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Looking at upcoming emission legislations for two-wheelers, it is quite obvious that the fulfilment of these targets will become one of the biggest challenges within the engine development process. The gradual harmonization of emission limits for two-wheelers with existing automotive standards will subsequently lead to new approaches regarding mixture preparation and exhaust gas aftertreatment. Referring to these future scenarios, a state-of-the-art in development of catalytic converters for two- or three-wheeler applications should be presented. After choosing a suitable test carrier, which has already been equipped with EFI components including an oxygen sensor for λ=1 operation mode, a basic injection system calibration was used to optimize the combustion process. Based on this setup, a variable exhaust system was manufactured to be able to integrate different catalyst configurations.

To get an overview of the emission situation in the field of small non-road mobile machinery powered by various types of SI engines, the Association for Emissions Control by Catalyst (AECC), together with the Institute for Internal Combustion Engines and Thermodynamics (IVT) of Graz University of Technology, conducted a customized test program. The main goal for this campaign was to derive information regarding the emissions of regulated gaseous components (following European Directive 97/68/EC) as well as particulate matter. With regard to the big variety of different engines that are available on the European and North-American market, the most representative ones had to be chosen. This resulted in a pool of test devices to cover different engine working principles (2-Stroke and 4-Stroke), technological standards (low-cost and professional tools) and different emissions control strategies (advanced combustion and exhaust gas aftertreatment).

Meeting future legislative targets for SI engines by means of low cost technologies is a big challenge for engineers. Despite the use of simple and cost efficient components these engines have to fulfill customer requirements in terms of power and fuel economy, representing the most important selling arguments. Without the possibility of integrating modern technologies like fuel injection systems for mixture preparation instead of simple carburetors, it is very complex to find viable solutions that enable the achievement of these targets. A main key to improve emission behavior, fuel economy and performance on carbureted engines is to get an insight in the mixture preparation process, especially under transient conditions.

Usually the power output of 50 cm₃ two wheelers is higher than necessary to reach the maximum permitted vehicle speed, making engine power restriction necessary. This publication deals with different power restriction strategies for four-stroke engines and their effect on exhaust emissions. Alternative power limitation strategies like EGR and leaning were investigated and compared with the common method of spark advance reduction to show the optimization potential for this certain engine operation conditions. From these tests, a substantial set of data showing the pros and cons in terms of emissions, combustion stability and fuel economy could be derived for each speed limiting technique.

The European emission legislation for two-wheeler vehicles driven by engines of ≤ 50 cm₃ is continuously developing. One of the most important issues in the near future will be the finalization of the European Commission's proposals for future steps in the emissions regulations as well as the verification of the impacts of current standards on the market. To have a basis for the discussion about these topics, the Association for Emissions Control by Catalyst (AECC) with the Institute for Internal Combustion Engines and Thermodynamics of Graz University of Technology (IVT) carried out an extensive test program to show the actual emission situation of state-of-the-art mopeds including mass and number of particulate matter as well as unregulated gaseous components. One of the main goals of these tests was to measure exhaust emissions without any modifications to the engines of standard production vehicles available on the European market.

Looking at the market for 2-wheelers driven by small capacity four stroke engines, it turns out that the legislation for exhaust emissions is mostly combined with a regulation of vehicle speed. Most of the vehicles in this category are still driven by engines equipped with carburetors which, unlike fuel injection systems, do not give the possibility to cut off fuel metering when high speed is achieved. When a carburetor is applied with a simple ignition unit, a reduction of spark advance is the only way to ensure correct vehicle speed, but there are a lot of disadvantages in terms of exhaust emissions and fuel economy coming up with this method of engine power restriction. This leads to the idea of using exhaust gas recirculation (EGR) to reduce engine power when necessary.

More and more stringent emission legislation is implemented in the world wide market of motorcycles leading to higher product costs. But not every market is ready for high technological levels. Therefore the main topic of interest is: “Will a small one cylinder motorbike engine need an electronic device for fuel metering or is it possible to use standard carburetors in combination with some smart but simple ideas, to fulfil EU III cold start emission regulations?” The described ideas deal with a novel secondary air supply, an improved cooling system and simple NOx reduction methods, always paying attention to the performance and driveability of the vehicle. After describing the prototype design of the engine modifications, the achievable results with their pros and cons are discussed. Online recorder measurements give interesting emission plots of HC, CO and NOx. The homologation measurement results point out the obtainable values of the limited emissions.