The New Zealand Railways Magazine, Volume 1, Issue 4 (August 24, 1926)
The steam locomotive is a wonderful piece of mechanism and upon it has been built up our great railway system, but, in these days of high operating costs and keen rivalry from road transport, we cannot remain satisfied with a motive power which returns only £5 to £7 worth of train propulsion for every £100 worth of fuel consumed.
One of the most efficient prime movers to-day is the internal combustion engine, the engine which has made possible nearly all the Railway's rival forms of transport. It is, then, little wonder that so many railway engineers should strive to introduce the internal combustion engine into the field of rail transport.
The type of engine most favoured for this class of work is the Diesel or Crude Oil Engine which has a money return of £35 for every £100 of fuel expenditure.
The Diesel engine differs very considerably from the familiar petrol engine. It is simpler, stronger, slower running and cheaper in operation than the petrol engine. It uses as fuel, crude or semi-refined petroleum oil, which can be had for quarter the cost of motor spirit. No carburettors, spark plugs, magnetos, or battery ignition devices are required; fuel is simply sprayed into the cylinders and ignited by the heat of compression.
Unlike the petrol engine which draws its fuel into the cylinder ready mixed with air, the Diesel keeps the fuel and air separate until the commencement of the impulse stroke. In the case of the petrol engine the petrol and air mixture is slightly compressed in the cylinder, and at the critical moment in the cycle, is violently exploded by an electric spark admitted to the cylinder. The Diesel compresses the supporting air for combustion to a high pressure, and to a temperature sufficiently high to produce spontaneous combustion when the fuel is sprayed neat into the cylinder.
Fuel injection in the Diesel continues for some considerable portion of the stroke, with the result that the initial pressure of combustion is sustained during the whole period of fuel injection. This produces a piston impulse very similar to that of the steam engine, and enables it to work against a load at slower speeds than the petrol engine.
One characteristic of all internal combustion engines is that they require to be set in motion by some outside force before the cycle of operations can be established. In this respect, and in very slow running, the internal combustion engine is at a disadvantage compared with the steam engine which has its power at all times supplied to the cylinders from an outside source. These two principal obstacles have to be overcome in adapting the internal combustion engine to rail traction, but where necessity arises, resourcefulness generally finds a way.
The starting of the Diesel engine is now effected by any of the following means:—
(a) Compressed air,page 15
(b) Auxiliary petrol engine
(c) Storage battery electric starter.
The difficulty experienced in starting loads and running at slow speeds has been overcome by the introduction of flexible transmissions, which now place the internal combustion engine in a position superior to the steam engine. The transmission most used at present is the electric, although the hydraulic and straight mechanical are likely to command attention in the near future.
With the electric transmission, the Diesel engine applied for heavy rail traction, appears as an electric locomotive independent of a central power station and transmission system. It is directly coupled to an electric generator of somewhat unusual character.
The output from the generator is delivered direct to traction motors geared to the locomotive.
The speed of the locomotive, and power at starting or climbing grades is governed entirely by the speed at which the Diesel engine is run. Unlike the steam locomotive, the engine runs fastest at slow speeds of the locomotive, and slowest at high speeds of the locomotive. The driver controls the power and speed of the locomotive by merely opening or closing the engine throttle.
Successful Diesel electric locomotives have been running on the Continent of Europe since 1924, and are now becoming familiar sights at the New York terminals of all the main trunk railways entering that city. Experience with a dozen or more of these machines has clearly proved that the Diesel locomotive is a motive power to be reckoned with in the future of railways. Already it is having the effect of delaying action where main line electrification or extensions were contemplated. One railway, the New Jersey Central, has for the present shelved its electrification policy in favour of the Diesel electric locomotive, which they can introduce gradually and at little expense compared with straight-out electrification, which must be established with one big initial outlay.
The Diesel electric locomotive, with few exceptions, will fulfil all the functions of the straight electric locomotive, and in addition has qualities which make it superior to the straight electric. A few of the more important advantages of the Diesel electric locomotive over the straight electric locomotive are as follows:—
Elimination of central power stations and sub-stations and overhead or third rail transmission systems.
Freedom from interruption to train services through failure of power supply.
No stray electric currents from ground rails, and no interference with water mains, gas mains, electric power and telephone cables in the neighbourhood of large towns.
Thin train services and occasional specials at awkward hours can be run profitably, and without the need to keep central power stations and transmission systems in operation.
The Diesel electric locomotive is not confined to any particular area for its operation, as is the straight electric locomotive. It can operate wherever there is standard steam track.
Quite apart from the heavy cost of standard electrification, the Diesel electric locomotive returns £21 to £27 page 16 useful work for every £100 of fuel bill, whereas the straight electric locomotive returns only £10 to £15 per £100 of fuel bill.
Compared with the steam locomotive the Diesel electric locomotive has the following advantages:—
High factors of adhesion and continuous torque (turning effort).
The full horse power of the Diesel motor is always available irrespective of speed of locomotive and can be brought to bear when starting trains or climbing steep grades.
For similar axle loads and horsepower the Diesel electric locomotive can exert, at starting, a tractive effort three times greater than the steam locomotive.
It is smokeless, and operates without noise.
It eliminates the fire hazard in dry weather.
It has no unbalanced revolving parts, and is easier on the permanent way than the steam locomotive.
Two or more locomotives can be coupled together, and operated by one locomotive crew as one locomotive when multiple heading is necessary.
It eliminates coal stations, water stations and turntables.
It can carry fuel for several days continuous working.
It furnishes more hours of service per annum than the steam locomotive.
It costs only half as much for repairs as the steam locomotive, and operates for one-third to one-sixth the cost of the steam locomotive.
In view of the many transport projects at present facing the Railway Administration of this country, the foregoing facts deserve careful consideration.