my experience with wet stacking

[sewerzuk]

Everybody seems to like to discuss this, and I have run across my fair share of diesel engines that have experienced it. But today, I wrenched on an -005a that had the worst case of wet stacking I've ever seen...

It was a backup generator for a business that faithfully ran it for 1 hour each month, under zero load. It hadn't seen any load for years, accumulating several hundred hours of runtime at no load. Total hours were under 500.

The new owner of this set trailered it down to me so I could give it a look-over and short load test.

I fired it up and let it run for a minute or two under no load to warm it up, then put a 5kw load on it (1/6 rated load). It dropped almost 5hz under that load indicating an engine that was pretty weak; but after a minute or two it recovered. I bumped it up to 15kw; white smoke POURED out of the exhaust, and the engine nearly stalled. Black, tarry, oily junk began to run out of every seam in the exhaust system. I backed it down to about 10kw (1/3 of rated load), which the engine was barely able to pull. After about 15 minutes, tiny burning chunks of carbon were raining down out of the sky, and about a 40ft radius around the generator was covered in soot. The engine had began to run smoother at this point, so I bumped it up to 20kW (2/3 rated load). It was barely able to pull this load at first, but after another several minutes of smoke and carbon "rain", it recovered and was back to 60hz. I bumped it up to 30kW for the final step and experienced the same thing. I ran it there for over an hour. Every 5 minutes or so I had to adjust the throttle down to bring it back down to 60hz (engine was beginning to make more power as the buildup burned off of the valves/rings/cylinder walls/etc.). After roughly an hour at 100% load, the engine was purring away and had almost zero smoke in the exhaust. It was even able to pull a 50kW load (166% rated load) without significant droop.

Obviously, this was pretty extreme. But, those monthly maintenance runs almost rendered the set useless! It couldn't even pull a 5kw load. Had this been an -006 (or some other set with a turbo) it probably wouldn't be running at all. It is a good lesson in sizing the set appropriately, and putting a load on it when it does run.

 

[Trango]

Very interesting. Thanks for the write up.

 

[wsucougarx]

Outstanding info!

 

[Motownmike]

Load Bank

I need to go to Flint and source some used electric water heaters and drying machines to make a load bank for the new set.
Maybe I could set up a hot tub in the barn with the gen-set powering it outside, just for maintenance reasons, of course.
Seriously though, one of my concerns is wet-stacking. I don't have enough load at the house to excercise my 15k set properly so I need a makeshift load-bank for monthly runs.
On another note, when the power does go out, I wonder what the fuel consumption is at low loads, say 5kw constant?

 

[ichudov]

Fascinating writing. My home generator has a Onan L423 (Cummins L423D) engine. Do you think that it is also subject to Wet Stacking?

 

[DJones]

Great info thanks for sharing.

 

[M1031CMT]

Great info. Glad to see stuff like this posted.

Question: For those of us who don't have a professional load bank to connect up to our generators, what do you recommend that we use to put some sort of load? An old timer once told me to connect up some large heater units to put a load on it, but I was wondering what you would recommend? We have a 14kw diesel generator and other than connecting a heater, mig welder and dozen large lights, we never have put anywhere near the maximum load on the generator. But we would want to make sure it could take the load if the need were to arise.

 

[aczlan]

Interesting. Have to remember that when I get a genset.
Would a 002 or 003 wet stack as well, or is that just a watercooled engine thing?

Aaron Z

 

[uscgmatt]

Nice write up, thanks. I always enjoy your generator articles.

M1031CMT- I use 2 5kw heating elements (out of a heat pump hvac system)and a fan blowing over the elements. I use a relay with a switch to control it at 5 or 10 kw. Let me go get some pics.

ACZLAN- Air cooled will wet stack also, just not as bad as the engines run warmer with no load. Best to always have a load.

 

[sewerzuk]

Great info. Glad to see stuff like this posted.

Question: For those of us who don't have a professional load bank to connect up to our generators, what do you recommend that we use to put some sort of load? An old timer once told me to connect up some large heater units to put a load on it, but I was wondering what you would recommend? We have a 14kw diesel generator and other than connecting a heater, mig welder and dozen large lights, we never have put anywhere near the maximum load on the generator. But we would want to make sure it could take the load if the need were to arise.

In the past, I have used all sorts of stuff for artificial load; below I have listed a few of the things that are commonly available:

500W halogen lights. Only a few $$ from harbor freight or home depot, these work well for smaller generators. 10-20 of them won't break the bank, and they are easy to add in small increments. Wiring 20 of them up is a disadvantage; safely doing that requires lots of junction boxes and cable.

Electric clothes dryer. These are cheap (sometimes free) in your local craigslist; and you can add 5kw or more with one.

Hot water heater. Another cheap one from your local classifieds. The disadvantage here is that if you want to dump a lot of load, you need to flow a lot of water into the water heater.

Electric oven/range. With all of the burners and the oven on, you can put 6-7kw on your set. Usually easy to find in your local craigslist.

Space heaters. I once loaded up a generator with about a dozen small baseboard heaters. Works well, but wiring up a dozen of them can take a lot of cable and junction boxes.

My current load bank was purchased off of ebay for just a couple hundred $$. It is a resistance element heater; designed for placing a dummy load on a BIG generator. It can handle 300kw and 480v. I currently have it set up to handle 60kW at 240v (better suited to the sets I work on). I only have a few of the heaters set up, so I can add loads in 5kw increments. When I dump 60kW into it it makes a LOT of heat!

 

[Jesse6325]

In reply to ichudov, Any engine will wet stack, It's just a lot more common on diesels.
I nknow of one guy who used his class8 tractor for personal transport to work and back for a couple of years the relicensed for OTR hauling. He said the first time he put a good
heavy load on it the thing looked like it was fire for about 20 miles!
For proper routine maintenance any engine needs to be loaded occasionally

 

[jaxsof]

We occassionally have locomotives that sit and idle for several days. When they finally get loaded it blocks out the sun for several acres. The 2-strokes seem to be the worst though, but 2- and 4- stroke both will have a decent stack fire. Had a 12 cyl GE (7 liters per cyl) burn down the overhead catenary because of a bad injector.

 

[M1031CMT]

M1031CMT- I use 2 5kw heating elements (out of a heat pump hvac system)and a fan blowing over the elements. I use a relay with a switch to control it at 5 or 10 kw. Let me go get some pics.

In the past, I have used all sorts of stuff for artificial load; below I have listed a few of the things that are commonly available:

500W halogen lights. Only a few $$ from harbor freight or home depot, these work well for smaller generators. 10-20 of them won't break the bank, and they are easy to add in small increments. Wiring 20 of them up is a disadvantage; safely doing that requires lots of junction boxes and cable.

Electric clothes dryer. These are cheap (sometimes free) in your local craigslist; and you can add 5kw or more with one.

Hot water heater. Another cheap one from your local classifieds. The disadvantage here is that if you want to dump a lot of load, you need to flow a lot of water into the water heater.

Electric oven/range. With all of the burners and the oven on, you can put 6-7kw on your set. Usually easy to find in your local craigslist.

Space heaters. I once loaded up a generator with about a dozen small baseboard heaters. Works well, but wiring up a dozen of them can take a lot of cable and junction boxes.

My current load bank was purchased off of ebay for just a couple hundred $$. It is a resistance element heater; designed for placing a dummy load on a BIG generator. It can handle 300kw and 480v. I currently have it set up to handle 60kW at 240v (better suited to the sets I work on). I only have a few of the heaters set up, so I can add loads in 5kw increments. When I dump 60kW into it it makes a LOT of heat!

Thanks for the suggestions. I appreciate it!

 

[quickfarms]

How much load does an electric cook top require?

 

[Speedwoble]

In reply to ichudov, Any engine will wet stack, It's just a lot more common on diesels.
I nknow of one guy who used his class8 tractor for personal transport to work and back for a couple of years the relicensed for OTR hauling. He said the first time he put a good
heavy load on it the thing looked like it was fire for about 20 miles!
For proper routine maintenance any engine needs to be loaded occasionally

I bought a civilian gasoline generator(for like $50) years ago with horrible blowby. It had been run, lightly loaded, for it's entire short life and as a result the rings were gummed up and not sealing. The valves had deposits as well. Had to be dissassembled and cleaned/rebuilt.

The lesson is, size your generator to the load you expect to run.

 

[PeterD]

When I rebuilt my MEP-004's engine, one of the things I discovered was that the exhaust manifold was full of sludge. Cylinder 1 (front most, nearest the fan) was the worst, while #2 was noticeable but not as bad. Cylinders 3 and 4 had only a nominal amount of wet stacking. This led me to believe that the two front cylinders were running cooler than the rear two, but one day I measured the temp on the manifold near the exhaust port and found little difference between the four. I suppose it is possible that bad injectors may have been a partial reason, as I'd replaced them when I did the rebuild.

I think probably this summer I'll pull the manifold again and check it. I've run it about 25 to 30 hours now (lightly loaded, about 30% or so) and see how it looks (that's easy to do...)

 

[Beerslayer]

So for when the generator is setup to automatically exercise on a timer, do you think that a load should be cut into the circuit?

I am guessing the logic would work like this:

Generator exercise start [not power failure] - one or two minute run up - switch on load

Does that sound like it would take care of the wet stacking?

 

[amolaver]

just a little random extra data.. my 003 was a rebuild in '08 that had less than 5 hours on it. in messing around / testing i had put another few hours on it. once i got it running properly (battery charging system was borked), i hooked it up to the house for a few hours. water heater kicked on and off, range was used, heat pump was running, etc. each time i came outside to check on it, i noticed 'black rain' had fallen on the trailer and surrounding grass. i can only imagine the crud that would accumulate with hundreds of hours of low/no load.

i think this also has implications for folks using the exhaust extension hoses. if the gen is low/no loaded for a significant amount of time (i'd guess 10's of hours), there might be enough crud built up in the hoses to catch fire if the gen is suddenly heavily loaded for a significant period. keep an eye on things as you start running loaded with a generator you're not familiar with!

ahm

 

[Motorcar]

I was at Amtrak's Wilmington shops for a class in the '90's. There was a locomotive (F40) there that was used for employee testing that sat idle for ages never having been out on the road working a load in who knows when. Well...a couple of morons with just a tiny amount of knowledge got to playing with the layshaft and soon big globs of oil started raining down. Then big globs of flaming oil, then a five foot flame out of the exhaust stack from the turbo, then the accumulated oil on top around the stack caught fire. It was at this time an office gal looked out the window, saw flames and called 911 reporting the Wilmington Bear shops were on fire. By the time FD arrived the locomotive had cleared out and everyone was back to drinking coffee.

Worst case of wet stacking ever.

 

[sewerzuk]

So for when the generator is setup to automatically exercise on a timer, do you think that a load should be cut into the circuit?

I am guessing the logic would work like this:

Generator exercise start [not power failure] - one or two minute run up - switch on load

Does that sound like it would take care of the wet stacking?

I think so; based on my last experience, a full hour of heavy load was all that was needed to burn off years of accumulated oil and carbon from years of no load. I think that a warm up to normal operating temp under at least a 50% load would prevent it from occurring in the first place.

Who knows how much life was taken out of the pistons/rings/cylinder walls/valves/valve guides/ etc. There was a LOT of solid burning carbon chunks that came out of that set. It would be a GREAT thing to prevent.