International Transportation (67) 2 | 2015 36 PRODUCTS & SOLUTIONS Hybrid Rail Powerpack Ready to go MTU Hybrid Drive proves market readiness Hybrid drive systems, emission-free driving, noise emission, customized solutions Over three years, MTU Friedrichshafen GmbH ran trials with its Hybrid Powerpack, logging 15,000 km to verify its reliability and readiness for everyday operation. Result: MTU Hybrid technology is ready for the market. On local routes in particular, MTU’s advanced rail drive system offers considerable potential for increasing economic efficiency and reducing emissions in rail transport. In purely electric drive mode in particular, hybrid technology enables emission-free local travel in urban areas, underground stations and tunnels. In addition, the combination of electric drive and diesel engine helps keep trains on time and makes it easier to make up for delays. Authors: Benjamin Oszfolk, Matthias Radke, Matthias Kasch, Yvonne Ibele T he test vehicle was a Series VT642 Deutsche Bahn railcar, which had been converted to hybrid drive technology. Between January and March 2015, trial journeys were run on a 37- km line section including 13 stopping points operated by Westfrankenbahn near Aschaffenburg in Germany - and on a 23 km section including 9 stopping points operated by Staudenbahn in Augsburg, Bavaria. The vehicle was equipped with a comprehensive range of measuring technology to allow recording of system parameters such as current, voltages, GPS signals and diesel consumption. In addition, acceleration sensors were installed to calculate and monitor the forces acting on the vehicle. And a dedicated virtual driver system was developed to facilitate comparison of the various hybrid travel strategies with the diesel-based reference model. The virtual driver system included a monitor screen for the human driver. This display was used to continuously show the optimum speed required to remain on schedule given the current travel strategy, and it relayed control commands to the train driver. Prior to the actual test runs, a simulation environment developed in-house was used to run whole-vehicle simulations. Besides various travel strategies including peak speed with runout, moving off under electric power, and combustion engine shutdown, four additional strategies were investigated. Further parameter variations were implemented in simulation mode aiming to reduce fuel consumption and CO 2 emissions. The tests proved that the Hybrid Powerpack is able to achieve in practice the 18 % fuel savings compared to pure diesel operation which had been calculated during simulations (see figure 1). The illustration shows vehicle speed, the energy storage system’s State of Charge (SoC) and the accumulated fuel consumption of a given drive system over the travel period. To ensure comparability for all travel strategies, at the end of each test run the SoC had to match the initial value at the start of the test run. For this purpose, after the completion of each test run, the diesel engine was used to recharge the energy storage system up to the initial SoC. The additional fuel consumption involved was factored in when determining total consumption. The investigations and test results show that in comparison to conventional drives, the economic efficiency of the hybrid drive can be increased even further on routes involving multiple stopping points and higher speeds, and that further optimization can yield fuel savings of 25 %. In addition to runs for the purpose of consumption measuring, noise emission measurements were also conducted in line with TSI Noise. As had been forecast, it proved possible to shut down the diesel engine when the vehicle was stationary (i.e. at stations), thereby reducing the noise level-by up to 21 dB. The benefit of reduced noise levels was also obvious when the vehicle moved off, as it was driven purely electrically over the first few meters and the- diesel engine was only cut in at a later point. The test runs thus confirmed that, on local journeys in particular, hybrid technology contributes to more environmentally friendly and more efficient drive solutions as compared to conventional systems. In addition, the availability of simulation tools means that optimum hybrid drive configurations can be individually calculated for each route profile and each timetable and that reliable statements on achievable fuel savings can be formulated in advance. Hybrid drive components - Integration in the vehicle In essence, the core components of a hybrid drive system are a combustion engine, an electrical machine, power electronics, an energy storage system, drive control equip- Figure 1: The left figure shows vehicle velocity in red and SoC gradient in blue on the Staudenbahn track from Oberneufnach to Magertshausen. The rigth figure shows diesel fuel consumption in orange and hybrid fuel consumption in green. Total savings amount to 18 %. International Transportation (67) 2 | 2015 37 Hybrid Rail Powerpack PRODUCTS & SOLUTIONS ment and - depending on the configuration - a gearbox (see figure 2). To enable the realization of a range of hybrid drives, a modular component system was developed. This makes it possible to tailor the drive system to suit the vehicle and to cater for customer-specific operating factors such as timetables, route, etc. In principle, there are three viable installation concepts (see figure 3). The roofmounted design variant places the energy storage system on top of the vehicle. Fluctuating ambient conditions in the roof zone are irrelevant here as the energy storage system always has its own cooling system. Integration of the energy storage system in the vehicle’s own existing cooling system is also an option. The underfloor design variant involves fitting the energy storage system in the underfloor Powerpack compartment, but this variant requires the availability of adequate space and is primarily suited to new vehicles. Where neither roof mounting nor underfloor mounting are possible, the energy storage system can be accommodated in the vehicle interior. Its modular design provides a high degree of flexibility, both in planning new vehicles and for the conversion of existing rolling stock. Drive concepts at vehicle level Apart from the fuel savings they offer, hybrid-drive vehicles bring a number of other functional benefits. Since hybrid-drive vehicles have both an autonomous diesel drive and an electric drive, they open up additional potential for future uses. A-subsequent transition to a bi-modal vehicle requires only the integration of a pantograph in the intermediate electric circuit of the hybrid drive. A vehicle benefitting from this configuration is able to operate at high levels of energy efficiency on non-electrified routes in hybrid mode (i.e. drive system utilizing the diesel engine, the electrical machine and the energy storage system) as well as on electrified lines driven purely by the electrical machine powered from the overhead lines. Figure 3 shows possible combinations: • Diesel-mechanical drive • Parallel hybrid • Diesel-electric drive • Serial hybrid • Bi-modal hybrid Vehicles with bi-modal hybrid drive systems benefit from particularly flexible application capabilities. Bi-modal hybrid vehicles offer fleet operators and vehicle owners alike significant flexibility with regard to vehicle utilization. Consequently they can play a key role when it comes to the new allocation of route contracts. Economic aspects During the trial runs, the economic efficiency of the MTU Hybrid Powerpack was verified under actual working conditions. Calculated over the entire lifecycle of the unit, the procurement cost of the Hybrid Powerpack represents only a small fraction. Depending on the drive type, fuel costs for the Powerpack make up between 50 % and 60 % of its lifecycle costs. With a hybrid drive, the largest part of fuel savings is achieved through energy recuperation and the use of the energy recovered for acceleration. Further fuel savings are achieved because hybridization means that electrified auxiliary drive units can now be efficiently powered. The economic efficiency of the hybrid drive is therefore particularly high on routes with multiple stops, making amortization possible within just a few years. Summary Hybrid technology for rail applications is market-ready. Based on the Type 6H1800 engine, MTU’s Hybrid Powerpack demonstrated its reliability throughout a comprehensive program of test runs. The tests also confirmed prognostic results obtained from simulations. As a result, customers can expect reliable statements in areas such as economic efficiency, fuel savings, and reduced noise and exhaust emissions. What is more, customized hybrid solutions are feasible: The modular system combining different drive elements can be configured in line with individual customer specifications, generating the maximal benefit for the application and the customers. ■ Matthias Kasch, M.Eng. Research and Technology Development, Drive Systems Testing, MTU-Friedrichshafen GmbH, Friedrichshafen (DE) matthias.kasch@mtu-online.com Yvonne Ibele, B.A. International Business Sales Rail, Economic Feasibility, Hybrid Powerpack Project, MTU-Friedrichshafen GmbH, Friedrichshafen (DE) yvonne.ibele@mtu-online.com Matthias Radke, Dipl.-Math. Research and Technology Development, Function Development, MTU-Friedrichshafen GmbH, Friedrichshafen (DE) matthias.radke@mtu-online.com Benjamin Oszfolk, Dipl.-Ing. (BA) Research and Technology Development, Drive Systems Development, MTU Friedrichshafen GmbH, Friedrichshafen (DE) benjamin.oszfolk@mtu-online.com Figure 2: Modular set of components including combustion engine, energy storage, electric motor/ generator, power electronics and gearbox Figure 3: Drive system configurations: Parallel hybrid based on the diesel-mechanical drivetrain, serial hybrid based on the diesel-electric drivetrain. By connecting the hybrid system to the overhead line, a vehicle with bi-mode drive can be realized.