Fuel use is ever topical. Fuel economy is perhaps less so. Our Leaders’ advice, in the face of the hint of industrial action by tanker drivers, was to exhort us to top up our tanks – in effect to use even more. Nobody suggested that doing fewer miles might help or that the more efficient use of engines could be a good idea.

The railway industry has always had an eye on fuel efficiency – not that it was always obvious. Locos idling for hours (allegedly because they wouldn’t re-start), plumes of exhaust smoke out of the old Deltics and fuel tanks filled to overflowing, spraying diesel out on heavily canted track.

Despite all of this, there were drives to be more efficient. Take for example the re-engining of the HST fleet with the MTU power unit as reported in the rail engineer back in 2008. This was a particularly elegant solution because the rest of the control gear had no idea that it was talking to a new engine! Look too at the Selective Engine Technology of the class 185 DMUs run by First TransPennine Express using technology originating from Siemens.

Technology transfer

The railway’s room for manoeuvre is limited. When the Department for Transport commissioned the TRL in partnership with consultants Ricardo to look for fuel saving measures it was the complexity of the present industry, coupled with all the historic baggage, that made life very complicated.

The thrust of the research which has been published recently was to look for technologies from outside of the railway industry and investigate whether there is anything that could be transferred to good effect.

The railways use large power units, but these are not just limited to railway applications – far from it. Marine applications come to mind along with mining, generating and off-road heavy haulage. They’ve all developed in their own way and, to some extent, with more freedom to exploit innovations. The report did not limit itself to just the power units but looked also at a whole range of current technologies.

Complications – always complications

The reasons to look at fuel efficiency are compelling, if for no other reason because of cost. GB rail used 681 million litres of diesel (that’s 150 million gallons or over half a million tonnes!) in 2009/10 with passenger services using 482 million litres and freight 199 million litres. The proportion of the national network that is serviced by diesel powered trains is high (69%) in comparison with mainland Europe.

But straightaway there are complications. There are over 20 classes of passenger DMU used on the network. This daunting variety can be rationalised, however, by separating out the more recent DMUs which have newer versions of MTU and Cummins engines. These have been designed to be fuel efficient and to comply with more recent emission regulations. The scope for improvement is therefore limited. On the other hand there is a sizeable set of DMUs that have older Cummins and Perkins power units from classes 142 to 166. They differ slightly but there are similarities in engine technology and characteristics that lend them to accept fuel efficiency modifications.

The stock of freight locomotives can be similarly rationalised. Although there are still some locomotives that date back to the 1950s, there are not many of them and they cover very few miles. On the other hand, 48% of the freight fleet are class 66 locomotives that cover 87% of all freight miles. So, being the most heavily used unit and consuming significant quantities of fuel, any modifications to the class 66 fleet would have a significant impact on diesel consumption.

Idling away

Having boiled down the fleets to manageable numbers, the next complication was to determine what the units actually do on a daily basis – the typical duty cycle. Whether a unit is coasting, powering acceleration or idling will have a fundamental impact on how much fuel they use.

Passenger and freight trains have significantly differing duty cycles. And within the passenger sector, there are variations depending on whether the train is serving a local or intercity route. The former spends more time accelerating than the latter.

Unsurprisingly, freight locomotive engines really do spend a large proportion of their time idling and it is here that major fuel savings can be achieved.

The study looked at engines on the market that could be adapted to railway freight use. Counter-intuitively, the marine power units are not a favoured choice. In most cases they have developed from existing land-based units and have specific modifications to deal with seawater cooling – something the railway industry does not need apart from winter journeys through Dawlish Warren perhaps!

Of all the comparable engines considered, none performed any better at high loads compared with the baseline class 66 engine – the GM EMD 710 – although NOx and PM emissions would be greatly reduced.

However, up to a 20% improvement in fuel efficiency at idle could be obtained.

Shopping list

In addition to examining engine substitution, the report looked at a wide range of technologies that could improve rail sector powertrain efficiency. At the risk of producing yet another set of bullet points these were:

• Engine enhancements – Gas exchange systems, Combustion systems, Engine friction reduction and lubricants and fuel additives;

• Engine parasitic loss reduction through oil pumps, water pumps, compressors and auxiliary alternators, fans, heat exchange arrangements and cooling air flow rate;

• Waste heat recovery;

• Transmissions and driveline systems – mechanical, hydraulic, infinitely variable;

• Hybrid powertrain systems and energy storage;

• Additional Efficiency improvements – multiple engine stop/start systems, Auxiliary power units, integrated powertrain optimisation systems.

Breathing losses

From all the topics raised, the report went on to suggest a range of technology packages that could be considered for the passenger and freight fleet.

After rigorous evaluation, two packages were favoured – one for passenger and one for freight. The passenger solution was for a gas exchange system upgrade. This is one of the simplest to apply with the majority of benefits coming from the upgrade in turbo charging technology. Improvements to the engine gas exchange systems will improve efficiency by minimising engine breathing losses with a 3% improvement in fuel efficiency estimated over both the intercity and local duty cycle.

The enhancements are relatively simple, but the bespoke nature of the DMU fleet means that there is no ‘one-size-fits-all’ solution. But it is possible to apply the upgrade to all the engines in the group.

Close on the heels of the gas upgrade option is a transmission upgrade. This is already under consideration by the industry. Ever since 1969, the Voith T211 turbo-transmission has been used in the majority of DMUs. In fact there are over 10,000 T211 transmissions, or variations of it, in service on trains worldwide. They are efficient above a speed threshold at which the hydrodynamic coupling is locked up, but below this speed there are significant losses. Vehicles that operate at slow speeds or have a local duty cycle rarely achieve the optimum speed.

The alternative transmission that is showing significant savings is a mechanical version as offered by the manufacturer Voith and also now by ZF. Exchanging transmissions is a relatively simple modification compared with repowering or engine modifications.


For the class 66 freight locomotives, the favoured technology package mainly manages the issue of prolonged idling. It involves the engine being shut down and restarted using a lead acid battery system. The ‘hotel’ loads – that is the heating/air-conditioning of the driving cab – would be supplied by a 30kw lightweight diesel generator set. The gas exchange system would also be upgraded by modifying the compressor wheel in the turbo charger and upgrading the charge air cooler and cooling systems.

This package is all that is proposed for retrofitting to freight locomotives as there are limited options for improvements to the existing 2-stroke engine of the class 66. But addressing the idling could be highly beneficial as up to 41% of fuel is burnt at idle in the freight duty cycle.

Stringent emissions standards

As always, although the engineering is reasonably straightforward, it’s the “other factors” which make life very complicated – in the current railway industry doubly so.

Many technologies are not viable from an economic standpoint as the payback period makes a return on investment impossible within a franchise period or over the residual life of the asset.

Fragmented diesel fleet and vehicle procurement models result in low volume orders with little incentive for investment in R&D from suppliers.

Adoption of EU emissions standards (stage IIIB) has made the procurement of new engines, either as part of new rolling stock or for repowering of existing vehicles, unattractive. More stringent emissions standards also, in general, result in reduced efficiency due to the increased parasitic loads placed on the engine – predominantly for extra cooling. The standards take no account of what an engine unit achieves within an overall railway system. They just look at emissions per engine. So, a rail engine can haul 2000 tonnes of freight far further and far more efficiently than multiple road engines and yet it gets no ‘credit’.

A significant problem in evaluating fuel saving technologies is obtaining an accurate measurement of the fuel consumption before and after the application of the technology. Efforts are being made to develop direct measurements for precise monitoring of rail engines’ fuel consumption but, due to the nature of the fuelling systems in use, there are technical difficulties in achieving this.

Shared conclusions and recommendations

The report is positive overall. The key recommendation is that, by working together, the GB rail industry can improve the commercial viability of more fuel efficient technologies and implement better long-term solutions.

Owing to the complex nature and age profile of the diesel rail vehicle fleet, the study showed that smaller and more incremental changes applied to a large proportion of the fleet would deliver significantly greater fuel saving benefits than more radical innovations applied to a smaller number of vehicles.

This is a light-weight summary of a hefty piece of rail research. The very readable 162 page report (GB Rail Powertrain Efficiency Improvements) can be obtained through the Ricardo web site. The report and its conclusions and recommendations are now in the process of being shared with a range of industry stakeholders including rolling stock leasing companies, train operating companies, fleet maintenance and overhaul firms and rail freight operators.