Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Patent
1996-08-23
1998-08-04
Wolfe, Willis R.
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
60297, 60324, F01N 320, F01N 328
Patent
active
057877068
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an exhaust gas purification device for trapping combustion engine exhaust emissions, particularly hydrocarbons and particulate matter.
BACKGROUND OF THE INVENTION
For the last two decades, massive efforts have been made to reduce exhaust gas emissions as a result of increased environmental concern on the part of the general public and an increased knowledge concerning the harmful effects caused by the emissions. In terms of the otto-engine, replacement of carburettor systems by fuel injection technology and the first generation of catalytic converters was soon followed by three-way catalyst technology with closed-loop control of the air/fuel ratio. Despite the significant achievements provided by these technological milestones, even greater efforts will have to be made to satisfy more stringent forthcoming emission legislation.
One area in which improvement is needed is in cold-start emissions. The purification of toxic components in exhaust gases by catalysts is very much dependent on the temperature of the exhaust gas and when the exhaust gas temperature is low, for example immediately after cold start-up, hydrocarbons are hardly purified by the catalyst. Technical development for reducing cold start emissions from otto engines has resulted in a few promising approaches, for example the electrically heated catalyst (EHC) and the use of secondary air injection into the exhaust system. Cost and reliability aspects may, however, be limiting factors for the widespread adaption of these concepts. In short, there is still a need for substantial improvement of cold start emissions from otto engines. The same is true for diesel and gas turbine engines.
Diesel engines have, in addition, the drawback of emitting particulates which are generally believed to play an important role as carriers of carcinogenic poly-aromatic hydrocarbons. Particulate emission reduction, therefore, has prime priority for diesel engine designers. Besides recent progress in diesel combustion technology, achieved by more accurate control of cylinder flow and fuel injection, a large number of systems have been developed to reduce the particulate emissions by aftertreatment systems, most commonly through trapping and burning the particulates in the exhaust system. In this case, it is absolutely essential that the burning, or regeneration, of the device that traps the particulates is carefully controlled. Otherwise, the latent heat of the particulates may well cause a virtual fire, yielding complete failure of the system. Therefore, inventions which make control of the regeneration procedure more robust are certainly needed.
Relatively recently, a new trend in cold start emission technology has gained momentum. This trend is based on the use of adsorbents to trap the cold start emissions at low exhaust gas temperature and to desorb them at higher temperature when the downstream catalytic converter has reached its operating (or light-off) temperature. Typical problems encountered for devices that use this principle include: i) difficulties in controlling the adsorption/desorption phases precisely, ii) slower heating of the catalytic converter due to increased upstream thermal inertia, iii) parasitic power losses introduced by the increased flow resistance, and iv) the mechanical complexity of the device itself. The last class of problem is related to the first one, since the control of the desorption process is often achieved by means of complete or partial bypassing of the device, introducing the inherent complexity of valve systems. An absorbent trapper and bypass arrangement is disclosed in EP-A-0 424 966 in which exhaust gases below a first temperature are passed through an absorbent trapper. When the exhaust gas temperature reaches the first temperature, a valve is activated to feed the exhaust gases through a conduit to bypass the trapper. When the exhaust gases reach a second, higher, temperature, the exhaust gases are again diverted through the trapper.
SUMMARY OF THE INVENTION
It
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patent: 5709081 (1998-01-01), Bruestle
Backlund Ove
Dexell Bjorn
Jobson Edward
Lundgren Staffan
Smedler Gudmund
AB Volvo
Wolfe Willis R.
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