Energy efficiency and fuel consumption of fuel cells powered test railway vehicle K.Ogawa, T.Yamamoto, T.Yoneyama Railway Technical Research Institute, TOKYO, JAPAN 1. Abstract For the purpose of an environmental burden reduction and an improvement of energy efficiency, we (RTRI) have been developing the railway vehicle powered by fuel cells (FC) since the year 21. We made FC system for vehicle traction and high-pressurized hydrogen cylinder system experimentally, and constructed the FC test vehicle that can run as one car alone. We executed the running tests in our test facilities and evaluated FC energy efficiency and fuel consumption with the running data obtained from these running tests. Then, because our test vehicle could not run on a commercial line, we evaluated energy efficiency and fuel consumption under the condition of the commercial line by the running simulation. 2. Introduction Presently, diesel cars are running with engines in un-electrified sections and it is connected to the fossil fuel dry up problem. In addition, it has such problems as low energy efficiency, emission of CO 2 and NO x, heavy noise and vibration. With the consideration on these problems, we paid our attention on FC that generates powers with high efficiency from hydrogen, and started the study to use FC as the power supply for railway vehicle traction in the year 21. FC drains only the water produced by FC s internal reaction and a part of air that does not contribute to the reaction. So, we can use FC as a very clean power supply. In addition, by use of regenerative hydrogen energy, it is also a measure against fossil fuel dry up problem. In the year 25, we made experimentally 1 kw class PEMFC (proton electrode membrane type of FC) for railway vehicle traction and 35Mpa high-pressurized hydrogen cylinder, and installed them in the test vehicle and prepared the test vehicle powered by FC that can run as one car alone. In the year 26, we executed the running test in our test facilities and confirmed that test vehicle could be driven by FC. With the data obtained from these running tests, we calculated our FC s energy efficiency and verified the adequacy of FC energy efficiency of 4% that we had used in our running simulation. In addition, we also calculated fuel consumption that could be a barometer of fuel on board and evaluated it under various running conditions. As our test vehicle does not have the commercial registration, it is difficult to make our test vehicle run in the commercial line. Therefore, we executed the running simulation with commercial line s data and calculated energy efficiency and fuel consumption. In addition, we evaluated by simulation the advancement of energy efficiency and the reduction of fuel consumption quantitatively in the case of utilizing regenerative energy. We report the details in the following. 3. Characteristics of PEMFC Firstly, we will explain the structure and the principle of electric generation of PEMFC below (Fig 1). PEMFC has a thin membrane covered by platinum on the both surfaces. When hydrogen is supplied to one side and oxygen, to the other side of this membrane, hydrogen becomes hydrogen proton and electron by the platinum s catalysis. Only hydrogen proton passes through the membrane and moves to the oxygen side. When the external load is connected to the electrode installed on each side of membrane, electron moves to the oxygen side through it. Finally, oxygen, hydrogen proton, electron are combined to become water on the oxygen side and drain out. By this electron s move, electric current flows, and we can use FC as a power supply. Namely, PEMFC generates powers by the chemical reaction of hydrogen and oxygen, which can be taken from an air. In addition, the operational temperature of PEMFC is lower than other types of FC and it is possible to start up almost instantly. Therefore, PEMFC is noted as the power supply for mobile object such as automobile that are inquired the limited space of installation and the quick startup time and so on.
4. 1kW class PEMFC system Fig 1 Principle of electric generation of PEMFC We explain below the FC system that was made experimentally. Our FC system that we made experimentally is based on stationary system and is downsized for installation in the railway vehicle [1]. This system can output 1kW class powers needed for one vehicle traction. The exterior of the system is shown in Fig 2.1 and the specification, in Table 1. Fig 2.1 Exterior of 1kW class PEMFC system Table 1 Specification of 1kW class PEMFC system Rated power 12 kw (Net), 15 kw (Gross) Output voltage 6 V (rated), 85 V (no load) Load current 2 A (Net), 25 A (Gross) Mass 1,65 kg Dimension 1.65 m (L) 1.25 m (W) 1.5 m (H) Stack composition 18.75kW 8 series Start up time About 1min3sec We explain the major characteristics of our FC system below. The system can generate powers independently. Internal auxiliary powers of FC are supplied by self-generated powers. The system generates powers following a railway s fluctuated loads. The system achieves a hydrogen use rate of more than 99% by hydrogen recycle function. The system has the function to recycle the water produced by FC s internal reactions.
We executed the bench test and verified that our system satisfied the requirements of the specification nearly (Fig 2.2). 14 12 Output Power 12kW (185A, 65V) 14 12 Output Voltage[V] 1 8 6 4 Output Voltage Output Power 65V 1 8 6 4 Output Power[kW] 2 2 5 1 15 2 Load Current[A] Fig 2.2 Bench test result 5. Composition of FC test vehicle 5.1 Installation of equipments 1. FC system We installed FC system at the center of our test train so as to make us be able to check FC s operational state all the time. 2. High pressurized hydrogen cylinder system We installed hydrogen cylinder system under the floor of our test vehicle so the hydrogen not to be remained in the test vehicle when it leaks. This system consists of four cylinders and one cylinder can contain 4.3kg hydrogen high pressurized with 35Mpa. 3. Inverter for vehicle traction We installed the Inverter for vehicle traction at the back of test vehicle and fixed the control device that can change running parameters. At this time, the vehicle auxiliary powers (for air conditioner, compressor, room light) were supplied from the contact wire, but we are planning to build up FC powers so as the vehicle auxiliary powers can be supplied from FC powers in the future. By installation of these equipments, we composed the FC test vehicle that could run as one car alone (Fig 3.1). Fig 3.1 FC test vehicle
5.2 Composition of main circuit We explain the composition of main circuit of FC test vehicle in Fig 3.2. Circuit Breaker Rated 95kW 2 F C + - ) ( Filter Inductor Filter Capacitor I N V I M I M Fig 3.2 Composition of main circuit At this time, in order to obtain the characteristic of FC when we use only it for vehicle traction without energy storage device, we connected FC directly to main circuit. We used the same type of equipments as those used in the commercial electric railway vehicle in Japan. But as FC s output voltage and powers were lower than those of it, the inverter controlled operation with the limits in voltage and powers. By these compositions, we executed running tests in RTRI s test facilities. 6.Running test results in RTRI s test facilities 6.1 Running tests at test track At this time, we executed the running test at the test track (Fig 4.1). Our test track is about 65 meters long each way and the velocity limit at the curve is set to 4km/h. As the result of this running test, the maximum velocity was 42km/h in the straight section and FC peak power was 9kW. We show the one example of test track test results in Fig 4.2. From this test result, we can see that the test running pattern in which velocity was less than 4km/h and FC outputted 9kW occupied a large part of the total running test time. 1 7 9kW 9 6 8 FC output 7 running distance 5 6 4 5 42km/h 4 3 3 2 2 velocity 1 1 2 4 6 8 running time [sec] 1 12 Fig 4.1 Running test at test track 6.2 Running tests at rolling stock test plant velocity [km/h], power [kw] Fig 4.2 Example of running test result at test track Running test at test track has the limits for a test velocity and a running distance. Therefore, we executed running tests at our rolling stock test plant to obtain the characteristic of FC test vehicle at a higher velocity. Rolling stock test plant is the facility that is equivalent to chassis dynamo of automobile and there are no restrictions in a test running distance. We executed the running test to verify the maximum velocity under the condition of an actual inertia loads (16t/axis 2axes) (Fig 4.3). As the result of this test, the maximum velocity was saturated at 15km/h for the reason that FC output voltage was in shortage and sufficient powers were not obtained at a high velocity. We show the example of running tests at rolling stock test plant in Fig 4.4. From this test result, we can see that the test running pattern in which velocity was about 1km/h and FC outputted about 4kW occupied a large part of the total running test time. running distance [m]
velocity [km/h], power [kw] 12 1 8 6 4 2 9kW FC power velocity 15km/h running distance 2 4 6 8 1 12 running time [sec] Fig 4.3 Running test at rolling stock test plant Fig 4.4 Example of running test result at rolling stock test plant The running condition at test track and that at rolling stock test plant are different from each other as shown below. at test track; the running pattern with low velocity and high powers occupies a large part of total running test time. at rolling stock test plant; the running pattern with high velocity and low powers occupies a large part of the total running test time. 7. Evaluation of running test results By using the data obtained from the running tests, we calculated FC energy efficiency and fuel consumption, and evaluated them by the running conditions [2]. 7.1 FC energy efficiency We defined FC energy efficiency by the equation (1). FCoutput energy( kwh) energy efficiency(%) = 1 (1) electric energy obtained from consumed hydrogen( kwh) We show the relationship between FC output power and energy efficiency of our FC system in Fig 5. energy efficiency (%) 1 8 6 4 2 2 4 6 8 1 12 FC output power (kw) Fig 5 Relationship between FC output power and energy efficiency FC energy efficiency has a peak at about 4-45kW: it is better at 4-45kW than at 9-12kW. Based on the equation (1), we calculated FC energy efficiency (Table 2). Table 2: FC energy efficiency in each running condition Running condition Test track Rolling stock test plant FC output energy (kwh) 1.38 13.3 Electric energy obtained from consumed hydrogen (kwh) 2.77 25.3 Energy efficiency (%) 49.9 52.7 3 25 2 15 1 5 running distance [km]
We could understand that FC energy efficiency is about 5% in both running conditions and is more than 4% that we had used in our running simulation. In addition, the energy efficiency obtained at the rolling stock test plant test is better by about 3% than that at the test track. This is because the test running curve at rolling stock test plant has such a characteristic that the running pattern with a high energy efficiency (about 4-45kW) occupied a large part of the total running test time. 7.2 Advancement of energy efficiency in case of utilizing a regenerative energy We calculated energy efficiency in case of utilizing regenerative energy with the data shown in Fig 4.2 and Fig 4.4. We assumed that 73% of kinetic energy at the start of braking operation was available as regenerative energy. 73% is the value that was obtained by multiplying all equipments efficiencies together considering the energy circulation from motor-end to inverter-input by way of battery. <Equipments efficiencies assumption> Motor : 92% Gear : 97.5% Inverter : 97.5% FL : 99% DC/DC converter for Battery: 97.5% Battery : 9% (worst state) Kinetic energy => 92% (Motor) => 97.5% (Gear) => 97.5% (Inverter) => 99% (FL) => 97.5% (DC/DC) => 9% (Battery) => 97.5% (DC/DC) => 99% (FL) =>Inverter-input Table 3: Energy efficiency advancement in case of utilizing regenerative energy Running condition Test track Rolling stock test plant Energy efficiency (use only FC) (%) 49.9 52.7 Regenerative energy calculated from kinetic energy.47 3.7 (kwh) Energy efficiency utilizing regenerative energy (%) 65.2 64.9 From this calculation result, we could understand that about 12-15% advancement of energy efficiency was expected by utilizing regenerative energy. 7.3 fuel consumption We explain fuel consumption below. We defined fuel consumption by the equation (2). running distance( km) fuel consumption( km / kg) = (2) amount of hydrogen consumed in the running( kg) The amount of hydrogen consumed in the running is obtained from the difference of the amount of hydrogen stored before and after a running. The amount of hydrogen stored is obtained by the equation (3). stored pressure( MPa) cylindervolume( l) 273( K) The amountof hydrogenstored= ( ) compressedcoefficient 273( K) + stored temperature ( Celsius) 1 2 1 3 ( kg) (3) 22.4( l)
Based on the equation (2), we calculated the fuel consumption under the running conditions that we showed in Fig 4.2 and Fig 4.4 (Table 4). Table 4: Fuel consumption under each running condition Running condition Test track Rolling stock test plant Running distance (km).65 26.6 Consumed hydrogen (kg).84.77 Fuel consumption (km/kg) 7.6 34.6 The difference of running curve affected fuel consumption and the fuel consumption of running test at rolling stock test plant is better by about 4.6 times than that at test track. 8. Running simulation under the condition of commercial line We can t execute a running test on a commercial line because our test vehicle doesn t have the commercial registration. Therefore, with the actual commercial line data (running distance is 27.5km, the number of stations is 13), we calculated energy efficiency and fuel consumption by the running simulation. In addition, we also simulated a running performance in case of utilizing of regenerative energy and evaluated the advancement of energy efficiency and fuel consumption. 8.1 Running condition We assumed two running conditions as shown in Fig 6.1 below. Case 1: use only FC for a power supply 1,5V FC FL FC Chopper Inverter IM Auxiliary (99%) (97.5%) (97.5%) IM Case 2: use FC and battery for a power supply 1,5V FC FL FC Inverter IM Auxiliary FL Battery Chopper (99%) (97.5%) IM Battery Fig 6.1 Running conditions Case 1 is the running condition in which only FC is used for a power supply. This case has the same composition of equipments as our test vehicle. Case 2 is the running condition which FC and
battery are used for a power supply. In both cases, vehicle auxiliary power is supplied from imaginary contact wire. The numerical values in the parenthesis represent equipment s efficiency, which is constant. 8.2 Algorithm of power control of Case 2 We show the algorithm of power control of Case 2 in Table 5 below. Table 5: Algorithm of power control of Case 2 Powering Coasting Regenerating Stopping Battery Output with priority. If SOC drops to 5%, then output stops. If SOC recovers to 55%, then output restarts. Charge Charge Charge FC If SOC drops to 5%, then output 12kW fully. If SOC recovers to 55%, then output stops. Output 12kW fully Not output Output 12kW fully Inverter Energy consume - - Energy storage - - We assumed the battery data as follows. Initial SOC : 6% Maximum power : 12kW (the same powers as FC) This algorithm is aimed at making SOC recover possibly to initial SOC (6%) when vehicle starts stations. It is not aimed at optimizing fuel consumption or energy efficiency. 8.3 Vehicle characteristics and running pattern We assumed the vehicle data as shown below regardless of running conditions. formation : 1 car empty vehicle weight : 3.3 ton equipments weight : 5 ton (including only 2 operators) Vehicle performances are changed by the weight of vehicle (including weight of equipments). Therefore, in order to avoid that the difference of them affects fuel consumption, we assumed the same vehicle data regardless of running conditions. We show the powering characteristic in Fig 6.2 and the braking characteristic in Fig 6.3. As for braking operation, an air braking operation was executed in all velocity areas in Case1, and a regenerative braking operation was executed in Case2 when vehicle velocity is more than 5km/h. At the velocity area below this, vehicle was stopped by an air braking operation completely.
Tractive Effort (kgf/mm), Motor Voltage (V) 15 1 85kgf 5 Motor Current Tractive Effort Motor Voltage 15 1 5 Motor Current(A) 2 166kgf 15 Motor Current Tractive Effort (kgf/mm), Motor Voltage (V) 1 5 Tractive Effort Motor Voltage 2 15 1 5 Motor Current (A) 2 4 6 8 1 12 Velocity (km/h) Fig 6.2 Powering characteristics 5 1 15 Velocity (km/h) Fig 6.3 Braking characteristics We assumed the running pattern as follows. Speed limit : 8 km/h (in all sections) Stop time at station : 4 sec (at all stations) By these assumptions, we executed the running simulation. 8.4 Simulation result We show the simulation results in Fig 6.4 and Fig 6.5. Velocity(km/h), Running distance(km) 8 25 Incline Velocity 7 2 6 15 1 5 5 4 3-5 2 Running -1-15 1 distance -2-25 5 1 15 2 25 3 time (sec) Incline( ) Power (kw) 2 1-1 -2-3 -4-5 Regenerative power 5 1 15 2 25 3 time (sec) Fig 6.4 Result of running curve Fig 6.5 Result of power curve of Case 2 The running time was about 42 min (Fig 6.4). It was a little later than the actual commercial time, but we could understand that even the vehicle with the present composition could run in the time almost equal to the commercial one. In Fig 6.5, we can see that the vehicle run with switching output power between battery and FC by SOC. In the Case2, the simulation finished after SOC recovered to the initial SOC (6%) after the completion of all the running. Energy efficiency Battery power We show the energy efficiency in each running condition in Table 6.1. Table 6.1: Energy efficiency in each running condition Case 1 Case 2 FC output energy (kwh) 41.25 27.85 Regenerative energy (kwh) - - 14.81 Electric energy obtained from consumed hydrogen (kwh) 8.5 56.3 Energy efficiency (%) 51.3 75.7 FC output energy FC power 3 25 2 15 1 5 Energy (kwh)
From this result, we could understand that energy efficiency was improved by about 24% with the utilization of regenerative energy. Namely, it was more than energy efficiency advancement in test track result (15%) with the improvement difference of 9%. As one of the reasons, it is supposed that the difference of potential energy maybe affects energy efficiency (Table 6.2). The rate of potential energy to FC output energy was + 3.4% in the test track, -.97% in the simulation. With respect to reminded about 4.5% differences, affections by the resistance at curve in test track and so on may be considered. Table 6.2: Comparison of potential energy Test track Simulation Difference in height (m) +.5-2.8 Potential energy (kwh) +.45 (+3.4%) -.269 (-.97%) Fuel consumption We show the fuel consumption in each running condition in Table 6.3. Table 6.3: Fuel consumption in each running condition Case 1 Case 2 Consumed hydrogen (kg) 2.44 1.71 Fuel consumption (km/kg) 11.3 16.1 Fuel consumption for Case 1 resulted in about 1.5 times of test track result (7.6km/kg), and for Case 2 it resulted in twice of it. In Case1, firstly, the rate of running time at high velocity and low powers is large against all the running time; secondly, coasting time is included in the simulation. In Case 2, in addition to the above reasons, battery was mainly used and a regenerative energy was also utilized, accordingly it is considered that FC output time was shortened and hydrogen consumption was reduced. We could understand that fuel consumption in Case2 was improved by 3% compared to that in Case1. 9. Conclusion We made 1kW class PEMFC for vehicle traction and 35MPa high-pressurized hydrogen cylinder system experimentally, composed the FC test vehicle that could run as one car alone, and executed the running tests in our test facilities. With the data obtained from the running tests, we evaluated our FC system s energy efficiency and fuel consumption. We verified that FC energy efficiency was a high value of about 5% and was more than 4% that we had used in our running simulation. In addition, with respect to fuel consumption, we verified that the larger the rate of time to run with a high velocity and low powers of about 4-45kW was, the better the fuel consumption was. Then, because our test vehicle can t run on a commercial line, we calculated the advancement of energy efficiency and fuel consumption under the condition of commercial lines by the running simulation. We verified the advancement of 24% in energy efficiency and 3% in fuel consumption by the use of regenerative energy. 1. Acknowledgements This development has been partially financially supported by the Ministry of Land, Infrastructure, Transport and Tourism of Japan. 11. References [1] K.Ogawa, K.Kondo, T.Yamamoto, T.Yoneyama Development of 1kW class fuelcell (FC) system for railway vehicle traction, THE27 ANNUAL MEETING RECORD I.E.E. JAPAN, Vol.5, No.157, pp.236-237 (27).
[2] K.Ogawa T.Yamamoto T.Yoneyama Evaluation of efficiency and fuel consumption rate in running test of fuel cells powered railway vehicle, The27 Annual Conference of I.E.E. of JAPAN. Industry Applications Society, Vol.3, No.35, pp. 239-242, (27).