How to Avoid Wet Stacking with Diesel Generator No-Load Exercising

A new white paper from Kohler Power Systems explains the feasibility and benefits of no-load exercising for diesel generators, and how it can help to prevent wet stacking issues.

“Wet stacking” or engine slobber is a common problem faced by diesel generator operators. A buildup of unburned fuel in the exhaust system, “wet stacking typically occurs when generators frequently run with little or no load because the generator is improperly sized for the power required or because adequate load is not available during the exercising period.” According to the paper, this is a common problem for data center operators because historically, their generators are oversized for their usual load.

“When generators run at less than 30% of capacity for extended periods of time, their engines are unable to sustain the optimal operating temperatures needed to burn fuel completely.” – Kohler Power Systems, “Data Center Generator Maintenance: Feasibility and Benefits of No-Load Exercising“

Wet stacking can be damaging to the generator in the long term, leading to poor performance and reducing the lifespan of the engine. The paper explains that the solutions to wet stacking are often costly and increase emissions. This includes “exercising the generators at 30% of the rated capacity once a month to burn off unused fuel or prevent buildup.” However, the load-bank testing commonly used to avoid wet stacking “were drawn up years ago and have never been revisited” as technologies have changed and improved.

The author asserts that with advancements in technology, this exercising schedule can be adjusted to just once a year for many modern diesel generators. Kohler notes a number of the latest diesel technologies to support this assertion, including “several technologies that enhance operating efficiency and reduce the gaps between pistons and rings that allow unburnt fuel to escape.” The paper also says that the costs savings of switching from monthly to annual load testing are “compelling.”

Because of the improvements in modern diesel engines, Kohler suggests data center operators revisit their old assumptions around maintenance schedules by working with a qualified service provider.