ECN Forum
Posted By: Rewired Off the wall question - 01/23/07 10:56 PM
First off I want to apologize for not logging on the forum in a while, BIGTIME computer problems.
I do have a question regarding term
"wet stacking" when it comes to diesel generators, or I assume diesel engines in general?
Am I wrong but does it mean that if you have a diesel that "wet stacks", it is where there is a buildup of unburnt fuel in the engine and exhaust system, caused by the engine not being run long enough and hard enough to get up to proper operating temperature and therefore not completely burning all fuel injected into the engine?
I am just wondering the exact meaning, I heard the term come up again and was not sure ~exactly~ what it meant.
Thx again!
A.D
Posted By: RobbieD Re: Off the wall question - 01/24/07 12:24 AM
Wet stacking occurs in a diesel engine when the engine is run at too light of a load during the run-in (also known as load banking). This causes unburnt fuel and oil to collect in the exhaust stack. The exhaust stack will be coated with a black, sticky, tar-like substance. If you run a new unit at light loads and/or idle for too long, the rings will not seat properly. If it is a diesel, wet stacking may occur. Both of these conditions will cause poor engine life and performance.

This info is from www.gendco.com
Posted By: Roger Re: Off the wall question - 01/24/07 12:51 AM
Wet stacking in diesel generators is a perfect example of "bigger is not always better".

I am involved with a hospital that sized it's Generators for future growth and have a wet stacking problems at present due to light loading.

Roger
Posted By: LarryC Re: Off the wall question - 01/24/07 02:26 AM
It is very similar to creosote build up in a chimmey of wood burning stoves. By it self, it is not too bad, BUT if you then heat up the chimmney by overfiring the stove or heavily loading the diesel engine, the fuel coating can ignite, resulting in a chimmney / exhaust system fire.

That is one reason when running the generator for annual testing, it should be put under full load.
Posted By: WFO Re: Off the wall question - 01/24/07 03:53 AM
OK, this piques my curiosity. Our company recently purchased a standby diesel generator. When it gets set up to test run on a weekly basis, we are not planning to actually switch load. Will this running without load cause build up?

[This message has been edited by WFO (edited 01-23-2007).]
Posted By: WESTUPLACE Re: Off the wall question - 01/24/07 04:26 AM
WFO answer YES All standby gensets should always be run under load during exercizing or testing. Here on the Gulf Coast many businesses and public safety people discovered their standby systems failed after a few hrs of running during the Hurricane due to not exercizing them under load. Some systems have load banks they use during exercizing.
Posted By: Rewired Re: Off the wall question - 01/24/07 06:00 AM
Ok so the way I understand it, IF it happens on a new engine it can cause poor seating of the rings and short engine life and poor performance, BUT it is possible for this to happen on an older unit if it were run a lot while not under load?

I am asking as I am also curious if this could apply to a truck engine, as my boss starts up his one diesel truck that never leaves the yard and shuts it down while still ice cold. The other truck that leaves the yard once in a blue moon he does almost the same thing to.. I guess what he should be doing is not bother to be starting them once a week if they are sitting there months on end, BUT if he does want to fire them up, he should be taking them out and getting them good and hot? Just curious as I don't want him to screw up the "new used" trucks he has bought.
Thanks again!
A.D
Posted By: BigB Re: Off the wall question - 01/24/07 01:47 PM
Some diesel engines are more succeptable to wet stacking than others. For example, the Mercedes Benz diesels can idle for days without wet stacking problems.

[This message has been edited by BigB (edited 01-24-2007).]
Posted By: Trainwire Re: Off the wall question - 01/24/07 02:02 PM
Our GE 44 Ton locomotive has two 40's vintage Cat d17000 v-8 deseasels in it.

Most of it's time is spent idling around the yard, one or two cars, a quick jolt of power to get things moving.

Had to bring a two heavyweight passenger cars up the hill from the other end of the line.

Wide open, down to about 10 mph, the stacks starting blowing like the steam engines, black smoke, red embers, even some flames out the top of the pipes. Took a good 3 or 4 minutes of running before it cleaned up. Fortunatly it had just rained and everything was sopping wet.

In that case though, the wet stacking is because they are worn out [Linked Image]

Another issue with the standby gennies, would be the length of the exhaust system. A short pipe would be less prone than a long one. The raw fuel condenses in the cool portions of a long pipe and drains back.

Our gensets here at the railroad use oil cooled engines, and they seem to warm up quicker and are less prone to piddling all over themselves.

FWIW

TW
Posted By: frenchelectrican Re: Off the wall question - 01/24/07 04:16 PM
Hello guys and ladies :


anyway for wet stacking on diesel engines it is pretty common with just about any size diesel engines running with no or very light load due very low exhaust tempture.

Like example one diesel generator i been working on { Detorit Diesel old two stroker } if running on very load the exhaust temp will show about 400 to 550 degress but by time i put a full load the temp climb up to range of 850~950 degress it will burn off any soot or wet oil off the exhaust manfoid.

the same thing with diesel truck as well with my DT466 diesel truck at idle [ fully warm up ] it will idle with 350-450 degress but full load it will spike up near 1000 degress but on crusing mode useally 750 to 850 degress range.

Natural Gaz and Propane units [ spark ingited units ] wil expect much higher exhuast temp for sure useally about 800 and above

if more question please do post it i will try to get more details on it

Merci , Marc
Posted By: Rewired Re: Off the wall question - 01/24/07 10:57 PM
Hey thanks again for all the responses, the more I read the more it is interests me really..
The one truck in question that we have is an 86 international with a DT466 or a
DT 466"E", something like that anyway, the other truck of which I haven't really stuck my head in yet is a GMC but the actual model and engine I know nothing about at this time.

Unfortunately the International does not have an EGT gauge and I have no way of telling how hot the exhaust is getting.. the GMC MIGHT. As a matter of fact I will be trying to start that old pig tomorrow so I will find out.
Just off the wall again.. The bossman sent myself and 2 others for our DZ ( truck + air brake endorsement) licence, of which all three of us passed. Just wondering if there is any tips , advice or information we should know in general about these diesels or any diesel in general. Just things we should do or not do or watch out for kind of thing.
Thanks yet again fellas!

Oh ya, Trainwire: Black smoke, red embers and some flame out the top of the stack when the Cat was "stepped on" after being lightly worked for so long eh? THAT I would have loved to have witnessed, sounds impressive and scary at the same time. I guess basically it had a "chimney fire" of sorts?!


A.D
Posted By: frenchelectrican Re: Off the wall question - 01/25/07 12:16 AM
Rewired:

the truck engine you described that is 86 model year that is full mech engine that is non electronic verison they are rated from 185 to all way about 250-275 H.P range most common is either 210 or 250 H.P. and the DT466 useally last very long time kinda bullet proof engine and easy to rebuilt kinda like bread and butter truck engine [ very common med duty engine ]

speaking of flame up on exhaust yeah i ran into few of that one train with G.E. [ a.k.a. ALCO diesel ] they will spit heckva of flame if idle very long peroid of time especally that true during cold days it will show up.

i did that with few other diesel as well including one natural gaz engine i manged to get blue flame came out of the exhaust [ ran pretty rich on that setting [Linked Image] ]

Merci , Marc
Posted By: denversparky Re: Off the wall question - 01/25/07 01:28 AM
We have a 1200KW, 600KW, 400KW and a 300KW
generators we test under full load every month. Which is a good thing 'cause you find the problems under load not by idealing.
Posted By: BigB Re: Off the wall question - 01/25/07 02:39 AM
Trainwire, when I was a kid growing up just outside of Chicago I remember the engines on the commuter trains would be left idling all weekend and on holidays. They stopped doing it, I was told, because someone took one out for a joy ride one time!

I suspect there are other reasons to shut them down now days. I believe it takes more fuel to start one than it does to idle it for two days, does it not?

There was a story about a stewardess that worked out of Ohare, she had a Mercedes diesel and in the winter she would leave it idling in the parking lot the whole time she was in flight.
Posted By: JoeTestingEngr Re: Off the wall question - 01/25/07 03:02 AM
We have a 900KW CAT V12 driven genny as part of an automatic emergency switching scheme with two incoming AC lines. One downside is that the automatic mode will start the genset if either line drops, yet inhibit switching to it unless both lines drop. If we know that a line will be down for a while we will often put the switchgear into manual mode and switch to the genset. Our machinists used to run it unloaded every Friday. Now we switch to it and try to load it at least 300 amps per phase and for at least 1/2 hour. I warn that we have no right to expect more from our generator in an emergency than we observe it deliver under normal testing.

This better testing comes with its share of problems. Some of the high efficiency lamps will not maintain through the transfer and take up to 5 minutes to restrike. Failure to time our manual switching correctly might leave us in near total darkness. Folks have to be warned to close their programs and we have to allow them plenty of time before we act. It was a whole lot easier when we just flipped the control switch from "AUTO" to "ON".
Joe
Posted By: Trainwire Re: Off the wall question - 01/25/07 03:34 PM
Rewired, yea for all intents and purposes it was a chimney fire. and there are two of them, still a gutless wonder though. It wasn't that dramatic, so it was more of a "cool, look at that! Let's try that again!"

Modern railroad engines are not left running because of the noise issues, economy issues, and a few other things.

These big deseals don't mind idling and if it's cold out, sometimes getting them relit is a problem. There are ways out there to keep them warm now, little pony engines that run heaters to keep the block warm, thermostats that auto start the engine and shut it off when it reaches temp, a whole host of ideas.

Our engine gets plugged in at night, and yea, sometimes we wind up with a couple of 4'8 1/2" long extension cords. But that's what the gfi's for right?

The train has a couple of 25 KW gen on it. With really long exhaust pipes. We put cleanouts in the exhaust system to make it easier, so that they can be cleaned before it pukes all over the tourists.

TW

Familiarity breeds comtempt, but without familiarity you don't breed anything.
Posted By: Rewired Re: Off the wall question - 01/25/07 11:11 PM
Marc:
Yeah, that engine we have seems like a good one. I am suprrised it pushes that truck around that easily. I was surprised it even started considering it was -13*C out today and the truck was not plugged in.. Come to think of it I do not think there is a block heater of any kind on the truck.
Oh yeah, that "other" truck we have is a GMC "brigadier" ( year unknown) with a "Caterpillar 3208" under the hood.. I made an attempt at starting that this morning as well but no such luck. Even with triple batteries of which their state is not known, and a 200A booster/charger as well I got nothing more than a thunk of the starter engaging and a very audible "hum" from the starter. Got a little smoke off the booster's alligator clips and battery posts also, but the engine did not even move!.
I did find out later the block heater is toast and needs to be replaced.

TW: " Cool lets try that again"... Yep I would be saying the same thing!
there is a train yard kind of thing at the bottom of the escarpment not too far from here and I have noticed they shut the engines down overnight and whenever they sit for a long period of time.. I have noticed on more than one occasion when they go to fire them back up there is great plumes of blue smoke rising out of the yard. If your lucky it goes straight up.. but on occasion I have seen it fog out the yard and the houses around it.
A.D
Posted By: John Crighton Re: Off the wall question - 01/26/07 05:40 PM
Quote
Our engine gets plugged in at night, and yea, sometimes we wind up with a couple of 4'8 1/2" long extension cords.

Thanks, I had a nice LOL over that one!
Posted By: Scott35 Re: Off the wall question - 01/27/07 01:57 AM
(Regarding Locomotives):

The Class 1 carriers in my area (SP, ATSF, UP), used to leave Locos running continuously - only shutting down Prime Movers during Holidays (Switching duties on Branch Lines).

They started to shut down unattended Units around mid 1990's, where a Unit was to be unattended for more than 2 Hours, as to comply with EPA + Energy regs (reduction of pollutants, conservation of fuel).

Trains "Put In The Hole" (in sidings, waiting for Meets), also used to be kept running.

There is an area near me on the BNSF's San Bernardino Sub, which has 3 Main Tracks between 2 "Stations" (actually are main line crossovers).
At the ends of this Block Section, the 3rd Main Line ends, running back into the North Track via CTC type 50 MPH Turnouts.

"Non-High Priority" Freight Trains are commonly placed in this Hole, as to eliminate issues with Passenger Trains running through + stopping at Stations, to pickup Passengers.
Most of the Trains held in the Hole are Intermodal, but a few are Manifest.

Since 2006, the Prime Movers are shut down on all Units of these Trains, held in the Hole. They used to be left idling before 2006.

At times, there may be as many as 4 Trains in the same Hole, waiting for a Greenboard!

Cool thing is, the newer GE "Dash 9's" (C44-9W, AC44-9W, etc.) plus the newer EMD SD-75's, SD-80's, etc., have remote startup + shut down controls, from any Unit (normally from the Lead Unit); so all Units in a lashup + any RCE Helpers / Pushers can be shut down + started from the Lead Unit - and at the Engineer's Controller!

Prior to this, Units were started / shut down from controllers located behind the Hoods, near the Cab (on the Engineer's side).

Restarts are normally quick, and produce minimal smoke; plus there is normally minimal sparking / flames and very low (or no) smoke produced after the Train is started (put in motion).

The same is not true for the Branch Line Switchers, as they frequently experince the Wet Stacking issues when "Power Is Needed"

Quote

sometimes we wind up with a couple of 4'8 1/2" long extension cords

4' 8-1/2" long cords,... LOL!!! [Linked Image] [Linked Image]

Scott35
© ECN Electrical Forums