Technology
Fleet use offers niche for electric vehicles Short-range, commercial vehicles such as taxis, small buses, vans show promise as outlets for electric propulsion Given the present state of battery technology, the small urban runabout—a glorified golf cart suitable for shopping and neighborhood errands—offers the only real opportunity for near-term development of electric vehicles, right? Wrong, says Lucas Industries, the U.K.based automotive and electrical equipment conglomerate. At the Society of Automotive Engineering Congress and Exposition, held late last month in Detroit, Lucas engineers argued that the private car "is a difficult and probably inappropriate application of current electric drive technology." Much more appropriate, according to Lucas, is the development of electric fleet vehicles for urban applications: taxis, mediumsized buses, and light trucks in the 750to 1250-kg range. Most of the time, Lucas says, most cars travel daily distances that are well within the capabilities of an electric vehicle on a single battery charge. But the occasional need to travel several hundred kilometers in a day at high speed just can't be met with an electric vehicle. Even if new high-energy-density batteries are developed successfully, the company adds, very large investments would be required to provide the roadside backup facilities that vehicles fitted with such batteries would need. Urban fleet vehicles, on the other hand, make fullest use of the advantages of electric propulsion, Lucas contends. Daily operations tend to follow a predetermined schedule, and a working range of 120 km is sufficient. Such vehicles spend a significant portion of the time either stationary—when internal combustion engines would waste fuel at idle—or coasting, and thus not drawing energy from the batteries. Usually, they can return to a base during the day for battery exchange or boost recharge, if necessary. Following that philosophy, Lucas has been working on electric vehicles for about seven years. A year ago its first effort, a 34-passenger bus, went into service in Manchester. Since last summer the London post office has been evaluating a fleet of 20 electric-powered
Electric vehicle being developed by the U.K.'s Lucas Industries (above) for possible commercial use features a pullout tray for its lead-acid batteries vans. However, those vehicles are standard vehicles converted to electric drive. At the Detroit show, Lucas exhibited its first "purpose-built" electric vehicle, a taxi designed to meet the strict specifications for dimensions, comfort, and maneuverability set forth by the London police. In fact, the boxy taxi, although a meter shorter than the typical London taxi of today, has more generous interior dimensions. It weighs about 2250 kg with batteries, compared to an average 1600 kg for London taxis now in service. The taxi is powered by a 50-hp, 216volt motor, transversely mounted in front and driving the front wheels. Top speed is about 90 km per hour. Range is about 160 km—more than enough, Lucas says, to last through one eighthour shift in London traffic. A replaceable pack of 36 6-volt leadacid batteries furnishes energy for the taxi. The 1000-kg pack, with an energy density of 38 watt-hours per kilogram, comprises 40% of the vehicle's weight. Lucas contends that the lead-acid battery can meet the power needs of the next generation of electric batteries, and that the success of electric vehicles need not depend upon the successful development of zinc-chlorine, lithiumsulfur, or other high-energy-density batteries. In any event, the company believes, the lead-acid battery probably will be "it," for all practical purposes, for the rest of this century. Thus, instead of
waiting for breakthroughs in new battery types, one should take more note of the advances that have been made in lead-acid batteries. Lucas, pointing out that the lead-acid batteries of today have twice the energy density of those of just a few years ago, says it expects to make further progress in energy/ weight/volume ratios and also to produce a lead-acid battery with a life of several hundred charge-discharge cycles. In the Lucas taxi, power input to the motor is regulated by a chopper-type controller and associated solid-state circuitry. Lights and other electrical accessories are powered not by the traction batteries but by an auxiliary 12volt battery. The latter is kept charged by a converter unit energized by the traction batteries. This arrangement, Lucas explains, makes it possible to use the accessories while the main battery pack is being exchanged. The taxi is kept warm by a kerosine-fueled heater. Lucas admits that the initial price of March8, 1976 C&EN
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an electric vehicle will be, at least in the foreseeable future, higher than that of its internal combustion counterpart. However, the important cost is not the first cost but the total cost. In start-stop driving situations, Lucas believes, a combination of lower operating costs and reduced maintenance requirements will make electric taxis and similar urban vehicles more economical overall. Lucas' assessment of the outlook for private electric autos may not be altogether valid for the U.S., where second cars are a commonplace. An Energy Research & Development Administration study concludes that "even lead-acid battery technology probably will enable electric autos to be widely applicable in urban areas as second cars." Along that line, the Copper Development Association has commissioned the development of an electric "town car." Results of the program to date were presented at the SAE meeting. The CDA car, although definitely an urban vehicle, is a sporty little subcompact, not a golf cart. With an overall length of 3.68 m and a curb weight of 1330 kg, the
car carries two passengers with reasonable space and comfort. Like the Lucas taxi, the CDA town car was designed from the ground up as an electric vehicle. For instance, the battery "tunnel" is also the car's main structural member. A 40-hp motor accelerates the vehicle to 50 km per hour in 11.2 seconds and gives a top speed of 100 km per hour. The battery pack consists of 18 6-volt batteries mounted in a tray and removable from the rear of the vehicle. The system can operate at either 54 or 108 volts. Range is about 120 km, and completely discharged batteries can be recharged in about eight hours. A minicomputer provides electrical control. An auxiliary 12-volt battery, charged from the main pack, powers electrical accessories. The passenger compartment is warmed and defrosted by a gasoline heater. Despite the vehicle's sponsorship, the CDA car's body is made of steel, not copper. Of course, those motor windings do take a lot of copper. Also, the vehicle uses copper alloy brake drums, which
New system monitors stack gas pollutants A continuous, long-term method for pollutant monitoring of process and power plant stacks that eliminates difficulties of current methods has been developed by Dr. James K. Ferrell and Dr. Richard M. Felder of North Carolina State University's department of chemical engineering. Key to the method is use of a polymer tube as a selectively permeable sampling interface. Analysis of stack gas effluents—once limited to batch sample removal and wet chemical techniques—now is often done by continuous instrumented methods, Ferrell notes. However, gas samples withdrawn from stacks usually must be "conditioned" before passing to a wet chemical sampling train or continuous analyzer. This conditioning entails removal of condensable vapors, acid mists, solid particulates, and other chemical species that would interfere with analysis for the desired pollutant, and might involve heating to maintain the pollutant gas above its dew point. What Ferrell and Felder, with several graduate students, have done is to develop a method eliminating the need for such conditioning. The scientists insert a hollow, V4-inch-diameter U-tube containing a polymer segment into a stack through a conventional port. They continuously pass a carrier gas (cleaned, dried air) through the U-tube. The pollutant being measured permeates from the stack gas through the polymer segment walls into the carrier gas, which sweeps it out to a flame photometer or other continuous analyzer. This determines and continuously records the pollutant concentration. The Raleigh scientists calibrate the polymer tube in situ by sliding a hollow closed jacket over the tube and passing 20
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pollutant gas of known concentration through it. (There are a few instruments now available that use a permeable polymer interface within the instrument, Ferrell notes. However, no one is working on a system similar to his, as far as he knows, and samples still must be conditioned before passing to the available instruments.) The polymer tube in the North Carolina State system passes only the pollutant under observation, and screens out other materials. Water vapor causes no problems, for example, despite high stack humidities. With support from the Environmental Protection Agency, the Raleigh team so far has developed and tested systems to monitor sulfur dioxide and nitrogen oxides (NO x ). They find Teflon and fluorosilicone rubber tubes suitable for use as interfaces between SO2 stack gas concentrations of tens to thousands of parts per million and SO2 analyzers with ranges of 0.1 to 1 ppm. Teflon also can be used for NO x . Different wall thicknesses are used for different applications. The Raleigh scientists have carried out successful field tests on several power and process plant stacks, including the sulfur trioxide absorption tower of a sulfuric acid plant. They also found that the method accurately and rapidly monitored changes in power plant effluent SO2 when boiler feed was switched back and forth between clean natural gas and fuel oil containing 1.9% sulfur. Ferrell notes that the method should be able to monitor any effluent gas component present at moderate or low levels whose molecules are sufficiently permeable—for example, vinyl chloride,
are said to increase braking capacity and drum life. Even if electric vehicles find their niche, they won't be the ultimate remedy for energy and environmental problems. From the standpoint of total energy consumption, several studies have shown electric vehicles to be less efficient than gasoline-powered vehicles of comparable performance and payload. Use of advanced batteries and higher efficiency electrical components—with accompanying weight reductions— won't reverse that situation, according to investigators at General Motors Research Laboratories. "Only if petroleum is unavailable is there any energy consumption advantage for electric vehicles," they conclude. The ERDA study reaches similar conclusions, but adds that where petroleum conservation is the important factor, the electric can render useful service. But overall air quality would be little affected, and costs of auto travel would be substantially higher until battery advances allowed major reductions in battery depreciation costs. D chloroform, or hydrogen sulfide. His group now is working on light hydrocarbons. The system also might be used via a feedback control loop to modify process conditions when too much of a pollutant is produced. The method's economics have not yet been studied closely. It may cost about the same initially as existing systems, but its greater simplicity and less expensive maintenance should be advantages. Work on the SO2 and NO x systems at North Carolina State is nearly wound up, and "it's up to instrument makers to take it further now," Ferrell says. He has "neglected" to make commercial contacts or to apply for patent protection as yet, he observes. Indeed, his system may no longer be patentable, because of publication about it. D
Dr. James Ferrell tests permeable interface system for stack gas monitoring
