• Electrical
• Diesel Engine
• Steam

Diesel Engine

The diesel engine is the most common prime mover for the electrical generator set. It is robust, and very reliable. It works on the principle of internal combustion of diesel oil. Once started, it is almost self-sufficient. All the lubrication, cooling, fuel injection, and speed control, is carried out within the diesel engine itself.

Principle of Operation

Diesel engines are designed for 2-stroke or 4-stroke operation. Emergency generators normally use 4-stroke operation so it is described here.

4-Stroke Operation

The following briefly describes the 4-Stroke Operation:

1. Power Stroke The piston is at top dead center. Diesel is sprayed as a fine mist into the hot compressed air space on top of the piston. The fuel ignites as an explosion. The air above the piston top quickly expands. The high pressure generated by the explosion pushes down the piston. The downward motion of the piston is converted to rotary motion by means of a connecting rod. This drives the crankshaft.

   Mechanically linked suction and exhaust valves at the cylinder heads are timed to open or close according to the position of the piston in the cylinder. In this instance, both the suction and discharge valves are closed.

    

2. Exhaust Stroke Due to the momentum of the turning crankshaft, the piston goes up again after passing the lowest point.

   On the upward stroke, the exhaust valves opens. The up-moving piston drives off exhaust gases.

    

3. Suction Stroke On reaching the top dead center, the momentum again causes the piston to reverse direction. The piston moves down. The suction valves open and the discharge valves close. Air is sucked into the cylinder by the down-moving piston.

    

4. Compression Stroke The piston again changes direction after reaching the lowest point. It moves up.

   This time, all the suction valves and exhaust valves are closed. The air inside the cylinder becomes compressed to a high pressure. The temperature of the air rises rapidly.

   As the piston nears to the top dead center, highly pressurized fuel is injected through an injector in the power stroke. The fuel is atomized to a fine mist and quickly ignites.

   The cycle repeats again.