In a sample cell in Scania to Ny Teknik see the tests of the combustion chamber in the next generation of engines. A single cylinder is connected to a series of measuring instruments. Will the test results good testing the new combustion chamber in a six-cylinder engine.
– How does it look, says development engineer Håkan Sarby and draw in Ny Teknik’s notebook. This engine we build without compromise. We have 46 percent efficiency and can handle all the treatment requirements of the Euro 6 by far.
What happened? I thought you had to put on one purification technique after another to satisfy the requirements, and that it made engine tougher and thirstier.
– That we thought too, until a few years ago. But there has been a technological leap in post-processing. Our SCR catalytic converter can handle 98 percent purification, from the previous 80 percent. This means that we can do without EGR and with almost halved injection pressure compared to the previous engine generation, says Håkan Sarby, which works to reduce fuel consumption and emissions.
Behind these acronyms and concepts are different methods to reduce emissions of toxic nitrogen oxides (NO x ) and particles from a diesel engine. EGR (Exhaust Gas Recirculation) is about bringing back the exhaust gases to the combustion chamber to lower the combustion temperature and prevent the formation of NO x . Extremely high injection pressures, typically 2400 bar, is used to reduce the appearance of particles in combustion. These methods counteract each other, and also stands in contrast to the low consumption and high efficiency.
Scania and other manufacturers fought long to Balancing these methods and complement with a particulate filter.
– We had all the time to compromise. More EGR produces less NO x but more particles and less effect. Higher fuel pressure produces smaller particles but more NO x . We passed the Euro 3, 4 and 5, but the development costs rose constantly. As recently as 2010-2011, it was unclear if any manufacturer would be able to take the next purification steps yourself, says Per Johansson, Supervisor for those who work with legal requirements at Scania.
The answer was in the form of SCR, Selective Catalytic Reduction, a technique that removes NO x in the exhaust gases by adding urea. The ammonia in the urea combines with NO x of a catalyst to form nitrogen and water. The technology is known since long, but Scania had been against it, partly because it required an extra tank of the car for urea (or Ad Blue, which is also called).
– Our slogans were” just add diesel “. It kept the Euro 5 standard, says Per Johansson.
Now forced Scania supplement with SCR to meet Euro 6. The engineers built up the SCR -katalysatorn with particulate filter and an oxidation catalyst and squeezed it all in the trucks silencers, a jar of 60 cm square (slightly smaller than an ordinary washing machine). The first version was presented in 2011 and took away 80 per cent of NO x . The particulate filter removed 99.9 percent of all particles. But the developers did not stop there.
– catalysts was much better. At the same time we worked really hard on improving the technology to vaporize the urea into the exhaust gases, says Håkan Sarby.
It took five years. Since the purification of NO x reside in 98 percent, and after reading so good that EGR and extreme injection pressure is not needed in the future. The engineers can concentrate on making the engine itself as efficient as possible. The last combustion chamber is the best so far.
But it is not clear then? To arrive at the best possible and then uses all this?
– You’d think so. But so far we have always managed to improve a little to says Håkan Sarby.
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