Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
1995-01-25
2001-03-27
Denion, Thomas E. (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S299000
Reexamination Certificate
active
06205777
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improved systems for control of exhaust emissions from gases containing fuel values. In one specific aspect the invention relates to catalytic systems for control of exhaust emissions from internal combustion engines. This invention also relates to passive emissions control devices for fuel-rich internal combustion engines.
2. Brief Description of the Prior Art
Exhaust emissions from small internal combustion engines, such as are used for lawn mowers and small generator sets, are a significant source of atmospheric pollution by hydrocarbons and carbon monoxide. Such engines typically operate fuel-rich and therefore are particularly dirty as compared to an automotive engine without a catalytic converter. Although automotive emissions are now controlled by use of catalytic converters, such conventional devices are not considered feasible for small engine use because of inherently large size, high cost and system complexity relating to the need for air addition. Effective means of suitable size and simplicity are required not only for the reactor itself but also for the addition and mixing of the air needed for oxidation of the exhaust fuel values to carbon dioxide and water.
The present invention meets these needs by providing a passive system for the combustion of the fuel values in the exhaust gases from engines which operate fuel-rich. The system is simple and relatively inexpensive.
SUMMARY OF THE INVENTION
Definition of Terms
As used in the present invention the term “passive” as applied to emissions control devices, systems or components thereof refers to such devices or components which do not require moving parts to function. For example, a conventional catalytic converter is a passive device but a converter system utilizing a mechanical air pump for air addition is not passive.
The terms “monolith” and “monolith catalyst” refer not only to conventional monolithic structures and catalysts such as employed in conventional catalytic converters but also to any equivalent unitary structure such as an assembly or roll of interlocking sheets or the like.
The terms “Microlith™” and “Microlith™catalyst” refer to high open area monolith catalyst elements with flow paths so short that reaction rate per unit length per channel is at least fifty percent higher than for the same diameter channel with a fully developed boundary layer in laminar flow, i.e. a flow path of less than about two mm in length, preferably less than one mm or even less than 0.5 mm and having flow channels with a ratio of channel flow length to channel diameter less than about two to one, but preferably less than one to one and more preferably less than about 0.5 to one. Channel diameter is defined as the diameter of the largest circle which will fit within the given flow channel and is preferably less than one mm or more preferably less than 0.5 mm. Microlith™ catalysts may be in the form of woven wire screens, pressed metal or ceramic wire screens or even pressed thin ceramic plates and have as many as 100 to 1000 or more flow channels per square centimeter. Flow channels may be of any desired shape.
The terms “carbonaceous pollutant” and “hydrocarbon” as used in the present invention not only refer to organic compounds, including conventional liquid and gaseous fuels, but also to gas streams containing fuel values in the form of compounds such as carbon monoxide, organic compounds or partial oxidation products of carbon containing compounds.
The term “muffler” as used herein means a multi-chamber device containing a baffle, through which the exhaust fumes of an internal combustion engine are directed to deaden sounds emanating from the engine.
The Invention
It has now been found that carbonaceous emissions levels from small internal combustion engines which operate fuel-rich can be reduced to very low levels by using the kinetic energy of the high velocity pulses of the exhaust flow to induct and mix sufficient air into the exhaust gases for thermal oxidation of fuel values to carbon dioxide and water in a subsequent reaction zone.
Advantageously, gas phase combustion of the mixture of air and exhaust gases is catalytically stabilized by contact with a catalytic surface. Although catalytic stabilization offers smooth combustion over a wide range of operating conditions, it has been demonstrated that if the exhaust gas is hot enough and sufficiently fuel-rich, gas phase combustion can be stabilized with the backmixing of a conventional baffled muffler even without catalytic stabilization. Thus, the present invention makes possible economic achievement of ultra low emission levels of carbon monoxide and hydrocarbons even with small internal combustion engines. The term “small internal combustion engine” as used herein means an internal combustion engine having a displacement of less than about 800 cc, preferably between 100 and 600 cc.
In a preferred embodiment of the present invention, the engine exhaust is ducted through a nozzle attached to the engine and jetted into the open end of a duct thereby entraining sufficient air for thermal oxidation of at least a major portion of the fuel values contained therein in a downstream reaction zone. Advantageously, the receiving duct may be a venturi tube. Advantageously, gas phase reactions are catalytically stabilized in a well mixed thermal reaction zone. The efficient, rapid thermal combustion which occurs is believed to result from the injection of heat and free radicals produced by the catalyst surface reactions at a rate sufficient to counter the quenching of free radicals which otherwise minimize thermal reaction even at combustion temperatures much higher than those found to be feasible in the method of the present invention.
REFERENCES:
patent: 3460916 (1969-08-01), Aronsohn
patent: 3776201 (1973-12-01), Sabet
patent: 70222 (1977-06-01), None
patent: 70223 (1977-06-01), None
Denion Thomas E.
Dreier & Baritz LLP
Precision Combustion Inc.
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