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Old 10-27-2011, 12:38 AM   #1
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Generators

Is there a method of calculating fuel consumption for diesel generators? I 've got a 7 KVA Onan and have no idea how much or little diesel they use under load?
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Old 10-27-2011, 04:28 AM   #2
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RE: Generators

Check what prime mover it is, Onans (Cummins) use Perkins I think and then get the model and you will find the power and fuel curves.
Should imagine yours is a 1500 RPM unit
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Old 10-27-2011, 08:03 AM   #3
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RE: Generators

Use*15 - 18*HP per gallon. One HP =*0.746 KW. On my 12.5 KW Westerbeke, rated at about 18 HP at 1800 RPM, fuel use seems about 0.6 gallons per* hour.
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Old 10-27-2011, 08:13 AM   #4
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RE: Generators

Quote:
shrimp wrote:
Is there a method of calculating fuel consumption for diesel generators? I 've got a 7 KVA Onan and have no idea how much or little diesel they use under load?
Somewhere I've got some literature that came with my boat that talked about fuel consumption and my recollection was it stated that the Gen set under load, burned about a quart per hour. *Mine is a MDJE 7.5 Onan, but I have never tested the burn rate. It draws off the shared starboard fuel tanks, so don't have an accurate measure. Compared to the fuel consumption of the mains, it was so minor I never felt the urge to check it. *Probably wouldn't be to difficult to do though as a previous poster suggested. *If you decide to check it, repost your results though. *
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Old 10-27-2011, 09:12 AM   #5
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Generators

Pick the spec sheet for the Onan unit closest to yours on the link below. Estimated fuel consumption for different degrees of loading are given.

http://www.cumminsonan.com/marine/support/literature


-- Edited by Shoalwaters on Thursday 27th of October 2011 09:17:25 AM
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Old 10-27-2011, 10:26 AM   #6
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RE: Generators

I figure half a gallon an hour but I got those figures here on TF a couple of years ago. That seems pretty close to the chart on the link Shoalwaters posted. Otherwise, I have no idea since my '98 vintage genset is no longer made nor do I have any charts for it.
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Old 10-27-2011, 10:47 PM   #7
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RE: Generators

FWIW

I tracked down the spec's, a 3 cylinder 7.5 KVA Onan 60Hz(120 Volt) on 1/2 load = .5GPH Full load = .8GPH(1.9-3.0 litres)
50Hz(240 Volt) on 1/2 load = .4GPH Full load = .7GPH(1.5-2.7 litres)
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Old 10-28-2011, 08:32 PM   #8
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RE: Generators

I have a 2003 Onan 9KW with a 3 cyl Kubota engine. The estimated fuel consumption is listed in the operators manual I am not looking at it right now but I believe it is 1/2 gallon @50% load.
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Old 10-29-2011, 07:44 AM   #9
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RE: Generators

My little 4kw Kohler driven by a Yanmar 2GM has the following fuel burn rate as stated in the manual.

.21 gph* @ 25%

.28 gph @ 50%

.34 gph @ 75%

.42 gph @ 100%

Interesting fuel use at 100% is only twice that of 25%

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Old 10-29-2011, 09:41 AM   #10
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RE: Generators

Per 10 hp of the motor at 60 Hz, you will use around .6 gph at full load and about .34 gph at half load, or so says Northern Lights for my 32 hp unit. *Loading makes a big difference even though they all run at a constant RPM.
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Old 10-29-2011, 09:44 AM   #11
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RE: Generators

Quote:
JohnP wrote:
My little 4kw Kohler driven by a Yanmar 2GM has the following fuel burn rate as stated in the manual.

.21 gph* @ 25%

.28 gph @ 50%

.34 gph @ 75%

.42 gph @ 100%

Interesting fuel use at 100% is only twice that of 25%

JohnP
*John, that is very interesting. From my NL 20 kw unit, I use 1.7 gph at full load and 1 gph at half load. *It looks like the smaller units are somewhat less efficient that larger units. *I wonder if this apparent efficiency gap disappears at some minimum hp threshold?
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Old 10-29-2011, 03:49 PM   #12
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RE: Generators

Quote:
Delfin wrote:*
*John, that is very interesting. From my NL 20 kw unit, I use 1.7 gph at full load and 1 gph at half load. *It looks like the smaller units are somewhat less efficient that larger units. *I wonder if this apparent efficiency gap disappears at some minimum hp threshold?
********* Maybe the smaller engined units use more of its available power driving engine accessories, (pumps, alternator)?* Also the Yanmar 2GM is a pretty old design engine and the newer engines probably run on less fuel.

******** JohnP
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Old 11-05-2011, 03:36 PM   #13
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RE: Generators

The older Onan generators (1980's vintage) were primarily the MDJ units. Some were the MDJE. These generators were all 2 engines in the 7KW units, and 4 cylinders in the 15KW generators.

These were the first generators I worked on as a young generator tech, many moons ago.

Figure that the 2 cylinder units will burn about 9-10 gallons per day on the average, on a moderately loaded boat.

*
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