| abstract |
Internal combustion exhaust gases are catalytically treated and cleaned in a catalyst bed in contact with the exhaust gas conduit of the engine while avoiding overheating and thermal distriction of the catalyst bed according to the present invention by selectively directing a continuous source of heated, secondary air into the catalyst bed then, when the catalyst reaches a predetermined temperature value, the heated air is discharged directly to the atmosphere cooling the exhaust gases, and reducing the temperature of the catalyst bed. The exhaust pipe, upstream of the catalyst, is provided with a double walled conduit and the secondary air is continuously passed through the outer conduit and selectively directed into the catalyst bed or vented to the atmosphere depending upon temperature conditions in the catalyst bed. |