Meeting 2010's Mandate
Reaching the next emissions hurdle will demand new technology.
Steve Sturgess
Executive Editor
One of the best attended technical sessions at the Technology and Maintenance Council's spring meeting in Tampa, was a panel on the technologies for the next emissions step in 2010.
Four speakers talked about the challenge of 2010 and the solutions to meeting the regulation, which will maintain particulates at the 2007 level, but reduce NOx from today's new 1.2 g/hp-hr down to 0.2 g.
There's no disputing it will be a challenge that will demand new technology. Those technologies were discussed by the panel and prompted many questions afterward.
Detroit Diesel's staff application engineer Chuck Blake summarized the options: In-engine NOx reductions may be achieved by the application of homogeneous charge compression ignition (HCCI), he said.
Another in-engine solution might be hydrogen-enabled combustion. Blake moved on to aftertreatment technologies that clean the NOx, introducing urea selective catalytic reduction (SCR) or an alternative Sigma SCR using gaseous ammonia. Eaton's on-board generator that is a combination hydrogen reformer, lean NOx catalyst and SCR doser was also presented as a self-contained aftertreatment technology.
HCCI technology is under study by most engine makers as well as General Motors, Bosch and Stanford University in a joint project. As with a spark ignition gasoline engine – fuel is mixed with air, but the proportion of air used in an HCCI engine is higher. The mixture is compressed by the piston diesel-style until it ignites, but at a far lower temperature.
The reduced temperature plus the high ratio of air significantly reduce NOx. On the down side, HCCI begs the use of computer control valves, variable compression ratio, variable valve timing, to name a few.
With hydrogen-enabled combustion, a plasma fuel reformer produces a hydrogen-rich gas from the diesel fuel on board the vehicle that can be used to enhance combustion. This allows for lower temperatures in the combustion chamber for NOx reduction, as in HCCI.
For aftertreatment, SCR is getting the most play and is the emissions technology already in place in Europe and Japan. In Europe, SCR has been used since 2005, said Blake, and there are on the order of 40,000 vehicles using the urea reagent Ad Blue. SCR utilizes urea injected into the exhaust stream where it reacts to form ammonia (NH3). This combines with NOx to form nitrogen gas and water vapor, both harmless components of the atmosphere. The Sigma variant SCR involves the direct injection of ammonia gas.
The Eaton solution combines a fuel reformer catalyst with a doser, SCR and a lean NOx trap (LNT).
The fuel reformer generates an optimal mixture of reformate gases to improve LNT regeneration efficiency. During "lean" exhaust conditions, the LNT stores NOx. During rich exhaust conditions (LNT regeneration), the LNT converts stored NOx to nitrogen and produces ammonia. This ammonia is stored by the downstream SCR catalyst and is used to convert remaining NOx that slips past the LNT. NOx reduction takes place in two stages – once by the LNT and a second time by the SCR catalyst. Basically it combines two technologies to reduce the NOx and, significantly, requires no urea tank or distribution infrastructure.
A technology not covered in Blake's opening remarks was addressed by Cummins' Bill Stahl. A NOx adsorber – the Environmental Protection Agency's favorite – has successfully been implemented for the Cummins ISB in the Dodge Ram pickup for the 2007-model year and available in March, three years ahead of the deadline. It works, said Stahl. NOx adsorption is more suited to light-duty diesel applications, he said.
The aftertreatment system includes a close-coupled diesel oxidation catalyst, a NOx adsorber catalyst and a combined diesel oxidation/particulate filter.
The NOx adsorber acts like a diesel oxycat. At the input, hydrocarbons, NOx and CO enter. From the exhaust, there's CO2, nitrogen and water vapor. But the NOx adsorber is easily poisoned by sulfur, so maintenance includes a periodic desulfurization. It is also necessary to manage three different regenerations, and no two can operate at the same time. According to Stahl, Cummins has overcome the challenge of how to feed fuel in and not impact fuel economy.
Like the light-duty Cummins solution, exhaust aftertreatment will likely be the way most manufacturers will address 2010. And that's sort of good news, hinted Mark Louzon, Volvo's chief engineer. If there's to be conditioning of the exhaust after it has left the combustion chamber, then there's a possibility that 2010 engines can be optimized for performance and economy, with the aftertreatment device knocking out the excess NOx that such optimization will cause.
Volvo has extensive experience with urea SCR, he said – 20,000 Volvos are already demonstrating that the technology works. He pointed out that urea is a common fertilizer, made from natural gas. It is an aqueous solution and considered a nonhazardous material. Louzon said the system is relatively compact and simple, but there are challenges: There's some more complexity, new controls, and of course, someone has to fill the urea tank. But there are benefits, too. SCR does work and it offers better fuel potential. It can also lower heat rejection and offers higher power density. Most importantly, the base engine stays the same.
Caterpillar's Brendt McClusky summed up the presentations and said that a year from now, we would have a much better idea of where we are headed for 2010. In a Q & A afterward, all the panel members were asked which strategy they were pursuing for the upcoming regulation. McClusky said he thought Cat was close to making a final decision, likely announcing in the spring. (Though elsewhere it was being said that Cat will be in the urea SCR camp.)
Cummins' Stahl said it may be a year before Cummins makes a final decision, though the company does have engines running urea SCR in Europe. Volvo and Mack would definitely be using SCR, said Louzon.
To a question about the cost of the urea solution, one of the panelists said it was anticipated to be around $1 per gallon and it would be injected at 1-3 percent of the diesel consumption. However, a British visitor from the audience said that in the UK the price was between $2.75 and $4 (at current exchange rates) and that dosage rates were as high as 7 percent.
Emissions Authority continued
