Generator sets are designed to operate under substantial load. This may seem unimportant, but loading a generator set properly is essential to healthy engine operation and long engine life. The ideal operation targets of each generator set will depend on the application and rating. Generally speaking, standby – rated diesel generator sets are designed to operate between 50 and 85 percent load, while continuous – rated diesel generator sets are optimized between 70 and 100 percent load.
Operating a diesel generator set at load levels less than 30 percent of rated output for extended time periods impacts the set negatively. The most prevalent consequence is engine exhaust slobber, which is also known as exhaust manifold slobber or wet stacking. Engine slobber is a black, oily liquid that can leak from exhaust manifold joints due to extended low or no-load scenarios.
Within the engine, soot can cause internal glazing of the cylinder bores, sticking of the piston rings, reducing compression and the injectors are likely to have a build-up of carbon causing more un-burnt fuel to pass through the combustion chamber into the exhaust.
The first sign of this problem is heavy smoke from the exhaust, eventually; the un-burnt fuel will condense in the exhaust and mix with the soot, to create a thick dark liquid that looks like engine oil. This liquid will seep from the exhaust, and will appear to be an oil leak. This liquid can build up in the exhaust silencer and there is the risk of it igniting from the increased heat of the exhaust fumes, if the generator is subsequently put under full load.
These conditions can lead to power losses, poor performance and accelerated wear of components, which can cause increased maintenance costs and unplanned downtime or failure. If a generator continues to be operated with no load or very light load there is a possibility that permanent engine damage can occur.
To help minimize the effects of under loading, it is critical to have proper load estimation, operation and maintenance plans in place to maintain the health and reliability of the complete system and your generator set.
If you need assistance in this regard, contact John Holt Engineering, the trusted name in diesel generators.