EMISSIONS STANDARDS
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Scania is making changes for the Euro-6
From 2013, heavy commercial vehicles must comply with the Euro-6 emissions standard, and Scania is trying to minimise the impact this will have on operators. CM reports from the firm's Technical Centre.
Words: Steve Hobson For truck makers, the constant ratcheting up of emissions standards. which started even before Euro-1 was introduced in 1992, has meant a constant battle to improve fuel efficiency while reducing emissions of pollutants such as NOx and particulate matter (PM) from the exhaust
Per Hallberg is Scania executive vice-president, responsible for R&D, and Jonas Hofstedt is senior vice-president for powertrain development. Together they have led the development of Scene's latest generation of modular engines to meet the tough emissions coming in Europe and the rest of the world.
For Hofstedt, the road to Euro-6 started in the 1980s with the snappily-titled ECER49 -20%. which required a 20% cut in the existing limit of 18g NOAWH.
'That was difficult as we had to modify the fuel injection, the fuel pump and the injection timing and adapt the turbocharger," he recalls. "For Euro-1 we had to do a lot more — that was my first really tough emissions project?'
To put things in context. Euro-1 stipulated emissions of 8g NOx/kWh and 0.36g PM/kWh. while Euro-6 will cut these limits to under 0.5 NOx/kWh and 0.01 PM/kWh.
"Reducing emissions is about controlling the injection timing and duration says Hofstedt. Too early means a lot of NOx, too late means high particulates and burning oil on the liners, which is then scraped down into the engine oil: Euro-3 came along in 2001, requinng more big changes in engine and fuel injection design "We had to go to unit injectors and more combustion recipes — including bowl shaped combustion chambers, more nozzle holes, a flatter spray into the piston bowl — and changes to the charge cooling systems."
To meet Euro-4 in 2006, Scene developed the high pressure injection (HPI) system plus turbo compounding for its exhaust gas recirculation (EGA) fiveand six-cylinder inline engines while the bigger V8 engines needed selective catalytic reduction (SCR)
Moving to SCR
"For Euro-4 on the V8 engine, we didn't have cooling capacity for EGR so we knew we had to learn about SCR" says Hofstedt. "It was very convenient to use SCR on the V8 for both Euro-4 and Euro-52 The main reason for moving to SCR for the V8 was the limit on cooling capacity. as EGA increases exhaust energy lost to the cooling water. The latest R Series cab has been built with Euro-6 in mind, with extra vents to maximise airflow to the engine, as this will be required even with SCR.
The company has invested in its own wind tunnel at its Sodertalje, Sweden factory to improve the cooling, and the new R Series has 5% better airflow around the engine. It is planning a new wind tunnel that will enable it to simulate rain and snow, as a build up of snow on the grille can cause overheating. Scania spends 4% of its turnover on R&D, 85% of which goes on engine development.
• For Euro-6, Scania is experimenting with different combinations of fuel injection, variable geometry turbos (which are more efficient, and faster when changing gear), two-stage intake cooling, EGR, SCR and combustion pressures to achieve emissions limits without compromising fuel efficiency It is likely that both SCR and EGR will be required because in cold operating conditions which would include low speed, stop-start type operations in the UK and colder climates— the catalyst does not get hot enough quickly enough for SCR to be effective. But EGR remains efficient at low exhaust temperatures, and Euro-6 will require exhaust temperature monitoring and post-injections to keep up the exhaust temperature.
"Our ambition is to keep down emissions and have less cleaning to do afterwards as this will help overall efficiency" says Hofstedt.lt will be necessary to monitor exhaust temperature to keep the after-treatment system working!'
Scania developed its own extra high-pressure injection (XPI) system for its Euro-5 EGR inline engines and the 730hp V8, and this will be used on more Euro-6 applications. XPI is a common rail injector that operates at an average pressure of 1,800 bar and a maximum of 2,400 bar. Apart from the higher injection pressures that improve the fuel/air mixture, the electronic control means that each injector can make several fuel injections per combustion cycle.
One consequence of this quest for ever cleaner exhaust emissions was a halt in the progress manufacturers had been making in the fuel efficiency of heavy truck engines. EGR involves redrculating exhaust gas back into the engine air intake, reducing the efficiency of the engine. while SCR requires treatment of the exhaust with AdBlue additive, again reducing efficiency and increasing running costs.
Lowering emissions within combustion
'When the emissions regulations started, it flattened out the possibility to reduce fuel consumption," says Hofstecft. "There is a contradiction in that the high efficiency burning of diesel creates NOx. We managed to meet Euro-5 with EGR, but we know we have to reduce emissions within combustion."
Lowering NOx emissions can be done by keeping down peak combustion temperature, because nitrous oxides only form at high temperatures, but this can affect fuel efficiency. One way of reducing combustion temperatures is to introduce a lot of carbon dioxide, which has higher heat capacity than air, but this increases risk of forming soot — high injection pressure and careful injection timing are required to avoid this. The combustion pressure of the new V8 has been increased to 200 bar, compared with165 bar in the old V8, a step up made possible by the use of new materials such as compact graphite iron (CGI).
Euro-5 to Euro-6 is another big step in emissions reduction, which will see NOx cut from 2.0 glkWh to 0,46 g/ kWh and PM from 0.03 g/IkWh 10 0.01 g/kWh.Truck makers must also ensure these standards are met for seven years or 700.000km after the truck is delivered.
Scania is developing a particulate filter that will be monitored and automatically cleaned in day-to-day operation.
-If we are successful, there will be no consequences for the driver as the filter will be cleaned automatically;' says Hallberg 'When soot is accumulated, it will start regeneration and there will be a lot of supervision of temperature, pressure drop, etc:
The filter will have to be cleaned manually every 303,000km when the vehicle is run on conventional diesel, more frequently when a high biofuel blend is used •