Rail Engineer’s feature on hydrogen trains in the January issue (issue 159) raised the possibility that, despite its good green credentials, the rail industry’s use of rail diesel traction could soon become unacceptable. A few weeks later, Transport Minister Jo Johnson said exactly this in a speech stating that he wished to see “all diesel-only trains off the track by 2040” and saw “alternative-fuel trains powered entirely by hydrogen” to be a prize on the horizon. His speech also called on the industry to provide a vision for how it plans to decarbonise and report back by the autumn.

That recent feature on hydrogen trains concluded that, in the long-term, the replacement of DMUs by HMUs is a realistic goal. Readers may also have gathered that Rail Engineer is a fan of hydrogen. Not only does it provide zero emissions and a possible zero-carbon means of transport but, as an energy vector, it also offers large-scale energy storage to absorb excess off-peak wind power generation.

The tiny Orkney island of Eday provides an interesting example. The island has installed a 0.5MW electrolysis plant to export its surplus wind power as hydrogen to Kirkwall, on Orkney’s mainland, where it is used to power the grid.

Part of the solution

For these reasons, hydrogen has got to be part of the solution, although it cannot be the only one. As with all technologies, it should only be used when appropriate. A limiting factor for hydrogen is its energy density of 2.7MJ/litre (at 350bar on Alstom’s hydrogen iLint train) which is less than a tenth that of diesel (35.8MJ/litre).

Alstom’s iLint hydrogen train is a hybrid unit that makes clever use of a 225kW traction battery to supplement the power of its 200kW fuel cell to give the same performance and range as a diesel multiple unit train.

For much of the time, the fuel cell keeps the batteries fully charged. When accelerating, the iLint is powered by both its traction battery and fuel cell to deliver a maximum power to weight ratio of 8kW /tonne, comparable with a diesel-powered Hitachi bi-mode.

Battery-powered trains also offer zero emissions at the point of use. However, they are limited by the low energy density of batteries which ranges from 0.56MJ/litre for lead acid to 2.63MJ/litre for lithium ion. Furthermore, unlike diesel trains, batteries cannot be instantly refuelled. For this reason, battery-powered trains are generally only suitable for journeys from an electric line onto a short non-electrified branch.

Such an IPEMU (independently power electric multiple unit) application was recently trialled on the Harwich branch where it ran for 50km under electric power and 30km powered solely by battery, as described in our “Batteries included” feature (issue 125, March 2015).

Liquid Natural Gas (LNG) offers lower fuel costs and reduced carbon and particulate emissions. There is significant interest in its use on North American freight railroads, which spend around $12 billion a year on diesel. Last year, the Florida East Coast Railway became the first US railway to operate its entire mainline fleet on LNG. The company claims that this results in an eighty per cent reduction in Nitrogen Oxide (NOx) emissions. In Russia, LNG is used to power a fleet of gas turbine locomotives.

An extensive refuelling infrastructure is required for LNG-powered locomotives, which need a separate tender vehicle containing an insulated double-walled tank in which the fuel is kept refrigerated at -160°C. At 22MJ/litre, LNG’s energy density is two-thirds that of diesel and the performance of LNG trains could be comparable to diesel trains.

Alternative fuel limitations

LNG is unlikely to be a practical proposition for rail passenger units. If used to power locomotives, it would require the train to be lengthened by an extra vehicle to carry the LNG tank.

Hydrogen and battery technologies offer significant benefits, which will no doubt be developed further. However, their low energy densities will always be a significant constraint. For this reason, there is no prospect of self-powered rail traction using alternative fuels for high-power rail traction. Rail Freight Group executive director Maggie Simpson made this point in her response to Johnson’s statement. She noted that, whilst battery and hydrogen ‘may show promise for lightweight passenger trains, their application for heavy duty freight is at best unproven and setting an arbitrary deadline of 2040 could well therefore be counterproductive, damaging the case for investment’. She advised that RFG would like to see the “continued affordable electrification of the strategic freight network”.

Yet, in his call for the railway to decarbonise, Johnson expects that batteries and hydrogen will replace the diesel engines on bi-mode trains. His advisers would seem to be unaware of the fundamental constraints of these technologies. In his speech, Johnson also seemed to dismiss electrification by stating that it was “unlikely to be the most cost-effective way to secure these vital environmental benefits”.

Zero-carbon electrification

Although Johnson’s expectation that greener alternatives will replace diesel is not unreasonable for lightly used lines, this aspiration is unrealistic for busy core routes that require high-powered traction. For these, electrification is the only option that offers the prospective of zero-carbon rail traction as an increasing proportion of Britain’s electricity becomes generated by renewals. The use of wind turbines to provide all the power for electrified railways in the Netherlands shows what can be done.

Furthermore, busy electrified routes carry far more traffic than rural lines, and so offer far greater environmental benefits than alternative-fuelled self-powered vehicles.

Whilst electrification’s high initial capital cost gives it a poor business case for rural routes, this is not the case for busy main lines. The economic case for electrification is recognised by many countries that have a high percentage of their rail network electrified. These include Netherlands (76 per cent), Italy (71 per cent) and Spain (61 per cent). In the UK, just 42 per cent of the network is electrified.

Electrification offers improved passenger benefits with its greater acceleration and speed. For example, a bi-mode class 800/2 has a power to weight ratio of 11.2kW/tonne in electric mode and 6.9kW/tonne in diesel mode.

Electrification also offers enormous operational cost savings. A recent report by the Office of Rail and Road (ORR) on rolling stock costs showed that, whilst the Virgin Trains fleet portfolio includes only 15 per cent diesel rolling stock, diesel accounts for 40 per cent of its total energy costs, making it around four times the cost of electric traction. One reason for this is that, unlike diesels, electric trains can absorb the huge amount of energy required to brake a train and regenerate it back into the grid.

The high maintenance and capital cost of diesel trains is illustrated in a National Audit Office report that considered the procurement of Hitachi IEP bi-mode trains, which includes a 28-year maintenance contract. This showed that the Great Western IEPs, which frequently operate under diesel power, cost £4 million more per vehicle than the mostly all-electric East Coast IEPs.

Unnecessarily high electrification costs

The Government, not unreasonably, considers the current high cost of electrification to be unacceptable and has cut back electrification schemes as a result. The recent feature “Electrification as it used to be” (issue 158, December 2017) showed that, at today’s prices, the cost of electrifying the Great Western main line is seven times the track-mile-cost of British Rail’s East coast electrification. Whilst this is not a totally fair comparison, given changes to standards and the increase in traffic since the days of BR, it does show the need to understand why Great Western electrification cost so much.

In its report ‘A breath of fresh air: new solutions to reduce transport emissions’, the Institution of Mechanical Engineers recommended that the “DfT instructs Network Rail to develop an appropriate specification for railway electrification, which will achieve an affordable business case for a rolling programme to complete the electrification of main lines between Britain’s principal cities and ports, and of urban rail networks through our major city centres.” In making this recommendation, the Institution believes it should be possible to drive down electrification costs and is also suggesting that having a rolling programme, as is the case in Scotland, is one way of doing this.

Jo Johnson is right to suggest that hydrogen and batteries can decarbonise rail traction. However, for very real engineering reasons, they can only be part of the solution.

The politics of electrification are such that the Government is forced to make misleading statements to justify its cutbacks. For example, Chris Grayling’s recent statement that, with bi-mode trains, “we no longer need to electrify every line to achieve the same significant improvements to journeys”, ignores the laws of physics – improved journey times requires more powerful trains. An electrically powered bi-mode is almost fifty percent more powerful than a diesel bi-mode.

The industry’s response to Johnson’s call for decarbonisation solutions must focus on engineering issues. If so, it can only reach the same conclusion that the Institution of Mechanical Engineers has, which is that cost-effective electrification is the only way to deliver significant carbon and emission reductions.

This article was written by David Shirres.

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