Hybrid technology enters the real world
Fuel savings of up to 20% are anticipated during tests of a power car and three DMUs fitted with a prototype hybrid battery-diesel system which reuses braking energy for acceleration
THIS MONTH East Japan Railway will put into revenue service its initial production series of three battery-diesel hybrid DMUs, which will begin carrying passengers on the Koumi Line between Kobuchizawa and Komoro.
The single-car units have 331 kW diesel engines and 15·2 kWh lithium-ion batteries, and manufacturer Hitachi expects deployment on the arduous commuter duties with frequent station stops will bring significant fuel savings and a cut in particulates of up to 60%.
Meanwhile, testing is now underway with 'Hayabusa', a much more powerful hybrid vehicle which Hitachi says is Europe's first battery-assisted diesel-electric power car. Hitachi's hybrid drive has been installed in a British HST power car to allow realistic trials of the prototype technology, which the Japanese firm and its development partners Brush Traction, Network Rail and Porterbrook Leasing anticipate could reduce fuel consumption by 20% and slash the most harmful engine emissions by half.
- Watch Hayabusa in action
The key to the system is an onboard energy management system, which forms an interface between the diesel engine and a high energy density lithium-ion battery bank which can be charged from either the engine or from energy regenerated during braking.
The hybrid train uses battery power alone to accelerate from a stand, with power fed from the battery through a DC to AC inverter to the newly-installed Hitachi 300 kW AC traction motors, which have replaced the previous DC motors. The peak power available is 1 MW, with the energy management system blending in power from the vehicle's existing Paxman Valenta diesel engine as the speed reaches 30 km/h. The management system ensures the engine runs at its most efficient speed, with excess power not required for traction being diverted to the charge the battery. The management system automatically draws on the battery if more power is needed at any point, perhaps on an adverse gradient or for further acceleration.
To reduce emissions the engine can be switched off when it is not needed, such as when standing in a station, and will start up as the train approaches 30 km/h.
The key to reducing energy consumption is the use of the battery to store energy from braking, which would otherwise be lost. During braking the traction motors act as generators, with kinetic energy converted to electricity, rectified and the resulting DC used to charge the battery rather than being dissipated as heat. Allowing for energy losses in charging and discharging, Hitachi expects that around 80% of the regenerated braking energy will be recovered for the next powering cycle.
Power car No 43 089, now named after the Japanese word for falcon, and a MkIII TGS coach were donated to the project by Porterbrook in November 2005. Modification of the vehicles was undertaken by Brush Traction in Loughborough.
The 48 high energy density 1 kWh lithium-ion modules weigh around 20 kg each, and limitations on weight distribution meant the 1 tonne battery bank could not be installed in the power car. As a result, the battery is located in custom-designed racks in the adjacent coach. Future new-build vehicles would have the batteries incorporated into the design from the start, allowing the modules to be distributed throughout the train and reducing the weight of the supporting structures.
Hitachi is expecting to see a 20% cut in fuel consumption from the prototype, but higher savings could be made with production vehicles, as the use of battery power for acceleration means that a new-build vehicle could have a smaller diesel engine, cooler group and fuel tanks, resulting in an overall reduction in vehicle weight despite the battery.
Further weight reductions are expected as battery technology advances, driven by demand from the automotive industry Hitachi supplies the batteries for Toyota's Prius hybrid car. 'Th