Flex... and flexibility

This helped fuel Simpson’s research: “When I started this project, battery technology was looking like an interesting option for the industry. I wondered whether this could be used on the Class 319s,” she tells RAIL.

“I initially explored both battery and hybrid technologies as options that would deliver a mid-life EMU capable of travelling off the electrified network.”

Simpson talks of “range anxiety” as being a concern, when looking at IPEMU. How far the train could actually operate on battery power is something train operators constantly ask, she says. 

“Batteries are definitely doable, but rail will have to overcome the current range limitations for traction power. We think traction battery technology will give you a range of around 20km to 30km before needing recharging, and this is not enough for most operators.”

Cost was another problem. “Eye-watering” is Simpson’s description of the whole-life cost when compared with the value of a mid-life train. 

“I looked at the size and weight of the components. There is space on the trailer cars, but you start to add weight. And the more weight you add, the more batteries you need. It could be done, but it would have a high weight penalty and is just so expensive.”

Porterbrook Commercial Manager Mark Isbern tells RAIL that the whole-life cost is key for the work. “You have ten years, maybe,” he says.

Simpson interjects that, currently, rail application traction batteries typically have three to five years’ life before they need changing. 

“So we couldn’t make it stack up,” she says. “Super-capacitors are interesting because they are small, light, efficient and relatively low-cost for a given power output. They are also quick to recharge. For these reasons, I might select them for discontinuous electrification schemes, or for areas that are difficult to electrify, but they are limited to just a couple of kilometres so weren’t suitable for the Class 319 project.”

The next option was hybrid technology. 

Says Simpson: “The optimum solution in terms of weight, space and power output for the range that we wanted would be to use a diesel engine supported by batteries for peak acceleration. We looked at timescales, cost and complexity for this, but it would have taken too long to develop.” 

Furthermore, Isbern points out that a hybrid solution needs to be closely tailored to a particular duty cycle with sufficient recharging time. Again, range anxiety becomes a problem, particularly during times of disruption when a hybrid train might suffer severely degraded performance. 

Consequently, the diesel-only genset option emerged as Porterbrook’s preferred way forward. Says Isbern: “This gives maximum range, maximum flexibility to operators, and the best cost-risk-benefit ratio.” 

To prove the concept would work, Porterbrook has teamed up with Wabtec/Brush Traction to develop a feasibility study, including detailed modelling work. 

Simpson wanted Brush to really test the concept before any metal was cut, revealing: “I wanted to test it against the worst route I could imagine.” After speaking with Northern, she chose Manchester Piccadilly-Buxton: “It’s uphill all the way and has 12 stops.” 

The ‘319’ Flex train performed admirably in modelling. It was able to complete eight return journeys per day to the current timetable, in effect performing like a four-car Class 15x formation. 

Simpson says other routes have been modelled across the country, and names Great Western, Wales and the West Midlands as areas she has investigated. 

“My motivation was around making the ‘319’ more attractive to the market. Once you think bi-mode you look at different routes and offerings. Electrification delays have supported our case, but they are not the reason we are doing this.”

The range was found to be limited only by the size of the fuel tanks. Says Simpson: “We set ourselves ambitious targets for range akin to a traditional DMU. Our modelling work shows that we can go for two days on a very arduous diagram.”
What exactly is the plan? 

Simpson says: “A four-car ‘319’ Flex train will have modified driving vehicles, where we fit a diesel engine and alternator under the floor. 

“We propose using a MAN D2876 engine - this is used in Europe and it’s suitable for underframe use. Its key attractions are the compact depth of the engine, the fact that it is rail approved, and that it is compliant with the latest stage IIIB low emissions regulations.” 

The diesel engine is linked to the alternator, which is manufactured by ABB and which is also used with the engine elsewhere in Europe, thereby meaning the complete drivetrain is proven. This reduces technical risk from the scheme.

Simpson explains: “The reason the engine is so efficient is not just because it’s modern. It runs at maximum efficiency all the time, whereas the engine in a diesel hydraulic DMU cycles through the rpm range when it’s running. This engine just runs at a near constant speed, in its maximum efficiency range, feeding the existing 750V line. 

“We are effectively tricking the traction system into thinking it is still a DC unit. It is effectively replacing the DC operation with diesel, but we could still retain the shoegear and have a tri-mode ‘319’ if it was needed.

“All the equipment is proven already. Brush, in particular, has a good record with its electrical interface work and conversions of this nature. It has converted ‘47s’ to ‘57s’ and upgraded the GB Railfreight ‘73s’, and this is much simpler than those projects. It is a very credible supplier.”