Onan QD 5KW generator fuel consumption

[bradf]

I’m trying to get a sense of generator fuel consumption on an R-31 equipped with a 5KW Cummins Onan QD generator. Does anyone have any “rules of thumb” for how much fuel this genset burns when running one or both AC units?

The fuel gauge on our R-31 is not very accurate. I rely mainly on the fuel flow calculation as represented in the fuel remaining indication on my Garman display (resetting to 180 gallons after each fill up). But I believe that fuel consumption is only related to the Volvo Penta fuel flow sensor and does not account for fuel used by the generator. So in order to calculate an accurate fuel remaining, it is necessary to deduct the fuel consumption of the generator based upon the number of hours used and the load. I’m trying to get a better sense of this.

Thank you!

 

[CaptT]

I found this on the Onan website. I believe it is fairly accurate as I have a NextGen 3.5 and it burns about 0.5 gallons per hour under load of my single ac.
Hope this helps,

Terry


Standard features
• Advanced digital electronic control providing extensive
diagnostic capability
• Shutdown with diagnostic indicator light for: high
engine coolant temperature, high exhaust temperature,
low oil pressure, over speed/voltage, starter overcrank,
no raw water flow, additional customer input and many
more
• Start-run-stop switch with glow plug preheat and fuel
pump priming modes for easy starting; run light and
diagnostic indicator light
• Start function has automatic glow plug preheat
providing better, cleaner starting
• Engine starter with automatic start disconnect
• Electronic governor allows the generator set to maintain
isochronous frequency control and close voltage
regulation to provide quality power for digital appliances
and computers

Engine details
Design: 4-cycle, water-cooled diesel
Cylinders: 2
Bore: 67 mm (2.64 in)
Stroke: 68 mm (2.68 in)
Displacement: 479 cm3 (29.23 in3)
Compression ratio: 23.5:1
Max fuel lift: 1.22 m (4 ft)
Lube oil capacity: 2.1 L (2.2 qt)
Coolant capacity: 2.1 L (2.2 qt)
Coolant flow rate:
50 Hz: 11 L/min (3 Gal/min)
60 Hz: 13 L/min (3.5 Gal/min)
Raw water flow rate:
50 Hz: 15 L/min (4 Gal/min)
60 Hz: 19 L/min (5 Gal/min)
Starting system: 12 V
Power (max): SAEJ1995
50 Hz at 2400 RPM 6.6 kW (8.8 hp)
60 Hz at 2900 RPM 7.9 kW (10.6 hp)
Fuel injection pump: Bosch MD type
Combustion Chamber: Spherical
Max Raw Water Lift: 1.22 m (4 ft)
************************
Typical fuel consumption
No. 2 diesel fuel, L/hr (Gal/hr) No load 1/4 load 1/2 load 3/4 load Full load
4.0 MDKBH-50 Hz 0.6 (0.16) 0.8 (0.21) 1.0 (0.28) 1.3 (0.35) 1.7 (0.44)
5.0 MDKBH-60 Hz 0.7 (0.20) 1.0 (0.27) 1.3 (0.35) 1.7 (0.44) 2.1 (0.55)
Alternator details Generator set performance
Design: Cummins Onan revolving field, 2-pole, drip-proof
construction, with encapsulated rectifiers
Voltage Regulator: Integral with the digital-control
Stator: Skewed stator and 2/3 pitch windings minimize
field heating and voltage harmonics; resin-coated for
corrosion protection
Rotor: Dynamically balanced assembly; supported by
pre-lubricated, maintenance-free ball bearings
Cooling: Rotor mounted centrifugal blower
Insulation system: Class H per NEMA MG1-1 -1.65 and
BS 5000
Operating environment: Generator sets are durability
tested at maximum ambient air temperature: 50° C (122° F);
raw water temperature 37.8° C (100° F)
Frequency regulation: Isochronous
Random frequency variation: Will not exceed +/-0.5%
of its mean value for constant loads from no load to full load

Edit: the website is not Onan's but Smithsdieselandpower.ca

 

[knotflying]

If you want to have an accurate read then you would have to subtract the approximate fuel used by the generator. However, I would think that the amount used by the generator is so small that it shouldn't affect running out of fuel when traveling.

 

[bradf]

Thanks for the replies. The Onan manual does say that the unit consumes 0.35 gph at 1/2 load and 0.6 gph at full load, so 0.5 gph seems like a good rule of thumb and probably on the conservative side.

I don’t often run the fuel down below 50 gallons before refueling, so any inaccuracies in the generator estimates are probably inconsequential.