344
Alternative Fuels for Transportation
difference between the coolant and the air. In the case of a conventional ICE,
the highest temperature of the coolant is about 110°C, so there is a temperature difference of 80°C when the ambient air is 30°C. In the case of a PEFC
stack, however, the difference is only ~50°C. Therefore, the radiator of the
PEFC-stack system must be 60% larger in size than that for an ICE. However,
it is difficult to find space for installing such a large radiator in a vehicle. A
high temperature membrane capable of withstanding temperatures between
110 and 120 o C needs to be developed to resolve this issue.
The fuel supply infrastructure for FCVs is critical to their popularization.
However, hydrogen supply infrastructure exists scarcely at present. FCVs
need to have the same range as ICEVs. The tank mileage of FCVs should
be at least 500 km. Current FCVs can travel almost 100 km/kg of hydrogen.
Therefore, the hydrogen storage material and system must be capable of storing at least 5 kg of hydrogen. There are many candidate materials and systems
for storing hydrogen. A high-pressure hydrogen gas tank might be promising at present. Capability of hydrogen gas containers has been rising from
25–30 MPa, and is expected to increase to 50 or 70 MPa in the near future.
Carbon nanotubes could be a promising material, but only store 0.5 wt.%
hydrogen. Metal hydrides can store around 2 wt.% hydrogen but their hydrogen storage capacity needs to be improved to > 5 wt.%. Another critical issue
for the use of metal hydrides is the time required to store hydrogen. Several
tens of minutes are required for refueling. Alkaline hydride compounds
have good hydrogen storage capacity, but are difficult to recycle. It might be
difficult to use existing hydrogen storage materials in automobiles. Recently,
ammonia borane has been projected as a promising hydrogen carrier. The
efficiency of peripheral systems such as the air supply system and the heat
release capability of the cooling system also need to be improved to achieve
a compact and high-performance FC system.
11.9 FCV Power Train Configurations
The challenge in designing automotive fuel-cell power systems is in converting the electrical output from the fuel-cell into usable power for varying
system sizes (Williamson and Emadi 2002). Furthermore, the goal is to realize the full potential of the fuel-cell technology by using efficient methods to
convert fuel-cell output to a useful electrical/mechanical energy. In addition,
the conversion process must be cost effective.
The primary power required is a three-phase variable AC output for the
traction motor of the vehicle. It is noteworthy that a high peak-to-average
power ratio is generally required for the power electronics. If there is an
auxiliary energy storage system, the fuel-cell also needs to maintain the critical power ratio to the maximum. Secondary converters would be used for
Alternative Fuels for Transportation
difference between the coolant and the air. In the case of a conventional ICE,
the highest temperature of the coolant is about 110°C, so there is a temperature difference of 80°C when the ambient air is 30°C. In the case of a PEFC
stack, however, the difference is only ~50°C. Therefore, the radiator of the
PEFC-stack system must be 60% larger in size than that for an ICE. However,
it is difficult to find space for installing such a large radiator in a vehicle. A
high temperature membrane capable of withstanding temperatures between
110 and 120 o C needs to be developed to resolve this issue.
The fuel supply infrastructure for FCVs is critical to their popularization.
However, hydrogen supply infrastructure exists scarcely at present. FCVs
need to have the same range as ICEVs. The tank mileage of FCVs should
be at least 500 km. Current FCVs can travel almost 100 km/kg of hydrogen.
Therefore, the hydrogen storage material and system must be capable of storing at least 5 kg of hydrogen. There are many candidate materials and systems
for storing hydrogen. A high-pressure hydrogen gas tank might be promising at present. Capability of hydrogen gas containers has been rising from
25–30 MPa, and is expected to increase to 50 or 70 MPa in the near future.
Carbon nanotubes could be a promising material, but only store 0.5 wt.%
hydrogen. Metal hydrides can store around 2 wt.% hydrogen but their hydrogen storage capacity needs to be improved to > 5 wt.%. Another critical issue
for the use of metal hydrides is the time required to store hydrogen. Several
tens of minutes are required for refueling. Alkaline hydride compounds
have good hydrogen storage capacity, but are difficult to recycle. It might be
difficult to use existing hydrogen storage materials in automobiles. Recently,
ammonia borane has been projected as a promising hydrogen carrier. The
efficiency of peripheral systems such as the air supply system and the heat
release capability of the cooling system also need to be improved to achieve
a compact and high-performance FC system.
11.9 FCV Power Train Configurations
The challenge in designing automotive fuel-cell power systems is in converting the electrical output from the fuel-cell into usable power for varying
system sizes (Williamson and Emadi 2002). Furthermore, the goal is to realize the full potential of the fuel-cell technology by using efficient methods to
convert fuel-cell output to a useful electrical/mechanical energy. In addition,
the conversion process must be cost effective.
The primary power required is a three-phase variable AC output for the
traction motor of the vehicle. It is noteworthy that a high peak-to-average
power ratio is generally required for the power electronics. If there is an
auxiliary energy storage system, the fuel-cell also needs to maintain the critical power ratio to the maximum. Secondary converters would be used for