Lesson Two Text Diesel Engine Construction (I)
Bedplate(机座) and Frame(机架) The bedplate, which in most cases isof the welded design, isbolted to the seatingwhich forms part of the double bottom of the ship.
Cylinder cover Tie rod Cylinder block A-Frame (Entablature) Bedplate Seating
It is secured (固定) in the transverse(横向的) direction by means of bolts known as side-chock bolts (侧楔螺栓)and in longitudinal(纵向的) direction by means of end-chock bolt (端楔螺栓).
The crankshaft rests(放置、坐落) in bearingbuilt into cross girders(横梁) of the bedplate.
Cross girder Bearing Housing
These bearings, known as main bearings, each consist of two shells(轴瓦) which are supported in housings(轴承座)machined in the bedplate and secured by means of studs(双头螺栓)and bearing caps(轴承盖).
The thrust blockor thrust bearing(推力轴承), located at the aft end of the engine, may be integral with, or separate from, the bedplate.
*On theflat(平的)upper surface of the bedplateare arrangeda number of A-shaped frames or entablatures(机架) which may be manufactured of cast iron or fabricated steel(结构钢).
At the top of the A-frames there is a strong cast iron frame called the scavenging air box, which is built of a number of sections provided with vertical flanges(法兰)enabling them to be bolted together to form a block for 1-3 cylinders in front of the chain transmission, and a block with 4-6 cylinders aft of the chain transmission.
The chain transmission, forming the connection between the crankshaft and the camshaft , is enclosedin a cast iron casingknown as the chain drive casing.
Cylinders and Covers On top of scavenging air box is mounted a strong cast iron frame for each cylinder.
These frames are known as cylinder blocks or cooling jackets(冷却水套), which are provided with verticalflanges enabling them to be bolted together intheforemost and aftmost groups in the same way as the scavenging air boxes.
The bedplate, frames and cylinder blocks are secured together by long tie-rods to achieve a greater rigid construction(刚性结构) with less deformation(变形)in service and lower vibration.
The cylinder linersare made of alloyed cast iron and the cylinder surfaces are sometimes chromium-plated(镀铬).
The cylinder liners are extendsomewhatdown in the scavenging air box, and sealing between the liner and the top of the scavenging air box is achieved by the rubber rings fitted into the slots machine-turned(机加工的) in the liners.
In the part of the cylinder liner inside the scavenging air box there is a series of openings known as scavenging air ports.
These ports are located at such a height that they are just exposed by the upper edge of the piston when the piston is in the bottom dead-center position.
The ports are drilled in the liners at an angle of approx. 20°, the result being that the scavenging air is given a rotary movement.
Each cylinder is closed at the top by a cylinder cover, made of a special heat-resistant steel (耐热钢).
The cover is mounted against a flat surface at the top of the cylinder liner and located on the liner by means of a machine-turned guide edge.
A sealing ring is inserted in a grooveturned in the conical(园锥形的) part of the cover. The fitting of the sealing ring in the conical surface must be carried out with great care.
The cylinder covers and the liners are bolted together by means of studs screwed into the cylinder frames.
The cylinder liner has drillings for cylinder lubrication, and, in later types, has drillings for cooling water at the uppermost part of it.
In each cylinder cover is a large central opening for mounting the exhaust valve, and two or three holes for the fuel valves.
The cylinder cover is also provided with holes for: the starting valve; the safety valve; the indicator cock(示功器旋塞); the cooling-water inlet and the cooling-water outlet to the exhaust valve cooling chamber.
Reading Material Sulzer Marine Diesel Engines
Sulzer RND-M Engine The RND-M Sulzer is a single acting slow speed，two-stroke, reversible(可倒转) engine.
The individual cylinder running gear is made up of a piston，piston rod and connecting rod joining the single throw(曲柄) of crankshaft.
The bedplate is fabricated as a double wall design with longitudinal box section girders.A-frames are mounted on the bedplate and support the entablatureand cylinder block．
The complete assembly of bedplate，A-frames and cylinder block are held together by tie rods to form a rigid structure.
To resist crankshaft-loading transverse bending(弯曲) the main bearingkeep(主轴承盖) are held down by jack-bolts(液压撑杆螺栓).
This strong structure is necessary to withstandthe combustion loads which pass via the cylinder head to the engine structure．
The crankshaft is semi-built(半总成式) with the crankwebs(曲柄臂) being designed to partially balance the rotating masses．
The cylinder cover is made in single pieceand containsthe central fuel injector，the starting air valve，relief valve(安全阀) and indicator cock．
Exhaust gas driven turbo-chargers operating on the constant pressure systemsupply scavenge air.
Loop type scavenging is employed and an electrically driven automatically operating auxiliary blower is provided for slow speed and maneuvering operations.
Lubricating oil is supplied to a low and a medium pressure system. The low-pressure system supplies the main and other bearings. The crosshead(十字头) bearings are supplied by the medium pressure system.
Articulated pipes(铰链管) supply the oil to the crosshead bearings. Water-cooling is used for cylinder jackets and heads and also the pistons. Telescopic pipes(伸缩管，套管式) provide the water to the pistons.
Fuel injection uses the Jerk pump(高压喷射泵) system and a Woodward type hydraulic governor(液压调速器) is used to control engine speed.
The RL engine is based on the RND-M and provides, with its increased piston stroke, a higher output and lower engine speed. New features include a single wall bedplate with integral thrust block.
Also the piston crown(活塞头) and other main components of the combustion chamber arebore cooled(钻孔冷却), i.e. by water circulatingin holes bored close to the hot surfaces.
Sulzer RTA Engine The Sulzer RTA 84C is a typical modern slow-speed, two-stroke, crosshead type, long stroke engine.
It has a bore of 840 mm, a stroke of 2,400 mm and an operating speed of 100r/min. It is available with between four and twelve cylinders and is particularly produced for the large, fast container ship(集装箱船) market.
Its design and construction is similar to other engines in the RTA series 2 which offer a number of cylinder sizes down to 380 mm.
A deep single wall-box type bedplate fabricated from welded steel plates and castings, and substantial(坚固的) welded ‘A’ frames surmounted(安在…顶上) by cast iron cylinder jackets bolted together to form a cylinder block, together give rigid overall construction.
The structure is pre-stressed(预加应力) by long vertical tie bolts. Cylinder liners are of alloy cast iron. A stiff(硬的) collar at the upper end resists the heavy gas load; this lands on the cylinder jacket.
It is bore cooled with water flow rates regulated to maintain correct temperatures throughout the liner. The lower end is uncooled within the scavenge space. Multi-level cylinder lubrication is used to reduce liner wear rates.