Power plants – Internal combustion engine with treatment or handling of... – Methods
Patent
1999-05-11
2000-09-26
Denion, Thomas
Power plants
Internal combustion engine with treatment or handling of...
Methods
60279, 60281, 60283, 123518, 123519, 123520, F01N 300
Patent
active
061229083
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a device for purification of exhaust gases. More particularly, the present invention relates to such devices for use in connection with the purification of exhaust gases in a motor vehicle, in particular for the reduction of exhausts of pollutants from the engine of the vehicle. The invention also relates to a method for the purification of exhaust gases.
BACKGROUND OF THE INVENTION
In connection with vehicles which use internal combustion engines, there is a general desire for reducing the exhaust of harmful substances in the exhaust gas from the engine. These harmful substances are primarily pollutants in the form of nitrogen oxide compounds (NO.sub.x), hydrocarbon compounds (HC) and carbon monoxide (CO).
In modern motor vehicles with gasoline engines, purification of the exhaust gases is normally carried out by means of an exhaust gas catalyzer in the exhaust gas system, through which the exhaust gases flow. In a so-called known three-way catalyzer, the main portion of the abovementioned harmful substances is eliminated by means of known catalytic reactions.
Although modern three-way catalyzers normally have a very high degree of purification, which to a very large extent limits the exhausts of harmful pollutants into the atmosphere, there are presently demands for even lower exhausts of harmful substances from motor vehicles. These demands arise, among other things, from increasingly restrictive legislation in various countries, with demands for extremely low exhausts of NO.sub.x, CO and HC-compounds. Modern conventional three-way catalyzers also have a drawback in that they have a relatively low degree of purification when cold-starting an engine, i.e. the catalyzer is not able to provide optimal purification from the start of the engine until the catalyzer has reached its so-called "light-off" temperature. In modern vehicles, the light-off temperature is from about 200.degree. to 350.degree. , and can be defined as the temperature at which the catalyzer provides 50% purification of a certain harmful component in the exhaust gases.
The initial period of time which elapses until the lightoff temperature is reached is, in modern vehicles, normally from about 30 to 90 seconds. During this time, a certain amount of harmful components in the exhaust gases will thus pass through the exhaust system of the internal combustion engine and out into the surrounding atmosphere. In order to minimize these harmful exhausts, there is thus a need to minimize the time which elapses until the catalyzer reaches its light-off temperature. This can be obtained, for example, by developing new catalyzer materials which exhibit constantly lower ignition temperatures, and by developing methods for rapid heating of the catalyzer. A reduction of the harmful emissions from an internal combustion engine can also be obtained by utilizing a HC-adsorbent which is arranged in the exhaust pipe in order to adsorb the undesired components in the exhaust gases, until that point in time when the catalyzer has reached its light-off temperature.
A previously known method for reducing the harmful exhausts from an internal combustion engine is to combine its regular catalyzer with another, electrically heatable, starting catalyzer which is placed upstream of the regular catalyzer. Since the starting catalyzer is heated rapidly using electricity, its catalytic deposition quickly becomes active, thus causing a significant purification of the exhaust gases at low idling flows. The exhaust gases which flow therethrough are heated further, which in turn shortens the heating time of the regular catalyzer. A device which comprises such a heatable starting catalyzer, which provides an improved purifying effect when cold-starting the engine, is previously known from International Publication No. WO 89/10470.
A drawback associated with electrically heatable starting catalyzers is that they require a very large current supply. This creates high demands on the electrical system of the vehicle, as
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AB Volvo
Denion Thomas
Tran Binh
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