The new 675-hp top rating for the QSX15 takes the Tier 4 Final engine 75 hp above the Tier 4 Interim top rating of 600 hp. The QSX11.9 engine also increases power output for Tier 4 Final with a new top rating of 525 hp. The 11.9-liter QSX shares the same engine technology and CPF-SCR ultra-clean after-treatment system as the QSX15. Engine power density for Tier 4 Final increases to 45 hp per liter for the QSX15 and 44 hp per liter for the QSX11.9.

To meet Tier 4 Final in 2014, particulate matter (PM) reduces to 0.02 g/kW-hr, and oxides of nitrogen (NOx) reduce to 0.40 g/kW-hr. Compared to Tier 3 emissions levels, these figures represent a 90% reduction for both PM and NOx. At Tier 4 Interim 2011 emissions levels, the QSX15 and QSX11.9 engines are capable of achieving up to 5% improved fuel efficiency compared to Tier 3, depending on duty cycle and machine optimization. Fuel efficiency will be further increased for Tier 4 Final 2014 by an additional 3% to 4%.

The SCR system developed by Cummins for Tier 4 Final is a next-generation design that moves beyond the SCR technology currently in use for Tier 4 Interim. The system incorporates a copper zeolite-based catalyst capable of up to 95% NOx conversion and able to operate more efficiently at lower temperatures. The system features advanced sensors to provide full closed-loop control. Diesel exhaust fluid (DEF) dosing levels are minimized with enhanced mixing in the decomposition pipe.

The Cummins Particulate Filter is retained from the Tier 4 Interim after-treatment used by the QSX engines. The CPF incorporates both a diesel oxidation catalyst and the wall-flow filter, providing an additional margin of PM emissions control at the higher engine loads and power outputs of heavy-duty engines. With this higher PM filtration efficiency, the engine combustion can be formulated to increase power density and lower fuel consumption. The integration of SCR into the exhaust after-treatment allows the CPF to reduce the frequency and duration of active regenerations below 1% of equipment operating time, creating a virtually full-time passive device.