Diesel engines

Four-cycle and two-cycle diesel engines are commonly used in marine practice. They may be single or double-acting, trunk-piston type, crosshead type, opposed-piston type.

In the four-stroke diesel engines the first

stroke is called the suction stroke. The piston moves downward and a charge of air is drawn in into the cylinder through the open inlet valve.

The second stroke is called the compression stroke. The piston moves upward. The charge of air is compressed into the clearance volume. At the end of the stroke the fuel injection valve opens and finely atomized fuel oil is sprayed in the combustion volume under high pressure. The fuel oil is ignited and burns generating hot gases. Hot gases expand and push the piston down on the third stroke.

The third stroke is called the working (expansion, combustion, power) stroke. The piston moves downward. Near the end of the stroke the exhaust valve opens and part of the hot gases escape.

The fourth stroke is called the exhaust stroke. The piston moves upward. All the products of combustion are forced out. The exhaust valve closes, and the cycle is repeated.

In the two-cycle diesel engine instead of an exhaust valve there is a ring of exhaust ports. In place of air inlet valves there are scavenging ports. Here one complete cycle requires only two strokes of the piston or one revolution of the crankshaft.

Marine power plant automation

Automatic means of remote control is commonly used for engines and other equipment in marine practice. Automatic control is more accurate and continuously watchful than manual control. The automatic control results in saving of fuel, maintenance costs and out-of service time due to the failure. The main advantage of shipboard automation is the saving in operating cost as a result of a crew reduction.

The main items which can be controlled from the remote control room are: main engine, steam plant generators, auxiliary machinery, pressures, levels, temperature regulation and readings, alarms, communications, boiler service. The Bridge Control System is a control system for main Diesel

engines. The said system is used on ship with (periodically) unnamed engine room. Standardized units and operational reliability are characteristic of this system. Easy installation and a small number of spare parts are characteristic of this system as well. The fact is that starting and reversing of main Diesel engines is provided by -logic circuits.

Marine Diesel engines are fitted with a governor. The principal function of the governor is to prevent racing when the ship is pitching and the propeller is partially out of water. The speed governor regulates the speed of the turbine rotation. In conclusion a few words should be said about a pneumatic automatic boiler level control system. Its purpose is to keep drum level at a preset value by varying feed-water flow in the drum. Thus it can be seen that automation is really a subject which receives considerable attention in marine spheres.