The International Steam Pages
Proposals for a Modern Steam Locomotive Design
Dominik (from Germany) has emailed me these ideas. If you want to get in touch to discuss them, please email me as below.
Steam engines need by far more fuel than diesel engines, even with the most advanced design. The only advantage in this regard is the ability to use cheap fuels like coal, crude oil or wood which are not suitable for diesel engines. The modern tourist steam locomotives of the DLM use light oil for environment reasons, this will help to reduce the pollution, but it means that the such a locomotive will need about two or three times as much of the same high price fuel as a diesel locomotive. This is surely not an attractive way of operating big locomotives, especially if the CO2 emissions are regarded.
Industrial burners for Bio Oil are already available and there is no need to develop a new one. The main difference between traditional steam locomotive firing and useful oil firing is, that the fresh air should be blown into the boiler instead of sucking out the hot combustion gases. The smokebox gases are typically twice as hot as the environment (in Kelvin), this means it will take twice as much energy to pull them out instead of blowing them in! Even with the best front end design, an injector is by far less effective than any standard fan drive, this will further reduce the energy consumption. The energy needed to pump the combustion gas (45000 kg/h) at full evaporation on the „Red Devil“ would be only about 40kW, if a fan blower were to be used! The energy losses due to exhaust back pressure from the Lempor injector are much higher. At this point, already 70kPa, back pressure is necessary, at 80 km/h, this would cause a loss of energy of more than 260 kW. As long as a locomotive is using solid fuels with a fire door in the cab, it is impossible to use a blowing fan because the combustion gases would enter the cab. For liquid fuels, there is no need for a fire door, hence there is no need for an injector.
Firebox and Boiler:
A rectangular firebox design as used for grate firing is obsolete for a liquid fuel. The best design is cylindrical, for combustion as well as for mechanical reasons. In combination with a spherical backside, the design can be simplified and will result in a lightweight stay free design which will allow higher steam pressures. Since the firebox is not deeper than the rest of the boiler, it is possible to place the firebox over the driven wheels. The steam/water separation can be done by conventional steam domes, but a design without big holes in the boiler should be better for higher steam pressure. I would prefer a solution like the „Brotan Boiler“ with many small holes which connect the boiler with a steam collection tube above the boiler.
Condensing locomotives have strong advantages, like lower exhaust pressure (higher
efficiency, enables the use of high efficient Uniflow cylinder), reduced water consumption and nearly no boiler scaling.
It is of course impossible to use an exhaust injector on a condensing locomotive, therefore fans where installed to suck the gases out of the smokebox. The lifetime of such fans is very limited because of the dirty and hot smokebox gases. The use of a blowing fan instead of a suction fan will prevent such problems.
Lubricating oil separation:
The cylinder oil has to be separated from the condensed water, this was usually not a big problem in good maintenance conditions, but it means additional cost and labour. The use of oil free cylinder will eliminate any need for oil separation.
On the condensing locomotives of the SAR, the condensers had to work in an extremely dirty environment because of the self cleaning frontend, which meant that all the char is blown in the air, a clean combustion will solve that problem.
Power consumption and weight:
Although the power consumption of all the fans on a condensing SAR Locomotive (including the suction fan in the smokebox) was lower than the losses due to the back pressure of a conventional injector, it is useful to reduce the weight and power consumption. A good compromise between condensing and not condensing locomotives is an evaporative tender. The cooling of the heat exchanger can be dramatic improved if the outer surface of the heat exchanger is wetted with water. In the past, such a tender was build, but it worked with a complicate rotating drum type cooler which dipped into a water bath. Rally cars uses a simpler way to get the same result, some water is sprayed on the intercooler to boost the performance. Such a system would enable the use of much smaller cooler and cooling fans. The cooling water can be separated from the boiler water to remain a closed cycle for the boiler. The consumption of cooling water would still be much lower than the water consumption of a conventional steam locomotive. For extreme hot days, an additional tank car may be used for the cooling water, so the size of the condenser surface and the water tank can be very small.
The condenser heat exchangers should have vertical pipes for the steam, so the steam will enter the pipes and the condensed water will run down by gravity. Such a condenser won’t need any water or steam pump and no freezing can destroy the tubes of the heat exchanger.
With these modifications a condenser will cause no more trouble and cost than any cooler of a diesel locomotive, which isn't a critical part for cost and reliability. Just some scaling might occur on the outer surface, when water will evaporate there, so some cleaning may be necessary.
No longer necessary due to carbon piston rings, Spilling steam engines show us that modern steam engines can operate without any cylinder lubrication and steam temperatures of 450°C. Another example is that of Stirling engines which used to work without lubrication as well and even at higher temperatures.
Uniflow cylinders can be very efficient if the back pressure is low, this is of course the case on a condensing locomotive. One problem with Uniflow cylinders is the very different heat expansion between the end parts and the middle of the cylinder. These problem might be solved by the use of conical cylinders, one for the front and one for the back cylinder. Conical cylinders are widespread in air-cooled flight engines which have similar problems.
When Uniflow cylinders are used, compounding is not necessary for higher efficiency, but there are some strong advantage for a compound with conventional high pressure cylinder and low pressure Uniflow cylinder. The reciprocating masses of the Uniflow cylinders can be much smaller if they don't have to work with the full steam pressure. The engine would also run more even because of longer cut offs on all cylinders. The problems of different heat expansion are lower. An intermediate overheating as well as intermediate fresh water pre heating can be applied.
The locomotive should have an auxiliary power steam engine (e.g. a spilling engine) to power the fans, water pump, compressor and generator.
Torque variations are an inherent problem of steam engines, the torque peaks reduce the usable traction effort. It could be possible to develop a fast acting electronic controlled braking system which cuts of the torque peaks when starting a standing train. This results in a very smooth starting and maximum traction effort at low adhesion values.
Variable axle load:
Steam locomotives usually needed guiding wheels to be suitable for higher speeds. If the locomotive weight is below 80 tons, four axles are sufficient to carry the complete load for most tracks worldwide, otherwise the use of guiding wheels is necessary for higher speed. For low speed and high traction, there is no need for guiding axles, so the axle load of the guiding wheels can be reduced as much as possible. At higher speed, the driving wheels should operate with a reduced axle load and a big part of the load can be transferred to the guiding wheels. Air suspension is today very often used, even in rail vehicles and enables such a feature without difficulties.
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