Stationary diesel engines are commonly used for electricity generation, but also for powering refrigerator compressors, or other types of compressors or pumps. Usually, these engines run permanently, either with mostly partial load or intermittently, with a full load. Stationary diesel engines powering electric generators that put out alternating current, usually operate with an alternating load but fixed rotational frequency. This is due to the mains’ fixed frequency of either 50 Hz (Europe), or 60 Hz (United States). The engine’s crankshaft rotational frequency is chosen so that the mains’ frequency is a multiple of it. For practical reasons, this results in crankshaft rotational frequencies of either 25 Hz (1500 per minute) or 30 Hz (1800 per minute).
