Fresh and sea water cooling systems for marine diesel engines

Fresh and sea water cooling systems for marine diesel engines

Engines are cooled by flowing a cooling liquid through internal tubes. The cooling liquid is therefore heated and chilled by a sea water circulating chiller. Without appropriate cooling, certain engine parts that are subjected to extremely high temperatures as a result of fuel combustion might fail prematurely.

Cooling allows the engine metals to keep their mechanical characteristics. Because of its corrosive nature, salt water is not commonly utilized as a cooling. Lubricating oil is sometimes used for piston cooling because leaks into the crankcase are not a concern. Yet, because of its lower specific heat, approximately twice as much oil than water would be required.

Piped water is used to cool machinery. The primary engine is cooled by two independent but related systems: an open system (sea-to-sea) in which water is taken from and returned to the sea (seawater cooling), and a closed system in which freshwater is circulated around an engine casing (freshwater cooling).

Freshwater is used directly to cool machinery, whereas seawater is utilized to cool freshwater that has passed through a heat exchanger. A unique aspect of an engine cooling system is continuous fluid flow. Fluid motion promotes abrasive corrosion and erosion. To lessen the effects of turbulent flows, seawater systems integrate large diameter mild steel pipes, the ends of which exit to the sea through sea chests with gate valves.

If a seawater cooling line explodes, both suction and discharge valves must be closed to prevent engine room flooding. Open and close the valves at regular, perhaps monthly, intervals to ensure they work properly when needed. Seawater pipes are typically made of mild steel, however galvanized steel, copper, or copper alloy are also used. Freshwater cooling pipes are typically composed of mild steel.

Fresh water cooling system

Figure depicts a water cooling system for a low-speed diesel engine. It is separated into two systems: one for cooling the cylinder jackets, cylinder heads, and turbo-blowers, and the other for cooling the pistons.

After exiting the engine, the cylinder jacket cooling water is sent to a seawater-circulated cooler and then to the jacket-water circulating pumps. It is then pumped around the cylinder jackets, cylinder heads, and turbo-blowers. A header tank in the system allows for system expansion and water make-up. Vents are connected from the engine to the header tank to allow air from the cooling water to escape. A heater in the circuit circulates hot water to help warm the engine before starting it.

The piston cooling system uses similar components, except that a drain tank is utilized instead of a header tank, and the vents are then routed to high locations in the machinery space. A separate piston cooling system is employed to limit pollution from piston cooling glands to the piston cooling system exclusively.

Sea water cooling system

Sea water cools the numerous cooling solutions that circulate the engine. Individual coolers are used for lubricating oil, jacket water, and the piston cooling system, with each cooler being circulated by sea water. Several modern ships have a 'central cooling system,' which consists of a single huge seawater-circulated cooler. This cools a supply of fresh water, which is subsequently circulated to the other Individual coolers. Corrosion concerns in this system are greatly decreased because there is less equipment in touch with sea water.

One of a pair of sea-water circulating pumps draws sea water from the suction and circulates it through the lubricating oil cooler, the jacket water cooler, and the piston water cooler before dumping it overboard. Another branch of the sea water main provides sea water to directly chill the charge air (for a direct-drive two-stroke diesel).

While in port, the upper sea suction valve is utilized to keep dirt and sand out of the cooling system. It is also utilized when sailing in shallow waters. When traveling in deep water, the lower sea suction valve prevents air from entering the cooling system when the ship is rolling or pitching.

Central cooling system

The sea water circuit in a central cooling system is made up of high and low suctions, usually on either side of the machinery space, suction strainers, and many sea water pumps. The sea water is cycled through the central coolers before being released overboard.

The fresh water system has both a low-temperature and a high-temperature circuit. The fresh water in the high-temperature circuit circles the main engine and may be used as a heating medium for an evaporator if necessary. The low-temperature circuit circulates the primary engine air coolers, lubricating oil coolers, and all other heat exchangers. A regulating valve regulates the mixing of water between the high-temperature and low-temperature circuits. A temperature sensor generates a signal.

The benefits of a central cooling system include: less maintenance due to the fresh water system having cleansed treated water fewer salt water pumps with attendant corrosion and fowling concerns simplified and easier cooler cleaning Higher water speeds are feasible with a fresh water system, resulting in smaller pipe dimensions and lower installation costs.

The number of valves made of expensive materials is considerably decreased, and cheaper materials may be utilized throughout the system to maintain a constant level of temperature, regardless of seawater temperature, no cold startings, reduced cylinder liner wear, and so on.