Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Reexamination Certificate
1999-03-22
2001-02-27
Denion, Thomas (Department: 3748)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
Reexamination Certificate
active
06192686
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to an engine and more particularly to a reduction of exhaust emissions.
BACKGROUND ART
The use of fossil fuel as the combustible fuel in engines results in the combustion products of carbon monoxide, carbon dioxide, water vapor, smoke and particulate, unburned hydrocarbons, nitrogen oxides and sulfur oxides. Of these above products carbon dioxide and water vapor are considered normal and unobjectionable. In most applications, governmental imposed regulations are restricting the amount of pollutants being emitted in the exhaust gases.
In the past, NOx emissions have been reduced by reducing the intake manifold temperature, retarding the injection timing, and modifying the injection rate shape. And, the adverse effects on fuel consumption, particulate emissions engine performance have largely been alleviated through improvements in the basic engine design and fuel selection. For example, at the present time smoke and particulates have normally been controlled by design modifications in the combustion chamber and injection pressure. Particulates are also controlled by traps and filters, and sulfur oxides are normally controlled by the selection of fuels being low in total sulfur. This leaves carbon monoxide, unburned hydrocarbons and nitrogen oxides as the emission constituents of primary concern in the exhaust gas being emitted from the engine.
Many systems have been developed for recycling a portion of the exhaust gas through the engine thereby reducing the emission of these constituents into the atmosphere. The recirculation of a portion of exhaust gas is used to reduce NOx pollution emitted to the atmosphere. In a naturally aspirated engine this process is relative simple. But, with a turbocharged engine, the recirculation of a portion of the exhaust gas into the intake air becomes more complex because the intake pressure may be higher than the exhaust pressure during many operating conditions. In many of such past system a volume of the exhaust gas from the engine was redirected to the intake air of the engine through the turbocharger and/or an aftercooler and to the engine. Such systems caused the premature plugging of aftercooler cores and malfunctioning of the systems. Additionally, with such recirculation system deterioration of the exhaust flow was caused by deposit buildup.
Various approaches have been used to address the adverse pressure gradient issue. For example, throttling valves have been installed in the air inlet, back pressure valves in the exhaust gas, intake manifold venturi tubes, etc. to provide sufficient pressure drop to get the exhaust gas to flow to the intake air. Although this provides the necessary pressure drop to functionally operate an exhaust gas recirculation system several disadvantages, such as, fuel consumption, emissions, and/or performance occur.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the invention an exhaust gas recirculation system is used with an engine. The engine defines a plurality of operating parameters, has a rotatable crankshaft through which an engine speed can be defined and a plurality of cylinders being defined as a part of the engine. The exhaust gas recirculation system is comprised of a flow of intake air entering a respective one of said plurality of cylinders. The intake air is pressurized to a preestablished pressure. A supply of combustible fuel enters the respective one of the plurality of cylinders. A combustion process within the respective one of the plurality of cylinders defines a flow of exhaust gas having a preestablished pressure being less than the preestablished pressure of the intake air during at least a portion of the engine operating parameters. A portion of the exhaust gas is circulated to the intake air defining a flow of exhaust gas recirculation. The flow of exhaust gas recirculation is cooled prior to being pressurized to a preestablished level and the pressurization of the flow of recirculated exhaust gas being by a positive displacement pump and being at a pressure at least equal to the preestablished pressure of the intake air. An on-off valve is interposed in the flow of exhaust gas recirculation. The on-off valve is movable between a closed position and an open position. And, in the open position the flow of exhaust gas recirculation is supplied to the positive displacement pump. A variable speed motor drives the positive displacement pump.
In another aspect of the invention an exhaust gas recirculation system is used with an engine having a plurality of operating parameters and a cylinder. The engine defines a speed. The engine has a flow of intake air being at a first preestablished pressure and a flow of exhaust gas being at a first preestablished pressure being less than the first preestablished pressure of the intake air during a portion of said plurality of operating parameters. The exhaust gas recirculation system is comprised of a portion of the flow of exhaust gas being recirculated back to the cylinder and forming a flow of exhaust gas recirculation. The flow of exhaust gas recirculation is cooled. A positive displacement pump compresses the flow of exhaust gas recirculation to a second preestablished pressure. The second preestablished pressure of the flow of exhaust gas recirculation is at least equal to the first preestablished pressure of the intake air. A quantity of the flow of exhaust gas recirculation is controlled by an on-off valve. The on-off valve is operatable between an open position and a closed position. And, a variable speed motor drives the positive displacement pump.
In another aspect of the invention a method of reducing exhaust emissions from an engine is disclosed. The engine has a plurality of operating parameters, a flow of intake air being at a first preestablished pressure, a flow of exhaust gas being at a first preestablished pressure being less than the preestablished pressure of the intake air during a portion of the operating parameters. The method of reducing exhaust emission is comprised of the steps of extracting a portion of the flow of exhaust gas forming a flow of exhaust gas recirculation. Cooling the flow of exhaust gas recirculation. Increasing the pressure of the flow of exhaust gas recirculation from the first preestablished pressure to a second preestablished pressure being at least equivalent to the first preestablished pressure of the flow of intake air. And, driving a positive displacement pump at a variable rate of speed and varying the variable rate of speed depending on an operating parameter of the plurality of operating parameters of the engine.
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Coleman Gerald N.
Feucht Dennis D.
Lawrence Keith E.
Cain Larry G.
Caterpillar Inc.
Denion Thomas
Trieu Thai Ba
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