Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1999-02-02
2001-05-08
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S276000, C060S285000, C060S280000, C123S039000, C123S478000
Reexamination Certificate
active
06226981
ABSTRACT:
TECHNICAL FIELD
This invention relates to internal combustion engines and fuel systems therefore, and particularly to an arrangement of apparatus and a method for control of the air to fuel ratio (&lgr; or A/F) in engines fueled with a gaseous fuel subject to variation in composition.
BACKGROUND OF THE INVENTION
“Gas” engines in the context of the present description are those designed for operation with a fuel that is gaseous under normal ambient conditions. The fuel can be any of various hydrocarbon gases, carbon monoxide, hydrogen, and mixtures of two or more gases. Such engines are frequently used in stationary applications and use fuel supplies where the composition of the fuel can vary considerably, including landfills and pipelines. Typical engine ratings can be, for example, 50 HP to 5000 HP. The air to fuel ratio of an engine running on a gas fuel is adjusted to load and speed. Where the fuel has a varying composition, its composition and molecular weight are usually not known. Variation in the fuel composition may result in undesirably high NOx emissions.
U.S. Pat. No. 4,867,127, Sep. 19, 1989, proposes a system based on the idea of adjusting the air to fuel ratio &lgr; (lamda) based on reading the air and fuel mixture pressure upstream of the inlet valves to the engine. For example, if a constant engine output is required, an increase in that pressure can be caused by an increase in &lgr; (or a leaning of the mixture). In such a system, all the relevant input signals for the control of &lgr; are sensed on the input side of the engine.
SUMMARY OF THE INVENTION
In accordance with the invention, a fuel system for a gas engine includes an air to fuel ratio controller supplied with input signals from the exhaust so the controller can cause an adjustment in the air to fuel ratio according to the mass flow of exhaust gases. The adjustment can be made by operation of a valve at the fuel inlet before mixing with air. For example, the controller may receive a signal representing mass flow from a hot wire anemometer in the exhaust or a plurality of signals can be supplied to the controller including exhaust gas pressure, and exhaust gas temperature. Volumetric flow of exhaust gas can be measured by a pitot tube. The controller can determine mass flow from the volumetric flow and/or from the measured exhaust gas pressure and temperature. Preferably, there is a signal also for the temperature of the inlet mixture of air and fuel so the controller can take variations in such temperature into account.
In practice of the invention, the described A/F control may be one loop (e.g., the outer loop) of a two loop control circuit. The other (inner) loop would normally be for load and speed control affecting actuators such as a throttle valve or a waste gate. Two loop control systems have been previously used but not with the A/F ratio control based on exhaust gas mass flow, particularly for running on fuels of varying composition.
A variety of different sensors may be employed but it is not necessary to monitor the chemical composition of the exhaust gases directly. The apparatus and method of the invention may be used alone or, if desired, in concert with other methods of NOx estimation or air to fuel control or as a reasonableness check or back up method.
For example, in some prior engine fuel systems, an oxygen (O2) sensor was used in the exhaust to provide readings for accurate adjustment of the A/F ratio. Use of such O2 sensors can provide safe operation of a gas fueled, lean burn engine with low NOx emission. However, if an O2 sensor failure occurs, an engine may have to be shut down. But now, with the present invention, highly reliable sensors can be used to control the A/F ratio according to exhaust gas flow, either by itself or in conjunction with, or as a back up to, control with an O2 sensor (or other sensor of exhaust composition).
Molecular weight differences of various fuels cause smaller differences in the exhaust than in the intake fuel mixture which is an advantage for more precise control.
The invention can be especially suited for use when it is considered desirable to have air to fuel controlled according to the exhaust mass flow. The exhaust mass flow is in direct relation to emissions, at a given load and speed. The present technique is a highly accurate NOx control technique but without a need for having a NOx sensor (or other gas composition analyzer) in the exhaust, which would incur substantially greater cost.
These and other aspects of the inventive apparatus and method will become more apparent from the following description.
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Bruch Kevin L.
Neuenschwander Peter
Caterpillar Inc.
Denion Thomas
Telfer Gordon H.
Trieu Thai-Ba
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