Two-wheelers and small-engine equipment
Motorcycles and mopeds
The emissions regulations for motorcycles and mopeds also cover on-road tricycles and quadricycles. They therefore include vehicles such as the small 3-wheel light trucks used in some parts of Europe.
4-stroke petrol engines
Recent motorcycles for the European market may use either oxidation catalysts or three-way catalysts to meet the emissions regulations. Since the introduction of the third stage of motorcycle emissions regulations in 2006, all new 4-stroke motorcycles have been equipped with three-way catalysts.
The principle of operation of these catalysts is the same as for car engines. For the three-way catalyst the exhaust system will include an oxygen sensor or air:fuel ratio sensor that monitors the oxygen content of the exhaust and continuously adjusts the fuelling to match the conditions. This also ensures that the system alternates rapidly between very slighty fuel-lean and very slightly fuel-rich conditions. In this way both the oxidation functions (conversion of CO and HC to CO2 and water) and the chemical reduction function (NOx to nitrogen) can operate simultaneously. For motorcycles, of course, space is a limiting factor. The catalyst generally has to be quite small and built into a short exhaust pipe. Metal matrix catalysts are often used in this type of application.
A typical motorcycle catalyst system
2-stroke petrol engines and diesel engines
The emissions limits for this class of vehicle fitted with 2-stroke petrol engines or diesel engines are such that they may not require emission exhaust gas treatment. Nevertheless, it is possible to use oxidation catalysts (or diesel oxidation catalysts) with these engines. There have been no applications using particulate filters or NOx-control systems to date.
Small non-road equipment
The emissions requirements for engines for small non-road equipment (less than 19kW) form part of the emissions directives on non-road mobile machinery (NRMM), with specific classes for small hand-held and non hand-held equipment. The type of equipment is very varied.
Hand-held equipment includes:
- chain saws and portable saw mills,
- edge trimmers, string trimmers and rotary tillers
- sprayers and vacuum equipment
Catalysts are used on small equipment
- portable generators and irrigation pumps
- ride-on and pedestrian-controlled lawn mowers, lawn sweepers and waste disposers
- golf carts
- welders and air compressors
Unlike motorcycles, where the complete motorcycle is tested, the emissions test for small equipment uses only the engine, as the same type of engine may be used in very many different applications. The engines used for small non-road equipment have similar constraints on size as do motorcycles - in many cases even greater constraints. It is, though, still possible to fit a catalyst and many are now in use on this type of equipment.