The series of exhaust emission regulation changes of the past 20 years have come thick and fast. The latest emission reduction to affect Europe will be introduced in 2013. Euro 6 sees a reduction in nitrogen oxides allowed and a sizeable tightening on the amount of particulate matter in exhaust gases. Scania’s development team in Sodertalje, just outside Stockholm in Sweden, explained to Prime Mover what has had to be done to the engine systems over the line to meet the latest regulations.
Euro 6 comes into effect as of 1 January 2013 for new models and extends to all truck models in Europe on 1 January 2014. Scania has already released some of the new models onto the European truck market in anticipation of some governments offering incentives to trucking operators who moved to the cleaner trucks earlier than they are mandated. Low emission incentives were effective in bringing forward the adoption of Euro 5 technology in many countries in Europe. However, no major European country has yet announced any measure, either reduced road tax or reduced road tolls.
The European Union only recently finalised the Euro 6 emission level figures first suggested in July 2009, giving truck manufacturers a tight deadline. Apart from the usual limits of allowable pollutants in exhaust gases, a new kind of limit was introduced. This restricts the number of individual particles permitted to be emitted. Nitrogen oxides are reduced by 80% when compared to Euro 5 levels, down to 0.4g per kilowatt hour. Particulate matter is halved to 0.01g per kilowatt hour with carbon monoxide unchanged at 1.5 and hydrocarbons reduced by 75% to 0.13.
“Euro 6 has been, and is, a challenge to us,” says Bjorn Westman, Scania’s Engineering Director, Head of Engine Development. “In practice, the mass limit for particulates has made the amount of particulate matter the engines can emit much smaller than the regulators imagined, I think. When we started looking at Euro 6, particulate counting was not on the table. Different scenarios with nitrogen oxide levels and particulate matter mass were discussed along with their effects on fuel economy.
“The politicians set the limits knowing it would drive a 2% fuel economy penalty when compared to continuing with Euro 5. It was clear to us it would be possible to achieve half the particular mass emissions without having to use diesel particulate filters (DPF). The authorities did not like that, they wanted to push diesel particulate filters on all diesel vehicles. So they added in the particulate number count. So the industry was forced to add particulate filters. DPF’s add maintenance costs, exhaust back pressures and a further loss in fuel efficiency.”
The new European legislation also specified a new ‘World Harmonised’ test cycle to be used when assessing trucks for the new regulations. The new test includes much more simulated city driving, and tests both cold and warm engines. This increases the level of difficulty for the truck manufacturers as DPFs have to work even harder in stop start operation. The new test cycle is the toughest of its kind in the world, surpassing the strict Japanese testing procedures. In the past higher particulate matter levels were allowed in transient cycles with lower levels specified when the vehicle was stationary.
The cleanliness of the new exhaust gas particulate filters can be demonstrated by the fact the paper filters are completely clean after 30 minutes operation when compared with the same filter from a Euro 5 engine. Further proof of the much improved particulate matter output in the Euro 6 engines is in the fact the new exhaust pipes are completely clean inside and over time will become rusty rather than dirty.
“Politicians are not supposed to push technology but they have clearly done that in this case,” says Bjorn. “We now have to deal with a regulation which limits us to 800 billion particles per kilowatt hour. This is hard to count, and measurement technology has been tough to develop to meet this new part of the rules.
“However, we do believe that Euro 6 is the last major step in the reduction of particulates in exhaust gases. We think the next step in exhaust emission regulation will concentrate on carbon dioxide. Even without Euro 6 we have seen a huge drop in the level of nitrogen oxides and particulate matter emitted by truck engines out on the roads.”
So far, Scania has released two engines from its range as Euro 6, the 440 and 480 hp 13 litre. The company says its new engines will achieve the same fuel economy possible with its Euro 5 product. This has been achieved by changing the EGR settings in a way that increases nitrogen oxide emissions but also increases fuel economy, running more efficiently. The increased nitrogen oxides are cleaned up by the introduction of SCR technology after treatment. Upstream is the diesel particulate filter, and the combination of this and the SCR unit increase exhaust backpressure which increases fuel economy back to the levels currently available on Euro 5.
Looking at the development of technology in strategic terms, Scania sees keeping control of the development of the injection systems as the most important followed by EGR and SCR technology. SCR, especially, has taken the company down research routes unfamiliar to a large truck manufacturer. This has required an injection of a number of chemists into the development teams to fine tune the work of the catalyst in cleaning up nitrogen oxides.
“We have a tight relationship with Cummins, a 50/50 joint venture to develop fuel injection technology and these new engines have the Scania XPi injection systems which were developed by this venture,” says Bjorn. “This is the second injection system we have developed with Cummins, we have invested a great deal in the people and infrastructure to develop new systems and we are in it for the long haul.”
The chemical balance within the exhaust can be critical to its efficient cleansing. One of the issues which the new chemists in the research team have had to deal with is the balance between nitrous oxide (NO) and nitrogen dioxide (NO²) in the exhaust stream. The SCR catalyst works most efficiently when the two nitrogen oxides are present in roughly equal amounts. Scania has had to work on the combustion process in order to keep these two compounds in balance.
The company also creates all of its own software for the engine management system and the Opticruise automated manual transmission. In terms of development dollars, the move from Euro 5 to Euro 6 has been substantially more expensive than any of the previous five steps in emissions regulations. It is not only engine development that is required but also chassis layout design with the inclusion of after treatment and Adblue tanks into the equation.
As with all DPF technology, the issue of filter regeneration does add in some complexity to the vehicle’s systems. In all of its testing, Scania has failed to find a situation in which the filter cannot regenerate automatically during normal operation and cause minimal disruption to the driver. However, the company has built warnings into the system, rising from a simple instruction to increase rpm levels in order to heat up the DPF and burn off excess soot to a warning to pull the truck over and allow it to run an automated burn off cycle.
Due to the increased backpressure caused by the after treatment systems, finer control of incoming air is required and this is achieved by using a variable geometry turbocharger which can work together with the EGR valve to keep air and exhaust flow stable. Throughout the air and exhaust management system both pressure and temperature, as well as nitrogen oxides, are closely monitored by a number of sensors. These sensors indicate how much Adblue needs to be injected and when to initiate DPF reformation procedures.
Scania has managed to package the new exhaust system including a DPF and SCR unit in the same amount of space as its current exhaust muffler.
When the Euro 6 prime movers eventually make it to Australia, the chassis layout will include a battery installation at the rear of the chassis and two 75L Adblue tanks.
One of the new innovations to be included in the Scania engine block for Euro 6 is something called a plasma coated cylinder liner. Bjorn says the company fully expects the new smooth cylinder liners to be able to last for the total lifetime of the truck.
The improvement is achieved by coating the liners with a chemical which has a carefully controlled porosity. This enables the most efficient oil flow across the surface. As a result, the liner surface is completely smooth, and there is no need to mark the surface to enhance oil flow.
With the initial launch of the new Euro 6 trucks, Scania has announced that the new trucks will cost an extra €12,000 ($21,000 AUD) in the European market when compared to their direct counterparts at Euro 5. Whether this kind of increase will be necessary in Australia is impossible to ascertain as any release is well down the track.
For future trucks, Scania is looking at waste heat recovery systems to increase the fuel efficiency of the vehicles even further. Even small increments will be important as carbon taxation bites on transport operators who will be incentivised to save fuel.
“The most popular version of waste heat recovery today is a steam boiler to boil a fluid, it could be water or maybe ethanol, or even an organic fluid,” says Bjorn. You take heat from the exhaust and the EGR cooler to heat the fluid and use a turbine expander or a piston expander to return the energy back to the flywheel. Of course, when batteries become less expensive and there are more hybrid vehicles being made, the expanders could be used to generate electricity.
“The best systems I have seen discussed today have returned an improvement in fuel consumption of 7%. This means we can expect to get at least 5% when these technologies come online. However, we are talking about technology which will come on stream, probably, in 10 years or so. I have not yet seen a system which makes economic and reliability sense but a lot of people are working on them around the world.”
The solution used by Scania to get the 440 and 480 hp engines over the Euro 6 line can be expected to be repeated throughout the company’s engine range as it comes on stream. However, due to complicating factors it may be the case that other technologies may have to be employed additionally to reach such an exacting target. At this point in the development cycle Bjorn is still not sure exactly which technologies Scania will have to employ to become compliant in the future.
The implications for the Australian market of the introduction of Euro 6 are still not clear. The regulatory framework for the introduction of ADR 80/04 has not been finalised but we can expect it will allow for the exhaust emission levels to be compliant with either Euro 6, US EPA 2010 or the Japanese New Long Term rules. The date for the introduction is also, as yet, unclear but can be expected to arrive around 2015.
We can expect the issues faced by Scania to be repeated across the range of all truck manufacturers. US engine manufacturers have already had to bite the bullet and are running trucks at this exhaust emission level in the US today. By the time these technologies make it to our shores the picture will be a lot clearer about the precise effect ADR 80/04 will have on truck operations. The news from Scania is its ability to retain the same level of fuel consumption as is available in the current generation of new trucks. This should be encouraging to truck buyers worried about the consequences of even more emission regulation.