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Engine Drive Systems: Options - Reciprocating

Natural gas-fired reciprocating engines are used extensively in the natural gas industry. Their primary application is as prime movers to drive compressors in the production, processing, transmission, and storage segments of the natural gas industry. Engines also drive electrical generators to meet station backup or primary power requirements.

In this module three types of reciprocating engines will be discussed: the Otto-cycle engine which is the familiar gasoline engine used in automobiles and small airplanes, the semi-industrial engine which is a diesel-cycle engine, and the industrial engine which is a sleeved engine.

All three types of reciprocating engines produce work using an internal combustion 2 or 4 stroke cycle. The following figure shows a four-stroke Otto-cycle engine.

During the intake stroke, air and fuel (mixed outside the combustion chamber in the carburetor) are drawn (naturally aspirated) or forced (turbocharged) through the intake valve. This mixture of fuel and air is then compressed on the compression stroke. Next, a spark form a spark plug ignites the air/fuel mixture. The rapid pressure buildup of the burning gases forces the piston down towards bottom dead center. On the exhaust stroke, the burned gases are pushed out of the cylinder through the exhaust valve as the piston travels back towards top dead center.

Diesel engines operate differently than the gasoline engine, although the four-cycle strokes are basically the same. On the intake stroke, only air is drawn or forced into the compression chamber. On the compression stroke, the air is compressed and therefore heated; just before the piston reaches top dead center, fuel is injected under high pressure. The air/fuel mixture is ignited by the heat of compression at the beginning of the power stroke. A diesel engine is illustrated below.

Otto-cycle engines are low cost gasoline-derivative automotive engines which are generally rated at less than 200 hp. They have higher operating speeds and lighter construction. Typically, it is less expensive to replace rather than overhaul or rebuild gasoline-derivative engines.

Semi-industrial engines are diesel-derivative and are generally much larger than automotive engines. They generally cost more than automotive engines but less than the industrial grade engines. They are able to displace more heat than the Otto-cycle engine and operate at medium speeds. Traditionally, these engines are larger, heavier, and are designed to be overhauled or rebuilt.

Industrial grade engines are heavy duty diesel-derivative engines. These engines operate at slower speeds and have a longer life expectancy. The cylinder walls and wear components have a sleeve that goes through the engine hole, making repairs quick and easy by simply replacing the entire sleeve of components. The drawback of these engines are the size and weight of the engines as well as the high purchase cost.

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