Technology Description of Reciprocating Engine
Technology Description
2.3.1 Basic Processes
There are two primary reciprocating engine designs relevant to stationary power generation applications – the spark ignition Otto-cycle engine and the compression ignition Diesel-cycle engine. The essential mechanical components of the Otto-cycle and Diesel-cycle are the same. Both use a cylindrical combustion chamber in which a close fitting piston travels the length of the cylinder. The piston connects to a crankshaft that transforms the linear motion of the piston into the rotary motion of the crankshaft.
Most engines have multiple cylinders that power a single crankshaft.
The main difference between the Otto and Diesel cycles is the method of igniting the fuel. Spark ignition engines (Otto-cycle) use a spark plug to ignite a pre-mixed air fuel mixture introduced into the cylinder.
Compression ignition engines (Diesel-cycle) compress the air introduced into the cylinder to a high Catalog of CHP Technologies 2–3 Reciprocating IC Engines pressure, raising its temperature to the auto-ignition temperature of the fuel that is injected at high pressure.
Engines are further categorized by crankshaft speed in revolutions per minute (rpm), operating cycle (2- or 4-stroke), and whether turbocharging is used.
Reciprocating engines are also categorized by their original design purpose, such as automotive, truck, industrial, locomotive and marine. Hundreds of small-scale stationary power, CHP, irrigation, and chiller applications use automotive engine models.
These are generally low-priced engines due to the economies of scale of large production volumes.
Truck engines have the cost benefit of production volume and are designed for a reasonably long life (e.g., one million miles). A number of truck engines are available as stationary engines. Engines intended for industrial use are designed for durability and for a wide range of mechanical drive and electric power applications. Their sizes range from 20 kW up to 6 MW, including industrialized truck engines in the 200 to 600 kW range and industrially applied marine and locomotive engines above 1 MW.
There are 2-cycle engines in stationary power applications, particularly in standby service. However, most spark ignition and the diesel engines relevant to stationary power generation applications complete a power cycle in four strokes of the piston within the cylinder as shown in Figure 2-1.
1. Intake stroke – introduction of air (diesel) or air-fuel mixture (spark ignition) into the cylinder.
2. Compression stroke – compression of air or an air-fuel mixture within the cylinder. In diesel engines, the fuel is injected at or near the end of the compression stroke (top dead center or TDC), and ignited by the elevated temperature of the compressed air in the cylinder. In spark ignition engines, the compressed air-fuel mixture is ignited by an ignition source at or near TDC.
3. Power stroke – acceleration of the piston by the expansion of the hot, high pressure combustion gases.
4. Exhaust stroke – expulsion of combustion products from the cylinder through the exhaust port.
