Caterpillar will add an SCR module to its existing emissions control system to reach Tier 4-Final standards. The module will be located behind the current DOC/DPF unit and will require no engineering modifications in any of its machines.
“We’ve designed with the end in mind,” said Tana Utley, chief technology officer and vice president, explaining that the Tier 4-Intermin engineering design changes allowed room for the Final systems.
Urea is injected into the exhaust stream in a mixing tube located between the DOC/DPF unit and the SCR unit. SCR will be added to all diesels beginning with the Cat C4.4 and running through the C18. It will be used “as required” in the large end, ranging from the Cat C27 through C175.
Utley said net fluid consumption will be reduced by up to 5 percent, which is the volume of diesel plus the volume of the urea diesel exhaust fluid (DEF). Total consumption will go down even with the additional fluid (DEF) because fuel efficiency will increase, Caterpillar said. Because the SCR system is coupled with the existing EGR system, Caterpillar said it can program the engine for higher combustion and increase fuel efficiency, while letting the SCR system remove the NOx.
In addition, DEF consumption will be 3 percent of the diesel fuel consumption, Caterpillar said. And with current DEF prices in the $1.50 range, costs will be considerably less than that for diesel fuel.
The engine itself has no changes other than software in order to meet Tier 4-F. The rigid supporting cradle, holding both units, will be mounted into the machine and shock-isolated to protect componentry, such as ceramics, throughout the life of the engine, Caterpillar says.