Mercedes-Benz adopts Bluetec technology

Mercedes-Benz is turning blue to be green by employing the European favoured Selective Catalyst Reduction (SCR) technology, or Bluetec as Mercedes-Benz calls it, to meet the new 2008 exhaust emission rules.

SCR, along with Exhaust Gas Recirculation (EGR) is one of the two most common technologies being used by truck makers globally to meet the tough new exhaust emission rules.

It is generally seen as the simpler way of achieving the end goal of reduced emissions than EGR because it's a relatively simple technology that doesn't require any changes to the base engine as EGR requires.

Instead, SCR injects Adblue, a water-based additive, into the exhaust stream. In the process ammonia is released, which converts the harmful NOx into harmless nitrogen and water.

It's an out-of-cylinder approach whereas EGR is an in-cylinder approach to cleaning up the exhaust that needs major changes to the engine itself.

The benefits of SCR are that the engine can be run in a dirtier state because any extra emissions produced can be cleaned up in the exhaust stream after they leave the engine.

That allows the engine designers to tune the engine to develop more power and better fuel economy, without being hamstrung by the need to make the engine itself clean. As a result, the retuned Mercedes-Benz engines run a higher compression ratio and are putting out as much as 20 horsepower more than the current engines.

An SCR engine will also run cooler so there's no need to bulk up the truck's cooling system as there is with EGR, which causes the engine to run hotter.

For the operator that means better performance and lower running costs.

Most operators who have had the chance to sample one of the many test trucks being evaluated in Australia by those manufacturers using the SCR strategy — Iveco, MAN, DAF, Scania, Volvo and UD — report better performance and driveability from the new trucks compared to their own trucks, and most claim improved fuel economy.

The downside for operators is that they have to cover the extra cost of the Adblue, which is generally added at a rate of 3-5 per cent. Adblue is carried in a separate tank on the chassis. It's generally around 80 litres in capacity, which was enough to get a B-double from Brisbane and Adelaide and back in recent testing done by Volvo.

Mercedes-Benz has six SCR-equipped trucks under evaluation locally, including two Atego rigids, one Axor prime mover, and three Actros prime movers. All are being put to the blowtorch in some of the toughest applications in the country to ensure they're fully prepared for the introduction of the new rules in January.