Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
1999-03-22
2001-05-15
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C123S559100, C123S563000, C123S568150, C060S278000, C060S605200
Reexamination Certificate
active
06230695
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 is 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 and has a rotatable member, such as a crankshaft through which an engine speed can be defined. A plurality of cylinders are 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 the 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 that the preestablished pressure of the intake air during at least a portion of the engine operating parameters. A portion of the exhaust gas being circulated to the intake air defines 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 as great as the preestablished pressure of the intake air. And, a mixing valve is interposed the flow of intake air and the flow of exhaust gas recirculation. The mixing valve is movable between a closed position and an open position. In the open position, intake air is supplied to the positive displacement pump.
In another aspect of the invention an exhaust gas recirculation system is used with an engine. The engine has a plurality of operating parameters, a cylinder and a rotatable member or crankshaft. The engine has a turbocharger defining a compressor section compressing a flow of intake air to a first preestablished pressure and is driven by a flow of exhaust gas having a first preestablished pressure. 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 portion of the flow of intake air is further compressed to a second preestablished pressure by a positive displacement pump during a portion of the operating parameters of the engine. The flow of exhaust gas recirculation is compressed to a second preestablished pressure by the positive displacement pump. The second preestablished pressure of the flow of exhaust gas recirculation is at least as great as the first preestablished pressure of the intake air. And, a quantity of the flow of exhaust gas recirculation is controlled by a mixing valve. The mixing valve has an open position in which the portion of the flow of intake air is further compressed to a second preestablished pressure flowing therethrough and a closed position in which the flow of intake air is blocked.
In another aspect of the invention a method of reducing exhaust emissions from an engine having a flow of intake air being at a preestablished pressure, a flow of exhaust gas being at a preestablished pressure being less than the preestablished pressure of the intake air is defined. The method of reducing exhaust emission uses 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 with a positive displacement pump to a quantity being at least equivalent to the pressure of the flow of intake air; and blending the flow of exhaust gas recirculation and a portion of the flow of intake air prior to the pressure of the flow of exhaust gas recirculation being increased to a quantity being at least equivalent to the pressure of the flow of intake air.
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pat
Coleman Gerald N.
Feucht Dennis D.
Lawrence Keith E.
Cain Larry G.
Caterpillar Inc.
Nh Hai Huy
Wolfe Willis R.
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