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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, or (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 downward 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 graphic below shows the step-by-step process.
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.
 Diagram showing the four cycles in a spark-ignited reciprocating engine: intake, compression, power, and exhaust. In the intake phase, as the piston moves downward 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 forces the piston down, thereby turning the crank shaft and producing power. In the exhaust phase, the piston moves back up to its original position and the spent mixture is expelled through the open exhaust valve. |
Commercially available reciprocating engines for power generation range from 0.5 kW to 6.5 MW. Reciprocating engines can be used in a variety of applications because of their small size, low unit costs, 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 in power generation include continuous or prime power generation, peak shaving, back-up 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 bio-fuels. Reciprocating engines also make up a large portion of the combined heat and power (CHP), or cogeneration, market. Cogeneration accounts for 7% of the electricity produced in the United States and approximately 6% (200 MW) of worldwide capacity annually.
For more information, visit the DOE Gas-Fired Reciprocating Engines Web site.
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