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Cylinder Combustion in Marine Diesel Engines Fuel oil is a hydrocarbon consisting of hydrogen and carbon, together with other elements most of which are unwanted. Hydrogen has a higher calorific value than carbon, therefore, more heat may be obtained from fuels containing higher Hydrogen/Carbon ratios. The lower specific gravity of hydrogen than carbon allows a rough rule of thumb to be; the higher the Specific Gravity, the lower the Calorific Value (and quality) of the fuel. The presence of impurities clouds the issue slightly For efficient combustion an ignition source and sufficient oxygen need be present to completely oxidise the Hydrogen to water vapour and the carbon to carbon-dioxide. The combustion is required to occur in a short period of time in an internal combustion engine, there are five essential requirements to ensure this: 1. Correct Air/fuel ratio  -There must be sufficient oxygen to burn not only the hydrogen and oxygen present but also any othe...

A simple mechanical governor must overcome friction in the linkages and exert a control force. These forces act in different simple servo is however unstable because the pilot valve allows full oil to the servo or it drains the servo thus giving full fuel on or off conditions. Stability could be provided by making the value larger than the servo supply ports. This would however reintroduce a dead band. The solution is to provide feed back from the fuel linkage and this comes about with speed droop i.e. graph of % speed against engine load directions depending upon whether the load is increasing or decreasing. This in fact produces a dead band in which the governor will not exert any fuel control. By having the rotating weights only move a pilot valve which directs oil to or from a servo. The control force and friction forces are eliminated and hence the dead band is removed. The Speed control is carried out by varying the main spring tension acting on the flywheels. Feed b...

Rotation of camshafts in an engine may be by gears or by chain turned by the main crank. The disadvantage of using gears is difficulty in alignment, lubrication and disadvantage to wear from foreign materials as well as their increased cost.The disadvantage of chains is the requirement for tensioning and their finite life. Although for large installations this can be very long. Wear on the chain pins, bushes as well as the chain sprockets can all lead to a slackening off of the chain. This can lead to 'slap' and changing of cam timing.This alters the leads of the fuel p[umps and exhaust valves.. The degree of angular displacement by checked using a manufacturer supplied poker gauge. Chain damage occurs if the chain is too tight or too slack and the result is fatigue cracking of the links. If the tension is too tight, then this adds to the working stress of the chain. Insufficient tension leads to 'slap' with resultant damage to chain and rubbing strips. Vertical...

AIR COOLER TUBES FAILURE Reasons for Turbo charging are: 1. Increased air charge density permitting more fuel to be burned. 2. Increased engine output. 3. Reduced thermal load on engine mechanism. 4. Improved Scavenge efficiency of engine Turbocharger is compressing the air thus an increase in charge air temperature will transpire. This will trim down the density of the air entering the engine. To reduce this effect the air is cooled. This is the function of the Air cooler. Cooling the air also reduces the thermal load. The volume and density of scavenge air establishes the maximum amount of fuel that can effectively be burned in a diesel engine. An efficient heat transfer across the air cooler will lower the air temperature whereby increasing the density, which ultimately results in an increase in air compression, mean effective pressure and combustion rate. This will eventually also lead to reduced specific fuel consumption and NOX emissions. However, scavenging air dra...

THE ENGINE FRAME: The engine frame of a modern 4 stroke medium speed diesel can be produced as a single casting or fabricated from cast steel sections and steel plates welded together. With this design, there is no separate bedplate, frame and entablature as with a 2 stroke slow speed engine. The photograph above shows the frame of an engine with the liners and crankshaft in place. An alternative method of construction consists of a separate bedplate, which is bolted to an entablature which holds the underslung crankshaft. When the Crankshaft is underslung, the load on the bearing caps is transferred back to the frame by the use of tie bolts. Note the use of the side tie bolts - which locate the bearing cap, and prevent sideways movement. THE CONNECTING ROD : The connecting rod in a medium speed 4 stroke engine is subject to an inertia whip loading due to the mass of the con rod swinging about the piston pin. (Because of the lower speed of a 2 stroke engine...

MARINE DIESEL ENGINE STRUCTURE THE BEDPLATE : The Bedplate is the foundation on which the 2 stroke engine is built. It must be rigid enough to support the weight of the rest of the engine, and maintain the crankshaft, which sits in the bearing housings in the transverse girders, in alignment. At the same time it must be flexible enough to hog and sag with the foundation plate to which it is attached and which forms part of the ships structure. If the bedplate was too rigid, then as the hull flexed, the holding down bolts, which secure the engine into the ship would be likely to break, and there would be a danger of the bedplate cracking. Basically the bedplate consists of two longitudinal girders which run the length of the engine. Connecting these longitudinal girders are the transverse girders which are positioned  between each crankshaft throw, and either side of the thrust collar. Built into the transverse girders are the main bearing pockets for the cranksh...