Overview#
The Cummins QSK78 is a 2750 kW standby diesel generator set built on the massive QSK78-G14 V-18 engine -- one of the largest reciprocating engines in the Cummins power generation lineup. With 78 liters of displacement from 18 cylinders, it delivers the power density required for data centers, large hospitals, campus infrastructure, and utility peaking applications.
The G14 designation indicates EPA Tier 4 Final compliance, which requires an exhaust aftertreatment system with diesel particulate filter (DPF) and selective catalytic reduction (SCR). This adds complexity and weight but achieves the lowest emission levels of any Cummins high-horsepower diesel platform.
Engine specifications#
The QSK78-G14 is a purpose-built power generation engine:
- V-18 configuration: 170 mm bore x 190 mm stroke, 15.5:1 compression ratio
- Turbocharged and low-temperature aftercooled: Optimized for maximum air charge density and power output
- 1800 rpm rated speed with 2100 rpm overspeed limit and 266 kW regenerative power capability
- Gross engine output: 3028 kWm (4060 bhp) standby, 2737 kWm (3670 bhp) prime
- 413 liters lube oil capacity: Generous oil volume for extended drain intervals and thermal stability
Fuel and DEF consumption#
The QSK78 burns ultra-low sulphur diesel (15 ppm sulphur maximum):
| Rating | Load | Fuel (US gph) | Fuel (L/hr) | DEF (US gph) | DEF (L/hr) |
|---|---|---|---|---|---|
| Standby | 100% | 183.4 | 694 | 12.62 | 46.69 |
| Standby | 75% | 143.4 | 542 | 6.40 | 23.68 |
| Standby | 50% | 103.4 | 391 | 3.29 | 12.17 |
| Prime | 100% | 169.0 | 639 | 10.37 | 38.37 |
| Continuous | 100% | 145.5 | 551 | 7.64 | 28.27 |
DEF consumption is significant at full load -- ensure adequate DEF storage and supply chain for extended run scenarios.
Cooling system options#
Three cooling system configurations are available:
- High ambient (ship loose): 43C standby / 40C prime ambient design, 738 L coolant capacity, 90 kWm fan load
- Enhanced high ambient (ship loose): 51C standby / 49C prime ambient design, 1061 L coolant capacity, 107 kWm fan load
- Remote radiator: For installations where the radiator must be separated from the genset, with dual-circuit (jacket water + aftercooler) piping
Alternator selection#
The QSK78 offers one of the widest alternator selections in the industry, spanning voltages from 380V to 13,800V across multiple temperature rise classes:
- Low voltage (480V-600V): Temperature rises from 80C to 150C, motor starting up to 14,781 skVA
- Medium voltage (2400/4160V): For campus distribution and utility paralleling
- High voltage (12,470V-13,800V): Direct utility interconnection without step-up transformers
Our service experience#
The QSK78 is a serious piece of industrial equipment. At over 50,000 lb wet weight plus another 12,734 lb for the Tier 4 aftertreatment system, installation planning is critical -- structural engineering, rigging, and ventilation all require detailed analysis. The Tier 4 aftertreatment adds a maintenance dimension that earlier QSK78 variants did not have: DPF regeneration management, DEF quality monitoring, and SCR catalyst inspection. Facilities with Tier 4 QSK78 units should budget for aftertreatment expertise or a Cummins Power Generation service agreement.
FAQ#
What is the standby rating of the Cummins QSK78?#
The Cummins QSK78-G14 is rated at 2,750 kW standby / 3,438 kVA at 0.8 power factor, 60 Hz, 1800 rpm. Prime rating is 2,500 kW / 3,125 kVA. Continuous rating is 2,100 kW / 2,625 kVA.
What engine does the Cummins QSK78 use?#
The QSK78 uses the Cummins QSK78-G14 — a 78-liter, V-18 cylinder, turbocharged and low-temperature aftercooled diesel with 15.5:1 compression ratio. The G14 designation indicates EPA Stationary Non-Emergency Tier 4 Final compliance, requiring a diesel particulate filter (DPF) and selective catalytic reduction (SCR) aftertreatment system.
What are the service intervals for the Cummins QSK78?#
Oil and filter changes are due at 500 hours or 12 months. Fuel filter replacement is scheduled at 500-hour intervals. Air filter replacement is due at 1,000-hour intervals. Coolant change is recommended at 6,000 hours or 5 years. Annual load bank testing is recommended. Major overhaul interval is 40,000 hours under standard operating conditions. The aftertreatment system (DPF/SCR) requires additional inspection and service per Cummins' aftertreatment maintenance schedule.
Is the Cummins QSK78 EPA compliant?#
Yes. The QSK78-G14 is EPA Stationary Non-Emergency Tier 4 Final certified. This is the most stringent emissions tier and requires DPF and SCR aftertreatment with diesel exhaust fluid (DEF). DEF consumption at full standby load is approximately 12.62 US gph.
Can the Cummins QSK78 be paralleled?#
Yes. The QSK78 with PowerCommand controls supports genset-to-genset paralleling. It is used in major data center and campus paralleling arrays. Medium-voltage alternator options from 4160V through 13800V are available for direct distribution system connection.
What fuel type does the Cummins QSK78 use?#
The QSK78-G14 requires ultra-low sulphur diesel (15 ppm sulphur maximum) to protect the SCR catalyst. Conventional diesel (500 ppm sulphur) will damage the aftertreatment system. DEF (diesel exhaust fluid, 32.5% urea solution) is also required and must be stored and supplied separately.
What is the warranty on the Cummins QSK78?#
Standard Cummins warranty for new generator sets is 2 years or 2,000 hours for standby applications. A Cummins Power Generation service agreement is strongly recommended for Tier 4 units given the aftertreatment system complexity.
