Exhaust particulate management for gasoline-fueled engines
A thin layer of low mean-pore-size filter material that permanently accommodates the accumulation of exhaust particulates (as soot or a soot cake) is carried on a porous ceramic support. The supported filter material is closely coupled with the exhaust manifold of the engine, for the purpose of passive regeneration of stored particulates, and removes particulate matter from the exhaust which is directed through the filter layer and ceramic support. The oxygen content of the exhaust oxidizes the particulate matter on the filter material. In a preferred embodiment, a thin layer of the filter material is supported on inlet channel walls of a wall flow-through ceramic filter body to remove the particles from the exhaust. The filter body comprises an upstream exhaust gas flow inlet face with openings to a plurality of inlet channels and a downstream face with a like plurality of openings from outlet channels. The inlet channels are closed at the downstream face and the outlet channels are closed at the inlet face. So the exhaust stream enters the inlet channels and flows through the filter layers and supporting channel walls to an outlet channel. The filtered exhaust stream exits the outlet end of the filter body and is combined into an exhaust passage downstream of the filter body for further treatment as may be necessary.
1. A method of removing carbon-containing particulate matter from an oxygen gas-containing exhaust gas stream exiting an exhaust manifold of a spark-ignited, gasoline-fueled engine, the method comprising:
passing the exhaust gas stream with its oxygen gas and carbon-containing particulate matter from the exhaust manifold of the spark-ignited, gasoline fueled engine through a porous filter layer washcoat composition supported on a flow-through ceramic wall to remove the carbon-containing particulate matter from the exhaust gas of the spark-ignited gasoline fueled engine, the pore size of the material in the filter layer being about four micrometers and the flow-through thickness of the filter layer being up to about one hundred micrometers, the flow-through ceramic wall having pores that are larger than the carbon-containing particulate matter to be removed from the exhaust gas stream, the supported filter layer being located closely coupled with the exhaust manifold to retain the heat of the exhaust for passive oxidation of carbon-containing particulate matter entrained in the filter layer by the oxygen gas in the exhaust gas stream, the carbon-containing particulate matter containing exhaust encountering the filter layer after flowing no more than about eighty centimeters from the exhaust manifold; and
oxygen gas in the exhaust stream exiting the exhaust manifold of the spark-ignited, gasoline-fueled engine serving to passively oxidize carbon-containing particulate matter removed into the filter layer.
2. A method as recited in claim 1 in which the filter layer washcoat composition is deposited on supporting wall surfaces of a ceramic filter body and the exhaust gas flows through the filter layer and then through the supporting wall of the filter body.
3. A method as recited in claim 1 in which the exhaust gas flows over an exhaust gas treatment catalyst layer lying against the filter layer washcoat composition.
4. A method as recited in claim 2 in which the porosity of the wall of the ceramic body is about 50% or larger.
5. A method as recited in claim 1 in which an oxidation or three-way exhaust flow-through monolithic catalytic converter is located upstream in the exhaust gas flow with respect to the filter body to promote exothermic reactions in the exhaust gas flow and heat the exhaust gas to promote oxidation of the entrained particulate matter, the inlet face of the filter body being located within two centimeters of the outlet face of the catalytic converter.
6. A method as recited in claim 1 in which the total volume of the inlet channels and outlet channels is at least equal to the displacement of the reciprocating pistons of the engine producing the exhaust.
7. A method as recited in claim 1 in which the washcoat composition applied to the walls of the inlet channels of the filter body incorporates a catalyst.
8. A method as recited in claim 1 in which the washcoat composition applied to the walls of the outlet channels of the filter body incorporates a catalyst.
9. A method as recited in claim 1 in which a layer of catalyzed washcoat is applied over a layer of washcoated filter material.
10. A method as recited in claim 1 in which a layer of catalyzed washcoat is applied under a layer of washcoated filter material.