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91. FUEL CELLS AND ADVANCED TECHNOLOGIES. Figure 91-1 Ford Motor Company has produced a number of demonstration fuel-cell vehicles based on the Ford Focus. Figure 91-2 Hydrogen does not exist by itself in nature. Energy must be expended to separate it from other, more complex materials.
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91 FUEL CELLS AND ADVANCED TECHNOLOGIES
Figure 91-1 Ford Motor Company has produced a number of demonstration fuel-cell vehicles based on the Ford Focus.
Figure 91-2 Hydrogen does not exist by itself in nature. Energy must be expended to separate it from other, more complex materials.
Figure 91-3 The Mercedes-Benz B-Class fuel-cell car was introduced in 2005.
CHART 91–1 Fuel cell types and their temperature operating range.
Figure 91-4 The Toyota FCHV is based on the Highlander platform and uses much of Toyota’s Hybrid Synergy Drive (HSD) technology in its design.
Figure 91-5 The polymer electrolyte membrane only allows H+ ions (protons) to pass through it. This means that electrons must follow the external circuit and pass through the load to perform work.
Figure 91-6 A fuel-cell stack is made up of hundreds of individual cells connected in series.
Figure 91-7 A direct methanol fuel cell uses a methanol/water solution for fuel instead of hydrogen gas.
Figure 91-8 A direct methanol fuel cell can be refueled similar to a gasoline-powered vehicle.
TECH TIP: CO Poisons the PEM Fuel-Cell Catalyst Purity of the fuel gas is critical with PEM fuel cells. If more than 10 parts per million (ppm) of carbon monoxide is present in the hydrogen stream being fed to the PEM anode, the catalyst will be gradually poisoned and the fuel cell will eventually be disabled. This means that the purity must be “five nines” (99.999% pure). This is a major concern in vehicles where hydrogen is generated by reforming hydrocarbons such as gasoline, because it is difficult to remove all CO from the hydrogen during the reforming process. In these applications, some means of hydrogen purification must be used to prevent CO poisoning of the catalyst.
Figure 91-9 Powertrain layout in a Honda FCX fuel-cell vehicle. Note the use of a humidifier behind the fuel-cell stack to maintain moisture levels in the membrane electrode assemblies.
FREQUENTLY ASKED QUESTION: What Is the Role of the Humidifier in a PEM Fuel Cell? The polymer electrolyte membrane assembly in a PEM fuel cell acts as conductor of positive ions and as a gas separator. However, it can only perform these functions effectively if it is kept moist. A fuel-cell vehicle uses an air compressor to supply air to the positive electrodes of each cell, and this air is sometimes sent through a humidifier first to increase its moisture content. The humid air then comes in contact with the membrane assembly and keeps the electrolyte damp and functioning correctly.
Figure 91-10 The Honda FCX uses one large radiator for cooling the fuel cell, and two smaller ones on either side for cooling drive train components.
FREQUENTLY ASKED QUESTION: When Is Methanol Considered to Be a “Carbon-Neutral” Fuel? Most of the methanol in the world is produced by reforming natural gas. Natural gas is a hydrocarbon, but does not increase the carbon content of our atmosphere as long as it remains in reservoirs below the earth’s surface. However, natural gas that is used as a fuel causes extra carbon to be released into the atmosphere, which is said to contribute to global warming. Natural gas is not a carbon-neutral fuel, and neither is methanol that is made from natural gas. Fortunately, it is possible to generate methanol from biomass and wood waste. Methanol made from renewable resources is carbon neutral, because no extra carbon is being released into the earth’s atmosphere than what was originally absorbed by the plants used to make the methanol.
Figure 91-11 Space is limited at the front of the Toyota FCHV engine compartment, so an auxiliary heat exchanger is located under the vehicle to help cool the fuel-cell stack.
Figure 91-12 The secondary battery in a fuel-cell hybrid vehicle is made up of many individual cells connected in series, much like a fuel-cell stack.
Figure 91-13 The Honda ultracapacitor module and construction of the individual cells.
Figure 91-14 An ultracapacitor can be used in place of a highvoltage battery in a hybrid electric vehicle. This example is from the Honda FCX fuel-cell hybrid vehicle.
Figure 91-15 Drive motors in fuel-cell hybrid vehicles often use stator assemblies similar to ones found in Toyota hybrid electric vehicles. The rotor turns inside the stator and has permanent magnets on its outer circumference.
Figure 91-16 The General Motors “Skateboard” concept uses a fuel-cell propulsion system with wheel motors at all four corners.
Figure 91-17 The electric drive motor and transaxle assembly from a Toyota FCHV. Note the three orange cables, indicating that this motor is powered by high-voltage three-phase alternating current.
Figure 91-18 The power control unit (PCU) on a Honda FCX fuel-cell hybrid vehicle is located under the hood.
Figure 91-19 Toyota’s FCHV uses a power control unit that directs electrical energy flow between the fuel cell, battery, and drive motor.
Figure 91-20 This GM fuel-cell vehicle uses compressed hydrogen in three high-pressure storage tanks.
Figure 91-21 The Toyota FCHV uses high-pressure storage tanks that are rated at 350 bar. This is the equivalent of 5,000 pounds per square inch.
Figure 91-22 The high-pressure fitting used to refuel a fuel-cell hybrid vehicle.
Figure 91-23 Note that high-pressure hydrogen storage tanks must be replaced in 2020.
Figure 91-24 GM’s Hydrogen3 has a range of 249 miles when using liquid hydrogen.
Figure 91-26 Carbon deposits, such as these, are created by incomplete combustion of a hydrocarbon fuel.
TECH TIP: Hydrogen Fuel = No Carbon Most fuels contain hydrocarbons or molecules that contain both hydrogen and carbon. During combustion, the first element that is burned is the hydrogen. If combustion is complete, then all of the carbon is converted to carbon dioxide gas and exits the engine in the exhaust. However, if combustion is not complete, carbon monoxide is formed, plus leaving some unburned carbon to accumulate in the combustion chamber. - SEE FIGURE 91–26 .
Figure 91-27 Both diesel and conventional gasoline engines create exhaust emissions due to high peak temperatures created in the combustion chamber. The lower combustion temperatures during HCCI operation result in high efficiency with reduced emissions.
Figure 91-28 A typical electric vehicle charging station on the campus of a college in southern California.
Figure 91-29 A conductive-type charging connector. This type of battery charging connector is sometimes called an AVCON connector, named for the manufacturer.
Figure 91-30 An inductive-type electric vehicle battery charger connector. This type of connector fits into a charging slot in the vehicle, but does not make electrical contact.
FREQUENTLY ASKED QUESTION: What Is NEDRA? NEDRA is the National Electric Drag Racing Association that holds drag races for electric-powered vehicles throughout the United States. The association does the following: 1. Coordinates a standard rule set for electric vehicle drag racing, to balance the needs and interests of all those involved in the sport. 2. Sanctions electric vehicle drag racing events, to: • Make the events as safe as possible. • Record and maintain official records. • Maintain consistency on a national scale. • Coordinate and schedule electric vehicle drag racing events. 3. Promotes electric vehicle drag racing to: • Educate the public and increase people’s awareness of electric vehicles while eliminating any misconceptions. • Have fun in a safe and silent drag racing environment. - SEE FIGURE 91–31 .
Figure 91-31(a) The motor in a compact electric drag car. This 8-inch-diameter motor is controlled by an electronic controller that limits the voltage to 170 volts to prevent commutator flashover yet provides up to 2,000 amperes. This results in an amazing 340,000 watts or 455 Hp.
Figure 91-31(b) The batteries used for the compact drag car include twenty 12-volt absorbed glass mat (AGM) batteries connected in series to provide 240 volts.
Figure 91-32 Wind power capacity by area. (Courtesy of U.S. Department of Energy)
Figure 91-33 A typical wind generator that is used to generate electricity.
Figure 91-34 The Hoover Dam in Nevada/Arizona is used to create electricity for use in the southwest United States.
