轮机英语课文

LESSON 2

DIESEL ENGINE CONSTRUCTION I

Bedplate and Frame

The bedplate, which in most cases is of the welded design, is bolted to the seating which forms a part of the double bottom of the ship. It is secured in the transverse direction by means of bolts known as side-chock bolts and in longitudinal direction by means of end chock bolts.

The crankshaft rests in bearings built into cross girders of the bedplate. These bearings, known as main bearings, each consist of two shells which are supported in housings machined in the bedplate and secured by means of studs and bearing caps. The thrust block or thrust bearing, located at the aft end of the engine, may be integral with, or separate from, the bedplate.

On the flat upper surface of the bedplate are arranged a number of A-shaped frames or entablatures which may be manufactured of cast iron or fabricated steel. The frames are mounted on and bolted to the bedplate cross girders. At the top of the A-frames there is a strong east iron frame called the scavenging air box, which is built of a number sections provided with vertical flanges 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 enclosed in a cast iron casing known 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, which are provided with vertical flanges enabling them to be bolted together in the foremost 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 with less deformation in service and lower vibration.

The cylinder liners are made of alloyed cast iron and the cylinder surfaces are sometimes chromium-plated. The cylinder liners are extend somewhat down 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 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-centre position. The ports are drilled in the liners at an angle of approx. 20o, 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. 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 groove turned in the conical 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; 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 engine. The individual cylinder running gear is made up of a piston, piston rod and connecting rod joining the single throw 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 entablature and 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 the main bearing keeps are held down by jack-bolts. This strong structure is necessary to withstand the combustion loads which pass via the cylinder head to the engine structure. The crankshaft is semi-built with the crankwebs being designed to partially balance the rotating masses. The cylinder cover is made in single piece and contains the central fuel injector, the starting air valve, relief valve and indicator cock.

Exhaust gas driven turbo-chargers operating on the constant pressure system: supply scavenge air. Loop type scavenging is employed and an electrically driven automatically operating auxiliary blower is provided for slow speed and manoeuvring operations.

Lubricating oil is supplied to a low and a medium pressure system. The low-pressure system supplies the main and other hearings. The crosshead bearings are supplied by the medium pressure system. Articulated pipes supply the oil to the crosshead bearings.

Water-cooling is used for cylinder jackets and heads and also the pistons. Telescopic pipes provide the water to the pistons,

Fuel injection uses the Jerk pump system and a Woodward type hydraulic governor 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 speeds. New features include a single wall bedplate with integral thrust block. Also the piston crown and other main components of the combustion chamber are bore cooled, i.e. by water circulating in holes holed close to the hot surfaces.

Sulzer RTA Engine

The Sulzer RTA 84C is a typical modern low-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 100 r/min. It is available with between four and twelve cylinders and is particularly produced for the large, fast container ship 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 welded 'A' frames surmounted by cast iron cylinder jackets bolted together to form a cylinder block, together give a rigid overall construction. The structure is pre-stressed by long vertical tie bolts.

Cylinder liners are of alloy cast iron. A stiff 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.

The solid forged steel cylinder cover is bore cooled to reduce thermal stress and to conduct heat from the fuel injector pockets. A centrally positioned large exhaust valve cage has its valve seat intensively cooled, taking water from the cover. The valve is manufactured of Nimonic 80A alloy and is rotated by vanes fitted to its spindle. It is opened by hydraulic pressure from a cam driven actuator and is closed under the action of an air spring.

The piston has an alloy steel crown and has five compression rings fitted in chromium plated grooves. There is a short cast iron skirt. The piston is oil cooled using both the ’s haker’method and small jets to propel oil into bore holes close to the underside of the crown and behind the ring grooves. Oil for cooling is supplied and returned through a bore in the piston rod from swinging links at the crosshead. The single piece crosshead has the piston rod bolted to its upper surface and a continuous full-length lower half, top end bearing, which is of white metal and lubricated with high pressure oil. Guide shoes are attached to each end of the crosshead.

A semi-built up crankshaft has slim webs to allow large bearing areas; maim hearing caps are secured by jackbolts from the engine frames. The main camshaft is gear driven, and is fitted with servomotors to re-time fuel pump cams and the air start distributor when operating the engine astern.

Fuel pumps are of the cam-driven valve timed type, with variable ignition timing to adjust timing and maintain efficient combustion at low speed. Each pump supplied three uncooled fuel injectors placed symmetrically in each cover. Hot fuel oil circulates the valves when not injecting.

The engine has through-scavenge and constant pressure turbocharging with a high efficiency, uncooled turbocharger supplemented at very low speeds by two constant speed, electric driven auxiliary air blowers.