Diesel engines are the most common prime mover for backup power systems. When run with insufficient load, diesels can suffer from accumulation of unburned residues in their exhaust systems, a condition known as wet stacking. This article explains how load banks can be used to avoid this condition.
The Problem with Wet Stacking
Diesel engines combust fuel without the aid of an ignition system, such as those used for gasoline-fueled engines. Instead, diesel engines compress an air/fuel mixture at high ratios, causing a temperature rise that causes fuel to self-ignite. Recall the Ideal Gas Law:
Pressure x Volume = Amount of Substance x Ideal Gas Constant x Temperature
With all other variables constant, increasing pressure via compression raises the temperature, causing the fuel to combust. Because of their design, diesels provide efficient operation at high levels of output.
For ac power generation, the frequency of the ac sinewave is proportional to engine speed. Consequently, governors control engine-generator speed to keep frequency constant. They do this by adjusting the amount of power required to meet changes in load. When less or more power is needed, the governor provides less or more fuel to meet the corresponding load demand, without changing engine speed. Running at high loads produces a greater amount of heat than running at low loads, even though engines run at the same speed either way.
The Problem with Wet Stacking
Diesel engines combust fuel without the aid of an ignition system, such as those used for gasoline-fueled engines. Instead, diesel engines compress an air/fuel mixture at high ratios, causing a temperature rise that causes fuel to self-ignite. Recall the Ideal Gas Law:
With all other variables constant, increasing pressure via compression raises the temperature, causing the fuel to combust. Because of their design, diesels provide efficient operation at high levels of output.
For ac power generation, the frequency of the ac sinewave is proportional to engine speed. Consequently, governors control engine-generator speed to keep frequency constant. They do this by adjusting the amount of power required to meet changes in load. When less or more power is needed, the governor provides less or more fuel to meet the corresponding load demand, without changing engine speed. Running at high loads produces a greater amount of heat than running at low loads, even though engines run at the same speed either way.