GM/Detroit 6.2L diesel cogenerator?

[Number21]

I am considering moving to a location off grid. If so I will probably be building a large diesel cogenerator (trigenerator?) system. My desire is to use some percentage of WMO, mixed with #2 diesel, and also some propane injection to hopefully increase burn efficiency and clean deposits formed from WMO. (minimal propane, it would be the most expensive fuel) I plan on having at least two generators, one for small loads, under 5KW, and another for larger loads.

I know using WMO is a controversial topic. Some people report great success, while others warn of immediate failure. My intention here is to use an engine that is really cheap to replace, or has cheap cylinder liners, and expect that waste motor oil will cause an increase in cylinder wear, and replace as needed.

I have a desire to use the GM/Detroit 6.2L diesel for several reasons:
- It's cheap and common, I can have a stack of spare long blocks on hand.
- I can buy water cooled exhaust manifolds meant for marine use.
- It's indirect injection should work well with WMO.
- It gets really good fuel economy in the 1200-1800 RPM range when fully loaded. Best economy at 1200.
- They have a really heavy flywheel for an automotive engine (more than 50lbs)

I found some detailed BSFC graphs for this engine based on JP8 and JP8 with WMO as fuel for military vehicle use. I have determined that it gets best fuel economy fully loaded from 1200 to 1800 RPM. At 1200 RPM I can get 50HP, 1800 RPM about 90HP. It gets really good economy in this range, .375-.425 lbs/hp/hr.

One big problem: That's a little more horsepower than I need. I would like a machine that gets good economy at 15KW electric power output and less. That's about 50% load at 1200 RPM.

What if I removed the pistons and push rods on four of the cylinders? Could I make an engine with half the displacement? Would it it be too unbalanced? Would it get bad fuel economy? I was thinking I could modify the connecting rods by cutting off the rod part and making two bearing caps. Then bolt this onto the crankshaft to keep oil pressure up from the missing cylinders.

Now, when the first 4 cylinders wear out from WMO, I could hook the other 4 cylinders up and run until they wear out. Think it could work? I know they used to make gas powered air compressors that only ran on 4 cylinders, and compressed air with the other 4. They still had the other 4 pistons for balance though. Could I compensate by externally balancing the flywheel? (6.2L is already externally balanced)

[mike90045]

i think you have to find out the firing arrangement first, and then disable alternate cylinders, and hope the crank takes the odd stress?

[Number21]

i think you have to find out the firing arrangement first, and then disable alternate cylinders, and hope the crank takes the odd stress?

Looking at the firing order I think I would have to use two middle cylinders and 2 end cylinders on different banks, couldn't turn off one whole side. But that seems more balanced anyway.



The 6.2 is known for breaking cranks so I would have to be careful. With a good harmonic balancer on the front and maybe rebalancing the flywheel, I wonder how rough it would be? Definitely would keep the RPMs down, 1200-1400ish probably.

[mobile_bob]

just thinking out loud, and it is late, so i might be way off

some issues i see you would have to overcome

1. running only 4 cylinders, where is the fuel from the injection pump going to go for the other 4 cylinders, i don't think you can simply block the lines off without popping something.

2. balance issues are going to be tough to work out.

3. you will need some sort of bolt on collar to keep the con rods centered where they belong on each crank throw, and to cover the oil holes on that area where the missing conrods would leave uncovered causing a real loss in oil pressure

4. you will need to figure out how to block off the oil passages in the lifter bores, so you don't dump oil pressure in missing lifter bores?

just a few things, i am sure they could be overcome, but at what cost? i dunno

i am sure someone has done it, just need to find out who and see what the issues were he faced and what he did about them

bob g

[Number21]

1. running only 4 cylinders, where is the fuel from the injection pump going to go for the other 4 cylinders, i don't think you can simply block the lines off without popping something.

Well, first I'll admit I don't know anything about mechanical injection pumps. I do know it uses the same Stanadyne pump that many other engines from the era use. Would it be possible to fit a 4 cylinder version of the pump? My other thought would be to simply route the extra 4 fuel lines back to the tank, dump their extra fuel back in there. Would much energy be lost in the extra injection pulses?

Seems like it may be easier to permanently disable 4 cylinders and plug some oil holes than to try and reuse the extra 4 later on. Maybe I could just fill some extra oil holes with some kind of epoxy?

[Number21]

Another question about the injection pump:

Does anybody know if I would be able to crank the idle speed in the injection pump up to 1200 RPM or more, and if so, would it regulate speed there like a governor?

I understand the same or similar injection pump was used on constant speed equipment, but I can't tell what the differences are.

[mr.fixit]

Back in the day I took care of a small fleet of stepvans with 6.2's.
They were generally good for 175,000-200,000 miles.  Pretty much a disposable engine.

More than one,usually when mated to a manual trans, died with a broken crankshaft. Seems they used a cast crank or nodular iron or something,wasn't forged though.

My guess is running one with half the piston-rods will have the same results. At low loads though who knows?

But hey if you have one to try without much effort or cost give it a shot.

[mobile_bob]

i don't think the stock pump is ever going to be very good for stable rpm needed
for fix frequency work... however it might be good enough if you can stand a wider
rpm and frequency shift from no load to full load.

generally automotive governors are meant for variable speed variable load operation, wherein the goal is to regulate idle rpm and max rpm, leaving everything between to be regulated by your foot or in some cases a cruise control unit. 

i don't know how well or stable the rpm is with  a cruise control unit, but my bet is it is probably not as stable as most would like, but who knows till you try it.

another option is fit a belt driven governor such as an old unit off a stationary ag engine, they are belt driven and have an arm that connects to your throttle linkage, and i think they are probably good to a couple hz one way or another, probably could be made to be tight enough to do the job.

the belt driven unit is probably the direction i would look into, however

it might be possible to have the pump governor recalibrated so that full throttle is something a bit over your required 1200rpm so that there would be a bit of droop to get you something between say 58 and 62hz most folks seem to be able to find acceptable.

i think it would probably take new governor springs, and maybe different flyweights, so maybe it will take a rather good specialty pump shop to get it the way you want it.

i would look and see if you can find some reference to a 6.2 powering a generator at 1200rpm
or some other fixed speed compressor or pump where the engine is set to operate at that rpm.  at least then you could get the info on what pump governor parts you will be needing.

just thinking out loud here

bob g

[Number21]

What do you think about this idea?

I was looking at converted V8 air compressors and I learned that most are Ford V8 based because the firing order allows one side of the block to be an engine, and the other to be an air compressor. This is not possible on the 6.2L, but, I have found some examples of other Chevy V8s used as air compressors with two cylinders on each bank pumping air, and two burning fuel.

What if I built an air compressor like that out of a 6.2L, and then fed the compressed air to the intake to supercharge the engine? Would the increased efficiency make up for the drag of the dead cylinders? I could then leave all 8 pistons installed, keeping it balanced.

Here is a really old example of a turbo diesel V8 "monoblock" compressor, I think they never fully developed them since rotary screw compressors came out.
http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1425&context=icec

They even installed 4500w generators on some of the Ford 302 based monoblock compressors.

i would look and see if you can find some reference to a 6.2 powering a generator at 1200rpm
or some other fixed speed compressor or pump where the engine is set to operate at that rpm.  at least then you could get the info on what pump governor parts you will be needing.

I've been looking hard for any applications of the 6.2L outside of auto/marine use, and I don't think it ever existed, at least commercially. The best I can come up with is a military truck with a 6.2 and a 30kw generator powered by PTO. I need to try and figure out what they used for a governor. My best guess would be a belt drive unit, but the idea of an extra belt just for governor drive really bothers me. If I have to, I think I can come up with an electronic governor from another generator for $3-400 that works off the A/C hertz. Still seems like a lot to spend for something so simple, but belt drive governors are not cheap either. Would be fantastic if I could just modify the existing IP.

Some other crazy ideas:
- If I heat the intake air charge, through turbo or other means, would that help the WMO burn more completely, and, at the same time detune the engine at higher RPM?

- Could I install extra thick cylinder sleeves, and smaller pistons, creating a smaller displacement, and heavier duty engine?
If I could install a .25" thick liner I Would get an engine with a bore of 3.48" and 3.8" stroke. Would go from undersquare to oversquare to work better at lower RPM. The resulting engine would be 4.7L. Not sure what I could do for pistons, or if the valves would fit.


Thanks for the information everyone!

[Number21]

Maybe I am over thinking this a little bit. The BSFC curve I am looking at shows .375 lbs/hr/hp at 1200 RPM at full load. (50hp) That would make 31,705 watts with an 85% efficient generator head. That is equal to about 11.8 kilowatts per gallon.

The fuel consumption only goes up from 1200 RPM. At 3600 RPM it jumps to .5 lbs/hr/hp. That would only make 8.8 KWH/gallon.

Since I only need 50% power at 1200 RPM, how much will fuel economy suffer with an unmodified engine? I would be happy with 10kwh per gallon. Not happy with anything less. I can't find any BSFC curves at 50% load. I could periodically load the generator to 100% at 1200 RPM to burn off deposits.

Maybe there are other things I can do to reduce "full load" power of the engine, without disabling cylinders? Like feeding preheated air into the intake? Would it help fuel economy to turbocharge the engine, even though I don't want more horsepower? Without an intercooler I could keep EGTs up to burn WMO efficiently. Maybe also run the engine really hot, like 220 degrees or more.

[mobile_bob]

another thought,

look at other engines that use the same or similar injection pump, maybe that application
is used in 1200rpm gensets? if so then there would be parts available to convert your pump?

bob g

[mobile_bob]

btw
i would be absolutely shocked if you came up with a 1200rpm version of the 6.2 that delivered
anywhere close to 8kw/hr/gallon, i don't think that 10kw/hrs/gallon is even possible at the proposed power levels.

but i have been wrong before.



good luck
bob g

[Number21]

i would be absolutely shocked if you came up with a 1200rpm version of the 6.2 that delivered
anywhere close to 8kw/hr/gallon, i don't think that 10kw/hrs/gallon is even possible at the proposed power levels.

Why is that? I have no idea, I'm just going by what I read in this paper: (assuming their info is accurate)
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA349754
Page 21 of the PDF.

The graphs show 50hp at 1200 RPM and .375 lb/hp/hr fuel consumption. That's 2.67 GPH if we use 7lbs for diesel fuel weight.

Also, 50hp = 37,300 watts multiply by 85% efficient gen head, that's 31,705 watts. Let's just call it 30KW. (lose a little bit belting it up to 1800 RPM from 1200)

30KW divided by 2.67 gallons = 11.23 KW/gallon. Is my math wrong? Not trying to argue, just wonder if I missed something.

Those tests are actually with JP8, which I think has slightly less BTU/gallon than diesel. Just guessing it would burn even less #2 diesel. Interestingly, the fuel curve shows consumption going up with RPM, which is not what I expected. 1200 RPM seems to be the most efficient spot, just looking at those graphs. Also that's the N/A motor, I bet having a turbo would decrease BSFC, if I actually had a use for the extra power. Also if I injected a little bit of propane, I should get a more complete burn of the fuel. (in theory)

I've never owned one but I've always heard the 6.2 was kind of gutless but efficient. Not what I want in my truck but sounds good for a generator to me.   I would rather go with an old Ford (IH) 6.9L diesel but they don't sell water cooled exhaust manifolds. Seems like that would be really hard to fabricate. I literally want to cut an old pickup truck in half and turn the front into a generator on wheels.  

[mobile_bob]

don't get me wrong, i am not trying to rain on your parade

its late and i would need a rested mind and a bit of time to do the math

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.

again i am not sure of my math right now, i am exhausted.

having said that, the issues i have with 1200rpm and low relative output is this

its hard to imagine an 8 cylinder engine producing maybe 15hp being more efficient
than say a changfa 1115 at similar outputs, for at least one important reason... that being
parasitic losses... 7 more cylinders and all the related extra friction and pumping losses associated must have some detrimental effects on bsfc numbers.

also don't get me wrong,  i think what you are contemplating is interesting and worth doing provided you have a ready source for engines, and don't spend a fortune prototyping the thing.

if you are mechanically inclined and handy, and can source all the goodies needed reasonably priced, then why not? 

give it a whirl, and see how well it does?

me?  if i tried something like this, i think i would target for maybe 8kw/hr/gallon of diesel, and hope for maybe 9 and be thrilled if it hit 10kw/hr/gallon!  and i would consider myself a friggin hero of the first order if it got 11kw/hrs/gallon of pump diesel! 

i am serious, the risk reward might well be worth serious consideration.... i know there are lots of folks both here and on our sister forum that would move your stock way up!

i know i would be giving you kudo's for sure! 

now on with the project,  a few hopefully constructive comments

1. consider a fairly heavy flywheel, more inertia seems prudent for lower rpm operation.

2. do seriously consider finding a pump shop to rework the pump to operate reliably and steady at 1200rpm

3. consider slowing the timing a degree or so, that is unless the pump has some sort of variable timing built in, if that is the case just make sure the pump guy knows what you have in mind.

4. getting back to the flywheel a moment, consider maybe having a thick plate of steel cut and drilled to couple up with longer bolts to your existing flexplate/flywheel. and have it machined for a serpentine belt?  you can size the new plate to get the step up ratio that way without buying another expensive pulley and then be faced with making and fitting a pto shaft? 

5.  you might also consider a 15-20kw 3 phase genhead too, having 3 phase available means you can buy cheaper shop equipment, motors and such, and you can tap it for 120/208vac or maybe 230vac (the latter if iirc),  3 phase heads are generally a bit more efficient at least in generating 3phase, if not tapped for single phase.  the ability of getting more power might also be advantageous down the road? in any event the larger heads are a bit more efficient, i would expect a good single phase 15-20kw head to be maybe 82-83% efficient and in 3 phase maybe as much as 85% efficient.

fwiw
which admittedly might not be much this late 

bob g

[Thob]

Like Bob, I don't want to rain on your parade, but my advice would be to forget about the 6.2L engines.  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...)

Or look at the large Changfa that Bob mentions.

If you do decide to go with the 6.2, I'm interested in know how it turns out - what you do to the engine, actual fuel consumption, etc.  Please come back from time to time and post your results!

Again, I don't want to discourage you, but if it was me, I'd be better off getting an engine sized to the load and then spend my time building the mount, setup the radiator, air cleaner, muffler, fuel tank, engine shed (if stationary mounted) etc.