Low load/zero load running time can not last more than 10 minutes

Ideally, diesel generators should run at least 25%-30% of rated output. Low load/zero load operation time is less than 10 minutes.

What happens when a diesel generator set runs at low load for a long time?

Running the engine under load results in low cylinder pressures, which in turn results in a poor piston ring seal, since the piston ring seal relies on gas pressure to force the piston ring against the oil film on the bore to form a seal. Low cylinder pressures result in poor combustion, which in turn results in lower combustion pressures and temperatures.

This poor combustion results in soot formation and unburned fuel residue that can clog and stick the piston rings. This causes a further loss of sealing efficiency and exacerbates the initial low pressure. Glazing occurs as the hot combustion gases blow past the now poorly sealing piston rings, causing the lubricating oil on the cylinder wall to "flash" and form a glaze-like texture that smooths the bore and eliminates the effects of the complex honing marks machined into the bore surface. The purpose of these honing marks is to contain the oil and return it to the crankcase via the oil scraper rings.

Poor combustion also forms hard carbon, which is very abrasive and will scrape the honing marks on the bore, causing the bore to polish, which in turn will lead to increased oil consumption (blue smoke) and further pressure reduction, because the oil film trapped in the honing marks is designed to maintain piston sealing and pressure. Unburned fuel will leak out of the piston rings and contaminate the lubricating oil. Poor combustion will cause the injector to be blocked by soot, which further deteriorates combustion and produces black smoke.