G. Scott Samuelsen

Effect of ambient pressure on an airblast spray injected into a crossflow

The injection of a fuel spray into a cross stream was studied for its application in rapid fuel ‐air mixing for lean combustion processes. The fuel is injected as either a discrete stream or as a partially to fully atomized jet of droplets. Of particular interest was the penetration of the outer and inner edges of the spray of liquid fuel into the gaseous airstream. The experiment focused on exploring the effect of e ow conditions on the spray surface trajectories from the point of injection to a downstream distance of z/Dfuel = 35. Tests were conducted under ambient pressures of 1, 3, and 5 atm at atomizing air pressure drops varying from 0 to 4.8% for a jet-A fuel e ow of 0.18 g/s and a baseline crosse ow airvelocity of 38 m/s. A modie ed dee nition of the jet-to-crosse owmomentum-e ux ratioq2 wasdeveloped to accommodatea two-phasejetandwassubsequentlyused to obtaina relationshipbetween the e ow conditions and thespray surface trajectories. The effect of the degree of atomization in thespray resulting from the change in operating conditions was incorporated by implementing a pressure ratio correction factor into the correlating equation. Nomenclature Aairbl = area associated with the airblast air, assumed as the difference between Aspray and Aliquid Aliquid = area associated with the fuel injection orie ce Aspray = area associated with the spray injection orie ce Cd = orie ce discharge coefe cient cn = correlation constants, n D0;1;2;3 Dfuel = fuel injection orie ce diameter Dspray = spray injection orie ce diameter q1 = single-phase jet-to-crosse ow momentum-e ux ratio q2 = two-phase jet-to-crosse ow momentum-e ux ratio V = velocity Wecross = crosse ow-associated Weber number ΩairV 2 crossDfuel=ae x = penetration distance z = downstream distance Ω = density

Performance of Proton Exchange Membrane Fuel Cell at High-Altitude Conditions

The effects of oxygen concentration and ambient pressure on fuel cell performance are explored both in theory and in experiment For fuel cells in general the effect due to a change in oxygen concentration is shown to be fundamentally different than the effect due to a change in cathode pressure, even if partial pressure is held constant For a proton exchange membrane fuel cell, a significant reason for this difference comes from the nature of mass diffusion processes in the fuel cell structure, which infers that there is an optimum fuel cell design (macroscale and microscale) for a given operating pressure and oxygen concentration. In the experimental work a proton exchange membrane fuel cell was subjected to varying atmospheric conditions from sea level to 53,500 ft (16,307 m) with results analyzed up to 35,000 ft (10,668 m). The results showed that at low current density operation a decrease in either cathode pressure or concentration led to an increase in irreversible losses associated with reaction kinetics (activation polarization) and confirmed the differing effects of cathode pressure and oxygen concentration. Consideration of all these effects enables both fuel cell- and system-level optimization of aeronautical fuel cell-based power systems. Copyright

A methodology for developing Distributed Generation scenarios in urban areas using geographical information systems

The implementation of Distributed Generation (DG) may lead to increased pollutant emissions that adversely affect air quality. This work presents a systematic methodology to characterise DG installation in urban basins. First, a set of parameters that characterise a DG implementation scenario is described. Second, a general approach using Geographic Information Systems (GIS) data is presented. Third, the methodology is demonstrated by application to the South Coast Air Basin (SoCAB) of California. Results show that realistic scenarios in the SoCAB concentrate DG technologies nearby industrial zones and introduce pollutant mass increments no larger than 0.43% with respect to baseline emissions.

Fuel Cell/Gas Turbine Hybrid System Control for Daily Load Profile and Ambient Condition Variation

Fuel Cell/Gas Turbine (FC/GT) hybrid technology is promising, but introduces challenges in system operation and control. For base-load applications, changes in ambient conditions perturb the system and it becomes difficult to maintain constant power production by the FC/GT system. If the FC/GT hybrid system is load-following then the problem becomes even more complex. In the current study, a dynamic model of a FC/GT power plant is developed with system controls. Two cases are evaluated: (1) system controls are developed to maintain constant power and process control within acceptable constraints, (2) the FC/GT power plant is set in power following mode connected in parallel to the grid for a daily load profile scenario. Changing ambient conditions are employed in the dynamic analysis for both cases. With appropriate attention to design of the system itself and the control logic, the challenges for dynamic system operation and control can be addressed.© 2006 ASME

Fuel cell/gas turbine hybrid system control for daily load profile and ambient condition variation

Fuel Cell/Gas Turbine (FC/GT) hybrid technology is promising, but introduces challenges in system operation and control. For base-load applications, changes in ambient conditions perturb the system and it becomes difficult to maintain constant power production by the FC/GT system. If the FC/GT hybrid system is load-following, then the problem becomes even more complex. In the current study, a dynamic model of a FC/GT power plant is developed with system controls. Two cases are evaluated: (1) system controls are developed to maintain constant power and process control within acceptable constraints and (2) the FC/GT power plant is set in power following mode connected in parallel to the grid for a daily load profile scenario. Changing ambient conditions are employed in the dynamic analysis for both cases. With appropriate attention to design of the system itself and the control logic, the challenges for dynamic system operation and control can be addressed.

A Finite Volume SOFC Model for Coal-Based Integrated Gasification Fuel Cell System Analysis

Integrated gasification fuel cell (IGFC) systems combining coal gasification and solid oxide fuel cells (SOFC) are promising for highly efficient and environmentally friendly utilization of coal for energy production. Most IGFC system analyses performed to date have used non-dimensional thermodynamic SOFC models that do not resolve the intrinsic constraints of SOFC operation. In this work, a one-dimensional finite volume model for planar SOFC is developed and verified using literature data. Special attention is paid to making the model capable of supporting recent SOFC technology improvements, including the use of anode-supported configurations, metallic interconnects, and reduced polarization losses. Results are presented for SOFC operation on humidified hydrogen and methane-containing syngas, under co-flow and counter-flow configurations; detailed internal profiles of species mole fractions, temperature, current density and electrochemical performance are obtained. The effects of performance, fuel composition and flow configuration on SOFC performance and thermal profiles are evaluated, and the implications of these results for system design and analysis are discussed. Copyright

Dynamic Simulation of an Autothermal Methane Reformer

A dynamic autothermal methane reformer model has been developed and tested for the production of a hydrogen- and carbon monoxide-rich syngas. This study looks at potential advantages and disadvantages of an autothermal reformer, both operating in stand-alone mode and in conjunction with a high temperature fuel cell stack. The model uses a conservation of moles as the fundamental continuity relationship, and applies basic energy conservation equations to simulate both the gas and the catalyst bed energies. Chemical kinetic expressions using empirical constants for the Arrhenius rate terms that describe steam reformation of methane and partial oxidation of methane are simultaneously solved to provide an accurate picture of the reaction dynamics. This paper presents dynamic responses of reformer outlet temperature, hydrogen mole fraction, reaction rates and methane conversion to the perturbation of the reformer inlet variables of steam-to-carbon ratio, oxygen-to-carbon ratio and inlet gas temperature. Also explored is the concept of catalyst “light-off,” where there is found to be a lower temperature limit above which catalyst activity is substantially increased.© 2004 ASME

Development of a Dynamic Cathode Ejector Model for Solid Oxide Fuel Cell-Gas Turbine Hybrid Systems

Solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems are attractive for future power generation with ultra-low criteria pollutant and greenhouse gas emissions. One of the challenges for SOFC-GT systems is to sufficiently pre-heat incoming air before it enters the fuel cell cathode. An ejector for cathode exhaust recirculation has the benefits of reliability, low maintenance, and cost compared to either recuperators or cathode recirculation blowers, which may be also be used for air pre-heating. In this study, a dynamic Simulink model of an ejector for cathode exhaust recirculation to pre-heat incoming fuel cell air has been developed. The ejector is to be utilized within a 100 MW SOFC-GT dynamic model operating on coal syngas. A thorough theoretical development is presented. Results for the ejector were found to be in good agreement with those reported in literature.

Systematic Selection and Siting of Vehicle Fueling Infrastructure to Synergistically Meet Future Demands for Alternative Fuels

In order to meet the increasing demand for low carbon and renewable transportation fuels, a methodology for systematically establishing build-out scenarios is desirable. In an effort to minimize initial investment costs associated with the development of fueling infrastructure, the analytical hierarchy process (AHP) has been developed and applied, as an illustration, to the case of hydrogen fueling infrastructure deployment in the State of California. In this study, five parameters are selected in order to rank hydrogen transportation fuel generation locations within the State. In order to utilize meaningful weighting factors within the AHP, expert inputs were gathered and employed in the exercising of the models suite of weighting parameters. The analysis uses statewide geographic information and identifies both key energy infrastructure expansion locations and critical criteria that make the largest impact in the location of selected sites.

Diurnal Temperature and Pressure Effects on Axial Turbomachinery Stability in Solid Oxide Fuel Cell-Gas Turbine Hybrid Systems

A dynamic model of a 100 MW solid oxide fuel cell-gas turbine hybrid system has been developed and subjected to perturbations in diurnal ambient temperature and pressure as well as load sheds. The dynamic system responses monitored were the fuel cell electrolyte temperature, gas turbine shaft speed, turbine inlet temperature, and compressor surge. Using a control strategy that primarily focuses on holding fuel cell electrolyte temperature constant and secondarily on maintaining gas turbine shaft speed, safe operation was found to occur for expected ambient pressure variation ranges and for ambient temperature variations up to 28 K when tested nonsimultaneously. When ambient temperature and pressure were varied simultaneously, stable operation was found to occur when the two are in phase but not when the two are out of phase. The latter case leads to shaft overspeed. Compressor surge was found to be more likely when the system is subjected to a load shed initiated at minimum ambient temperature rather than at maximum ambient temperature. Fuel cell electrolyte temperature was found to be well-controlled except in the case of shaft overspeeds. Turbine inlet temperature remained in safe bounds for all cases.