Introduction: Published full-load fuel figures and base tank volumes give a workable runtime estimate, but real consumption shifts with load level, fuel properties, and tank fill.
Anyone comparing a 200 kW Cummins generator or reading through a 280L base tank spec runs into the same question: how long will this actually run before it needs refueling? The published numbers help, but they describe one condition. A machine that burns around 39 liters per hour at full load can burn far less at half load, and a tank listed at 280 liters rarely gives up all 280 usable liters before the engine stops. Reading those numbers as a model rather than a single promise is what turns a fuel spec into a usable runtime plan.
Full Load Fuel Consumption Figures for 200 kW and 250 kW Units
Published model data for this power range gives two useful reference points. The AT-200GFC is rated at 200 kW (250 kVA) and lists about 39.22 L/h at 100 percent load, paired with a 280L base tank. The AT-250GFC is rated at 250 kW (312.5 kVA) and lists about 49.02 L/h at 100 percent load, with a 300L base tank. Those figures also answer the 250 kVA full-load question directly: a 250 kVA machine rated at 200 kW burns roughly 39 liters per hour at its design point, and stepping up to 250 kW adds about ten liters per hour. "100 percent load" needs a clear meaning before the numbers can be trusted. It means the alternator is delivering its rated real power output — 200 kW or 250 kW — at the stated voltage, frequency, and power factor, under the ambient conditions listed with the data. A three-phase load measured in kVA is not the same as the kW the engine has to supply, because power factor sits between them. That distinction matters later when site load is compared against these full-load figures. The base tank for both units is described as supporting 8 to 10 hours of operation under stated conditions. That description and the full-load L/h figure measure different things. The L/h number assumes the engine holds its rated output the entire time; the 8-10 hour tank description reflects a typical operating load below 100 percent. Both are useful, and they are not interchangeable.
How Load Level and Fuel Properties Change Hourly Consumption
A generator does not burn fuel in proportion to load. In a three-phase system, real power follows √3 × voltage × current × power factor, so a site drawing 150 kW from a 200 kW machine sits at 75 percent load regardless of what the nameplate kVA says. That load percentage, not the model number, is what moves the hourly burn rate up or down. Two other inputs — the way partial load reshapes engine efficiency and the physical properties of the diesel itself — decide how far the actual figure drifts from the published reference value.
1. Why Partial Load Does Not Scale in a Straight Line
At half load, an engine does not use half the fuel. Fixed losses — friction, pumping, the cooling fan, alternator excitation, and governor response — stay roughly constant whether the engine is producing 200 kW or 100 kW. All of that overhead is spread across fewer productive kilowatt-hours, which makes consumption per kWh worse at low load. As a general pattern, a diesel generator at 50 percent load often burns somewhere in the range of 60 to 70 percent of its full-load hourly figure, and the ratio climbs further as load drops toward the bottom of the operating range. The exact curve belongs to the engine's fuel map, but the direction is consistent: running a 200 kW machine at 40 kW wastes more fuel per kWh than running it near its design point.
2. How Diesel Density and Tank Fill Affect Available Energy
Diesel density sits in a fairly narrow band, roughly 820 to 860 kilograms per cubic meter depending on grade and temperature, per published fuel property data. A liter of denser fuel carries slightly more mass and slightly more energy, so the same 280 liters can deliver a small but real difference in runtime between one fuel delivery and the next. Temperature works the same way: diesel expands as it warms, so a tank filled on a hot afternoon holds less mass than the same volume filled cold. Tank fill often matters more than density. A 280L base tank does not hand over 280 usable liters — air space above the fuel, the pickup height above the tank floor, and the practical decision not to run the engine dry all reduce the effective figure, in many setups to around 90 percent of nominal.
How to Estimate Base Tank Runtime Without Treating It as a Guarantee
Runtime comes from dividing usable fuel volume by hourly consumption at the actual load. The math is simple; the assumptions behind each input are what decide whether the result is useful. Start with the site load in kW. If connected equipment draws 150 kW from a 200 kW unit, the machine is at 75 percent load, not at its nameplate. Second, take the published full-load L/h and adjust it for that load percentage using the engine's fuel map, or the general shape described above if the map is not available. Third, settle on usable tank volume — take the nominal 280L or 300L figure and reduce it for air space and pickup clearance. Fourth, divide usable liters by the adjusted hourly burn. A worked example makes the model concrete. The AT-200GFC at 100 percent load uses about 39.22 L/h, and 280 liters divided by 39.22 gives roughly seven hours. That calculation assumes the tank empties completely and the load stays at full output, two conditions that rarely hold through the same run. At 75 percent load the hourly figure drops, and the same tank stretches past eight hours. This is why the published 8-10 hour tank description and the full-load L/h figure can both be right while pointing at different numbers. The tank rating describes a typical operating load below 100 percent; the L/h figure describes the engine at its design point. Maintenance is the last input that moves real-world results. CIMAC maintenance recommendations treat oil condition, filtration, and fuel system care as factors that keep consumption near the design curve. A clogged air filter, worn injectors, or degraded oil can push consumption above the reference figure with no change in load, which is one reason a runtime estimate is best treated as a range.
Conclusion
Reading fuel use on a 200 kW or 250 kW diesel generator is a matter of building a small model, not memorizing one number. Published full-load figures such as 39.22 L/h and 49.02 L/h are the starting point. Load percentage, fuel density, usable tank volume, and maintenance state are what move the final runtime. Anyone estimating runtime for a specific site can run those four inputs through the arithmetic and hold the answer as a range. The AOTEMU 200 kW-280 kW Cummins specification page lists base tank volume and full-load consumption for each model in the range, which is a practical place to start when checking how the numbers line up for a given configuration.
FAQ
Q: How much fuel does a 200 kW Cummins generator use per hour at full load?
A: The AT-200GFC reference figure is about 39.22 L/h at 100 percent load under the conditions stated with the published data. That figure corresponds to the 200 kW / 250 kVA rating and assumes the engine holds its rated output for the full hour. Real sites rarely sit at exactly 100 percent load, so actual hourly use usually lands below this number.
Q: How long can a 200 kW generator run on a 280L base fuel tank?
A: Dividing 280 liters by 39.22 L/h gives roughly seven hours at continuous full load, assuming the tank empties completely. The base tank for this model is described as supporting 8 to 10 hours under stated conditions, which points to a lower average load. At 75 percent load, the same 280L tank typically stretches past eight hours. Treat the result as an estimate and adjust for load profile and usable volume.
Q: Why is actual fuel consumption different from the published L/h figure?
A: The published figure describes one condition: rated output, standard fuel, and a maintained engine. Site consumption shifts because load level changes engine efficiency, fuel density varies slightly between deliveries, base tanks hold less than their nominal volume in practice, and ambient temperature affects both fuel and combustion. Maintenance state matters too — a clogged filter or worn injector can raise consumption above the reference number with no change in load.
Sources / References
Fuels - Densities and Specific Volumes
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