Catalytic Exhaust Emission Control of Small Internal Combustion Engines



Gaseous emissions present in the engine exhaust of on-road motor vehicles are subject to stringent exhaust emission 2ontrol standards for carbon monoxide (CO), hydrocarbons, and oxides of nitrogen (NOx). All major automobile manufacturers utilize three-way catalytic converters to meet these standards.

There are millions of small engines in on-road and off-road applications whose exhaust emissions are currently not subjected to any form of regulations. This situation may change In the near future as the exhaust pollution control standards become more stringent. In many in-door applications where ventilation is not sufficient, small engine-powered equipment requires an exhaust pollution control system to meet carbon monoxide standards for a confined environment.

This paper illustrates the design of a new catalytic emission control system for application in small engine powered equipment. High exhaust purification, low exhaust gas restriction, low catalyst activation temperature and high mechanical l thermal catalyst durability are discussed.

Three catalytic exhaust emissions control systems consisting of various catalyst formulations and catalyst configurations are tested in a 3kW generator with a 242cc, Ccycle gasoline engine and their performances are analyzed. It is shown that high exhaust purification of small internal combustion engines can be achieved in a simple and reliable manner.


To control CO, HC and NOx emissions from automotive engines, a three-way catalyst with an aidfuel ratio electronic control unit is used.

The three-way catalyst simultaneously oxidizes HC and CO and reduces NOx if the exhaust airlfuel ratio is held close to a stoichiometric point. A lambda sensor located in the exhaust system measures the oxygen content of the exhaust gas entering the catalyst. A correction signal is sent from the lambda sensor to the electronic control unit to keep the airlfuel ratio near stoichiometry, i.e. within the catalyst window.

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