Risks and Consequences of Using Generator Sets at a Low Load

How can we detect that something is malfunctioning?

Generator sets are designed to work at their maximum power and their correct care and maintenance is, therefore, essential for them to function optimally. All the equipment must work at a minimum of 50% power load and their continued use at inferior percentages – that is to say at a low load – is counterproductive and may have serious consequences.

“We saw engines working continuously for 24 hours at a tenth of their load and exhaust manifolds with six centimetre holes reduced to one centimetre by the accumulated cinder and oil”, Genesal Energy Technical Director Guillermo Docampo explains.

Why does low-load functioning in a repeated and continuous way cause an increase in oil consumption? In reality, when an engine works at a low load, the ideal working temperature of the engine is not attained. This favours oil flow towards the upper part of the piston, because a correct adjustment within the piston-rings-cylinder assembly was not achieved. This is due to the lack of dilation resulting in an increased consumption of oil; the oil flows more easily between the valve guides and the stems due to a greater clearance because there was no sufficient warming.

Main symptoms of something malfunctioning

One should be concerned when:

  1. The engine gives off oil mixed with fuel through the exhaust manifold – including the exhaust outlet or the muffler.
  2. There is oil spillage, dripping of oil of a very dark colour, as if burnt.
  3. The exhaust gives off a white smoke, more smoke than usual is seen or there is soot coming out of the exhaust outlet.
  4. The valves and tubing are clogged by dirt (presence of cinder).

Negative effects of low load:

  1. Large accumulation of soot (cinder) in the pistons, in the grooves of the piston rings, in the valves and the turbocharger. If, subsequently, the engine functions at full load the pistons may be blocked by faulty lubrication.
  2. Low temperatures will result in insufficient combustion of the fuel, which, in turn, will cause the lubricating oil to be diluted and lose its properties because part of the fuel has mixed with the oil.
  3. Grinding of the cylinder liner. Excessive wear.
  4. The non-consumed fuel and the lubricating oil will also penetrate the exhaust manifold and will possibly exit through its seals, being very obvious -almost scandalous- because of its burnt aspect and by the stains it causes ((see photo below)).

How to prevent malfunctions? Is it possible to reduce the risks?

  1. It is recommended to reduce the low-load functioning period to a minimum. If periodic tests of functioning without load are carried out, the time of such tests must not exceed 10 minutes. For this reason, at Genesal Energy this weekly and automatic test takes between 3 and 6 minutes.
  2. In emergency generators, the engine must be started at full load for approximately 4 hours a year. This will allow the engine to eliminate the soot deposits which it holds inside as well as in the exhaust system. Moreover, this will give the possibility for the cinder sediments in the engine itself and in the exhaust pipe to be burned. This test must not be started with more than 50% of the load, which will have to be increased gradually while constantly controlling the equipment because, due to the accumulated oils and carbon, the unforeseen high-temperature problems could arise in the exhaust circuit.
  3. In the photo above, one can see the appearance of the valve of an engine which has worked at low load for many hours continuously. Visible consequences: impurities, cinder, and a kind of tar are accumulated in the valve. Therefore, they cannot function properly and the engine ends up failing and clogging the exhaust exit holes, manifolds etc.