Setting the stage: meeting Stage IIIB engine compliance
By Steve Skinner07 January 2009
With Stage IIIB emissions legislation for 130 kW to 560 kW engines due to be implemented in 2011, all of the main engine manufacturers are now well down the road to developing and trialing systems that will ensure their products meet the legislative restrictions on nitrous oxide (NOx) and particulate emissions on time.
Manufacturers have adopted one of two fundamental systems to achieve the necessary reductions in NOx and particulates, the first being exhaust gas recirculation (EGR) in tandem with diesel particulate filters (DPF) and the second, selective catalytic reduction (SCR).
EGR systems use re-circulated cooled exhaust gasses to displace approximately 15% of the oxygen in the firing cylinder leading to a cooler ignition. NOx is produced at temperatures above 16500 C so cooling the ignition reduces NOx at source. “In our high powered engines, we are aiming to reduce NOx by -50% through our EGR system,” said Ben Reed, Stage IIIB product engineering manager at Perkins.
EGR systems necessarily require additional after-burn treatments to further reduce NOx and diesel particulates. “To achieve a -95% particulate reduction we’ve adopted a ceramic DPF lined with cordierite in conjunction with the EGR ignition,” said Mr Reed. “We will also install a through flow diesel oxidation catalyst to reduce carbon monoxide and hydrocarbons. This will be fitted with a platinum and palladium coated honeycomb core.”
The SCR method of reducing NOx and particulates is purely an after burn treatment that adds an aqueous urea injection into the exhaust stream before it channels through a catalyst. The catalytic reaction converts the NOx into harmless nitrogen gas and water.
CatalystAgco Sisu power in collaboration with Bosch has committed to SCR technology because it believes the system offers better fuel economy, lower heat rejection, less particulate matter and longer service intervals due to a reduction in soot contamination of lube oil.
“We are convinced that to achieve Stage IV legislation in 2014 - when manufacturers will have to achieve a -97% reduction in both NOx and particulate matter compared to non-regulated engines – everyone will need to adopt SCR technologies,” said Mauno Ylivakeri, director of research and development at Agco Sisu Power. “We believe that adopting SCR now will enable us to use emission technology as a differentiating factor.”
Scania Engines too has elected for an SCR solution. “We will use the SCR system to fulfil Stage IIIB legislation,” said Johan Berggren, manager of product planning and technical information at Scania Engines. “We have of course investigated all available systems and our conclusion is that the SCR system gives us excellent performance for off-highway applications.”
“The SCR route means that Scania Engines customers will also be well prepared for Stage IV in 2014 because only minor changes will need to be made to reach the tougher emissions criteria,” said Johan Sporre, head of marketing and communications for Scania Engines. “Our SCR system is designed to be robust and reliable. Although Stage IV compliance will not be achievable as a simple retrofit, OEM equipment will only need minor modifications and we believe this will be greatly appreciated by our OEMs.”
Director of commercial and industrial sales at MTU, Scott Jenkins said, “The SCR system requires minimal service. The system does add cost, but you cannot get to the next level of emissions compliance without some additional cost. We deem SCR to be a cost-effective means of bringing our existing engine family to Stage IIIB levels.
“Besides being cost-effective, SCR preserves the inherent fuel efficiency our 900 Series engines and required no major changes to engine design,” continued Mr Jenkins. “Furthermore, SCR doesn’t increase heat rejection, which can be a problem with EGR. OEMs want smaller cooling packages to improve operator visibility and smaller, slower fans to reduce noise. Neither goal can be accomplished when heat rejection is increased.”
Tim Leverton, group engineering director at JCB believes that SCR will probably be adopted by all manufacturers for Stage IV compliance. “I think, ultimately, it will be difficult to escape using some sort of SCR NOx after treatment for Stage IV. I believe that a combined EGR/SCR system will prove to be the preferred solution for attaining Stage IV compliance.
“That said, JCB is pursuing an EGR solution to Stage IIIB compliance,” confirmed Mr Leverton. “Our philosophy, since we first entered the engine manufacturing business, has been to develop the combustion system to minimise the ‘engine out’ emissions using the characteristics of our engine. These characteristics include a stiff crankcase structure and a solid bottom end so that we can operate at high pressures.
Recirculation“We went to a common rail fuel system for Stage IIIA and as we move forward we’re developing the combustion system to use an EGR based solution. We used an internal EGR approach for Stage IIIA (this uses either the inlet or exhaust valve to allow exhaust gas back into the cylinder and is operated by the cam shaft) on our mechanical and common rail engines and we’re moving to external EGR (an electronically controlled valve for the introduction of cooled re-circulated gas) for the next stage,” confirmed Mr Leverton.
Volvo too has opted to use an EGR and DPF solution. “So far, I’ve not seen anyone publish a DPF solution without EGR,” said Mattias Nordin, vice president of research and development at Volvo Construction Equipment.
“The system we’ve developed is very good for the local environment and for the health and safety of the driver and workers on the site because it removes virtually all of the particles. That’s important to us because these issues as well as environmental responsibility are core values of Volvo,” said Mr Nordin.
“We looked at various systems to meet Stage IIIB compliance but none could match our EGR and DPF solution regarding quality assurance. This time around we’re not just producing an engine, we’re producing an engine system with a full after treatment package. This requires a completely different methodology for handling the quality assurance. I believe that quality assurance is going to be a key differentiator between us and other suppliers,” said Mr Nordin.
“Another important area is the regeneration strategy - how you deal with burning out the filters. I think we have some fairly good solutions that don’t stop the operation, which I think will differentiate Volvo from other manufacturers. Not having to stop for regeneration of the filters should be advantageous to our customers.”
Cummins introduced its integrated air intake to exhaust solution at ConExpo in March last year. “For our engines above 129 kW we are using a Cummins particulate filter for a particulate matter reduction of -90% and cooled EGR to reduce NOx by -45% compared to current Stage IIIA engines,” said Kevan Browne of off-highway communications for Cummins.
“We have also adopted a high pressure common rail fuel system and a variable geometry turbocharger to enhance performance,” continued Mr Browne. “We envisage that that our Stage IIIB solution will give customers up to +5% improved fuel efficiency, depending on rating, and also an increased top-rated power. Our next generation QSB 6.7 litre engine for example, will increase its rating from 205 kW to 224 kW.”
PackagingAll engine manufacturers have acknowledged that packaging will be one of the issues of Stage IIIB compliance. “It is no longer a case of slinging an engine at a machine,” said JCB’s Mr Leverton. “Stage IIIB systems are much more intrusive into the machine itself, so really you have to think conceptually about the whole thing. If you’re an innovative engineering company the opportunity certainly throws up some interesting possibilities.
“We faced the issue by considering the implications quite early on in our machine product cycle planning, and because of that we’ve been able to anticipate some of the demands and integrate them early into our product changes. I think we’ve found some good solutions, but it is a real problem,” continued Mr Leverton.
Allister Dennis, product marketing manager at Perkins echoes the point, “Stage IIIB compliance requires a huge collaboration with our customers. The engines themselves are the most compact that we’ve ever designed, but with the necessary filter systems the physical characteristics of the whole package represents a considerable increase.”
Cummins has gone some way to minimising packaging issues by adopting a highly flexible DPF that can be operated alongside or above the engine in either a vertical or horizontal position. “The Cummins DPF has rotating ‘clock ends’ so we have total mounting flexibility,” said Mr Browne. “Furthermore, the DPF replaces the silencer so although it does require more space it’s not that much more.
“We already have 400000 to 500000 on-highway vehicles using our DPF technology, so we’re happy that we’re using proven technology,” said Mr Browne.
IssuesTwo significant issues that cannot be engineered out of the compliance equation are the build-up of ash in the DPF and the absolute requirement for ultra low sulphur diesel.
Ash is formed from the trace elements that remain from lube oil additives after the combustion process, consisting of calcium, zinc and phosphorous. “Ash is a real problem for everyone,” said Mr Nordin of Volvo.
“The dimensioning feature will be the size of the filter and how much ash it can contain. It cannot be burned-off through regeneration, so it needs to be filtered and then the filter de-ashed, although in the US there are already strict regulations as to how often you can have planned de-ashing.
“The onus is really on making the DPF big enough and designed in such a way to distribute ash efficiently throughout to get the right durability,” said Mr Nordin.
High levels of sulphur in diesel fuels can render the DPF ineffective and cause damaging back pressure in the exhaust system. It is therefore imperative that Commission mandated 15 ppm sulphur content diesel fuel is generally available by 1 January 2011 according to Cummins.
“Sulphur is an important issue,” said Mr Nordin. “It is critical that fuel legislation is brought in before Stage IIIB legislation so that there’s guaranteed availability of ultra low sulphur diesel. Anything less could be catastrophic to the whole process of Stage IIIB compliance.”