Posts

CHARGE AIR COOLING AND AIR COOLERS ON SHIP

Image
Charge Air Cooling : The air density determines the maximum weight of fuel that can be effectively burned per working stroke in the cylinder, it also determines the maximum power that can be developed by the engine. The increase in air density is fractionally offset by increase in air temperature resulting from compression by turbochargers. Much of this potential loss can be recovered by charge air coolers. Charge air cooling has double effect on engine performance : By increasing the charge air density it increases the weight of air flowing in cylinder and by lowering the air temperature it reduces maximum cylinder pressure, exhaust temperature and thermal loading. Air Cooler : The most common type of cooler is water cooled design with finned tubes in a casing carrying sea water over which the air passes. For efficient cooling velocity of air should be low and cooling area large. This is obtained by making air inlet connection divergent and outlet is convergent t
Post a Comment
Read more

Crankcase Explosion? Cause, Indication and Action !

Image
CRANKCASE EXPLOSION   For a explosion to occur there must be source of air (oxygen),fuel and ignition. Under normal conditions the oil/air concentration is too weak and the possibility of ignition by heat source is too low. Crankcase oil should normally have a high flash point (above 200 C) and this must be maintained to reduce risk of explosion. CAUSES : The cause of the crankcase explosion is a hot spot or overheated part within or adjacent to the crankcase of an operating engine. A local hot spot may arise due to overheating of bearings, piston rod gland, timing chain, hot combustion gases or sparks from piston blow-past in engines where no diaphragm is fitted, or from fires in scavenge spaces. PRIMARY EXPLOSION : If a hot spot exists, some oil will come in contact with it and will be vaporized.  It will circulate to cooler parts of the crankcase and will condense to form a white oil mist. The oil droplets in this white mist are very small. If this oil mis
Post a Comment
Read more

Engine room on ship?

Image
What, that is heart for humans is the engine room for the ship. It is what which is most important something which keeps it alive to sail across. Its loud and hot and you have to watch your steps on stairs to avoid any trouble. What the book says is: On a ship, the engine room, or ER, is the propulsion machinery spaces of the vessel. To increase a vessel's safety and chances of surviving damage, the machinery necessary for operations may be segregated into various spaces. The engine room is generally the largest physical compartment of the machinery space. It houses the vessel's prime mover, usually some variations of a heat engine - diesel engine, gas or steam turbine, or some combination of these (such as CODAG; see Category: Marine Propulsion). On some ships, the machinery space may comprise more than one engine room, such as forward and aft, or port or starboard engine rooms, or may be simply numbered. On a large percentage of vessels, ships and boat
Post a Comment
Read more

TURBOCHARGERS & ITS SURGING

Image
Turbocharger Shown in the sketch is a section of turbocharger fitted on a large 2 stroke engine. It consists of a single stage, axial flow exhaust gas driven turbine mounted on a common shaft with centrifugal air compressor. Turbine : The exhaust gas enters through the nozzle ring and is then directed to the turbine rotor blades at high velocity. The nozzle ring converts the energy in the exhaust gas to kinetic energy. The turbine blades are firmly fitted on the wheel by fir tree shaped roots which give positive fixing and minimum stress concentration. The blades are held together at the free end by lace wire to dampen vibration. The nozzle ring, turbine wheel, blades and rotor shaft are manufactured from heat resisting nickel chrome alloy steel to withstand high working temperatures. The turbine casing is of cast iron with adequate water cooling spaces. In modern slow speed 2 stroke engines with relatively low exhaust gas temperatures the casings are un-cooled.
Post a Comment
Read more

Scavenging - marine diesel engine

Image
The process of exchanging the gases present in the cylinder after completion of expansion with a charge of uncontaminated fresh air is termed as scavenging. The performance of marine diesel engine depends to a large extent on the efficiency of the scavenging. There are few requirement's for that which are:  The exhaust valves should open early,in advance of the scavenge ports for the effective removal of the exhaust gases. Scavenge ports should be closed after the process of gas exchanging is carried out. Loss of fresh air escaping through the exhaust valve should be minimized. The Scavenging process is different for two and four stroke engines. It is so because in 4 stroke engine have in between opening and closing of exhaust and scavenge valves. But for the 2 stroke engine the overlap is limited and so there is always slight mixing of fresh air with exhaust gases inside cylinder. Different method's of scavenging: Scavenging can be of many types which can
1 comment
Read more

Work Of fourth engineer on ship!

Image
Fourth  Engineer being the first promotion in engine department is stumbled upon by lots of responsibilities. But they have been trained to do so in their cadet ship. The only difference now is that, they have to implement all what they have learnt at that time, to present. As per experts, 4th engineer should do his or her work, and side by side, needs to learn what other engineers are doing. But this case is valid for all engineers, because of the very basic fact that, machinery are different every time (Yes basic background remains the same), thus one cannot be utmost sure about everything. Although there are handfuls of manufacturer of machinery in the world, but they too strive for making something different every time, so that, best output can be obtained from the machines.     Work Of fourth engineer on ship: Pumps of centrifugal, screw, gear and reciprocating types are also under the working area of 4th engineer. Engine room of a ship is nothing or you canno
Post a Comment
Read more

Exhaust valve operation and maintenance

Image
Two stroke cross-head engine have a single exhaust valve mounted in the center of cylinder head. Exhaust valves open towards inside in the cylinder,such away that the gas pressure inside cylinder ensure positive closing & helps to avoid  building up carbon on the valve seat.The valve opening and closing is controlled by cam mounted on the camshaft. Modern 2 stroke cross-head engines work on hydraulically operated air spring  exhaust  valves. Now a cam operate hydraulic pump instead of the push rods in earlier versions. The pump which displaces Oil from the engine LO system operate a piston in the exhaust valve which push valve to open. Here in place of the mechanical spring there is  an “air spring”. Air at 7 bar through a non return valve goes  to the underside of the piston attach to the valve spindle. when valve open, air underneath is then compressed. When hydraulic pressure is released, the expansion of the compressed air assist in the closing of valve. Air also taken d
Post a Comment
Read more