An industrial diesel engine is any engine used for industrial purposes that runs on diesel. Industrial diesel engines are used to power a major portion of industrial machinery -- from motorbikes to bulldozers, generators to pumps, forklifts to trucks. They range in size from a few pounds to a few tons, supplying anywhere from a few kilowatts(kW) to a few gigawatts. Engines are also rated in terms of horsepower.
The use of diesel engines is mandated by many large organizations. For example, all NATO machinery runs on either diesel or aviation-grade kerosene. At our current level of technology, fossil fuels, especially diesel, are the most convenient and economical means of powering a variety of equipment and backup generators.
Industrial diesel engines may be air-cooled or water-cooled. The smallest engines for residential purposes typically provide about 10 kW and cost a few thousand USD. Small-scale industrial diesel engines provide a few hundred kW and also cost a few thousand USD. These small-scale engines power much of the mobile machinery we see around us every day -- trucks, farming equipment, small boats, stationary process machinery, earthmovers, and so on.
Medium-scale industrial diesel engines provide power levels between about a few hundred kW and a few thousand kW and are sold for prices in the tens of thousands of US dollars. These are used for larger machinery such as large mining equipment, oil rigs, trains, large boats, military equipment, and more. The largest industrial diesel engines provide 10,000 to 80,000 kW, sold at prices in the millions of US dollars, and are used for ultra-heavy machinery, electric power generation, and the largest ships. These industrial diesel engines can be 15m (49 feet) wide and run on low-grade diesel. Especially in places like China, where there is a demand for decentralized power sources, these huge-scale industrial diesel engines are often employed.
Industrial diesel engines are also classified in terms of their speed, i.e., rpm (rotations per minute). High rpm engines are used for the lighter, most common applications, like trucks and other land equipment. Medium rpm engines are used for power generation. Low rpm, high torque engines are used for the biggest equipment, such as marine applications. Some of the world's leading manufacturers of industrial diesel engines include Cummins Inc. of the USA, Mitsubishi Heavy Industries of Japan, and Sulzer Ltd. of Switzerland.