Cummins Tier 4 final QSK engines to use urea-SCR, no DPF

May 3, 2011

Cummins announced that the QSK high-horsepower engine range will meet US EPA Tier 4 final nonroad emission standards (2015) with a combination of clean in-cylinder combustion and a urea-based selective catalytic reduction (SCR) aftertreatment system. Fuel efficiency of the QSK engines will be improved by 5-10%, depending on the equipment duty cycle.

The new SCR system will be utilized on 19-60 liter QSK Tier 4 engines in the 800-3000 hp (597-2237 kW) power range. The SCR system will be also scaled-up for QSK engines above 3000 hp, including the new larger-displacement engine platform, with details to be released in September.

The SCR system reduces NOx emissions to the applicable Tier 4 limit of 3.5 g/kWh (2.6 g/bhp-hr), representing a more than 40% reduction compared with the Tier 2 level (NOx+NMHC = 6.4 g/kWh). By controlling NOx via aftertreatment, Cummins avoided any major change to the external engine platform and could optimize the combustion process for high performance, low PM emissions and improved fuel efficiency.

PM emissions are reduced by 80% to meet the 0.04 g/kWh level for Tier 4 final. This is achieved by the use of higher-pressure fuel injection and enhancements to the power cylinder design. Highly efficient PM reduction in-cylinder eliminated the need for either a diesel oxidation catalyst or diesel particulate filter (DPF) aftertreatment.

The fuel savings achieved in Tier 4 QSK engines more than offsets the cost of urea (diesel exhaust fluid, DEF) required for the SCR catalyst, according to Cummins. Depending on duty cycle and application, fuel efficiency should be improved by 5-10% compared with Tier 2 engines, with DEF consumption at 2-3% relative to fuel consumption. As 1% of urea consumption typically corresponds to a NOx emission reduction of approximately 1 g/bhp-hr, these urea consumption figures would indicate engine-out NOx of around 5 g/bhp-hr.

The new SCR system is an integrated aftertreatment package specifically developed for high-horsepower applications. The systems utilizes an “innovative DEF decomposition process process to significantly reduce space claim”, said Cummins, but no details were given. The SCR system also features an integral urea dosing injector with a high-efficiency spray pattern. Low urea consumption is achieved by a “series of advanced sensors” monitoring the operation of the SCR system. SCR logic control is driven by the QSK electronic engine management system, upgraded with extra processing power so that the engine and SCR aftertreatment operate as a single, integrated system.

For applications below 1500 hp (1119 kW), a single SCR catalyst system is used in varying lengths sized to engine output. A twin SCR catalyst system is used for applications above 1500 hp, with each catalyst aligned with a cylinder bank and matched to engine power output. For most applications, the SCR system replaces the current muffler within an equivalent size envelope and provides similar sound attenuation.

Before choosing the SCR aftertreatment path, Cummins evaluated alternative Tier 4 final technologies such as exhaust gas recirculation (EGR) and variable valve actuation. Both of those approaches were deemed less effective for large high-horsepower platforms, as they require major re-engineering of the base engine, generate additional heat rejection for the equipment cooling system to manage, and compromise serviceability, said Cummins.

The SCR system integrated with the Tier 4 final QSK engines is designed and manufactured by Cummins Emission Solutions, one of the world’s largest suppliers of exhaust aftertreatment, with 350,000 SCR systems produced. The first Tier 4 final QSK engines with the integrated SCR system will begin production in 2014, ahead of the January 2015 Tier 4 deadline for engines above 560 kW. Concurrent with the Tier 4 final production, Cummins will maintain full production of all current QSK and K Series high-horsepower engines for worldwide applications requiring less stringent emission levels.

The QSK engines are used in a diverse range of high-horsepower applications, including mining, locomotives, marine vessels, oil and gas equipment, power generation, large cranes and other industrial equipment.

Source: Cummins