Small Diesel Generators Buying Guide

the text below is based on the authors 35 years experience in the diesel generator business

Residential and Light Commercial Applications

Engine lifetime is another factor to consider when selecting your generator in prime power applications. In the author's experience, the following table outlines expected run time before overhaul for various engines:

Gasoline Portable 3600 rpm 500 to 2000 hours - typically not overhauled

Natural Gas or Propane fueled 3600 rpm stationary generators 1000 to 2000 hours- typically not overhauled

Natural Gas or Propane fueled 1800 rpm stationary generators up to 6000 hours - overhaul or exchange engines available

Lombardini, Perkins, Yanmar 1800 rpm diesels up to 15000 hours - overhaul possible, economy of rebuild vs replace depends on engine failure

kubota 1800 rpm diesels up to 20000 hours - overhaul possible, economy of rebuild vs replace depends on engine failure

(note - hours are estimated, there are obviously exceptions, but based on my thirty-five years in the engine industry)

Diesel Engine Wet Stacking

Diesel engines are designed to operate with a load. When a diesel engine operates considerably below the rated output level the engine can start to over-fuel or "Wet Stack". Diesel engines perform most efficiently in the 70-80% range of rated output. When an engine operates for a prolonged period of time below 40% of the rated output it begins to over-fuel. This occurs because the injection tips began to carbonize and disrupt the fuel spray pattern. In commercial generator standby/emergency systems where loads can vary and low output conditions can occur more frequently because of the diverse load applications, an automatic load bank is normally used. A load bank will place a "false" load on the generator system to keep the diesel engine properly loaded to prevent a "Wet Stack" condition. In residential or small business applications a "false" anti-wet stack load condition can be accomplished with the use of an electric heater or other high load appliance to make sure the diesel engine generator system is not allowed to operate for prolonged periods of time below an acceptable level. Once a diesel engine begins to "wet stack" the only way to correct the problem is to load the engine for a couple of hours to burn off the excess fuel and clean up the engine. Some diesel engines are less prone to "wet stacking" than others. Generally, electronically controlled engines and engines with advanced emission systems are less likely to "wet stack". Unfortunately, all diesel engines will "wet stack" if operated for long periods of time considerably below the rated output level. It is for this reason that proper sizing and design is important. We can help you with all your sizing and design considerations. It is part of our Sales Engineering Service program and it is free.

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