U.S. Department of Energy - Energy Efficiency and Renewable Energy

Advanced Manufacturing Office – Industrial Distributed Energy

Gas-Fired Reciprocating Engines

The reciprocating, or piston-driven, engine is a widespread and well-known technology. Also called internal combustion engines, reciprocating engines require fuel, air, compression, and a combustion source to function. Depending on the ignition source, they generally fall into two categories: (1) spark-ignited engines, typically fueled by gasoline or natural gas, and (2) compression-ignited engines, typically fueled by diesel oil fuel.

The four-stroke, spark-ignited reciprocating engine has intake, compression, power, and exhaust cycles. In the intake phase, as the piston moves down in its cylinder, the intake valve opens, and the upper portion of the cylinder fills with fuel and air. When the piston returns upward in the compression cycle, the spark plug emits a spark to ignite the fuel-air mixture. This controlled reaction, or "burn," forces the piston down, thereby turning the crank shaft and producing power.

The compression-ignition engine operates in the same manner, except the introduction of diesel fuel at an exact instant ignites in an area of highly compressed air-fuel mixture at the top of the piston.

In the exhaust phase, the piston moves back up to its original position, and the spent mixture is expelled through the open exhaust valve.

The graphic below shows the step-by-step process.

Illustration of the intake, compression, power and exhaust cycle in four-stroke, spark-ignited reciprocating engine.

Commercially available reciprocating engines for power generation range from 0.5 kilowatt (kW) to 6.5 megawatt (MW). Reciprocating engines can be used in a variety of applications because of their small size, low unit cost, and useful thermal output. They offer low capital cost, easy start-up, proven reliability, good load-following characteristics, and heat recovery potential. Possible applications for reciprocating engines include continuous or prime power generation, peak shaving, backup power, premium power, remote power, standby power, and mechanical drive use. When properly treated, the engines can run on fuel generated by waste treatment (methane) and other biofuels.

For more information, please visit theĀ Advanced Reciprocating Engine Systems page.

For information about DOE accomplishments in this technology area over the last decade, please see Combined Heat and Power: A Decade of Progress, A Vision for the FuturePDF.