Wet Stacking Prevention Technologies for Cat 3500 Diesel Generator Sets
Caterpillar · Roger Rosborough
Caterpillar LEXE20210-00 (Roger Rosborough, 2021) explains wet stacking on diesel generator sets run for long periods at light load, and the engine features Cat uses on 3500 Series units to mitigate it. It applies to data-centre gensets routinely exercised unloaded or lightly loaded.
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Overview
Wet stacking arises from extended operation at low load (under 30%) and shows as black liquid at exhaust joints. Prolonged under-loading also accelerates component wear, with further detail left to white paper LEXE0832.
The mitigations split into hardware and software. Hardware means piston-ring and oil-scraping design and exhaust valve stem seals. The two software strategies disable injectors so the firing cylinders stay hot.
Cold Cylinder Cutout (CCC) switches off one unit injector at a time during cold start and extended low load. Idle Cylinder Cutout (ICC) cuts several injectors in sequence at rated speed when load is between 0% and an engine-specific limit, typically about 10-25%. If both sets of conditions are met, CCC takes priority, and either strategy deactivates immediately when a parameter leaves its range.
Key points
- Wet stacking comes from extended operation below 30% load and appears as black liquid at exhaust joints.
- Prolonged under-loading accelerates component wear (see LEXE0832).
- Hardware measures: piston-ring/oil-scraping design and exhaust valve stem seals.
- Cold Cylinder Cutout turns off one injector at a time during cold start and extended low load.
- Idle Cylinder Cutout cuts multiple injectors in sequence at rated speed between 0% load and an engine-specific limit of about 10-25%.
- When both conditions are met, CCC takes priority.
Using it in design
- Warn when planned monthly exercise or normal running load is under 30% of rating, and recommend load-bank testing or a reduced set count.
- Add a low-load mitigation field (cylinder cutout) to the generator catalog.
- Include periodic load-bank runs in commissioning templates for lightly loaded data-centre gensets.
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Who should read it
Operations and design engineers planning testing, maintenance and commissioning of data-centre generators.
Related standards
- NFPA 110
Publication details
- Authors
- Roger Rosborough
- Publisher
- Caterpillar
- Year
- 2021
- Document number
- LEXE20210-00
- Document language
- English
- Source type
- Manufacturer
- Access
- Free to read
- Licence
- Copyright retained; citation only — the publisher’s terms apply to the original document
Citation
Roger Rosborough (2021). Wet Stacking Prevention Technologies for Cat 3500 Diesel Generator Sets. Caterpillar. LEXE20210-00. https://www.finning.com/content/dam/finning/en_gb/Documents/Industries/ElectricPower/cat-white-papers-march-2024/Wet%20Stacking%20Prevention%20Technologies%20for%20Cat%C2%AE%203500%20Diesel%20Generator%20Sets%20(LEXE20210-00).pdf
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