Sticking to the recipe: in-cylinder designs, new fuel systems key to Tier 3 off-highway emissions for Cummins

When Joe Loughrey made that pronouncement at ConExpo in 2002, it didn't exactly go unnoticed. But it's fair to say Loughrey's statement was somewhat overshadowed by the more immediate news concerning Cummins Inc.' launch of the A Series engines and the general flurry of news coming out of ConExpo.

It's also fair to note that a lot of people in the industry were skeptical as to the ability of Cummins--or any other engine builder for that matter--to meet the more stringent Tier 3/Stage 3 engine emissions standards without the addition of significant new technologies such as exhaust gas recirculation, variable geometry turbochargers, aftertreatment, etc. At that point in time, with Tier 3 implementation some years off, there were those who believed that significant changes to both engines and equipment might be needed to achieve the reductions of N[O.sub.x] and PM mandated by the EPA and EU regulations.

That skepticism might have been further sharpened by the fact that Cummins didn't say much concerning Tier 3 beyond Loughrey's initial statement--leading some to suggest that the company's emissions path to Tier 3 and beyond wasn't really clear. But it's evident now that Cummins' focus on keeping its off-highway emissions solution as simple and straightforward as possible--no EGR, VGT, aftertreatment, etc.--never really wavered. The evidence of that was first revealed at the Bauma 2004 exhibition in Munich, where the company unveiled its newest generation of Tier 3/Stage 3 engines. More recently, Cummins further detailed its Tier 3 engine technologies and foreshadowed its Tier 4 strategies at its headquarters facility in Columbus, Ind.

All of Cummins' near Tier 3 engines rely on a combination of technologies to not only achieve the necessary emissions compliance, but to do so while keeping an eye on the customer's needs for performance, durability and fuel economy, according to Dave Crompton, executive director of Cummins' Midrange Engine Business Sales and Marketing.

"In the normal course of any development, there are tradeoffs," Crompton said. "It's easy to focus on compliance and perhaps end there and live with the tradeoffs. But customers aren't taking that as an answer these days. So figuring out a way to get compliance, but also meeting their performance targets is key."

The method Cummins has employed in its Tier 3 development focuses primarily on what the company calls "analysis led design," which puts an emphasis on achieving the lion's share of emissions improvements within the cylinder. That "emissions recipe" as the company terms it, is based on fundamental research into the physics and chemistry of combustion. While a lot of that work was done in Columbus, the company also relied on technical partnerships with organizations such as the Combustion Research Facility at Sandia National Labs in Livermore, Calif., as well as academic institutions like the University of Aachen in Germany, a specialist in chemistry.

Through those associations, Cummins was able to develop modeling technology that served as one of the lynchpins of its emissions efforts.

"Became of our models, we can now predict what happens with each little packet of air at each point in the combustion process within the cylinder," said Bharat Vedak, vice president, Industrial Customer Engineering. "And what's more important, not only do we have the models that predict, we also have models for our subsystems with which we can influence what happens.

"If you look at combustion, there is a combination of factors. There is the swirl of the fuel in terms of the injector hole patterns--how many are there, where are they, how big are they? There is the combustion bowl itself, the geometry of that. There is the timing of the fuel injection and if you have multiple injections, how much in one, how much in the second, how much in the third, when do they occur?

"There are all of these individual air packets and through our research, we found we can influence their behavior by changing some of the external parameters to get the result we want. It's going to the basics of thermodynamics, of chemistry and how the design factors influence that chemistry.

"So through a thorough understanding of combustion chemistry, with our advanced analytical models and our ability to influence the combustion phenomena, we can give our customers a very robust and what we consider the best value Tier 3 solution."

Along with the modeling capability, the other key aspect of Cummins efforts has focused on fuel systems technology, and not surprisingly this has resulted in the adoption of high-pressure common rail fuel systems across several engine platforms, including the QSB, QSC and QSK19 families. "Migrating to that fuel system is one of the things that allows us to make Tier 3 with minimal changes from our Tier 2 products," said Vedak.

Looking specifically at the engines, the Tier 3 versions of the QSB engines are in part, a fruit of one of Cummins' most interesting international partnerships, the European Engine Alliance (EEA). A joint venture between Cummins, Iveco and New Holland, the EEA was established in mid-1996 to develop a range of 1 L/cyl engines, primarily for off-highway applications. Over the last several years, EEA-spawned engines have been seen in some equipment, primarily in Europe, but this is the first time outside of automotive applications--the company's Euro 3 ISB is a derivative of the EEA design, as is the ISB for the Dodge Ram, minus the rear gear train--that Cummins has chosen to market them directly. "For Tier 2, we chose not to use the EEA product because our OEM partners were trying to establish it," Vedak said. "For Tier 3, we're going to that product.