The resulting gas is held in tanks on a train at pressures of 350-700 bar, before being fed into fuel cells. These cells are usually put together into stacks of hundreds of individual cells to give power outputs varying between 70kW and 200kW. Stacks can then be combined to give higher outputs.
In researching his PhD thesis at Birmingham University in 2013, Andreas Hoffrichter found that stack lives were comparable with DMU engines, and gave electrical efficiencies of up to 60%.
Hoffrichter closely examined well-to-wheel efficiencies and emissions for diesel, electricity and hydrogen, and took into account the distance that the fuel or energy needed might be moved. His study found that hydrogen was a suitable energy carrier for rail vehicles, and that it offered lower emissions and well-to-wheel efficiencies similar to electric and diesel traction.
He then took a diesel-electric multiple unit based on a Stadler design, and (using computer modelling on Birmingham-Stratford duties) compared it with a similar train powered by hydrogen and with a hydrogen-hybrid equipped with batteries to store energy from braking. He assumed the hydrogen came from natural gas and so emitted carbon dioxide.
Modelling showed that all three could achieve a day’s work. The hydrogen hybrid consumed 690kWh of primary energy for a Birmingham-Stratford run, while the hydrogen-only train used 1,017kWh and the diesel-electric 1,548kWh. Well-to-wheel carbon emissions were 533kg, 862kg and 1,895kg respectively (had the hydrogen come from renewable sources, the first two figures would be even lower). Vehicle efficiency as modelled was 45%, 41% and 25%, and well-to-wheel efficiency was 26%, 24% and 21%.
The hydrogen train tipped the scales at 77 tonnes, giving an axle load of 22.5t. The diesel-electric and hybrid were around 70t, giving 20t axle loads.
Alstom’s iLint multiple unit uses hydrogen as fuel and has batteries than can store energy recovered from braking, making it a hybrid. It is on test as a self-powered train, rather than one that can also take direct electrical power from overhead wires. In this way, it’s a direct replacement for conventional diesel multiple units rather than a unit that could cope with discontinuous electrification.
Alstom based the train on its established Coradia Lint DMU. It expects the same 140kph (87mph) top speed, and has tested iLint to 80kph in Germany. Hydrogen tanks and fuel cells sit on the roof of the train, while traction convertors and batteries sit under the floor. The batteries store energy from braking and supply it to boost that provided by the fuel cells when the train is accelerating.
Following its 80kph test last spring, Alstom Vice President Didier Pfleger said: “This test run is a significant milestone in environmental protection and technical innovation. With the Coradia iLint and its fuel cell technology, Alstom is the first railway manufacturer to offer a zero-emission alternative for mass transit trains. Today our new traction system, so far successfully proved on the test ring, is used on a train for the first time - a major step towards cleaner mobility in Europe.”
To make the case for using hydrogen as the secondary power on partially electrified lines, it must be combined with an EMU to form a bi-mode train. There’s a great opportunity for a rolling stock owner with redundant EMUs to use one as a test bed - indeed, Angel Trains Chief Executive Malcolm Brown told RailReview in early August that he could foresee just this.
Hoffrichter’s and Alstom’s work shows that hydrogen can replace diesel as the fuel in a train with electric transmission. It follows that it should be possible to combine hydrogen fuel cell stacks with straight electric power, as Hitachi and others have done in combining diesel engines into electric trains. Space for equipment and gas storage will be important, as will overall weight, but with most redundant EMUs comprising four cars there should be scope for conversion - at least as a test bed.
The other consideration for partially electrified lines is the effect of gaps on performance and journey times. This is another area that has come under Birmingham University’s study. It looked at the Great Western Main Line and put gaps where tunnels exist, including the 7km (4.3-mile) tunnel under the River Severn and Chipping Sodbury’s 4km (2.5-mile) tunnel.
It compared the HSTs that Great Western Railway uses on the route today with Class 390 EMUs (as Virgin uses on the West Coast Main Line) and with Hitachi’s IEP in its electric and bi-mode variants. Birmingham’s work dates from a few years ago, when IEP’s specification was changing. The Department for Transport has settled on all IEP units being bi-mode, but this doesn’t negate Birmingham’s conclusions because they show the comparison between types.
The Class 390 and electric IEP variant would need to coast through unwired sections, and so their resistance to motion as derived from the Davis Equation is important. This depends on the mass and velocity of a train.
Results gave a 112-minute journey for an HST between Paddington and Cardiff. With the line fully electrified, a Class 390 achieved 100 minutes, which grew to 103 minutes with partial electrification. Without wires through the Severn Tunnel, the ‘390’ was reduced to a low of 25kph in the tunnel (which dips at 1-in-100 before climbing at 1-in-90 towards Wales). Meanwhile, an eight-car electric IEP took 104 minutes with wires all the way and 107 minutes with gaps, while the equivalent bi-mode reached Cardiff in 105 minutes.
It’s no surprise that full electrification gives the faster journey, but even with gaps for tunnels journeys are quicker than with a diesel HST (see table, page 48). Whether the small cut in journey time is worth the cost of electrifying between tunnels and providing a new fleet is something for transport economists to debate. It’s possible that passengers might see only minimal improvements in journey times for considerable expense.
As NR plans stand, there is doubt that wires will be erected through Bath and on to Bristol. A bi-mode train on that route will run 83 miles from London to Wootton Bassett Junction on electric power, and then switch to diesel for the 24 miles to Bath and the further 11 miles to Bristol Temple Meads. That’s 30% of the Paddington-Temple Meads route under diesel power, compared with tunnels comprising 6.5% of the route between London and Cardiff in Birmingham University’s study.
In the absence of figures from modelling London-Bath-Bristol, these percentages hint that passengers will experience only a small reduction in journey times between the capital and Temple Meads, despite the cost and disruption of electrification. They should, however, see some benefit from new trains replacing HSTs that date from 1976.
TransPennine Express has ordered 19 bi-mode trains from Hitachi for use from 2019. It also has 66 Mk 5 coaches on order, to be hauled by diesel locomotives. When NR had plans to electrify the line from York through Leeds to Manchester, it would have been simple to switch the diesel locomotive for an electric one and run the coaches between Newcastle and Manchester/Liverpool. The bi-mode trains would run as electric before diverging to serve Hull or Middlesbrough with diesel.
These bi-mode trains could cope with partial electrification if, for example, revised plans meant OLE wasn’t erected through Huddersfield’s or Stalybridge’s tunnels, or through Standedge’s 5km (3.1-mile) darkness under the Pennines.
While Standedge is level, there’s a 1-in-96 rising gradient through the tunnels at Huddersfield for trains heading west. Eastbound trains must cope with a rising 1-in-145 at Stalybridge and Scout Tunnel’s 1-in-125. At Morley, an underground summit marks the switch between 1-in-410 and 1-in-500 gradients.
That makes switching the coaching stock from diesel to a straight electric locomotive very difficult, particularly westbound at Huddersfield where all TPE trains on that route stop. Switching to Class 88s provides a chance that little time might be lost because they pack a 710kW diesel engine, although their performance is considerably better when using their 4,000kW electric power.
This makes partial electrification a possibility for trans-Pennine. And there’s a similar case for the Midland Main Line, where the Department for Transport cancelled its wiring north of Kettering in July.
Bidders for the next Midland franchise will be required to procure bi-mode trains, according to the DfT. “Bi-modes will deliver passenger benefits sooner than electrification would without the disruption from putting up wires and masts along the whole route,” it said in its July public consultation document.
How much faster London-Sheffield journeys become remains to be seen. The next franchise’s bi-mode trains will run on electric power for their first 74 miles to Kettering North Junction, before becoming diesels for the remaining 90 miles to their South Yorkshire terminus. They will need sufficient diesel power to cope with MML’s stiff gradients, not least the 1-in-100 to Bradway Tunnel (a few miles south of Sheffield), that affects trains in both directions.
Partial electrification and bi-mode trains provide the possibility of filling in the missing parts later. This can deliver a substantial slug of improvements to journey times and pollution levels, by wiring the easy stretches first. It also provides the opportunity for extending current limits of electrification. This means that should the DfT be convinced to execute another electrification U-turn, then MML’s wires could be extended from Kettering to Leicester, then Derby/Nottingham, and then on to Sheffield.
Partial electrification provides a route to recover something from the mess of recent electrification projects, although there are problems still to solve, notably around pantographs if short sections of line are to be left without any constraining wire against which a pan could run.
Should raising or lowering the pantograph be left to the driver, or should it be automated to reduce the risk of human error? If automation is the way forward, should it be linked to systems such as ETCS that monitor a train’s position? Should Britain (once again) develop systems that make its trains different from others in the world?
The railway must remove its reliance on burning diesel. Hydrogen appears to satisfy many of the requirements, but it’s still to be tested within Britain’s tighter loading gauge and still to be combined within an EMU to make a hydrogen bi-mode.
Work could usefully extend to mapping how to swap from diesel bi-mode to hydrogen bi-mode in a cost-effective manner that doesn’t involve scrapping trains and building new.
Such a project could extend beyond just one train operator, and this invites some form of central co-ordination. This could fall to the DfT, but Government has a poor record of creating plans and then sticking to them. Decarbonising rail travel is a suitable strategic goal for a government. But should it embark on such a course, it must be careful not to change its mind as it’s done with electrification.
