“If you look at off-highway equipment, there are so many engines, so many duty cycles,” Rhein said. “NOx (nitrogen oxide) and particulates opposes each other. If you have the most efficient engine in the world and it produces no particulates, your NOx skyrockets. They knew at the beginning of the emissions changes how to get NOx down…by producing an inefficient engine.”

Blake says the reality is that the technology is going to have to “morph” into something standard. He said he expects the industry to go through “a bumpy period where no one really knows what the right answer is,” and Tier 4 will “kind of marry” EGR and SCR together. “The billions of dollars in research have to be recovered somehow,” Blake said.

Each manufacturer will be looking at which is the most inexpensive technology and what produces the best fuel economy, Rhein said. “Based on this, they will come up with their final resolutions. Cooled EGR is a very inefficient engine. SCR has brought it back to be more efficient.”

For a more detailed report, including future-planning scenarios, see an upcoming digital edition of Aggregates Manager.