GM/Detroit 6.2L diesel cogenerator?

[Number21]

fwiw, iirc we figure 7.15lb/gallon of pump diesel
and we figure about 80% efficiency for genheads that are around 7-12kw capacity and belt driven
that is if the belt system is well engineered.

That only makes it sound better with those numbers.  

50hp * .375lb = 18.75lb divided by 7.15 = 2.62 gallons

50hp * 746 watts = 37,300w * 80% efficiency = 29,840w

29.84 KWH divided by 2.62 gallons is 11.38 KW/gallon!

With that said, my engine will be high mileage, burning waste oil, and not running at full load, so definitely it will be less. But just as a baseline for guesses, shouldn't a new engine with clean fuel make 11.38 KW/gallon at a full 30KW load? Or it's just not possible to calculate out like that?

But all that begs the question how much does efficiency go down at 50% load? And can I "cheat" by detuning the engine and calling it "full" load at the same RPM?

[Number21]

Find something locally available in a 3 or 4 cylinder Kubota, Yanmar, CAT/Perkins, or Isuzu engine that is more suitable to the load you have.  Run those engines at 1800 RPM, direct coupled to a 4 pole gen head for 60 HZ.  I see those engines come up (used) on Craigslist, either take outs from high end mowers or from refrigerator units on semis.  I've also seen the occasional APU from a semi for sale as well.  (I found a (much smaller than you're looking for) used Kubota D600, on a riding mower, that I converted into the worlds only self-portable riding diesel generator with hydrostatic transmission.  It only cost me $200 for the mower, in running condition...)

There really doesn't seem to be much of that available in my area, and if there is, they think it's made out of solid copper. I've looked all over craigslist, and the only cheap diesels are crappy car motors with 500,000 miles. Kubotas and such are almost always a few grand at least. I found an older lawn tractor with a twin cylinder kubota diesel the other day and got excited, until I saw the $1500 price. Find me one of those for $200 and I'll take it all day long!!

On the other hand I can show you around five running/driving 6.2L trucks and Suburbans on CL for under $1000. I could scrap the back half for a few hundred bucks too. If I burn one up with bad fuel there are always a bunch more cheap ones and I still have the core value of the old one.

The other thing is I'm not sure how well those motors tolerate WMO? I'm looking at the 6.2L specifically because it is indirect injection. Don't know about some of the foreign ones. Also water cooled exhaust manifolds are available for the 6.2, not sure on some of the smaller diesels. (I know they still use some in boats though)

Don't get me wrong, I'll have a smaller generator I can run as well. But I'm not interested in paying $5-10 grand for a 15-20KW generator and then run WMO oil in it. My small generator will be a more modern design high efficiency type that burns cleaner fuels.

I do want to load the engine with an A/C compressor also. Several tons. But won't always be needing that either.

[Number21]

Another plus for the 6.2(or 6.5), if my cheap prototype works well I can get a brand new block for $1689. Hard to get a used smaller diesel for that price in my area.

http://www.ebay.com/itm/6-5-L-6-5L-Diesel-NEW-ENGINE-BLOCK-Updated-amp-Improved-/161072520139?_trksid=p2054897.l4275

I'd really love to build a nice tight new engine, with thermal barrier and other friction coatings throughout to increase efficiency. But that starts to loose sight of the "cheap disposable engine" idea.

[Number21]

Does anybody think it would run ok at 800 RPM or even 600 RPM to further reduce the 100% load power output? I know you aren't supposed to idle them for very long, but as long as I kept the cooling system nice and hot would there be a problem? Would I have a problem getting high enough EGT to fully burn WMO mixes?

I realized a stock 4BT 4 cylinder Cummins engine and 6.2L Detroit V8 produce approximately the same horsepower stock, with the 6.2 making a little more torque. The Cummins engine has a lot more BSFC information available, and shows only slightly higher BSFC at lower speed (800 RPM). (the test data I have on the 6.2 stops at 1200 RPM) Unfortunately a good 4BT cost 4 times as much as a 6.2L or I would just use that!

[vdubnut62]

From my experience with a 6BT Cummins, running that slow, under about 1000rpm for long periods will absolutely beat the bottom end out of it.
Your 6.2 may be different, and like the slow speed, but I myself doubt it.. YMMV
Ron.

[Number21]

I've been looking a lot closer at the HP/BSFC curves from Cummins on the 3.9L 4 cyl and 5.9L 6 cyl. I'm only looking at the Cummins info because they are much more detailed than anything I can find for a GM engine. It's interesting to compare the 4 cylinder and the 6 cylinder, since they are essentially the same engine.

http://img.photobucket.com/albums/v494/zmoz/39.gif
http://img.photobucket.com/albums/v494/zmoz/59.gif

If you notice, the 4BT makes 123HP at 1900 RPM. The 6BT makes 120HP at 1500 RPM. At 80% efficiency they both could make 71 kilowatts at those speeds.

If we use 7.15lb per gallon for diesel fuel, the 4BT consumes 5.88 GPH, and the 6BT would use just 5.53 GPH. The six cylinder burns less fuel spinning slower than the 4 cylinder for the same horsepower output! I just blew my own mind!  

In theory the six should have more drag, and worse efficiency at slower speed, and more thermal loss from higher surface area. But it still overcomes that somehow. Is my math right??

[Dualfuel]

Some thoughts on the 6.2...
I first started working with them in 1987, in the Humvee. Since then, I have owned several dozen. and have one on the ready line right now.
A 6.2 will make a good offgrid generator engine. It is a very quiet engine. I have a Kubota 3 cyl generator whose sub sonic sound transmission goes a much greater distance then an idling 6.2. I have never blown up a 6.2. There would be no need for long blocks, 4 cyl. configs, or any armchair modifications, if you want to improve the fuel economy, simply turn down the injector pump.

I do not recommend WMO in a 6.2, unless you are going to filter down to 1 micron, AND allow time and means to flocculate the carbon particles. 6.2s get fantastic bsfc numbers because the injector pump sprays extremely small amounts of fuel, which means really small orifices. Dirty WMO will damage, or plug these orifices, and the injector pump will fail. I have damaged many a snub shaft in a DB2 by using thick viscous fuel.
Ironically, the International 6.9 engine using a Stanadyne DB2 CAN burn WMO directly with no diesel mixing, with no damage, but, these engines are much louder, and use a lot more fuel.

The weak point with a 6.2 is the injector pump. You will be hard pressed to find a new one (NOS). I never have.
I would not worry about fuel consumption, for an off grid application.
I would be more concerned with noise, and automatic operation.
I love my Kubota, because it provides seemingly unlimited hours of hands off operation (over 10000).
The ideal 6.2 configuration would be:
an industrial bellhousing allowing a PTO for your needs (i.e. hydraulic, generator, or shaft power)
a Hoof belt drive governor
removal of the electric fuel shut off solenoid, and replacement with a mechanical valve, facilitating the use of heated WVO.
water cooled manifolds

Sadly, this is all armchair speculation, and unlikely to really happen, because the truth is, a suitable used diesel generator is out there for you, and it will be cheaper to simply buy it and go, then to configure a 6.2. Kipor sells yanmar clones that will burn BD, and have wireless remote starting...or Marathon Electric used light plants...Or somebody will hand you a Detroit Diesel 371 for $150 and away you'll go. Funny how poverty is actually the determining factor.

[Number21]

Great information Dualfuel. Would you try and run the 6.2L any slower than 1200 RPM to get real work out of it?

Sadly, this is all armchair speculation, and unlikely to really happen, because the truth is, a suitable used diesel generator is out there for you, and it will be cheaper to simply buy it and go, then to configure a 6.2. Kipor sells yanmar clones that will burn BD, and have wireless remote starting...or Marathon Electric used light plants...Or somebody will hand you a Detroit Diesel 371 for $150 and away you'll go.

I don't know about all these cheap diesel generators everyone keeps talking about. Looking at craigslist, the cheapest water cooled diesel generator 15KW or larger is $2500 and let's say not brand new. Air cooled is not an option, I want to pump all the heat into a central location to use for both my house and my shop. If you find somebody selling a 371 generator for $150 I'll take ten!!!

Then if it dies from WMO I have to find another deal on a whole new unit. If I used a "disposable" engine connected to a more expensive gen head/governor system, then it's not a big deal if I burn it up with WMO. I can just get another engine. It's going to be an experiment as to how much WMO I can burn. (It will be heated and centrifuged first) I don't really know of a disposable diesel engine besides an air cooled clone or an old Chevy/Ford pickup truck. Everything else is really expensive in my area, even any kind of 4 cylinder diesel car. Kind of limited on options there...

[Dualfuel]

Ok, if I had those engineering constraints AND my experience with off-grid...I would purchase a 6.2 in a truck or a suburban. I would pay to have an adapter machined to fit on the splined out put shaft of the transmission. I would be looking for a well balanced adapter. I suppose I would start out turning a big three phase motor and making it an induction generator. Usually suburbans have 700R4 automatics so you'd have some variation in speeds between motor and engine shafts to play with. I would mount the motor right behind the transmission, using a transfer case cross member. I would cut away sheet metal in the floor so as to be able to service this from inside the cab or body.  These are  the basic low cost components...

The place I would place all my efforts, at first, is configuring a Hoof belt drive governor. I would get that engine turning around 1800 to 2200 rpm and that motor putting out its 208/120vac @ 60hrz. I would concentrate on making reliable electric power at the turn of a key. If you get that far, and get 200hrs on the generator, and are satisfied with its performance, THEN I would start thinking about waste motor oil.
I use pump diesel in my Kubota....er mostly...some BD but mostly off road. So what I am trying to say is that your generator might be cheaper to run on pump fuel when the convenience factor is considered...like if your BSFC is .4 and you make 20hp for 200hrs, thats 1600lbs of fuel or 228 gallons which is about $685.  After 200hrs you will have dialed in your knowledge of how the generator operates, and then could start experimenting.
The caveat is that if and when you plug a fuel filter with WMO, and you were running a bread machine or something that depended on uninterrupted power, the allure of free fuel will vanish, and you will be much more willing to pay for, or make a cleaner more dependable fuel.

Some notes on WMO...centrifuges do not flocculate the carbon....google flocculation... it means clump up. If the fuel flocculates after being filtered into the tank, then it will plug up the primary filter at the engine. Thats a $10 bill. Settling helps, so does dilution with premium or diesel...if you dilute with RUG containing ethanol, the etOh will flocculate the carbon FASTER, and there goes another fuel filter, during Jeopardy.  Heating the fuel helps, but will destroy the fuel shut off solenoid in the pressure dome of the injector pump, defeating the purpose of having an automatic generator.
I would spare you all those little nigglng things, at first. Just buy pump fuel till you get your game on, then add WMO in small percentages...or old gasoline...6.2s will burn old gasoline, up to 30% dilution with diesel fuel.
Anyhow, I say go for it. Eventually you will be burning fuel in your machine, whose level of cost and labor, you find affordable. At that point the bragging can really begin.