David Gordon Wilson

Models for Predicting the Performance of Brayton-Cycle Engines

Gas turbine performance is the result of choices of type of cycle, cycle temperature ratio, pressure ratio, cooling flows, and component losses. The output is usually given as efficiency (thermal, propulsive, specific thrust, overall efficiency) versus specific power. This paper presents a set of computer programs for the performance prediction of shaft-power and jet-propulsion cycles: simple, regenerative, intercooled-regenerative, turbojet, and turbofan. Each cycle is constructed using individual component modules. Realistic assumptions are specified for component efficiencies as functions of pressure ratio, cooling mass-flow rate as a function of cooling technology levels, and various other cycle losses. The programs can be used to predict design point and off-design point operation using appropriate component efficiencies. The effects of various cycle choices on overall performance are discussed.

The utilization of recuperated and regenerated engine cycles for high-efficiency gas turbines in the 21st century

Abstract In the gas-turbine field ‘simple-cycle’ engines (compressor + burner + expander) have been dominant across almost the full spectrum of power-generation and mechanical-drive applications. Paced by aerodynamic and materials-technology advancements, efficiency values have progressed significantly over the last five decades. However, to reduce specific fuel consumption further (by say a step change of 30–40%) and to reduce emissions significantly, more-complex thermodynamic cycles that include the use of exhaust-heat-recovery exchangers are necessary. Clearly, there are discrete applications where the use of recuperators or regenerators will find acceptance on a large scale, an example being for gas turbines rated at less than about 100 kW for hybrid automobiles and small generator sets. The role that recuperators and regenerators can play in future gas turbines is put into perspective in this paper. Innovative engineering concepts will be required to meet the demanding high-temperature operating environment and low-cost requirements, and these will essentially necessitate the utilization of ceramic-composite heat-exchanger configurations that are amenable to large-volume manufacturing methods.

Energy supplies and future engines for land, sea, and air

The years 2012 and beyond seem likely to record major changes in energy use and power generation. The Japanese tsunami has resulted in large countries either scaling back or abolishing the future use of nuclear energy. The discovery of what seems like vast amounts of economically deliverable natural gas has many forecasting a rapid switch from coal- to gas-fired generating plants. On the other hand, environmentalists have strong objections to the production of natural gas and of petroleum by hydraulic fracturing from shale, or by extraction of heavy oil. They believe that global warming from the use of fossil fuels is now established beyond question. There has been rapid progress in the development of alternative energy supplies, particularly from on-shore and off-shore wind. Progress toward a viable future energy mix has been slowed by a U.S. energy policy that seems to many to be driven by politics. The author will review the history of power and energy to put all of the above in context and will look at possible future developments. He will propose what he believes to be an idealized energy policy that could result in an optimum system that would be arrived at democratically. Implications The combustion energy sector is believed to be a dominant component of environmental pollution. A multitude of technologies support this sector and many have the potential to replace elements of this sector with low-polluting processes. This review covers a selection of energy production technologies that are important for the future. A historical perspective is provided to advance the general knowledge about these technologies as options for the worlds increasing demand for energy. In addition, a decarbonization policy option for an energy fee is proposed as an alternative to carbon taxation or cap-and-trade approaches.

The resource potential of demolition debris in the United States

Abstract The scanty data which are available on the generation of demolition debris in the United States are reviewed. Estimates are made of the proportions of the constituent materials in debris which are recycled in any form. The institutional, economic and technological restrictions preventing a greater proportion of materials from being recycled are described, and suggestions are made of methods by which a higher level of recycling can be brought about.

U.S. building-demolition wastes: Quantities and potential for resource recovery

Abstract The economic and technical potential for recycling building materials from demolished buildings in the United States has been assessed. The first section of the study is a comprehensive analysis of the type and quantity of demolished building materials available nationwide, based on data collected from 27 cities and towns. The flow of demolition debris for the U.S. is estimated at 31 million metric tons (31 Mt, 34-million U.S. tons) for the mid-1970s. The factors correlated with the demolition-debris flow are studied to develop a model of the flow. Potential markets for the processed debris are examined, and options for the processing equipment for a central reclamation plant are evaluated. Such plants seem likely to be economical in most of the larger cities of the U.S. (>400 000 population).

Low-leakage modular regenerators for gas-turbine engines

One of the significant problems plaguing regenerator designs is seal leakage resulting in a reduction of thermal efficiency. This paper describes the preliminary design and analysis of a new regenerative heat-exchanger concept, called a modular regenerator, that promises to provide improved seal-leakage performance. The modular regenerator concept consists of a ceramic-honeycomb matrix discretized into rectangular blocks, called modules. Separating the matrix into modules substantially reduces the transverse sealing lengths and substantially increases the longitudinal sealing lengths as compared with typical rotary designs. Potential applications can range from small gas-turbine engines for automotive applications to large stationary gas turbines for industrial power generation. Descriptions of two types of modular regenerators are presented including sealing concepts. Results of seal leakage analysis for typical modular regenerators sized for a small gas-turbine engine (120 kW) predict leakage rates under one percent for most seal-clearance heights.

The future of the bicycle —Its problems and its potentialities

Abstract In this article the author argues that the bicycle will undoubtedly be improved upon, but it is not likely to be supplanted. It will continue to provide the most energy-efficient short-distance form of individual ground transportation. Whether or not its share of the number of person-trips made in urban areas will increase dramatically depends partly on the improvements which are made to the vehicle, partly on the increasing costs and restraints on motor-vehicle use, but to a greater extent on the success with which planners solve the highway-intersection problem.

A Low-Leakage Discontinuously-Rotating Regenerator Designed for a Motor-Vehicle Gas Turbine

A novel regenerator sealing concept is reported that can potentially reduce net compressed-air regenerator-seal leakage in gas turbines to unprecedented levels — near 1% of the net flow, greatly increasing the cycle thermal efficiency. The concept involves primarily discontinuously rotating a disk-type regenerator and implementing clamping seals. This work explains the principle of operation with discussions on preliminary-design calculations based on its use in a conceptual automotive gas turbine (Pfahnl and Wilson, 1995). Detailed regenerator-leakage calculations illustrate the drastically improved leakage rates.Copyright

Key Issues in the General Design of Motor-Vehicle Gas-Turbine Engines

Ideas and concepts are suggested for producing a motor-vehicle gas-turbine engine able to compete in performance and most likely in cost with similarly rated motor-vehicle spark-ignition and compression-ignition engines. Several of these ideas are discussed qualitatively, while others arc shown through simple performance analyses. Results predict the possibility of thermal efficiencies of over 50% and marked increases in the fuel economy (over 90%) if the gas-turbine engine is used, for instance, as a direct replacement for a standard motor-vehicle engine. The latter calculations were based on Federal-Test-Procedure driving cycles.Copyright

Thermodynamic Design Considerations for Steam-Injected Gas Turbines

Steam injection in gas turbines (steam raised from the energy of the exhaust and injected into one or more of the turbine stages) is an attractive option for cogeneration applications. From a thermodynamic point of view, however, there is little information available about methods for optimizing the use of the steam for injection into a gas turbine.A computer model for an aeroderivative gas turbine is used to analyze the effect of steam injection on net power output and overall efficiency. The effects of varying the quantity of steam injected, the stations at which the steam is injected, and the temperature of the steam that is injected are assessed on a normalized basis, with the turbine-inlet temperature maintained from the simple-cycle design point.The energy balance between the exhaust of the gas turbine and the flow of steam to be injected is the final constraint in selecting a steam-injected design point to maximize performance. For the engine in this study, increases of over 64% in net power output and 23% in overall efficiency can be achieved with roughly 16% steam/inlet air by mass, which represents all of the steam that can be produced by the exhaust stream for the given conditions.© 1993 ASME