Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Specific casing or vane material
Reexamination Certificate
1998-11-13
2001-07-03
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Specific casing or vane material
C416S24100B
Reexamination Certificate
active
06254341
ABSTRACT:
BACKGROUND
1. Field of the Invention
This invention relates generally to the deposition of particles on engine parts, and more particularly to a method and apparatus for reducing particle deposits on the surface of engine parts by coating the engine parts.
2. Description of the Related Art
Gas turbine engines use the well known Brayton cycle to generate a continuous flow of high-pressure, high temperature gas. In a typical gas turbine engine, air is drawn into a rotating compressor which compresses the air, and the air is then heated at constant pressure in a combustion chamber. The high-pressure, high temperature gas exiting the combustion chamber drives the turbine to produce rotational energy.
Gas turbine engines typically show decreasing compressor efficiency over time due to the accumulation of particles on the airfoil surfaces of the compressor. Accumulated particles can reduce the total airflow in the early compressor stages, reduce the pressure ratios in the later compressor stages, and initiate sulfide attack on the later compressor stages. Particles also build up on exhaust ducts as soot (carbon-based combustion by-products), particularly on the low flow and recirculation zone surfaces of the exhaust ducts.
In land-based turbines, filter houses have been utilized to reduce the number and size of particles entering the engine. The filter house comprises a series of particle traps which reduce the number of admitted particles, typically trapping substantially all particles which are larger than about 5 microns in diameter. However, such filter houses are not effective at trapping the smaller particles, e.g. less than about 5 microns in diameter, which pass through the filter into the engine. In addition, it is not generally feasible to use such filters on aircraft engines.
Soot production in gas turbine exhaust ducts is conventionally reduced through careful design of the combustor, i.e., by designing the combustor to efficiently bum substantially all of the fuel. However, it is difficult to produce a combustor which remains soot-free under all operating conditions.
Coatings are known which are applied to airfoil surfaces to protect the airfoils from corrosion. For example, Sermatech in Limerick, Pa. manufactures a coating (Sermatech 5380 DP) which includes aluminum particles and a phosphate glass seal. Such corrosion coatings, however, do not effectively reduce the susceptibility of the airfoil surface to particle deposits.
It would be desirable, therefore, to have a method and apparatus for reducing particle deposits on engine components which was effective and which could be applied to aircraft engines and other gas turbine engines to maintain compressor efficiency and reduce soot deposits on exhaust ducts.
SUMMARY
An engine, according to an exemplary embodiment of the invention, comprises a compressor which compresses inlet air; a combustor in which a mixture of fuel and air is combusted; a turbine which is driven by gases from the combustor; and a dielectric coating applied to a surface of at least one of the compressor and the turbine, the dielectric coating having a dielectric constant of at least 3.0 and a loss tangent of at most 0.1. The dielectric coating reduces the magnitude of an electrostatic force which attracts particles flowing through the engine to the surface of the engine.
The invention also relates to a method for controlling the flow of particles through an engine comprising the steps of coating a surface of the engine with a dielectric coating, the dielectric coating having a dielectric constant of at least 3.0 and a loss tangent of at most 0.1, and electrostatically controlling the flow of particles through the engine with the dielectric coating.
The surfaces of the engine to which the dielectric coating may be applied include surfaces of the turbine, fan, compressor, and exhaust system exposed to the main airflow of the engine (“airflow surfaces”). Typically, the dielectric coating is applied to airfoil surfaces of components of the turbine, compressor, and fan (e.g. airfoil surfaces of blades and vanes), to platforms of the blades, and to components of the exhaust system. The dielectric coating can also be applied to engine surfaces which are not directly exposed to the main airflow of the engine such as shanks and dovetails of turbine blades.
In operation, only a thin layer of particles typically accumulates on the dielectric coating. While the dielectric coating reduces the magnitude of the electric field which attracts particles, the repulsive force produced by the accumulated particles repels additional particles of the same charge. By reducing particle deposits, the problems of decreased compressor efficiency, sulfide attack on high-temperature compressor parts, reduction in airflow in the early compressor stages, reduction in pressure ratios in the later compressor stages, and accumulation of soot on exhaust ducts can be avoided. The invention thus reduces degradation in engine performance and provides significant cost savings through avoidance of maintenance.
REFERENCES:
patent: 4339719 (1982-07-01), Rhines et al.
patent: 5759699 (1998-06-01), French
patent: 5851679 (1998-12-01), Stowell et al.
patent: 6109018 (2000-08-01), Rostrup-Nielsen et al.
T. Horvath and I. Berta,Static Elimination, ix-x, 1-105 (1982).
Ackerman John Frederick
Ivkovich Dan
Johnson Robert Alan
Khang Soon Jai
Park Sang Yeng
General Electric Company
Johnson Noreen C.
Look Edward K.
McDowell Liam
Stoner Douglas E.
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