Diesel engine technology
Scania benefits from experience1 October 2006
How Scania is using the weight of its truck engine experience to future proof its generator engines in preparation for new EU and US emissions legislation
The first series of national emissions regulations for on-road diesel engines was put into force in the early 90s, and by the end of the decade the first emission regulations for the off-road diesel business had come along. This process is continuing: emission legislation to be introduced in steps until 2014 will have a considerable impact on engine manufacturers, and the high costs of implementing it will favour those makers that can call on the economies of scale. The rewards though are very great in a market that is expanding quickly, especially for prime power, and where makers can meet the growing demand for reliability, quality and fuel efficiency.
In January this year stringent emission regulations, known as Tier 3, were put into force in the USA. By next year Stage II of the EU regulations will be put into force in Europe for generator sets, and by 2014 we will have the same emission standards for on road and off road diesel engines,
The major manufacturers, including Swedish genset and and truck maker Scania, have therefore been developing products that meet the anticipated legislation. Scania has developed a range of diesel engines equipped to meet the more stringent emissions regulations that came into force in the USA this year and their EU equivalents due in January 2007. It is already fitting EGR and SCR based technology in its trucks and buses, and considers itself well prepared to meet future emission standards for non road engines.
Meeting emissions legislation
Currently in the USA all industrial engines (motive power and generating sets) are subject to Tier 3 limits (HC + NOx 4.0 g/kWh, PM 0.2) while in Europe variable speed engines are covered by Stage 3A (also HC+NOx 4.0 g/kWh, PM 0.2) and single speed engines by TA Luft until end 2006, then from 2007 by Stage 2 (HC 1.0g/kWh, NOx 6.0 g/kWh, PM 0.2), a situation that will persist until 2010 when the tougher standards of Tier 4 and Stage 3A/3B will come into effect simultaneously for all industrial engines.
On-road legislation is well ahead of off road at present, By the time Tier 4 is fully implemented the standards for on and off read will have nearly converged. By that time there will also be fuel standards legislation, with low sulphur fuel being specified in Europe for industrial engines. But even in January 2007, when Stage II comes into force in the EU, the two main standards, for the USA and for Europe, will still be significantly different. Manufacturers, then, must for the time being make different engines for the different markets, or one engine suitable for both.
The primary changes suitable for achieving Stage II are seen as EGR (exhaust gas recirculation) and SCR. EGR has the effect, owing to its higher injection pressure, of slightly improving fuel efficiency. The effect of both technologies is seen in the charts below.
Scania’s next development will be for Europe. And EGR is already incorporated in all the company's in-line engines, although there is a hidden cost in the greater degree of cooling required. Scania engines can already meet Stage II requirements without EGR, and will be able to meet Stages 4 and 5 for industrial engines with EGR alone.
Applying EGR and SCR together is expected to be sufficient for at least the next 10 years, but by 2012 Scania expects to offer customers two further innovations – XPI (extra high pressure injection), a pulsed system, and HCCI (homogeneous charge compresssion ignition) a low NOx solution based on lean combustion and expected to be available by 2015.
An advantage of such a level of worldwide sales in truck engines is that it can finance a higher level of R & D than would normally be appropriate for the company's level of genset sales. 5700 were sold in 2005, more than half of them for gensets, compared to 60 000 trucks and buses. 60% of R & D now goes into engines.
And the US market, a weak area for Scania dominated by Cummin and Caterpillar, is becoming easier for non-US makers as their more economical engines help to offset high fuel costs, which is now becoming a bigger factor in the US especially for prime power gensets, but even for standby if the engine has to run often and for several hours. Scania claims its engines are 10-15% more fuel efficient than the US manufacturers' models.
For power systems the company makes a family of thee engines, the 9 litre 250-350 kVA DC9 EMS, the 12 litre 350 – 500 kVA DC12 EMS, and the 16 litre 450-650 kVA DC16 EMS, all in 1500 and 1800 rpm versions. Each engine family is built on the modular concept throughout, with as many identical components as possible including a single optimised combustion chamber. Other features include individual cylinder heads for each cylinder, an own design ems, Bosch unit injectors and a centrifugal oil cleaner.
Reliability is a primary concern. Careful design is critical to achieving a reliable and competitive engine, seen in the exhaust manifold with separated channels, the high location of the camshaft and locating the transmission at the rear of the engine.