What is wet stacking?

Wet stacking is a condition that can affect all diesel engines, not just generators. Wet stacking means that not all the fuel is burned and the unburnt residue goes into the exhaust side of the turbo and into the exhaust system.

Main Causes

The main cause for diesel generators is that the engine is running at a low proportion of its total capacity.

Symptoms

The symptoms of wet stacking are generally a black ooze awet stackinground exhaust pipe connections and around the turbo, along with continuous black exhaust from the stack when under a constant load.

A diesel engine requires exactly the right air to fuel ratio,  to sustain the operational temperature it was designed to run at, for a complete burn of the fuel.

When a diesel generator only has light loads, it’s not able to reach the correct operating temperature. meaning not all the fuel is combusted. This inturn leads to wet stacking.

Over time permanent damage can occur as the deposits erode the engine surfaces. Additionally, the piston rings do not get to their designed temperature. Causing unburned fuel and gases to escape into the oil pan. This dilutes the lubricating properties of the oil. Thereby leading to premature engine wear.

Run the generator on load to avoid wet stacking. With at least 75% of  maximum load capacity. Reach optimal running temperature. Achieved this by doing an on load test using the building load, or using an external load bank. If wet stacking has already occurred but it is at its early stages, carrying out the same should burn off the unburnt fuel and solve the problem. If wet stacking has occurred for some time, it might be necessary to carry out an engine rehaul to resolve.

How to avoid wet stacking

Wet stacking is a condition that can occur on Diesel Engines, where not all the fuel is burned. Consequently the unburnt residue goes into the exhaust side of the turbo and into the exhaust system. The main cause is that the engine is running at a low proportion of its total capacity.

The best way to avoid wet stacking is to ensure that the generator is run on load. Running with at least 75% of its maximum load capacity. This will ensure that the generator reaches its optimal running temperature. This can either be achieved by an on load test using the building load, or alternatively using an external load bank. If wet stacking has already occurred, an on load test should burn off the unburnt fuel and solve the problem. If wet stacking has occurred over some time, it might be necessary to carry out an engine rehaul to resolve.

It’s possible the generator capacity you have on site is bigger (even double) than your peak building load. The reason is to make sure that in the event of a power cut, the generator would be able to take the entire load immediately, rather than having to load shed. This therefore means that the building load will never be sufficient to suitably loadbank the generator. If this is the case, the solution is to use an external load bank. This will allow the generator to be run up to its full capacity. Not only will this prevent any wet stacking, but it will also give you confidence in your generator’s ability to run at full load.

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