UK: Chiltern Railways has put into passenger service its HybridFLEX hybrid multiple-unit, which is fitted with a battery pack to store regenerated braking energy which can then be used to provide emission-free operation in stations and urban areas without needing new infrastructure.

The project is seen as an interim measure for the expected remaining life of the DMUs, while a case is made for electrification of the only remaining diesel-only route out of London.

Chiltern Railways HybridFLEX DMU 168329 (Photo Tony Miles) (4)

Two-car diesel-multiple unit 168 329, which was originally delivered as a Class 170 Turbostar DMU in 2000, has been fitted with two MTU Hybrid PowerPacks comprising a 6H 1800 engine compliant with EU Stage V emissions standards, an electric motor, and a Rolls-Royce MTU EnergyPack battery system.

This is expected to provide a 25% reduction in fuel consumption, 25% lower CO2 emissions, a 70% cut in NOx and a 90% drop in other pollutants, as well as reducing noise by 75%. There is also a significant reduction in brake dust and brake pad replacement costs, as most of the retardation comes from the regenerative braking with blending to friction brakes taking place at very low speeds.

The aim is for the diesel engines to cut out 300 m before arrival at a station and to restart after an emission-free departure. The seamless transition between battery and diesel power takes place at approximately 45 km/h, triggered by GPS and digital maps of the optimal place to change.

Chiltern Railways HybridFLEX DMU 168329 (Photo Tony Miles) (2)

MTU’s Intelligent Drive Manager automatically switches to all-electric operation in urban areas and stations, meaning that the driver does not have to intervene at all.

The improved acceleration under battery power also offers the potential for reduced journey times in the future.

Technology partnership

HybridFLEX is the product of a four-year partnership between Chiltern Railways, leasing company Porterbrook and Rolls-Royce, with a letter of intent having been signed by Rolls-Royce and Porterbook at InnoTrans 2018.

Chiltern Railways HybridFLEX DMU 168329 (Photo Tony Miles) (6)

The partners say that unit 168 329 is the first 160 km/h battery-diesel hybrid passenger train on the national network.

It will mainly operate between London Marylebone and Aylesbury, with occasional forays to Oxford and other destinations. At times it will be paired with a standard DMU to confirm compatibility.

This operation under real-world conditions will allow Chiltern to develop a business case for the conversion of further DMUs, with an announcement on future plans expected this summer.

Chiltern Railways HybridFLEX DMU 168329 (Photo Tony Miles) (1)

‘This hybrid trial is massively important for Chiltern Railways’, said Managing Director Richard Allan when the train entered passenger service on February 10.

‘We are currently operating an old fleet of diesel trains, one of the oldest fleets in the industry, and we are determined to modernise and decarbonise our railway to ensure that it is as sustainable and environmentally friendly as possible.’

He said the operator looked forward to assessing the performance of the ‘cleaner, quieter and quicker’ train in daily service.

Porterbrook CEO Mary Grant said the start of passenger service was ‘a significant first step in demonstrating how improvements to this fleet can reduce emissions and improve air quality’, with HybridFLEX being ‘part of Porterbrook’s growing portfolio of alternative traction systems designed to help deliver a more sustainable railway’.

Chiltern Railways HybridFLEX DMU 168329 (Photo Tony Miles) (5)

Noting that HybridFLEX technology could play a part in the government’s ambition to remove diesel-only trains from the network by 2040, Dr Lei Berners-Wu, Rolls-Royce Vice-President for Global Industrial, told Rail Business UK that the MTU Hybrid PowerPack ‘is an excellent example of how we are becoming a provider of integrated sustainable solutions with pioneering technologies. We started this project in 2018 and we are very happy that the dream and the groundwork have come into reality.’

Other operators have expressed interest in the MTU system, with Ireland’s Iarnród Éireann to undertake trials using its Hyundai ICR diesel sets. It is also understood to be under consideration for the small fleet of hybrid CAF Class 195 trainsets which is being procured by Northern.