Industrial engines can be as small as 40 or 50 kw or as large as several megawatts. Today, continuous duty applications are dominated in southern California by the spark ignited engine for air quality reasons. Emissions from reciprocating engines using diesel oil as a fuel are difficult to sufficiently control. Reciprocating engines can provide useful heat in the form of hot water and larger engines can provide 15 psig steam. A modest amount of high pressure steam can be generated from the exhaust heat.
Reciprocating engines have decent efficiency even in the smaller sizes.
Reciprocating engines are well understood technology with a large existing service infrastructure. Reciprocating engines start rapidly and deal well with load transients. Reciprocating engines are relatively inexpensive.