Reciprocating internal combustion engines are a widely used and well-known technology. Typically, the engine uses natural gas with a spark ignition to drive an electric generator. They range in size from 50 kilowatts to 5 megawatts. These engines are generally low-cost and have a proven reliability with proper maintenance. They are most often used for emergency generation but are also well suited for peak power needs, or combined heat and power applications for commercial and light industrial applications.