MODERN steam locomotives can provide an economic
alternative to diesel traction units and steam should once again be considered
as a viable form of motive power on the rail network.
That was the main thrust of a thought-provoking lecture given at IMechE
headquarters last week by a respected rolling stock engineer who has proved
the effectiveness of new steam locomotives on the Swiss railways.
Roger Waller is chief executive officer at engine builder Darnpflokomotivund Maschinenfabrik DLM. For 11 years, he has been applying modern steam technology to locomotives with astonishing results.
The locomotives, which have been carrying tourists or the picturesque Brienz-Rothorn Railway at inclines of up to 1:4, feature one-man operation, light oil firing, high superheat, all-welded lightweight construction and a unique preheating device. And Waller says the combination gives economical and clean traction fully competitive with diesel motive power.
Improved version
Most of the shortcomings of traditional steam traction have been eliminated on these modern locomotives. In operational readiness, availability and personnel costs they can match diesel and electric traction. Fuel costs now amount to a very low percentage of the operating costs and with the new oil fired locomotives, environmental nuisance is no longer a problem.
The fact that the operating costs of new steam locomotives are not higher than those of good diesel locomotives opens up a new field of applications. Whereas the use of modern steam has been explained by the needs of tourism, it can now be considered for other purposes as well. Waller and his team have designed a new rack steam locomotive to overcome the problems of traditional steam rolling stock. First, it was decided to make the new model oil fired, using light oil rather than heavy. A new firing system has been developed, with an enlarged, square-shaped firebox with four main burners to provide uniform loading. To ignite the main burners, there is a pilot burner in the middle, which is also used for standby and shunting.
Development work in its truest sense was needed to tune up the oil firing system to the required standard," says Waller. "With the first attempt, the combustion was awful, producing a lot of smoke. The airflow around the burners had to be changed radically. With these and other modifications, very clean combustion was achieved." Oil firing and weight limitations dictated an all-welded boiler. This is bolted to the cylinder block at the smoke box and rests on two swing-plates at the foundation ring to allow for thermal expansion. For feeding the boiler, the century-old system of the mechanical feed pumps was reinvented in a modern form. The feed pump is belt driven from a toothed wheel on the crankshaft. It delivers the feedwater taken from the side tanks via air exhaust steam heater to the side of the check valve. The boiler has no steam manifold, with auxiliary steam extracted at the dome.
Elementary changes
The regulator fitted in the dome is a commercial valve which allows finely graduated operation thanks to its special geometry. After the regulator, the steam passes through the regulator pipe, before being delivered to the superheater.
Waller adds: "Initial thermodynamic boiler calculations showed that superheating with elements in six series stages is necessary to achieve the desired steam temperature of 420oC. This called for special arrangement of the superheater elements, with superheated steam fed directly to the cylinders."
Another important technical achievement was the electric feedwater preheating device to improve operational readiness and to save man-hours for preparation. Water from the boiler flows by gravity to the circulation pump, which forces it through the electrical heater bask into the boiler. The forced circulation causes extremely uniform heating. The electric preheating device warms up the water slowly to the temperature set on the control thermostat.
The preheating device for the new rack steam locomotive is rated at 25kW. When starting with cold water, it takes 12-16 hours to reach 10 bar. The intention, is to preheat a cold loco overnight, ready for the morning. The heating device is then detached.
Waller says his team introduced many other technical improvements including work on a new design of steam engine and valve gear, frames, springs and drives, the exhaust system, brakes and electrical equipment.
The new steam locomotives are operated without a fireman, reducing staff costs to the level of diesel and electric traction.
Waller has carried out many cost comparisons
with diesel and electric locomotives, and the steam loco has proved as least
as economical. Workload trials have proved reliability.
The engine has been adapted and fitted to a paddle ship and Waller says
new applications may follow.
Until the end of February Wallet's paper - "Modern Steam: an economic and environmental alternative to diesel traction" - can be downloaded in pdf format from www.imeche.org.uk website, under the railways division heading.
Page created: 9 Sept 2003