Reciprocating Engine Generators

Reciprocating engines (Figure 1) drive the vast majority of on-site generation. They are mass-produced by many manufacturers around the world, cost less than other distributed generation (DG) technologies, and have a fully developed sales, maintenance, and repair infrastructure. All of these factors, combined with market familiarity, decreasing exhaust emissions, extended service intervals, and long engine life, continue to make reciprocating engines the most commonly used DG technology.

Figure 1: Reciprocating engines
Reciprocating engines have been the main option for distributed generation for the past few decades. Technological advances are improving their appeal as a low-cost, reliable option. Pictured here is a 334-kilowatt lean-burn natural gas generator set from Cummins, designed to have high fuel efficiency and low emissions for peaking, prime power, and combined heat and power applications.

All reciprocating generators have two main components: An internal combustion engine that burns diesel, propane, natural gas, or gasoline and an electrical generator that converts the shaft power of the engine into electricity. Electrical conversion efficiencies for natural gas–fired reciprocating engines in the 5-kilowatt (kW) range are about 24 percent. For larger engines in the 250-kW and higher range, efficiency can exceed 33 percent. If thermal energy is recovered from the exhaust gas and the engine cooling jacket and put to use, overall system efficiency can approach 80 percent.

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