Generator Diesel Fuel Consumption and Rules of Thumb with questions.

[dex3361]

I had to do some research for a large group of diesel generators sized from 6.5KW all the way up to 1200KW(1.2 Megawatt). Part of the research involved calculating the potential fuel consumption of the units. We all know that the fuel usage will vary with the load and that leaves an infinite number of variables. So I ran across a few rules of thumb that may be of interest to the crowd here on TBN. I also wanted to run it across the crown to see if anybody else has potential rules of thumb that will help out in using generators for sizing or other aspects of diesel generators.

1)When figuring diesel fuel consumption of a diesel generator and the generator is sized correct for the load so that the generator will operate in the 25%- 99% loading of the generator. You can figure that it will use between .07 and .08 gallon of diesel for each KW being generated. For example a 800KW generator supplying a load of 400KW would consume between,
400 x 0.07=28 gallons per hour or 400 x 0.08=32 gallons per hour.
This also works for smaller diesel generators such as a 6.5 KW generator supplying a load of 4KW would use 4 x 0.07=0.28 GPH or 4 x 0.08=.32GPH.

2) When sizing a 3 phase generator to start a 3 phase electric motor take the horsepower of the motor and multiply it by 2 and this will give you the minimum KW size of generator to start the motor. For example to start a 50 HP 3 phase motor it would take a 50x2=100KW generator to start the motor. This rule probable would not work for high torque loads but has worked very well on centrifugal pump loads.

Looking for input from others to see if these figures line up with what you have experienced.

For those that run a PTO generator do these figures seem to correspond with what you have experienced?

 

[Skyco]

Haven't run the math but I can say my Chinese Yanmar clone 6kW generator uses quite a bit less fuel powering an air conditioner and charging batteries at my camp, than does the 4kW gasoline Generac generator.:thumbsup:
Not defending the power companies by any means but I can also confirm if you think commercial AC power is priced too high , try making your own and see what that costs ya

 

[mrutkaus]

I remember reading about some small diesel Lombardini generators and the figure of something like 300g/kwh comes to mind.

Mike

 

[Chilly807]

We use 850 kw diesel generators on some of our ships. The last time we had one on the test bed with fuel consumption meters hooked up, I seem to recall it using 10 pounds of fuel per minute at 1140 kw output. They are turbocharged and aftercooled, which will boost efficiency somewhat.

Sean

 

[dex3361]

So puts the figures better than those of the rule of thumb if we assume that the fuel weighs about the same as water. I saw where diesel will weigh between .82 and 1.08 of what water does. This would put your consumption at around 0.063Gallon per kwh generated.

 

[Chilly807]

Typically you want to be at 80-90% of full load capacity to get the best life out of the engine, at least that's what we're told by the engine manufacturer. At that load the exhaust temps are high enough to keep cylinders clean, turbos are working well, and the engine isn't straining to maintain full power.

Sean

 

[dex3361]

Typically you want to be at 80-90% of full load capacity to get the best life out of the engine, at least that's what we're told by the engine manufacturer. At that load the exhaust temps are high enough to keep cylinders clean, turbos are working well, and the engine isn't straining to maintain full power.

Sean

Thanks for the info. The generators we run are typically running at 1/2 load because it such a huge draw of current to start the motors. The only motors that do not have that large draw to start are the ones running off of a VFD.

 

[Chilly807]

I see what you mean. Our switchboard software is set up so that as a generator reaches 70% load it automatically starts the next gen-set in the stand-by sequence. At least that's the way it's designed to work, they are often left in manual mode since the load doesn't vary a great deal once at sea.

50% or less can lead to carbon buildup, we try to run at least 75% load whenever possible.

Sean

 

[newbury]

I had to do some research

It's posts like that which gets me aggravated with this board!
No way to rep you!

GREAT post and thanks for the info.

I know my VW TDI 2.0 liter at idle uses 0.1 liter per hour, and is so efficient it won't warm itself up at idle in deep cold.

 

[hr3]

1.2mw = 1,200,000watts.. Kinda big for a home setup Ooo!!! and about 150 gal per hour