Some companies have proven that it’s possible to meet Tier 4 Final without use of a DPF.
For instance, Kohler Engines started with a “clean sheet” design and, while its engines still use a diesel oxidation catalyst (DOC), the DPF has been eliminated. “We developed engines clean enough to meet the emissions without a DPF,” says Jeff Wilke, Kohler Engines. This required a combination of technologies. “High-pressure common rail fuel injection was a big contributor. We went to a four-valve head and we centrally located the fuel injector in that four-valve head. A lot of work was done on the injector in terms of the spray pattern and the nozzle. It is a direct-injection engine.”
An electronic control unit (ECU) drives the fuel injection system. “We did a lot of work on the mapping of that ECU so that we have the right fuel ratio at all times to get the best fuel burn,” says Wilke. “We have a two-stage cooled EGR which is electronically controlled by the ECU. Turbocharging is also necessary and it has to be intercooled. This has an added benefit. It improves power density.”
The engine block design itself is a big contributor to eliminating the DPF. “A lot of work was done to reduce oil consumption because oil is definitely a contributor to particulate matter,” Wilke points out. “The block design helps the cylinders stay in the proper shape. We have a web structure that helps with the structure of the crankcase, as well. It was multiple newer technologies that were brought together to get an engine that would run clean enough that it didn’t require a DPF.”
Scania’s scalable approach
Scania has also been able to meet Tier 4 Final without the use of a DPF. “Low smoke has been a strategic decision for Scania for many years,” says Sterner. “This has forced us to continuously improve our engine. Several parts are important for this — our common rail system where we can have up to 2,400-bar injection pressure; our single cylinder concept, where we can put a lot of development in one piston bowl; and our completely own developed engine and aftertreatment management system. The DOC also helps us reduce particles for Tier 4 Final.”
Scania plans to use a common system to emissions solutions throughout its engine range.
“The system we have for Tier 4 Interim is our new engine platform (five, six and eight cylinder) with common rail (XPI) and SCR,” says Sterner. “For Tier 4 Final, we will add some EGR to reduce the NOx before the SCR system. This is to ensure that we have the required emission margin, including deterioration, to meet the emissions in all conditions taking in-use compliance into consideration.”
He adds, “To improve the efficiency in the SCR catalyst, we will also add a DOC. The system will be equal on all our engines, but there will be different sizes of catalysts. It’s important that we can meet any duty cycle with the same engine since it’s sometimes difficult to predict the use.”
The introduction of the DOC will affect the engines’ cost. “Since one more system is added, there will be a price increase,” says Sterner. However, differences in fuel consumption will be minimal. “In some cases lower and in some cases a bit higher, but very small changes. This depends on how we use EGR in combination with the variable vane geometry turbocharger and SCR system.”
John Deere continues “building-block” approach
To meet increasingly stringent emissions regulations, John Deere has followed a building-block approach, in which technologies have been systematically adopted to meet each regulatory tier. “To achieve compliance, we developed the Integrated Emissions Control system, a solution that optimizes engine performance, operating efficiency and reliability,” says Laudick.
The system encompasses any combination of aftermarket and emissions-reduction components. Solutions depend upon engine size.