Main Engine Systems
Lubricating Oil System
The engine lubrication system, with exception of cylinder lubrication, is supplied by one of two main pumps, which take suction from the sump tank and supply oil to the low pressure main bearing system. One of two crosshead lubrication pumps takes suction from the main bearing system, after the automatic back flush filter, and supplies the crosshead bearings and bottom end bearings with oil at increased pressure.
Main Bearing Oil System
Main bearing system oil, at an operating pressure of 5.5kg/cm2, is also supplied to the pistons at 2.5 – 3.5kg/cm2 in order to act as a coolant for the working piston crown; supply is to the crosshead, via a toggle lever pipe arrangement, and then to the piston via the hollow piston rod. The integrated crankshaft vibration damper (axial detuner) and the balancer are also cooled with bearing oil. Main bearing and crosshead oil systems are interconnected through a non return valve which allows oil to pass from the low pressure main bearing system to the high pressure crosshead system should pressure fall in the crosshead system. This means that should the crosshead bearing oil pumps fail, then the crosshead oil system may be supplied with oil from the main bearing LO system pumps. Under such conditions, the engine can only be operated at reduced load (Load indicator position, maximum 4.5).
Crosshead Bearing Oil System
The operating pressure of the crosshead bearing oil is 10-12kg/cm2, the supply to the crosshead is via a toggle lever pipe arrangement. High pressure crosshead bearing oil is also used to lubricate the connecting rod bottom end bearings, supply to these being via holes drilled in the connecting rods. The high pressure crosshead system also supplies oil for the engine reversing servomotors and as make-up for the exhaust valve actuator system. For actuating the exhaust valves, the oil pressure is raised by the actuator pumps to about 160kg/cm2.
Cylinder Lubrication System
The power dependent lubrication of the pistons, cylinders and exhaust valve spindles is performed by a separate cylinder lubrication system.
Cooling Water System
The engine is cooled by means of chemically treated fresh water and this cooling water must be treated with an approved cooling water inhibitor to prevent corrosive attack, sludge formation and scale deposits in the system. A central cooling system is employed to maintain the correct temperatures in the fresh water and lubricating oil systems of the main engine, generator engines, air compressors and auxiliary services.
Cooling Water System Description
The cooling water supplied by the jacket cooling water pump is divided into two separate streams, the separation being made after the jacket water preheater. One stream, comprising of about 15% of the total cooling water flow, bypasses the cooler and is led directly to the engine; this is designated as the basic cooling stream. This basic stream provides a minimum water flow to the engine cooling system. The main cooling water stream comprises about 85% of the total flow and this passes through the main jacket cooling water pipe to the engine cooling inlet. Some of this stream passes through the jacket water cooler, an automatic temperature control valve regulates the water flow through the cooler in order to keep the engine cooling water outlet temperature constant at 90ºC. Cooling water leaving the engine flows back to the pump suction, the line incorporates an automatic fl oat ventilation valve which removes air from the system. In order to allow for make-up of water leaking from the cooling system, a buffer tank, pressurized by compressed air from the service air system is provided, this has a connection with the flow return pipe just before the pump suction. The buffer tank water level is maintained by automatic starting and stopping of one of the two main engine high temperature circuit feed pumps which take suction from the jacket water feed and drain tank. The main cooling water flow to the engine connects with a three-way diverting valve. Load dependent control of the three-way diverting valve is made by remote control according to the engine load and speed. The three-way diverting valve distributes the water flow according to the load control command, one part of the flow going to the primary engine cooling water piping and the other part to the secondary engine cooling water piping. From the three-way valve the primary water stream passes through a connecting pipe to mix with the basic cooling stream from the jacket water circulating pump. This combined stream acts to cool the cylinder liners, the stream entering at the bottom of each cylinder liner cooling jacket and passing upwards to the top of the liner jacket space. After the three-way valve, the secondary stream flows directly into the water guide jackets via the engine secondary flow pipe. At this point primary and secondary streams unite and cool the cylinder heads as well as the exhaust valve cages.
From the valve cages the engine cooling water flows into the outlet collector main, where the cooling water is led through an air separator, which is permanently vented by an automatic vent valve. The tracing water flow is led to the buffer tank via a tracing water return pipe. In order to prevent thermal stress in the engine cooling system components the cooling water outlet temperature should be maintained as steady as possible under all load conditions. Maximum admissible fluctuations are at constant load ± 2°C and during load changes ± 4°C
Fuel Oil System
The fuel oil is delivered to the injection pumps through a supply pipe, a booster pump ensuring that adequate fuel is always available at the injection pumps. The fuel quantity delivered by the booster pump is considerably greater than that actually required by the engine; the surplus fuel is led via a booster return pipe back to the system mixing unit, from which the booster pump takes its fuel oil suction. The specified booster pressure is adjusted by means of a pressure-retaining valve located in the fuel return pipe from the engine. The main engine is designed to operate on heavy fuel oil during manoeuvring. All pipes to the fuel distributors on the cylinder heads are provided with trace heating and are insulated. Fuel distributors and injection valves are kept hot by circulation of heated fuel oil from the booster pump. Each distributor is provided with a priming valve to enable the system to be primed with fuel oil following the replacement of injectors. For reasons of safety, all high-pressure pipes are encased by a metallic hose. Any leakage is contained and directed to an alarmed tank.
Circulation System
Injection valves and fuel distributors are kept hot by circulation of heated fuel. For each cylinder there is a separate sub-system. A hot fuel circulating line is taken from the engine’s fuel supply pipe and the hot fuel oil is circulated through the cylinder fuel injection pump, the fuel injectors and the fuel distribution block. After fl owing through these, the fuel enters a return circulating line and then passes into a common return pipe. This common return pipe is connected to the booster return pipe via an orifice, located after the pressure-retaining valve and so the fuel used for injector and distributor heating can flow readily back to the mixing unit.
References:
Machinery Systems Operating Manual
by Iran Hengam