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 2001. 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 CO2
and NOx, 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 2001.
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 2005, we made experimentally 100 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 2006, 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 40% 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.
Fig 1 Principle of electric generation of PEMFC
4. 100kW class PEMFC system
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 100kW 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 100kW class PEMFC system
Table 1 Specification of 100kW class PEMFC system
Rated power
120 kW (Net), 150 kW (Gross)
Output voltage
600 V (rated), 850 V (no load)
Load current
200 A (Net), 250 A (Gross)
Mass
1,650 kg
Dimension
1.65 m (L) ×1.25 m (W) × 1.5 m (H)
Stack composition
18.75kW × 8 series
Start up time
About 1min30sec
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).
1200
Output Voltage[V]
140
Output Power 120kW
(185A, 650V)
1000
120
100
Output Voltage
800
80
600
650V
Output Power
400
60
40
200
Output Power[kW]
1400
20
0
0
0
50
100
150
200
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.
Rated 95kW ×2
Circuit Breaker
+
)(
IM
Filter Inductor
F
I
N
V
C
-
Filter Capacitor
IM
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
100
90
80
70
60
50
40
30
20
10
0
600
FC output
running distance
500
400
42km/h
300
velocity
200
100
0
0
Fig 4.1 Running test at test track
700
90kW
running distance [m]
velocity [km/h], power [kW]
At this time, we executed the running test at the test track (Fig 4.1). Our test track is about 650
meters long each way and the velocity limit at the curve is set to 40km/h. As the result of this running
test, the maximum velocity was 42km/h in the straight section and FC peak power was 90kW. 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 40km/h
and FC outputted 90kW occupied a large part of the total running test time.
20
40
60
80
running time [sec]
100
120
Fig 4.2 Example of running test result at test track
6.2 Running tests at rolling stock test plant
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 105km/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 100km/h
and FC outputted about 40kW occupied a large part of the total running test time.
30
105km/h
90kW
100
25
velocity
80
20
60
15
running distance
FC power
40
10
20
5
0
0
200
400
600
800
running time [sec]
1000
running distance [km]
velocity [km/h], power [kW]
120
0
1200
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
energy efficiency (%)
We defined FC energy efficiency by the equation (1).
FC output energy (kWh)
× 100
energy efficiency (%) =
(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.
100
80
60
40
20
0
0
20
40
60
80 100
FC output power (kW)
120
Fig 5 Relationship between FC output power and energy efficiency
FC energy efficiency has a peak at about 40-45kW: it is better at 40-45kW than at 90-120kW.
Based on the equation (1), we calculated FC energy efficiency (Table 2).
Table 2: FC energy efficiency in each running condition
Rolling stock
Running condition
Test track
test plant
FC output energy (kWh)
1.38
13.3
Electric energy obtained from
2.77
25.3
consumed hydrogen (kWh)
Energy efficiency (%)
49.9
52.7
We could understand that FC energy efficiency is about 50% in both running conditions and is more
than 40% 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 40-45kW) 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
: 90% (worst state)
Kinetic energy => 92% (Motor) => 97.5% (Gear) => 97.5% (Inverter) => 99% (FL) => 97.5% (DC/DC)
=> 90% (Battery) => 97.5% (DC/DC) => 99% (FL) =>Inverter-input
Table 3: Energy efficiency advancement in case of utilizing regenerative energy
Rolling stock
Running condition
Test track
test plant
Energy efficiency (use only FC)
49.9
52.7
(%)
Regenerative energy calculated
from kinetic energy
0.47
3.07
(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).
fuel consumptio n(km / kg ) =
running distance(km)
amount of hydrogen consumed in the running(kg )
(2)
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= (
)
×
273( K ) + stored temperature(Celsius)
compressedcoefficient
1
×
× 2 × 10−3 (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
Rolling stock
Running condition
Test track
test plant
Running distance (km)
0.65
26.6
Consumed hydrogen (kg)
0.084
0.77
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
1,500V
FC
Auxiliary
FL
FC Chopper
(99%)
(97.5%)
Inverter
IM
(97.5%)
IM
Inverter
IM
Case 2: use FC and battery for a power supply
1,500V
FC
FL
FC
FL (99%)
Auxiliary
IM
Battery
(97.5%)
Chopper
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
・ Output with priority.
・ If SOC drops to 50%,
Battery
then output stops.
・ If SOC recovers to 55%,
then output restarts.
FC
Inverter
Coasting
Regenerating
Stopping
Charge
Charge
Charge
Not output
Output
120kW fully
Energy storage
--
・ If SOC drops to 50%,
then output 120kW fully.
Output
・ If SOC recovers to 55%, 120kW fully
then output stops.
Energy consume
--
We assumed the battery data as follows.
・ Initial SOC
: 60%
・ Maximum power : 120kW (the same powers as FC)
This algorithm is aimed at making SOC recover possibly to initial SOC (60%) 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
: 30.3 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)
1660kgf
Tractive Effort
1000
100
850kgf
2000 Tractive Effort
Motor Voltage
500
50
0
20
40
60
80
100
Motor Voltage
1500 Motor Current
150
1000
100
500
50
0
0
200
0
0
0
120
Motor Current (A)
150
Motor Current
Motor Current(A)
Tractive Effort (kgf/MM),
Motor Voltage (V)
1500
50
100
150
Velocity (km/h)
Velocity (km/h)
Fig 6.2 Powering characteristics
Fig 6.3 Braking characteristics
We assumed the running pattern as follows.
・ Speed limit
: 80 km/h (in all sections)
・ Stop time at station
: 40 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.
Incline
Velocity
200
20
40
0
30
-5
-10
20
Running
distance
10
0
0
5000
10000 15000 20000
time (sec)
-15
-20
-25
25000 30000
Fig 6.4 Result of running curve
Power (kW)
5
30
25
0
10
50
Battery power
FC output energy
FC power
100
15
60
Incline(‰)
Velocity(km/h),
Running distance(km)
70
25
20
Energy (kWh)
80
-100
15
-200
10
-300
5
-400
Regenerative power
-500
0
5000
10000
15000 20000
time (sec）
25000
0
30000
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 (60%) after the completion of all the running.
Energy efficiency
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
80.5
56.3
consumed hydrogen (kWh)
Energy efficiency (%)
51.3
75.7
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, 0.97% 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)
+ 0.5
- 2.8
Potential energy (kWh)
+ 0.045
(+3.4%)
- 0.269
(-0.97%)
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 30% compared to that in
Case1.
9. Conclusion
We made 100kW 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 50% and was more than 40% 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 40-45kW 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 30% in fuel consumption by
the use of regenerative energy.
10. 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 100kW class fuelcell (FC) system
for railway vehicle traction”, THE2007 ANNUAL MEETING RECORD I.E.E. JAPAN, Vol.5, No.157,
pp.236-237 (2007).
[2] K.Ogawa T.Yamamoto T.Yoneyama “Evaluation of efficiency and fuel consumption rate in running
test of fuel cells powered railway vehicle”, The2007 Annual Conference of I.E.E. of JAPAN.
Industry Applications Society, Vol.3, No.35, pp. 239-242, (2007).