We've done a number of successful episodes on technologies and engine attributes, and we wanted to share some insight on a challenge many users face called "Wet Stacking". Retuning to the show is Roger Rosborough to help us better understand the condition.
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We've done a number of successful episodes on technologies and engine attributes, and we wanted to share some insight on a challenge many users face called "Wet Stacking". Retuning to the show is Roger Rosborough to help us better understand the condition.
Email us: powerbytes@cat.com
LinkedIn: https://www.linkedin.com/showcase/cat-electric-power/
Facebook: https://www.facebook.com/Caterpillar.Electric.Power/
Lou: Good Day and welcome everyone to Power Bytes! I am your host Lou Signorelli and Power Bytes is your destination Podcast for power generation conversations. As always please know how much we appreciate you, our listeners. We hope you find our topics helpful and interesting. There are several ways for you to get in touch with the show. You can send us an email at powerbytes@cat.com, visit us at Cat Electric Power on Facebook or LinkedIn. Please remember to subscribe, leave comments and like our show wherever you listen to your favorite podcast.
Lou: We've done a number of successful episodes on technologies and engine attributes, and we wanted to share some insight on a challenge many users face called "Wet Stacking". There are any number of other names you might recognize for the same condition such as 'slobber', but wet stacking is the proper name for the condition. Joining me today to help us better understand the situation is Roger Rosborough. Roger 20 years of experience and is a PhD in Mechanical and Manufacturing Engineering from Queens University in Belfast, N. Ireland.
Lou: Welcome back to the show Roger!
Lou: Let's start with a definition or description of Wet Stacking.
Roger: As you mentioned Lou, the term "slobber" is another common name for the condition of wet stacking. Also known as "exhaust slobber" or "exhaust manifold slobber". How do you know if your engine suffers from this? Well, you will notice a thick black liquid seeping from the joints of your exhaust system. That could be from the exhaust manifold, the turbocharger or exhaust pipes. The liquid itself looks like used lubricating oil that should have been changed a long time ago - but it is not! The thick black liquid is actually typically composed of carbon particles combined with unburnt fuel.
Lou: What is the primary cause of Wet Stacking?
Roger: The primary cause is operating your diesel generator set at low loads (that is less than 30% of the rated load) for extended periods of time. The light loading means that the engine runs below its designed operating temperature and if this is the case for extended periods then unburnt fuel is exhausted into your exhaust system which "wets" the exhaust system hence the term "wet stacking"
Lou: How common is Wet Stacking?
Roger: It is pretty common because typically Generator sets are oversized because they are sized for a worst case scenario. As an example if you think about the process of purchasing a standby generator set for your home, you would add up all of the electrical loads in your house including the cooker, kettle, microwave oven, heating system, emersion heaters, air conditioning, fridge, freezer, dishwasher, all your lights, TVs etc. Making the assumption that you want the generator set to have the capability to run everything in your home at the same time. The same approach is taken in industry resulting in the possibility of generator sets running at low loads for extended periods.
Lou: Is it bad for the engine?
Roger: While having a thick black liquid dripping out of the exhaust connections looks bad, and could lead you to believe there must be big problems with the engine. That's not necessarily the case. However, that said, long periods of wet stacking is bad for the engine and can result in reduced performance and premature wear.
Lou: How does it eventually lead to damaging to the engine?
Roger: The unburnt fuel build up in the exhaust system can foul the fuel injectors, cause buildup of carbon on the exhaust valves, turbocharger and exhaust. These carbon deposits can lead to gases bypassing the valve seatings, increased exhaust backpressure, deposits on turbo blades which reduces the turbo efficiency. All of which will reduce the engine power output. The carbon deposits can scar and damage engine surfaces over longer periods. If the engine is running below design operating temperature for long periods, then unburnt fuel can leak past the piston rings (since they don’t expand enough to provide adequate sealing) into the oil pan thus diluting the lubricating oil, which reduces the engine lubrication leading to premature wear.
Lou: What are a few best practices to keep Wet Stacking from prematurely damaging an engine?
Roger: The best solution is avoid it by running with sufficient loading to maintain the designed operating temperature. If that isnt possible then to address this, NFPA 110 for example recommends exercising your genset at least once per month for 30 minutes, loading it so that the minimum exhaust gas temperature is maintained OR at the design engine operating temperature and not less than 30 percent of the standby rating. If adequate loading can't be provided for this, then portable Load banks can be used or even permanently installed load banks could be considered for this purpose.
Lou Summary: There you have it folks! I’d like to thank our guest Roger Rosborough for sharing is insights with us today and a special thanks to YOU our listeners. If you’d like to read more about “Wet Stacking” please go to cat.com/wetstacking.
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