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Kohler Generators

Fuel consumption/ Fuel tank size?

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Old 11-14-2018, 09:12:54 AM
Tbirddillon Tbirddillon is offline
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Default Fuel consumption/ Fuel tank size?

So I was wondering what kind of fuel consumption you guys are dealing with on the L600 engine, mine is a 3500 watt setup and it's a thirsty engine but it probably needs some tuning? That also leads into my next question what size gas tanks are you guys running? I'm in the process of going through mine and setting it up on a cart with a tank I just haven't decided on the size and shape yet. I plan on doing g a test at full load with a gallon of gas to see how long it runs but that is going to be a while.
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Old 11-14-2018, 03:19:44 PM
Vanman Vanman is offline
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Default Re: Fuel consumption/ Fuel tank size?

One thing to bear in mind is that the L600 engine is rated 12-1/2 hp @ 1800 rpm, and was used with generators up to 6-1/2 kW. At full load, that would be about 10 hp, leaving ~2-1/2 hp in reserve.

A 3-1/2 kW generator is only going to require around 5-1/2 hp to drive at full load, and so will be less than 1/2 load on the engine.
I've always said that the L600 powered 3-1/2 kW should have been 1200 rpm. That would be around 8 hp.

Things to consider to improve efficiency are spark timing, fuel mixture, and compression ratio. On your engine that will never see full load, you could likely get away with more advance, a bit leaner mixture, and higher compression.

I'm planning on setting up my 6-1/2 kW plant for running on propane, which has the equivalent anti knock properties of ~100 octane gasoline. So I plan on optimizing these elements as best I can as well.

I will be very curious to see what fuel consumption figures your experiment delivers.

To optimize before the test, I would set the timing to that which delivers the lowest manifold pressure (highest rpm) while at full load. Obviously back it off if pinging is observed.

I would set the fuel mixture *just* rich enough such that the engine does not stumble when going from no load to full throttle suddenly, after being fully warmed up.

After adjusting one, you may have to go back and fine tune the other.
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Old 11-14-2018, 03:37:54 PM
Tbirddillon Tbirddillon is offline
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Default Re: Fuel consumption/ Fuel tank size?

Thanks for the tips. I still have plenty of work to do before the experiment
Rebuild carb
Rig up some kind of exhaust
Clean radiator
New thermostat
Probably a few odds and ends I'm forgetting but I will post results when I get to do it.
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Old 11-14-2018, 07:17:05 PM
jack0 jack0 is offline
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Default Re: Fuel consumption/ Fuel tank size?

On my 3.5r21-l600.

Full load .75 gph
No load was less than .5

With a good engine and tuning. Yours should be close to the same.

As far as a fuel tank. I draw out of a 5 can.
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Old 11-15-2018, 09:27:20 AM
Tbirddillon Tbirddillon is offline
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Default Re: Fuel consumption/ Fuel tank size?

Thank you, I'll still do my experiment but that gives me a baseline.
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Old 11-15-2018, 09:32:39 AM
Kimbra Dean Kimbra Dean is offline
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Default Re: Fuel consumption/ Fuel tank size?

Six gallon boat tanks work great. You can get two and run off of one while you take the other to get filled.
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Old 12-03-2018, 01:12:11 PM
Tbirddillon Tbirddillon is offline
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Default Re: Fuel consumption/ Fuel tank size?

Just did a run today and on 2 quarts of gas it ran 45 minutes under a 1700watt load. I'll try doing a full load test soon.
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Old 12-05-2018, 12:02:08 PM
dkamp dkamp is offline
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Post Re: Fuel consumption/ Fuel tank size?

Empirical tests on YOUR unit, followed by tuning and re-testing, are the best way to get good data.

My 6.5R22 is running on two 800-gallon propane tanks... same as my 338ci Herkey-driven Kato by Consolidated Diesel Electric... and that's the SHORT story.

Here's the long one...

...take good notes... there'll be a quiz tomorrow...

When doing a fuel consumption analysis, there's more than just one number... and

First number is total output... when you're at full load... do it on a hot day, because that's the worst working circumstance for your machine's cooling system. Many of us drag out a half-dozen 'milkhouse' resistive heaters, and one pointy-headed Appalachian American has dabbled with adapting switchgear to an old electric furnace heating element, to make a resistive load bank for testing. Regardless of how you choose to do it, having a good approximation of a test load is necessary for gauging fuel consumption, getting good tuning, and finally... assuring that your electrical gear is up to snuff.

The second number is BASE CONSUMPTION. The synchronous generator, when running, requires a basic amount of fuel... first, just to spin the engine... to maintain oil pressure, to turn the camshaft, spin the radiator fan, and circulate coolant. Then, it takes a certain amount of fuel to spin the generator, to build an excitation field... then there's recharging system batteries.... and finally... generating noise and vibration. All these things add up to the MINIMUM amount of fuel necessary to just have it running.

When I fuel curve, I start with baseline tuning... I get it running, and apply a test load in 'buildup stages' until I have a unit that generates stable output at idle, midrange, and full load... and I fine-tune the adjustments so that it RESPONDS well to a changing load. I like it to stay close to goverened frequency, and be able to handle a rapid jump from nothing to full load (She starts the dryer...) without balking.

Once I have that, I put it at full load and let it grunt for a good long time... and I use my IR thermometer to sample places around the block, head, and cooling system... then the exhaust manifold, to make sure I have a thermally-stable machine.

After that, it'll be nice and warm. Running it with no load, I'll do a fuel measurement to figure out what that baseline consumption figure is. Then I'll apply load at medium low, medium high, and full, and do same.

Of course, propane consumption is greater in gallon-volume, than using gasoline, because the energy density of gasoline is higher per liquid gallon. When running off my big tanks, it's difficult to get a measurement of consumption... so when I did the testing on my little 6.5, I used a 20lb bottle on a bathroom scale.

With Propane being 4.2lbs/gal, and 91330btu/gal... that's 21745btu/lb I was getting a minimum fuel consumption of 2.6lbs/hr 56537 under no load, and 5.3lbs/hr (115248btu) under full load.

Looking at this from an EFFICIENCY output... 1 kw/hr equates to 3412.14 BTU/hr. My MINIMUM (zero load) burn was 16.56kw/h of thermal energy expounded just to run. My FULL LOAD was... 33kwh fuel burnt, for 6.5kw of electrical output.

Unloaded efficiency will ALWAYS be zero. Fully loaded will always be the best... in my case, 6.5kw / 33kw = 19.6% efficient.

You can do exactly the same calculations with gasoline (it's around 124000btu/gal).

That's seemingly pretty hideous efficiency, but that's entirely NORMAL... generating electricity from fuel... is lossy.

The next-most-important number... is your Maximum Minimum Load... which is... how much load you can put on that generator, before your MINIMUM Consumption figure starts to rise.

This is important to know... because it determines what you should be doing to get the most out of your fuel supply. Since my 7.5 is on a huge tank, and it's my 'smallest' machine, I haven't done a MaxMin load test... but I DID do one on my big red beast, and here's why:

The MaxMin load test tells you how much load you should put on the generator JUST to justify having it running.

Let's say my small machine pulls that same 2.6lbs/hr up to almost 2.4kw.
Let's compare that to my big machine is pulling 4.5lbs of propane at no load, and it pulls that same 4.5lbs all the way up to 5.5kw before the governor starts asking for substantially more fuel... that means the 'base fuel requirement' is justifyable once my SMALL generator reaches it's 3/4 load. I can run either the big generator at a light load, or the small generator at a heavy load, and have about the same fuel consumption.

Running the really big one at a load under 3kw is very, very wasteful... but running the small one under 1200w is even moreso. Realizing that there's an 'overlap' between the two coexist in efficiency means I choose according to my expected loads.

On a single-generator installation, it means that you SCHEDULE your loads around the machine's fuel curve. When I'm running the small machine, I make sure we're not running it for just one 7.5w LED bulb.

Now... if you wanna find a way to make all that wasted energy more useful... TURN OFF YOUR FURNACE. It's a liquid-cooled generator... nix the mechanical cooling fan and connect the circulatory pump to a heat exchanger, and flow that heat to someplace that needs it.

The generator is a wonderful source of waste heat, and when it's parked inside your workshop, it keeps you warm. If your house has hydronic heating, you can save your domestic heating by recapturing the generator's lost heat... thus, your fuel budget has now increased it's efficiency dramatically.

As an added bonus... you'll be gaining shaft horsepower by virtue of losing the static drag of spinning a cooling fan... and of course... all the noise that comes with it... so your minimum fuel burn number will go down a bit... It also means you'll have more available torque to respond to a rapid load change. The downside, is that the mechanical cooling fan provides inertia AND static load for the governor to 'work against'... thus, you'll have a little less stability... the governor will be a bit 'jumpy', perhaps overshoot your frequency range at extreme low end of the load spectrum.

Think about it... my 6.5 burns 115248kbtu to give me 22178btu of electricity, that's 93,000btu unaccounted for. if a THIRD of this 'missing' energy is noise, that means the other 60,000btu is waste heat. At MINIMUM load, you'd have over half of it's 21000btu in available waste heat.

(and that minimum doesn't seem like much, but if you figure that on a cold day, a home with a 48,000btu furnace running 25% of the time comes out to 12000btu continuous... and that generator is running continuous... you can save quite a bit by capturing that fuel.

Oh... and if the house is heated by electricity... a small generator won't pull that... but it'll generate enough waste heat to totally MAKE UP for it.
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