A partial oxidation catalyst is interposed between an exhaust manifold and a catalytic converter in the exhaust system of a gasoline, natural gas, or propane fueled engine. The engine is started from a cold-start and the exhaust gas stream emitted during an initial period of operation after the cold-start has a .lambda. value <1 as a result of a rich combustion mixture provided to the engine during cold-start operation. Hydrocarbons passing through the partial oxidation catalyst during the initial engine operating period are partially oxidized and hydrogen produced as a result of the oxidation process is used to promote faster light-off of the catalytic converter in the exhaust system. Also, hydrocarbon emissions discharged into the surrounding environment are reduced during the initial period following cold-start.
Gordon J. Bartley