Illustrated Encyclopedia of World Railway Locomotivesby P. Ransome-Wallis (Editor), Ransome-Wallis
In this volume, noted Columbia University Professor of Architecture Cyril M. Harris offers a unique tour through the entire history of architecture: an extraordinary compendium of clear, concise definitions for over 5,000 important terms. This thoroughly accurate and comprehensive gathering of architectural knowledge is complemented by an unprecedented
In this volume, noted Columbia University Professor of Architecture Cyril M. Harris offers a unique tour through the entire history of architecture: an extraordinary compendium of clear, concise definitions for over 5,000 important terms. This thoroughly accurate and comprehensive gathering of architectural knowledge is complemented by an unprecedented collection of over 2,000 line drawings that richly illustrate significant aspects of architectural styles. Unusual cutaway views, close-ups of intricate details, and precisely rendered plans show many of the greatest architectural achievements of all time.
From ancient ruins to twentieth-century Modernism, the Illustrated Dictionary of Historic Architecture covers the full spectrum of architecture's rise and development. Subject areas include the following periods: Ancient, Islamic, Greek and Hellenistic, Mesoamerican, Roman, Romanesque, Early Christian, Gothic, Renaissance, Chinese, Japanese, Indian, and Modern. This volume is an important research tool that places particular emphasis on clarity and accuracy. For the architect, artist, historian, student, teacher, or architecture enthusiast, this valuable guide offers indispensable information and lucid illustrations covering the whole of architecture.
Read an Excerpt
Illustrated Encyclopedia Of World Railway Locomotives
By P. Ransome-Wallis
Dover Publications, Inc.Copyright © 1959 P. Ransome-Wallis
All rights reserved.
Diesel Railway Traction
by J. M. DOHERTY
Part I. Engines
The exacting and often conflicting nature of the demands made on diesel traction engines employed for main line railway service, present the engine builder with a number of difficult problems. Failure in service can cause severe dislocation to traffic, and in order to secure maximum availability the engine must be capable of working for long periods between overhauls with the minimum of attention. A high degree of robustness and durability is therefore required.
Service demands create wide fluctuations in speed and power output, and engines may be required to work at or near their maximum capacity for long periods. Furthermore, severe limitations of weight and space are often imposed. To facilitate overhaul and servicing, careful attention must be given to accessibility, and this is intimately linked with the general design of the locomotive or railcar in which the engine is to be installed.
For low-powered locomotives which are not subjected to severe weight limitations, a robustly constructed low-speed engine, naturally aspirated, is often preferred. An engine of this type gives exceptionally long life coupled with low maintenance costs. A more difficult problem arises in the case of engines required for intensive duty, and subjected to severe limitations with regard to space and weight, such as occur in high-powered diesel-electric locomotives. In these cases it has become necessary to adopt every available means for improving the power-weight ratio even when this entails an increase in cost and complication. The principal problem facing the engine builder is to meet these exacting requirements, without sacrificing reliability or unduly increasing operating expenses.
The following types of engines are employed for traction duty:
(i) Low-powered engines operating at 600–800 r.p.m. suitable for shunting (switching) and low-powered freight locomotives.
(ii) High-duty, low-speed engines, operating at 600–800 r.p.m. provided with pressure chargers (see page 31) and sometimes with intercoolers (see page 31), suitable for high-powered locomotives where ample space is available.
(iii) Moderate speed engines operating at 800–1,200 r.p.m. with or without pressure charging according to requirements, suitable for both moderate and high-powered locomotives.
(iv) Moderately powered, high-speed engines used for railcars, operating at 1,500–2,000 r.p.m sometimes provided with pressure charging.
(v) High-speed engines operating at 1,200–1,600 r.p.m. provided with pressure charging and intercooling. Used in high-powered locomotives and diesel trains of advanced design.
Camshafts may be one or two in number, depending on the design of the engine. The drive from the crankshaft is through a train of helical gears, or by means of a duplex roller chain incorporating a device which automatically maintains the chain tension. In addition to actuating the inlet and exhaust valves, the camshaft also drives the fuel pumps and engine governor.
Connecting rods are steel stampings or forgings, the small ends having bronze bushes, press fitted, working on floating gudgeon pins, which are prevented from moving endways in the pistons by means of circlips.
The crankcase forms the principal structural member of the engine, and must be very rigidly constructed to resist distortion and preserve the alignment of the crankshaft bearings. The bottom part is usually made separate from the upper part, being structurally integrated with it to form the engine bed, which incorporates the lower halves of the crankshaft bearing housings (Plate 1A, page 41).
Alternatively, the bottom part may act merely as an oil sump. With this type of construction the crankshaft is underslung, the upper halves of the bearing housings forming part of the upper portion of the crankcase (Plate 1E, page 41). Whichever type of construction is used, a rigid assembly is secured by locating the bearing caps sideways in the crankcase. Additional security is sometimes provided by means of cross ties consisting of long bolts which pass through the crankcase and bearing caps.
The cylinder blocks may be integral with the crankcase or form separate units attached by means of studs (Plate 1D, page 41). Crankcases are constructed of cast iron or aluminium alloy but for the larger type of engine an all-steel fabricated construction is often preferred, in which the transverse members are sometimes steel castings.
In the tunnel-type crankcase used both by Maybach and Saurer, the crankshaft is supported in roller bearings mounted on the crankshaft webs which are circular in shape. The crankcase is of cast iron or fabricated construction, and forms a tunnel-like structure surrounding the crankshaft, closed at the bottom by the oil sump. A short and stiff crankshaft can thus be incorporated in conjunction with a very rigid supporting system.
Another type of construction is used by Sulzer Bros, in which the fabricated crankcase is extended at one end to form a bed for the electric generator. The crankcase extends above the centre line of the crankshaft, and incorporates deep U-shaped bearing housings. Massive bearing caps are let into the housings and held firmly in position by the cylinder block, no studs being used.
Crankshafts are generally steel forgings, hardened and ground on the wearing surfaces, with separate balance weights bolted to the webs. A vibration damper is frequently mounted at the free end to damp out torsional vibrations. Four-, six- and eight-cylinder V-type engines are inherently unbalanced, and require the addition of secondary balancing systems, gear driven from the crankshaft.
Crankshaft and big-end bearings are usually of the steel-backed precision type, in which a thin layer of lead–copper bearing metal is backed by a steel shell. Such bearings, which do not require hand fitting, are nonadjustable and must be scrapped when worn. One of the crankshaft bearings is generally designed to locate the crankshaft endways, and is provided with thrust faces which bear against the webs of the adjacent cranks.
Cylinders up to eight in number may be arranged vertically (Plate 2, page 42) or horizontally in line, the latter type of construction being suitable for underfloor mounting in railcars. When more than this number of cylinders are required, the V-type of construction is generally adopted, the angle between the cylinder banks ranging from 45° to 90° (Plate 3, page 43).
The cylinders in the opposing banks may be staggered so that the two opposing connecting rods can work side by side on a common crank pin. This arrangement is used by English Electric, Mirrlees, Crossley, M.A.N., Daimler and Deutz. Alternatively, the cylinders in each bank may be in line with those in the opposite bank, thereby enabling the overall length of the engine to be reduced. When this is done the connecting rods are constructed on the fork and blade principle, or an articulated construction is adopted which causes the stroke of one piston to be slightly greater than the opposite one. The fork and blade construction is used by Paxman and Maybach, but most European builders employ the articulated arrangement.
By increasing the angle between the banks to 180° the horizontal twin bank engine is produced, which is suitable for underfloor mounting in high-powered rail-cars. The vertical twin bank engine developed by Sulzer has two parallel crankshafts driving the armature of the electric generator by means of step-up gearing so that it revolves at about 1 ½ times the engine speed.
The Napier Deltic engine, originally developed for fast motor-boats, consists of three banks of opposed piston two-stroke engines, arranged in the form of an inverted triangle, with the three crankshafts located at the corners. The connecting rods are of the fork and blade pattern. A train of gears is used to couple the three crankshafts together, and drive the main generator. The gear train also provides drives for the auxiliary generator, centrifugal type scavenger blower, fuel pumps, etc. (Plates 4 and 12A, pages 44 and 70).
Another type of opposed piston engine has been built by Fiat, in which there are four banks arranged in the form of a square with the crankshaft at the corners. Each bank contains four cylinders, and the crankshafts are coupled together by gearing.
Cylinder heads containing the fuel injector, inlet and exhaust valves, are made of cast iron or aluminium alloy, and are attached to the cylinder blocks by means of studs. When single inlet and exhaust valves are used, the inertia of the valves and valve operating mechanism may be considerable, particularly at high speeds. Most makers, therefore, provide two inlet and two exhaust valves per cylinder, when the bore exceeds seven inches. Maybach provide six valves per cylinder. The valve rocker gear for each cylinder is mounted on the cylinder head (Plate 1C, page 41).
Cylinder liners of hard, close-grained cast iron, often specially treated to reduce wear, are inserted in the cylinder blocks, where they are held firmly in position by the cylinder heads. Wet type cylinder liners are in direct contact with the cooling water, and at the lower end, a sealing ring prevents the leakage of water into the crankcase. Dry type cylinder liners are press fitted into circular housings formed in the cylinder blocks (Plate 1B and D, page 41).
Pistons which are cooled by oil under pressure are frequently constructed of cast iron. In most other cases aluminium alloy, which possesses good heat conducting properties, is used, and effectively dissipates the heat generated by combustion.
The pistons are provided with three or more cast iron piston rings which retain the compression and prevent leakage. In addition, two or more rings with oil retaining grooves are provided to distribute the lubricant, and scrape the cylinder walls on the downward stroke, so as to prevent lubricating oil entering the combustion space. One of these rings may be located just below the compression rings and the other in the piston skirt.
The first internal combustion engine to use an injection system in which the fuel oil was forced into the combustion space under pressure from a pump, was constructed in 1890 in accordance with the patents of the English inventor Akroyd-Stuart, thus anticipating by many years the system of fuel injection which was ultimately generally applied to diesel engines. This engine was developed by the firm of Richard Hornsby & Sons of Grantham, under the name of the Hornsby-Akroyd oil engine, and in 1896 a small internal combustion locomotive was constructed incorporating an engine of this type.
The Hornsby-Akroyd engine employed a comparatively low compression ratio, so that the temperature of the air compressed in the combustion chamber at the end of the compression stroke was insufficient of itself to initiate combustion. In order to achieve this, combustion took place in an unjacketed combustion chamber, communicating with the cylinder through a passage, which prior to starting was heated by a blowlamp, and afterwards maintained at the required temperature by the heat generated during combustion.
The first compression ignition engine designed so that the temperature of the air compressed in the combustion space was sufficient to ignite the mixture of fuel and air, was completed in 1897 at the Augsburg Works of M.A.N. This engine was built in accordance with the patents of Dr. Rudolf Diesel, and gave a thermal efficiency exceeding 30 per cent compared with about 17 per cent for contemporary low-compression oil engines.
Air was sucked into the cylinder as the piston descended, and compressed to about 480 p.s.i. on the upward stroke. To obtain complete atomization and to ensure adequate penetration of the dense mass of air compressed in the combustion space, the fuel oil was injected through a cam-operated valve, mixed with a jet of compressed air at a pressure of about 1,000 p.s.i.
A disadvantage of this type of engine was the heavy and complicated auxiliary equipment required, consisting of a two-stage air compressor, an intercooler, storage bottles and piping. Maximum speeds also were limited to about 500 r.p.m. With the development of the light, high-speed compression ignition engine, solid injection came into general use, and a system was developed in which the fuel oil was forced into the combustion space by means of a plunger pump, through one or more minute orifices, controlled by a spring-loaded valve, which could be adjusted to give the required injection pressure.
In Great Britain, important pioneer work in connection with the development of compression ignition oil engines was undertaken by the firm of William Beardmore & Co. of Dalmuir, who constructed an engine using solid injection in 1922. The Beardmore engine employed direct injection, the fuel being sprayed through a number of fine orifices into the top of the cylinder. With this system there was very little turbulence to assist in the distribution of the fuel spray, and to obtain the necessary degree of penetration, a high injection pressure was required. It was, however, economical in fuel consumption, and the engine was easy to start from cold.
In 1928 this firm completed two engines for a large diesel-electric locomotive built by the Canadian Locomotive Co., each of which developed 1,330 B.H.P. at 800 r.p.m. with a power–weight ratio of only 20 lb./B.H.P. Much of the success achieved by the Beardmore engine was due to the work of a talented and versatile engineer, the late Alan Chorlton, a Past-President of the Institution of Mechanical Engineers. Probably Chorlton's most notable work in this connection was the invention of the jerk fuel pump embodying in principle the system of control now generally used, in which the quantity of fuel supplied by the pump can be varied by partial rotation of the pump plunger.
FOUR- AND TWO-STROKE CYCLES
Both the four-stroke and two-stroke cycles are employed for diesel traction engines. In the four-stroke cycle one power stroke occurs during two revolutions of the crankshaft. Air is sucked into the cylinder through the inlet valve and compressed to a pressure of 500–600 p.s.i. Just before the piston reaches the top of its stroke, injection of the fuel commences. The temperature of the compressed air, which is in the region of 1,000° F, is sufficiently high to cause the mixture of fuel and air to ignite accompanied by a substantial rise in pressure. The power stroke follows, during which combustion is completed and the gases expand performing useful work. During the final stroke of the cycle the exhaust valve opens, and the burnt gases are expelled (Fig. 1A).
In the two-stroke cycle one power stroke occurs during each revolution of the crankshaft, and the admission and exhaust phases overlap. It is therefore necessary that the air should be admitted to the cylinder under pressure in order to secure effective scavenging of the exhaust gas. A pump or blower driven from the engine is generally used for this purpose, supplying air at a pressure of about 2.5 p.s.i.
When the uniflow scavenge two-stroke system is used (Fig. 1B), two or more mechanically operated exhaust valves are located in the cylinder head. Air enters the cylinder through ports in the cylinder wall uncovered by the piston at the bottom of its stroke. Compression and fuel injection take place as in the four-stroke cycle. Before the power stroke is completed, however, the exhaust valves open and the burnt gases are released at high velocity. The high exit speed of the exhaust gases induces a large volume of air to sweep through the cylinder and out through the exhaust ports, thus not only effectively scavenging the cylinder but also ensuring that the maximum quantity of air is compressed by the rising piston.
Excerpted from Illustrated Encyclopedia Of World Railway Locomotives by P. Ransome-Wallis. Copyright © 1959 P. Ransome-Wallis. Excerpted by permission of Dover Publications, Inc..
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Most Helpful Customer Reviews
See all customer reviews