FOUR STROKE DIESEL ENGINE WÄRTSILÄ 46F
7. Cylinder head
The cylinder head is designed for easy maintenance with only four hydraulically tightened studs. No valve cages are used, which results in very good flow dynamics in the exhaust gas channel. The exhaust valve seats are water cooled and all valves are equipped with valve rotators. The seat faces of the inlet valves are Stellite-plated. In case the engine is specified for MDF operation only, also the exhaust valves are Stellite-plated. Engines that are intended for operation on HFO have Nimonic exhaust valves.
Further information: Project Guide Wärtsilä 46
Connecting rod Crankshaft
Cylinder liner Piston
Photos courtesy of Wärtsilä Corporation
Direct Water Injection (DWI) Differential Global Positioning System (DGPS) – An advanced form of GPS navigation
which provides greater positioning accuracy than the standard GPS. DGPS relies on error correction transmitted from a GPS receiver placed at a known location. This receiver, called a reference station, calculates the error in the satellite range data and outputs correction for use by mobile GPS receivers in the same locale. DGPS eliminates all the measurement errors in the satellite ranges, enabling a highly precise position calculation.
Diffuser – A chamber, which surrounds the impeller of a centrifugal pump or a compressor, in which some of the kinetic energy of the fluid is converted into pressure energy due to an increasing cross-sectional area of the flow path.
Digital – Referring to data in numerical form.
Digital display – A display in which the measured quantity is given in digital form.
Digital selective calling (DSC) – A technique using digital codes. It enables a radio station to establish contact with, and transfer information to, other stations complying with the relevant recommendations of the International Radio Consultative Committee (CCIR).
Diode – An electronic power component which allows for a flow of current in one direction only; from anode to cathode.
Direct Current (DC) – This is electrical current that does not alternate, the electrons flow through the circuit in one direction. As a result, DC does not generate reactive power.
This means that, in a DC system, only real (or active) power is transmitted, making better use of the system’s capacity. In order to transmit electrical power as DC, the alternating current generated in the power plant must be converted into DC. At the other end of the process, the DC power must be converted back into AC, and fed into the AC-transmission or distribution network. The transmission of DC current has very low losses. In the conversion between the two forms of power, known as rectification, incurs additional power losses and so it is worth while only when these losses are less than would be incurred by AC transmission, i.e., over very long distances (~1000 km for overhead lines,
~100 km for underwater).
Direct drive – A propulsion system arrangement where the engine is directly coupled to the shaftline. It is usually applied on low-speed engines.
Direct expansion system – A refrigeration system in which the refrigerant expansion occurs due to the direct absorption of heat from the primary medium to be cooled.
Direct Water Injection (DWI) – The method used for reduction of NOx emissions by the injection of water directly into the combustion chamber via a separate nozzle: 50-60%
NOx reduction with some fuel consumption penalty. The key element in the design concept is the combined injection valve through which both fuel and water are injected.
One needle in the combined nozzle is used for water injection, and the other one for fuel injection. Water injection starts before fuel injection in order to cool down the combustion space to ensure low NOx formation before fuel ignition. A high pressure water pump is used to generate water pressure of 200 – 400 bar. After filtration and dampening of pressure pulses, the water is fed to the injectors via a pressure regulating valve to provide the correct injection pressure. Water injection timing is electronically controlled and can easily be adjusted from a keyboard. The amount of water injected, i.e. the water/fuel ratio, is controlled by duration of injection. The DWI was an intermediary step used to comply with the Class 1 requirements. Other technologies such as NOx Reducer, exhaust gas recirculation (EGR) and Natural Gas as a marine fuel will need to be utilized in the future to meet the tighter emissions regulatory requirements.
Direct-printing telegraphy – Automated telegraphy techniques which comply with the relevant recommendations of the International Radio Consultative Committee (CCIR), (SOLAS).
Direction of rotation of a propeller – When viewed from astern, if the propeller revolves in a clockwise direction when going ahead, it is known as right-handed. If in an anti-clockwise direction, it is left-handed.
Disabled ship – A damaged or impared vessel not able proceed by its own.
Disc grinder – Any machine that grinds by the action of a rotating disc.
Discharge – Any release from a ship including any escape, disposal, spilling, leaking, pumping, emitting or emptying.
Discharge book – An essential document for officers and seamen as it serves an official certificate confirming their sea experience in the employment time.
Discharges – Any piping leading through the ship sides for conveying bilge water, cooling water, drains, etc.
Discontinuity – An interrption of the typical structure of a material, such as lack of homogeneity in its mechanicall, metallurgical, or physical characteristics. A discontinuity is not necessarily a defect.
Discreet Security Alert System – The purpose of this system is to send a covert signal from a ship which will be not obvious to anyone on the ship who is not aware of the alert system.
It is of use therefore in circumstances where a ship wishes to inform a person ashore of a problem with a minimum number of persons on board aware of the action. Besides the security alert function the DSAS can also be used to locate the ship throughout the world in a reliable manner.
Disembark – Refers to any time that the crew leave the ship, be it a port call or final destination.
Displacement – It is the weight of water displaced by this vessel at any waterline. It is the product of the volume of its underwater portion and the density of the water in which it floats.
Displacement curve – A curve showing the displacement of a vessel in fresh or salt water at any draft.
Displacement pump – A pump operating by the reduction or increase in volume of a space by mechanical action which physically moves the liquid or gas.
Displacement vessel – A craft that is supported by the buoyancy of the water it displaces.
Displacement water – Water added to the separator bowl to displace the oil and to ensure there is no loss of oil at sludge discharge.
Display – Means by which a device presents visual information to the navigator, including conventional instrumentation.
Dissolved gases – Any gas present in water. It may be released when boiled.
Dissolved solids – Any impurities existing in pure water either produced by an evaporator or used as boiler feed water.
Distillate