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11Статья поступила в редакцию 12.08.2010. Ред. рег. № 855
The article has entered in publishing office 12.08.2010. Ed. reg. No. 855
APPENDIX
From Nissan Technical Review No.59 (2006.Sep.)
PRESENT STATUS AND FUTURE ISSUES OF HYDROGEN STORAGE TECHNOLOGIES
H. Tamura, T. Iwase
Nissan Motor Co., Ltd.
1, Natsushima-cho, Yokosuka-shi, Kanagawa 237-8523, JAPAN
One of the important issues for fuel cell vehicles (FCVs) is further extension of the driving range. Possible solutions to this issue include improving fuel cell system efficiency, increasing the onboard hydrogen storage capacity and lightening the vehicle weight. The new 2005 model year X-TRAIL FCV is fitted with a 70-MPa high-pressure hydrogen storage system that achieves a driving range of 500 km. This paper describes the high-pressure hydrogen storage system adopted on the 2005 X-TRAIL FCV and reviews the current status and future issues of hydrogen storage technologies.
ПРИЛОЖЕНИЕ
Из бюллетеня «Nissan Technical Review», выпуск 59 (сентябрь 2006 г)
СОВРЕМЕННОЕ СОСТОЯНИЕ ДЕЛ И БУДУЩЕЕ ТЕХНОЛОГИЙ ХРАНЕНИЯ ВОДОРОДА
Х. Тамура, Т. Ивасе
Одним из важных вопросов развития автомобилей на топливных элементах является дальнейшее увеличение дальности пробега. Возможными подходами к решению этой задачи являются повышение КПД системы топливных элементов, увеличение емкости систем бортового хранения водорода, а также облегчение конструкции автомобиля. Новая модель автомобиля на топливных элементах X-TRAIL, представленная в 2005 году, оборудована системой высокого давления для хранения водорода под давлением 70 МПа, которая обеспечивает дальность пробега 500 км. В данной статье описана система хранения водорода под давлением, установленная на автомобиле 2005 X-TRAIL FCV, а также приведен обзор современного состояния дел и будущего технологий хранения водорода.
Organization(s): Planning and Advanced Engineering Development Division, Advanced Vehicle Engineering Department, Advanced Vehicle Development Group, Manager.
Hiroaki Tamura
Organization(s): Nissan Research Center, EV System Laboratory, Administration Group, Manager.
Takakuni Iwase
Introduction
This paper describes the hydrogen storage system adopted on the 2005 model year X-TRAIL FCV and reviews the present status and future issues of hydrogen storage technologies for fuel cell vehicles (FCVs).
Hydrogen Storage System used on 2005 X-TRAIL FCV
The 2005 X-TRAIL FCV adopts a high-pressure hydrogen storage system that compresses hydrogen for storage on-board the vehicle. This system comprises the following components: a hydrogen storage system consisting of a high-pressure hydrogen tank for storing compressed hydrogen; a hydrogen charging system for introducing hydrogen from a hydrogen fueling station into the high-pressure hydrogen storage tank; a hydrogen fueling system for reducing the pressure of the stored hydrogen to the specified level and supplying the fuel to the powerplant; and a detection system for informing the driver of the remaining hydrogen level in the tank and any detected abnormal conditions.
Hydrogen fuel is currently available at more than ten hydrogen fueling stations located mainly in the Tokyo metropolitan area. At a hydrogen fueling station, hydrogen is stored under high pressure in an accumulator and the charging of hydrogen to a vehicle is accomplished by using a pressure difference.
Overview of hydrogen storage system
The 2005 X-TRAIL FCV is fitted with one high-pressure hydrogen storage tank located under the rear-seat floor. Fig. 1 shows the location of the tank in the vehicle.
Fig. 1. Layout of the High-pressure Hydrogen Storage Tank
Fig. 2 is a photograph of the 35-MPa high-pressure hydrogen storage system used on the 2005 X-TRAIL FCV. A schematic of the gas circuit of the system is shown in Fig. 3.
An outline of the hydrogen storage system, hydrogen refueling system, hydrogen supply system and detection
system is given below.
Fig. 2. High-pressure Hydrogen Storage System (35 MPa)
Fig. 3. Gas Schematic of High-pressure Hydrogen Storage System (35 MPa)
Hydrogen storage system An in-tank valve assembly is provided at the inlet port of the high-pressure hydrogen storage tank and incorporates a solenoid for controlling the hydrogen supply electrically. The in-tank valve assembly also incorporates a safety valve that functions to discharge hydrogen and lower the high pressure inside the tank in the event the tank is exposed to extremely high temperature, such as in the case of a vehicle fire. A hydrogen temperature sensor is also incorporated in the in-tank valve assembly to measure the temperature of hydrogen inside the high-pressure storage tank.
Hydrogen refueling system Hydrogen is charged through receptacle that corresponds to the fueling port of a conventional gasoline vehicle. The receptacle incorporates a check valve to prevent the reverse flow of charged hydrogen. A check valve is also provided near the inlet of the in-tank valve assembly. A filter unit is provided in the piping between the receptacle and the in-tank valve assembly.
International Scientific Journal for Alternative Energy and Ecology № 9 (89) 2010
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Hydrogen supply system Hydrogen fuel is supplied from the high-pressure hydrogen storage tank to the powerplant via a high-pressure cut-off valve, a pressure reducing valve and a medium-pressure cut-off valve. The high-pressure and medium-pressure cut-off valves control the supply of hydrogen electrically. The pressure reducing valve functions to lower the high pressure of the hydrogen supplied from the tank to the specified pressure level. A pressure relief valve is also provided to release pressure if an abnormally high pressure is detected downstream of the pressure reducing valve.
Detection system Pressure sensors are provided at three locations and temperature sensors at two locations to measure the hydrogen pressure and temperature at various places in the system. If an abnormal pressure or temperature level is detected in the high-pressure hydrogen storage system, the hydrogen supply is shut off and a warning is issued to alert the driver.
Based on the output values of the pressure sensor upstream of the high-pressure cut-off valve and the temperature sensor incorporated in the in-tank valve assembly, the amount of hydrogen remaining in the high-pressure storage tank is indicated on the fuel gauge.
High-pressure hydrogen storage tank Fig. 4 shows a partial cross-sectional view of the high-pressure hydrogen storage tank, and Table 1 gives the major specifications of the tank.
The cylindrically shaped high-pressure hydrogen storage tank consists of an inner aluminum liner that is reinforced with an outer shell of carbon-fiber-reinforced plastic (CFRP). The in-tank valve assembly is provided at the inlet port. This high-pressure hydrogen storage tank allows a maximum tank pressure of 35 MPa and has an internal volume of 154 liters. It has been certified by the High Pressure Gas Safety Institute of Japan (KHK) as a compressed hydrogen fuel storage cylinder for automotive use.
Fig. 4. Cross-sectional View of Hydrogen Storage Tank (Type 3)
Table 1
Specifications of 35-MPa Hydrogen Storage Tank
Hydrogen charging and supply When hydrogen is charged to the high-pressure hydrogen storage tank in a short period of time, the hydrogen temperature inside the tank rises. Moreover, when hydrogen is supplied from the tank to the powerplant at a high flow rate, the hydrogen temperature inside the tank drops. The components of the high-pressure hydrogen storage system must be designed to take into account both the temperature rise during hydrogen charging and the temperature drop during hydrogen supply.
The 2005 X-TRAIL FCV ensures reliability against both the temperature condition during hydrogen charging at a hydrogen fueling station and the temperature condition during hydrogen supply to the powerplant.
Hydrogen charging The charging of hydrogen to the vehicle is accomplished at a hydrogen fueling station by making use of a pressure difference, but because the hydrogen fuel is again compressed inside the high-pressure hydrogen storage tank, the temperature of the hydrogen inside the tank rises.
Fig. 5 plots the hydrogen temperature rise in the tank as a function of the hydrogen charging time. The data indicate that the rise in hydrogen temperature inside the high-pressure storage tank increases with a shorter hydrogen charging time.
Max. charging pressure 35 MPa
Internal volume 154 liters
Materials Aluminum alloy & CFRP
Refueling time (min)
Fig. 5. Relationship between Refueling Time and Temperature Increase
Hydrogen supply As the hydrogen stored in the high-pressure storage tank is consumed by the powerplant, the pressure inside the tank decreases and the temperature of the hydrogen in the tank drops. This temperature condition is the opposite of what occurs during hydrogen charging.
Fig. 6 shows the drop in the hydrogen temperature inside the tank as a function of the hydrogen supply flow rate. The hydrogen temperature in the tank decreases more as the hydrogen supply flow rate increases.
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Fig. 7. 2005 Model Year X-TRAIL FCV 2005 (70 MPa)
Overview of 70-MPa high-pressure hydrogen storage system
Fig. 9 is a schematic of the gas circuit of the 70-MPa high-pressure hydrogen storage system. Similar to the 35-MPa high-pressure hydrogen storage system, the 70-MPa system also has one 70-MPa high-pressure hydrogen storage tank located under the rear-seat floor. In order to raise the storage pressure from 35 to 70 MPa, the durability of the system components was improved.
0 200 400 600 800 1000 1200 1400 1600 Hydrogen supply flow rate (NL/min)
Fig. 6. Relationship between Hydrogen Supply Flow Rate and Temperature Decrease
70-MPa Hydrogen Storage System
There is a need to increase the quantity of hydrogen stored on-board in order to extend the driving range, which is one of the critical issues of FCVs. As one approach to accomplishing that we have developed technologies for increasing the hydrogen storage capacity by raising the charging pressure from 35 MPa to a higher level of 70 MPa.
A version of the 2005 X-TRAIL FCV was also developed with a 70-MPa high-pressure hydrogen storage system specification that increases the vehicle's driving range to 500 km. Fig. 7 is a photograph of the 2005 X-TRAIL FCV equipped with this 70-MPa high-pressure hydrogen storage system. Fig. 8 is a photograph of the 70-MPa high-pressure hydrogen storage system that is fitted on some 2005 X-TRAIL FCV models.
This vehicle underwent driving tests that were conducted on a proving ground course and on public roads in Vancouver, Canada.
Fig. 9. Gas Schematic of High-pressure Hydrogen Storage System (70 MPa)
The number of piping connections in the 70-MPa high-pressure hydrogen storage system was reduced by concentrating and integrating the component parts into the in-tank valve assembly and the fuel supply module assembly. This also had the effect of improving the layout efficiency of the system in the vehicle.
70-MPa high-pressure hydrogen storage tank The specifications of the 70-MPa high-pressure hydrogen storage tank are given in Table 2. Compared with the 35-MPa high-pressure hydrogen storage tank, the 70-MPa tank adopts a high-elasticity, high-strength carbon fiber for the CFRP layer. The number of carbon fiber windings was also increased to enable the tank structure to withstand the high pressure of 70 MPa.
Table 2
Specifications of 70-MPa Hydrogen Storage Tank
Max. charging pressure 70 MPa
Internal volume 125 liters
Materials Aluminum alloy & CFRP
Fig. 8. High-pressure Hydrogen Storage System (70 MPa)
Under a high pressure of 70 MPa, the quantity of hydrogen that can be stored does not increase in proportion to the rise in tank pressure; instead, the rate of increase tends to decline owing to the nature of the actual gas. In addition, increasing the tank wall thickness is a factor that reduces storage efficiency. However, the
International Scientific Journal for Alternative Energy and Ecology № 9 (89) 2010
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development of this 70-MPa tank has increased the quantity of hydrogen stored on-board by 1.3 times compared with the 35-MPa tank, which contributed significantly to the attainment of a 500-km driving range.
This high-pressure hydrogen storage tank is Nissan's first such tank to be certified by KHK as a 70-MPa compressed hydrogen storage cylinder for vehicle use.
70-MPa in-tank valve assembly Fig. 10 is a photograph of the 70-MPa in-tank valve assembly. In addition to a cut-off valve, a safety valve and a hydrogen temperature sensor, the 70-MPa in-tank valve assembly also incorporates the check valve of the hydrogen charging system and the pressure reducing valve of the hydrogen supply system, thereby improving the efficiency of the in-vehicle layout.
This in-tank valve assembly is Nissan's first such component to be certified by KHK as a 70-MPa in-tank valve.
Fig. 10. 70 MPa In-tank Valve Assembly
Research on Future Hydrogen Storage Technologies
This section briefly describes other hydrogen storage technologies that are being researched, apart from high-pressure hydrogen storage systems, and touches on their principal issues.
Liquid hydrogen storage The technology for storing hydrogen in a liquid state is also being researched. In order to maintain hydrogen in a liquid state, its temperature must be kept at an extremely low level of -253 °C However, because current systems are unable to hold the temperature at such a low level for long periods of time, there is the issue that liquid hydrogen gradually evaporates and is discharged into the air.
Hydrogen-absorbing alloys This approach uses the properties of certain metals to absorb and store hydrogen. Compared with high-pressure hydrogen storage systems, hydrogen storage efficiency per unit of volume is superior, but storage efficiency per unit of weight is a problem because hydrogen-absorbing alloys are heavy. There is also the issue of how to process the heat of reaction accompanying hydrogen absorption and desorption.
High specific surface area materials (carbon materials and others) This technology makes use of the property that hydrogen is adsorbed on the surface of materials. The issues here concern the development of materials with good surface area efficiency and the technology for synthesizing such materials in large quantities.
Issues in High-pressure Hydrogen Storage Systems
As discussed above, high-pressure hydrogen storage technologies have the following issues:
(1) the quantity of hydrogen stored on-board must be increased to extend the driving range;
(2) measures are needed to prevent the hydrogen temperature rise that occurs in the tank when charging hydrogen quickly in a short period of time; and
(3) measures are needed to prevent the hydrogen temperature drop that occurs with a high hydrogen supply flow rate.
Another issue that must be addressed to popularize and diffuse FCVs in the future concerns:
(4) cost and weight reductions.
Further efforts are under way to develop the necessary technologies for resolving these issues and promoting the practical use of FCVs.
Chemical hydrides Hydrogen is stored as organic compounds or hydrogen compounds and extracted by pyrolysis or hydrolysis. In terms of FCV performance, the issues for pyrolysis include poor cold startability and insufficient transient response. One issue for hydrolysis is how to deal with the heat of reaction.
Conclusion
This paper has described the 70-MPa high-pressure hydrogen storage system fitted on the 2005 model year X-TRAIL FCV that enables the vehicle to attain a driving range of 500 km. While high-pressure hydrogen storage systems are steadily nearing completion, further technology development efforts are still needed to facilitate real-world use of FCVs. We are working to increase the on-board hydrogen storage capacity, while at the same time achieving further cost and weight reductions.
- TATA — LXJ
