Internal-combustion engines – Combined devices – Generating plants
Reexamination Certificate
1999-09-16
2001-03-27
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Combined devices
Generating plants
C123S0270GE, C123S527000
Reexamination Certificate
active
06205957
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a natural gas engine, and more specifically to an apparatus and method for operating a natural gas engine with in situ generation of an autoignition substance.
2. Description of the Related Art
Natural gas engines produced and operating around the world typically use a spark ignition source to ignite the natural gas in the engine cylinder. This technology limits the achievable performance of an engine using natural gas as the fuel source since the spark does not volumetrically ignite the natural gas. There are typically regions of “too rich” and “too lean” gas mixtures within the cylinder. This causes incomplete combustion and inefficiency. The result is unburned gases in the exhaust stream, and this can mean that the engine efficiency has been reduced. In addition, the regions of “too lean” gas mixture may cause production of nitrogen oxides (NO
x
), sulfur oxides (SO
x
), and other pollutants. Attempts to increase the brake mean effective pressure (BMEP) in natural gas engines with spark ignition are limited by considerations of engine knock as well as NO
x
emissions. Also, increasing the cylinder pressure makes the spark ignition problem more difficult. Higher spark voltages are required and this leads to more tip erosion on the spark igniter.
It is known that an autoignition fuel can be used in a micropilot fuel injector in place of a spark source to cause better combustion of the natural gas in the engine cylinder. Previous work concentrated on the use of diesel fuel as the autoignition fuel. The quantity of diesel fuel required is typically between 0.1% and 5% of the quantity of natural gas on a volumetric basis.
It is believed that there are no commercially successful implementations of this concept, because of concerns with the performance of the micro pilot injectors as well as maintaining two separate sources of fuel, i.e., natural gas and diesel fuel.
It is also known that dimethyl ether (DME) has excellent autoignition properties. It has a cetane number higher than diesel fuel with similar hydrodynamic properties. From a thermophysical perspective, DME is similar to liquid natural gas (LNG) in that it is a gas at standard temperature and pressure. At room temperature, approximately six atmospheres (atm) of pressure are required to liquefy DME. Continuing research and development programs are underway in the United States, Europe, and Japan in attempting to develop engines and fuel systems that operate on 100% DME. These programs are directed to substituting DME for diesel fuel oil in diesel engines that operate on 100% diesel fuel.
PCT Application No. WO96/23755 is directed to a process for the preparation of fuel grade dimethyl ether from synthesis gas.
U.S. Pat. No. 4,417,000 relates to a process for making dimethyl ether from syngas.
Of interest is European Patent Application EP 0 761 942A1 which describes a process for generating power in a gas turbine cycle using dimethyl ether and/or methanol as the primary fuel.
There still exists a need for an apparatus and method that allows a diesel-type engine (diesel-type engine as used herein is intended to refer to a diesel cycle engine which does not rely on a spark ignition source as opposed to an Otto cycle engine which does employ a spark source for the cylinder). Preferably, the apparatus and method will generate an autoignition product in situ with a portion of the natural gas intended to be the primary fuel for the engine.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to solving the aforementioned problems as well as others by providing an apparatus and method for generating an autoignition product for a diesel-type engine with natural gas. A multi-stage reformer connected to a supply of natural gas receives a portion of the natural gas and processes a portion of the natural gas to produce an autoignition substance. A pump connected to the multi-stage reformer receives the autoignition product and supplies the autoignition product to at least one microigniter in a diesel-type engine for ignition during the compression stroke of the engine. A controller connected to and in communication with the multi-stage reformer and the pump receives input signals from the reformer and the pump. In response thereto, the controller sends output signals to the reformer to generate a set amount of the autoignition product and then via the pump supply the autoignition product to the microigniter. A moderate size DME reservoir may also be utilized with the present invention.
The present invention is also directed to a method for producing an autoignition product for a diesel-type engine that uses natural gas as its primary fuel. A multi-stage reformer connected to the supply of natural gas receives a portion of the natural gas and processes a stream therefrom. The multi-stage reformer first forms a synthesis gas in a first reactor stage of the reformer. The next step employs a water-shift reaction to combine carbon monoxide and water in the synthesis gas stream to form carbon dioxide and hydrogen. A second reactor stage removes carbon dioxide from the gas stream. Additional methane is preferably added to the second reactor stage. A third reactor stage synthesizes dimethyl ether (DME) and methanol from the second reactor stage stream with preferably the addition of CO bleed stream. Impurities are separated from the DME and methanol. The fuel pump, responsive to the controller, supplies the DME and methanol mixture to at least one microigniter in at least one cylinder of the diesel-type engine.
The present invention is also directed to operating a diesel-type engine with natural gas using an autoignition product generated in situ. A diesel-type engine is operated on a supply of natural gas with a portion of the natural gas being supplied to a multi-stage reformer. The multi-stage reformer produces an autoignition product, preferably DME, from the process stream received from the multi-stage reformer. A fuel pump connected to the multi-stage reformer supplies the DME to a microigniter in each cylinder of the diesel-type engine for ignition to allow combustion of natural gas in the diesel-type engine. This allows the engine to operate exclusively on natural gas without a spark ignition source.
Accordingly, an object of the present invention is to provide an apparatus for generating an autoignition substance for operating an engine with natural gas.
Another object of the present invention is directed to a method for producing an autoignition substance for an engine.
Still another object of the present invention is to provide a method for operating a diesel-type engine with natural gas using an autoignition product generated in situ.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is described and illustrated.
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patent: 4098809 (1978-07-01), Pagani
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patent: 5218003 (1993-06-01), Lewnard et al.
patent: 5245110 (1993-09-01), Dijk et al.
patent: 5459166 (1995-10-01), Lee et al.
patent: 5485818 (1996-01-01), McCandles
patent: 5502243 (1996-03-01), Waller et al.
patent: 5714662 (1998-02-01), Vora et al.
patent: 5753716 (1998-05-01), Peng et al.
patent: 5908963 (1999-06-01), Voss et al.
patent: 0 761 942 A1 (1997-12-01), None
patent: WO 96/23755 (1996-08-01), None
Eaton Corporation
Huynh Hai
Johnston Roger A.
Kalka Daniel S.
Wolfe Willis R.
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