Off-highway engines advance beyond Tier 4

With Tier 4 Final/Stage IV needs met, engine OEMs direct their focus and competitive energies toward optimizing competitive solutions. At the same time, they need to keep a weather eye out for future regulations, which many expect.

“The technical solutions for Tier 4 Final are all there and in production,” said Andy Noble, Head of Heavy Duty Engines for Ricardo, during an interview with Off-Highway Engineering. “Engine manufacturers are now looking at taking cost out, for a more competitive solution.”

He explained there are four approaches for meeting the U.S. Tier 4 Final and EU Stage IV emissions regulations for engines with power ratings greater than 56 kW (75 hp). The first is to use only selective catalytic reduction (SCR). SCR removes NOx, but not other emissions such as particulates or soot. The second is to use a moderate amount of exhaust gas recirculation (EGR) coupled with an SCR system. He describes moderate EGR as 15% to 20% recirculation at full load. The third strategy is to use high EGR with aftertreatment that includes SCR, a diesel oxidation catalyst (DOC), and a diesel particulate filter (DPF). The fourth is to use very high amounts of cooled EGR with DOC and DPF while skipping the SCR.