The energy crisis, which started in mid-2022, promises to be long and is predicted to last for decades, requiring new solutions to old recipes. The problem is that from the old recipes for saving energy resources we know, we need to choose the optimal recipes, which have an acceptable balance between losses and benefits.

In this paper, we will look at the energy savings problem for European rail transport and its possible solution, which can be adapted to any similar infrastructure network. As a recipe for solving the problem of energy savings in rail transport infrastructure, the most effective means of saving resources that can stabilise the situation in the shortest possible time without significant investments will be discussed and proposed. And so, to start considering the issue, it is necessary to establish possible sources of energy resources saving for rail transport of the European road network. A list of consumption sources for energy savings, based on averages, is as follows (Table 1):

Table 1 – List of energy sources for rail transport in Europe

Name of energy resource

Percentage ratio

1

Electrical energy

79%

2

Diesel fuel

19%

3

Other energy and fuels

2%

Source: compiled by the author on the basis of https://rne.eu/downloads

As can be seen from this list in Table 1, the main energy sources for the European rail network are electricity and diesel. The search for a solution to the problem of energy savings in the rail infrastructure should be based on its versatility in application. For this purpose, it is necessary to establish which processes are used by rail transport to consume these resources.

Table 2 – Basic process energy costs for rail transport in Europe

Name of processes

Percentage ratio

1

Rail transport operation

65%

2

Rail infrastructure work

27%

3

Operation of additional infrastructure

8%

Source: compiled by the author on the basis of https://transport.ec.europa.eu/transport-themes_en

As a result, the data in Table 2 indicate that the main source of potential energy savings is the rail transport itself, namely its operating processes. It is now necessary to identify the list of energy inputs that make up the operation of European rail transport.

Table 3 – List of energy cost components for rail transport in Europe

Name of components

Percentage ratio

1

Traction mode of the rail train

83%

2

Runaway mode of the rail train

0%

3

Rail braking mode of the train

2%

4

Railcar train control systems

5

5

Auxiliary systems for rail vehicles

10%

Source: compiled by the author on the basis of https://transport.ec.europa.eu/transport-themes/digital-transport-and-logistics-forum-dtlf_en

From the above list in Table 3, the highest energy expenditure occurs in the traction mode of the train. This conclusion is not new to the issue, but it is necessary to build a continuous logical chain from cost to energy saving recipe. Thanks to the preceding data, the main application object of the savings recipe emerges, namely the traction mode of the train. Let us consider what parts it consists of, given the fact that diesel fuel in rail transport is ultimately used to generate electrical energy:

Table 4 – Basic energy consumption in traction mode for rail transport in Europe

Name of parts of energy costs

Percentage ratio

1

Costs of overcoming earth’s gravity

43%

2

Costs of overcoming the inertia of motion

25%

3

Costs of overcoming air resistance

22%

4

Costs of overcoming friction in the composition

2%

5

Costs of overcoming friction on the rails

3%

6

Costs of electrical losses in wires

4%

7

Magnetic loss costs in motors

2%

8

Switching loss costs in circuits

1%

Source: compiled by the author on the basis of https://alstom.canto.global/allfiles?viewIndex=0

Let’s analyse each of the above parts of the energy costs shown in Table 4 for suitability as a source of energy savings. And so, the first item is the cost of overcoming the Earth’s gravity. In this part, all limits have been reached and modernisation possibilities have been exhausted at this stage of technology development. The second item is the cost of overcoming the inertia of motion, which is not suitable for the source of energy saving for the reason that reduction of inertia can be achieved only by reducing the overall size of the train and the weight of its materials. Obviously, the overall size of the train cannot be reduced, as it has already been reduced to a minimum on European mainlines. It is potentially possible to work with the weight of the train, but only through the introduction of new construction materials, as the design itself is close to perfection. And changing the material will lead to a significant increase in production costs, which in the current economic climate will probably not have a payback period. The third point of energy costs for overcoming air resistance is the most promising in terms of energy saving and should be considered separately. From the fifth to the eighth point the energy costs are minimal and the design of the rail stock has reached perfection, having exhausted its savings potential at this stage of technology development. Consider in detail the energy consumption of the train to overcome air resistance. To visualise this, consider the animation of the acceleration process of the train, shown in Figure 1.

Figure 1 – Animation of the train acceleration process

The input conditions for the modulation of the rail train movement process in the air environment, are: the shape of the average streamlined head end, five motor cars with a total capacity of 10,000 kW and a mass of 100 tonnes each (the total loaded mass is 500 tonnes). Wind loads are not taken into account in this modulation, as they do not relate to system regularity factors. A rail train of five wagons, travelling at speeds of up to 350 km/h. The measurement reference points are from 50 km/h up to 350 km/h.

We start the analysis of the process of overcoming air resistance with the movement of the rail train in traction mode when it reaches a speed of 50 km/h, shown in Figure 2.

Figure 2 – Traction mode movements of a rail train at a speed of 50 km/h

As can be seen from the air flow diagram in Figure 2, which flows around the train at a speed of 50 km/h, there is no particular air resistance and the pressure does not exceed 1.7 kPa. As the speed of the train continues to increase, high pressure zones form at the top of the driver’s cab, under the first bogie, in the space between the cars and at the end of the train (behind the driver’s cab). These overpressure zones act as dampers, preventing acceleration and movement of the train. The nature of the overpressure zone is related to air turbulence and is studied in physics (the movement of gases through objects of different shapes). As the speed of the train increases, the following air flow distribution occurs.

Figure 3 – Traction mode movements of a rail train at a speed of 100 km/h

Considering the scheme of air flows in Figure 3, which flow around the train at a speed of 100 km/h, the air resistance is increasing, and the maximum pressure increases up to 2.6 kPa. With further increase in the speed of the train, zones of increased pressure increase in the upper part of the driver’s cab, expand under the first bogie, in the space between the cars and at the end of the train the overpressure goes out of the front parts of the car, behind the driver’s cab at the tail of the train the pressure increases due to eddies. As the speed of the train continues to increase, the process of air turbulence intensifies.

Figure 4 – Traction mode movements of a rail train at a speed of 150 km/h

At this stage of acceleration, when air flows are flowing around the train at a speed of 150 km/h, stabilization of motion directions should be noted with a slight increase in pressure in the vortex zones up to 3.2 kPa (Figure 4). However, with further increase in rail speed, the high-pressure zones retain the previous air flow pattern with the resulting stratification.

Figure 5 – Traction mode movements of a rail train at a speed of 200 km/h

At this stage of train acceleration at 200 km/h, new zones emerge in existing zones with pressure of 2.6 kPa (Figure 5), presumably with internal placement of high pressure area, where the pressure in the vortex core itself can reach up to 4.0 kPa. It is worth noting that the formed vortex nuclei are clearly visible in the air flow pattern and with further increase in velocity, there is no increase in these zones.

Figure 6 – Traction mode movements of a rail train at a speed of 250 km/h

The stabilisation of the generated airflow pattern at a rail speed of 250 km/h (Figure 6), is caused by a certain equilibrium between the rotational forces and the moving forces of the flow itself. This model can be compared to a wheel and a surface, with the wheel turning and the surface moving. The pressure in the swirling core can reach 4.2 kPa. As the speed of the rail train increases further, the process of breaking up the rotating zones of the airflow occurs.

Figure 7 – Traction mode movements of a rail train at a speed of 300 km/h

As a result of the air pressure build-up, a new airflow pattern emerges at a rail speed of 300km/h (Figure 7), created by the ruptured high pressure zones. Due to this event, the pressure increases not significantly up to 4.4 kPa, but in the entire initial region, effectively affecting the entire moving rail stock. With a further increase in velocity, the high pressure zone, which was previously the core, expands a considerable distance away from the moving rail stock.

Figure 8 – Traction mode movements of a rail train at a speed of 350 km/h

The stabilisation of the generated airflow pattern is not observed even at train speeds of 350 km/h, with eddies occurring at a distance along the train gauge and well behind the tail car (Figure 8). Thus, pressure increases throughout the train with peaks of 4.6 kPa occurring at the head end and in the space between the wagons of the train. The maximum speed for this simulation was achieved.

Analyzing the whole process of the conducted simulation, several air resistance zones with different characteristics are observed. For further analysis and interpretation of the data, the results obtained are correlated in a convenient graphical form.

As can be seen from the graph (Figure 9), there are a number of air resistance zones, which depend on the speed of the train. And so, consider each of the zones in detail. The blue “B” and green “G” zones have low air resistance and are suitable for economic operation. The yellow “Y” zone is characterised by a change in the airflow pattern with swirls and high pressure zones. The orange “O” and red “R” zones are characterised by strong eddies which counteract the acceleration and movement of the train. These zones are also characterised by high energy consumption.

Figure 9 – Air resistance zones to the movement of the train

To summarise the results, it is necessary to specify systematised figures by zone, for further analysis of the results of the modulation process taken.

Based on the information obtained earlier, the cost of overcoming the air resistance can amount to up to 22% of the total power of the rail train, i.e. 2,200 kW under our modulation conditions.

Proportionally integrating further ratios, we get the list of approximate values of reduced power consumption in relation to air resistance zones of rolling stock movement. The end point of equation is speed 350 km/h, for which the power consumption of rolling stock on overcoming of air resistance will be equal 2 200 kW. The resulting data is saved as Table 5.

Table 5 – Results of air resistance zone analysis

Code

Name of zone

Air resistance

Energy costs

B

Blue

5%

500 kW

G

Green

8%

800 kW

Y

Yellow

15%

1500 kW

O

Orange

19%

1900 kW

R

Red

22%

2200 kW

Source: Compiled by the author on the basis of calculations from previous materials

For the convenience of further analysis, the data in Table 5 are expressed graphically, with the main reference to the energy consumption in the areas where the train is moving. The main interest in this case is to determine the actual drag energy transmitted by the air flow to the rolling stock travelling on it. Figure 10 shows the results of the modulation of the process of interest, from which conclusions have to be drawn about the traffic zone that are reasonable in terms of energy savings.

Figure 10 – Results of air resistance energy modulation

Based on the data obtained, we draw the following conclusions. We have two types of train movement. The first, is the economic mode of movement, in zones “B” and “G”, animated visualisation of which is presented in Figure 11.

Figure 11 – Rail train movements in economy mode

This proposed mode is optimal in terms of resource consumption and occurs at speeds up to 150km/h. It does not require any special costs or investments, and is implemented by the usual change of traffic schedules. The reverse side of this mode of movement is the increase in time of movement of the rail train to the final station.

Now let us consider the second mode of movement, it is the high-speed mode of movement of the train in zones “O”, “Y” and “R”, animated visualization of which is shown in Figure 12. This mode is currently implemented on most European railways. It saves a significant amount of time and allows freight and passengers to move quickly to the entire mainline network. The downside of this mode of operation is high energy consumption, which ensures movement of rail vehicles at speeds of up to 350 km/h. The movement in the “Y” zone in this case is transitional, because in terms of physical processes this zone is not clearly marked, but by the nature of air resistance to the movement of the train it belongs to the second visualization.

Figure 12 – Speed train movements

This proposed mode of travel is extreme in terms of resource consumption and occurs at speeds of up to 350km/h.

Having analysed this material, we have a recipe for energy savings for European railways, where speeds on average are in the second type of speed range with “O”, “Y” and “R” zones. This recipe for saving energy is easy and requires little investment, and it can be applied right away, simply by changing the speed of rail vehicles to economy mode 1, with speed zones “B” and “G”. This recipe for saving resources will have an immediate effect, at up to 12% of the consumption of a moving rail train, which is a huge saving, but will increase the journey time to the final station. Therefore, in the end, the choice will be made by the consumer in an environment where energy is more expensive than time.

Dmitry Klyuchnikov

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