Rejuvenation control of palladium-only diesel oxidation catalyst

A method of assessing and maintaining the capacity of a palladium catalyst for the oxidation of carbon monoxide and hydrocarbons in the exhaust stream flowing from a vehicle engine in which combustible mixtures of air and fuel are delivered to combustion cylinders of the engine at an air-to-fuel mass ratio (A/F) under control of a computer-based engine and exhaust stream control system which varies the mixture of fuel and air from a stoichiometric or fuel-rich A/F to an A/F that is fuel-lean, and exhaust gases from the cylinders are combined into an exhaust stream comprising carbon monoxide, hydrocarbons, nitrogen oxides, oxygen, and water;

• the exhaust stream then flowing into and through an oxidation catalyst support body having exhaust flow passages coated with an oxidation catalyst consisting essentially of particles of palladium on alumina support particles;
• the exhaust gas then flowing through one or more additional treatment bodies for further treatment of the exhaust gas;
• the assessing and maintaining method comprising the following palladium oxidation catalyst assessment procedure:
• periodically, during engine operation and during an oxidation catalyst assessment time period predetermined by the engine and exhaust stream control system, measuring the temperature of the exhaust gas over a time period as the exhaust gas enters the oxidation catalyst support body (TOCin) and also determining and maintaining a record of A/F values over a predetermined time period of engine operation preceding the execution of each palladium oxidation catalyst assessment procedure, and using collected temperature and A/F values in the control system as follows:
• (a) considering a current A/F value and, if it is a stoichiometric value or a fuel rich value, terminating further assessment of the oxidation catalyst until a time for the next palladium oxidation catalyst assessment procedure, but if the A/F value is fuel-lean continuing to step (b);
• (b) considering the current value of TOCin and, if the current TOCin is greater than a first predetermined temperature, terminating further consideration of the oxidation catalyst until a time for the next palladium oxidation catalyst assessment procedure, but if the TOCin value is less than the predetermined temperature continuing to step (c);
• (c) considering whether the oxidation catalyst has been exposed to a TOCin during the specified time period that is greater than a second predetermined temperature and, if the oxidation catalyst has not been exposed to a temperature greater the second predetermined temperature, terminating further assessment of the oxidation catalyst until a time for next palladium oxidation catalyst assessment procedure, but if the catalyst has been exposed to a temperature greater than the second predetermined temperature continuing to step (d);
• and
• (d) using the engine control system to alter the engine operation mode from a fuel-lean A/F to a stoichiometric or fuel-rich A/F for a rejuvenation time period determined sufficient for the constituents of the exhaust stream to rejuvenate the palladium oxidation catalyst.