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This paper presents the results of an exploratory study examining the production of particulate matter (PM) by 2-wheel vehicles and the impact of catalytic aftertreatment on these emissions. Information is presented demonstrating the efficacy of catalytic aftertreatment for significantly reducing not only hydrocarbons (HC) and carbon monoxide (CO), but also PM emissions from motorcycles equipped with small 2-stroke engines. The generation of PM by 5 test vehicles during realistic driving conditions is discussed and the impact of catalyst performance characteristics on the reduction of these releases is examined. Vehicle based test data, obtained with a mini-dilution tunnel, clearly demonstrates the benefits to the environment achievable through the use of catalytic aftertreatment.

The inefficient use of fuel by small 2-stroke powered 2-wheel vehicles results in high releases of hydrocarbons and carbon monoxide to the atmosphere. The presence of significant levels of oxygen (O2) in the exhaust stream creates an environment that is favorable for the use of catalytic aftertreatment to oxidize hydrocarbons and carbon monoxide to carbon dioxide and water, thereby eliminating or reducing the deleterious nature of 2-stroke engine exhaust emissions. This investigation examines the impact of catalyst formulation, operating temperature, and exhaust gas composition, on the performance of catalysts designed for use with these small 2-stroke power plant applications. It is demonstrated that catalysts can be formulated to possess specific performance objectives through the appropriate combination of noble metals and washcoating components. The non-noble metal components of a catalyst formulation are observed to be crucial to catalyst performance.

The effectiveness of using catalytic aftertreatment to control excessive hydrocarbon and carbon monoxide emissions is well known. However, a thorough understanding of how the catalyst and vehicle work together as an integrated system is still in developmental stages. A major goal of the investigation was to examine catalyst performance under the dynamic conditions existing during normal vehicle operation. The impact of applying catalytic aftertreatment, with and without the addition of secondary air, to three small 2-stroke motorcycles is examined. It is found that catalysts respond well to the varied conditions encountered with 2-stroke engine powered vehicles. While the addition of secondary air is beneficial to increased hydrocarbon reductions, its impact on carbon monoxide can be variable and a function of vehicle operation.

Scooters and motorcycles are favoured as economical forms of transportation throughout much of Asia. This is particularly true of vehicles with 2-stroke powerplants, thanks to the high specific output produced by this simpler, less costly engine. However, a serious disadvantage of these vehicles is that they emit considerably higher volumes of gaseous pollutants per driven kilometer than do other automobiles. Reductions of greater than 50% in these gaseous emissions can be effected through the use of catalysts to treat the exhaust from these engines. In this paper, important aspects of the operating conditions and durability requirements which must be factored into the design of durable, active catalyst formulations for these vehicles will be described.