All six new MAN Lion’s City buses are much cleaner than is currently required by law. Their level of harmful emissions falls well below permitted levels. At present, the Euro 4 exhaust norm is in force and will be replaced from 2009 by the stricter Euro 5 norm. But the six new buses belonging to WVB already score well below the emission levels permitted by the Euro 5 norm, complying with the requirements of the EEV (enhanced environmentally-friendly vehicle) exhaust standard.
Four of the vehicles achieve this by running on natural gas instead of diesel. They are 12-metre scheduled-service coaches of the type MAN Lion’s City Ü CNG. High-pressure cylinders to hold the natural gas are fitted on the roof of the buses, out of sight beneath an aerodynamic roof deflector. Natural-gas combustion is much cleaner than diesel combustion, one main advantage being that it produces no soot particles. These buses are used on local routes into the Harz National Park.
Diesel EEV buses for city transport
However, the other two new WVB buses are the real innovation. They are midi-buses of the Lion’s City M EEV type. Their classification shows that they comply with the strict EEV exhaust standard even though they are not fitted with natural-gas engines; they achieve this with a D08 Common Rail diesel engine of the new MAN generation. They operate on the four city routes in Wernigerode.
MAN has found a different solution to that of some of its competitors for achieving this high degree of environmentalfriendliness in the new D08 and larger D20 Common Rail engines by not injecting an additive such as AdBlue (urea) into the exhaust-gas stream. The advantages are obvious: The bus does not require an extra tank for AdBlue and the depot does not have to set up the infrastructure required for this reducing agent. And it also avoids the risk of forgetting to add AdBlue to the tank, since if that happened, the exhaust emissions would not even comply with the Euro 3 norm.
Technical accomplishment
Let’s look at how MAN solved the technical side of the task, enabling its diesel EEV buses to comply with these strict exhaust standards. Firstly, the exhaust gases are cooled and re-circulated to the engine for further combustion. This contributes greatly to the cleaning process. Also, the twin-turbo charger means that a much lower level of exhaust gas is produced in the first place, thereby significantly reducing the quantity of oxides of nitrogen emitted. And all the engine components required for this process are completely maintenance-free.
On their final route to the exhaust pipe, the exhaust gases are further cleaned by an electronically-regulated CRTec®
particle filter. This is a closed filter system which absorbs up to 99 percent of the particles. This means that almost no diesel soot is released at all. The electronic monitoring system checks the filter for any deposits and simultaneously checks whether it requires maintenance. The days when mileage determined servicing intervals are now gone – the CRTec® particle filter indicates when maintenance is required and otherwise faithfully carries out its duty.
Another advantage is that the new Common Rail D08 and D20 engines are also very economical with fuel. They use around a further two percent less diesel than the previous MAN generation of engines, which at the time were already considered economical.