are conducted. The experiments show that the pollutant emission decreases significantly through the air-assist atomizers.

Commentary by Dr. Valentin Fuster

Solar Energy

2006;():375-382. doi:10.1115/IMECE2006-13511.

The objectives of this research are to design a photovoltaic/thermal hybrid solar power generation system and to develop a prototype. The design factor of consideration is the fan speed which transfers heat from the solar cells to water within storage tanks and controls operational temperature of the solar cell to obtain higher efficiency of power. Therefore the system identification, simulation, and series of tests of the temperature controller are also present in this research to evaluate the performance of the design system. The results show that if operational temperature of the solar cell is set under 50°C, which the temperature error is between ± 0.1°C and we can obtain the highest heat collection efficiency ηth (0.28), the performance of the heat collection system with this well designed temperature controller is better.

Commentary by Dr. Valentin Fuster
2006;():383-388. doi:10.1115/IMECE2006-14178.

The design of solar concentrators based on nonimaging optics provides an inexpensive, but highly powerful concentrating system with large angular tolerance and uniform cell illumination. However, multi-junction tandem-cell-based concentrators require high levels of concentration to become cost effective. The two-mirror design is capable of working at an average concentration over 800 suns with local concentrations below 2000 suns without a homogenizing kaleidoscope. With this level of concentration it is essential to analyze the thermal effects of the unit at different operating conditions. In this paper we analyze the coupled effects of natural convection and surface thermal radiation inside the air-filled enclosure formed by the primary mirror and the cover of the concentrator that holds the secondary mirror. A coordinate transformation is applied to the governing equations to generate a mapping from a parabolic domain to a rectangular domain. The results show an increase in the total Nusselt number with a decrease in the maximum temperature of the secondary mirror.

Commentary by Dr. Valentin Fuster
2006;():389-397. doi:10.1115/IMECE2006-14550.

One key advantage of solar power over more traditional power sources is its modular nature, allowing it to be used in remote locations or as a supplementary source of power. Recent studies show fuel cell technology as a good means of providing a continuous supply of electricity from a solar array, eliminating drawbacks caused by solar energy's cyclical nature. The high power density of such a system makes it ideal for use in areas such as unmanned aerial vehicles and space exploration. Due to the complexity and relatively high initial cost of current fuel cells, however, optimization of such a system is critical. This paper examines a dynamic model of a solar regenerative fuel cell system built in MATLAB Simulink. The system uses a polymer electrolyte membrane (PEM) fuel cell, running on stored hydrogen and oxygen, to produce power when solar energy is insufficient. It uses a PEM based electrolyzer to produce hydrogen and oxygen from water when solar energy exceeds demand. The mathematical model includes modules for each component, including solar cells, fuel cell, electrolyzer, and auxiliary systems. Models were built based on fundamental physics to the extent practical. The individual modules were first tested for their performances and then were integrated to form an integrated solar powered regenerative fuel cell system. The simulations were carried out for a day and night cycle and the results show that the closed loop system can be operated providing continuous supply of electric power.

Commentary by Dr. Valentin Fuster

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