Batteries are the Achilles's heel of the digital age. How about replacing them with fuel cells - or jet engines?
Battery research has been one of the embarrassing failures of technological civilization, up there with artificial intelligence, jetpacks, household robots, and finding a cure for cancer. The practical consequences of this failure range from millions of chronically exhausted laptops that poop out over Denver on a cross-country flight, to our inability to create a powerful electric car.
Stored energy generally comes in two flavors: cold batteries and hot engines. Batteries are either sealed cells of standing liquids (like the lead-acid battery that comes in your automobile) or solid packs of chemicals. They're small, light, and can run at room temperature. But they're also relatively weak. A century of research has explored ways to make chemical batteries as powerful as combustion engines with little success.
Continuously fueled combustion engines, on the other hand, produce lots of power per pound, partly because they don't need to carry all of their latent energy inside. In a turbojet engine, for instance, the outside air is pulled in, compressed by spinning blades, and mixed with atomized fuels. The blend is then ignited in combustion chambers to create a powerful thrust. Unfortunately, these engines are large, heavy, and hot.
The simplest and most efficient way of pulling current out of chemistry is the fuel cell, which is based on the scientific concept of electrocombustion. Fuel cells work by combining oxygen, which has a fierce passion for electrons, with hydrogen. When the two elements are introduced, the oxygen goes insane with electron desire. It yanks electrons off the hydrogen molecules and carries them back, generating electricity (and water). The basic idea for electrocombustion was hit on as far back as 1839. In practice, however, hydrogen and oxygen are tricky substances to work with, so electrocombustion rapidly leads to bulky, expensive structures.
That could be changing. About three years ago, the power-cost ratio of fuel cells started dropping; the price of cells plummeted while their power surged. Romesh Kumar, a fuel cell technology specialist at Argonne National Laboratory in Argonne, Illinois, says this development is made possible in part by computational fluid dynamics, a computer-based simulation technique. This technology allows engineers to employ advanced algorithms and heavy number crunching to quickly fine-tune the fuel cell fabrication process. Engineers use the data to extract more precise dimensions and ratios, allowing them to save on material costs and build more powerful, compact cells.
The result, for instance, is that more energy can be used to pull the car instead of power the system. This method may not lead to the immediate arrival of a practical electric car, but last May, Mercedes-Benz probed the market with a commercial model powered by a fuel cell running 50,000 watts - about the equivalent of a 67-horsepower engine.
Another solution to exhausted batteries: shrink the airbreathers. So far, work in this area has proven impractical. Turbine engines are complex chunks of precisely engineered machinery and their components aren't easily miniaturized. But an engineering project at MIT is using lithographic etching and layering techniques, developed by the computer chip industry, to construct a tiny jet engine. The gas turbine and generator together (sans the fuel supply) would be about one cubic centimeter, or about the size of a shirt button.
While the final specs are far from frozen, the tiny engine is expected to generate approximately 50 watts; it should last 50 times longer than a AAA battery.
The microjet could run at high speeds (2 million rpm) and is expected to generate extremely hot temperatures (1,600 kelvin), thus avoiding the production of pollutants. The unit's high heat is carried away by the jet exhaust. The approximately 1 million hertz-whir of the microturbine would be imperceptible to human ears.
Engineering the miniature turbine, however, could prove tricky. Few researchers are skilled in the nuances of micromechanics. Scientific challenges must be explored and overcome. For example, one of the greatest technical hurdles facing the researchers at MIT will be in microfabricating the materials needed for the tiny turbines. In order to solve this problem, the scientists are in the labs busily experimenting with silicon carbide-based materials of the type used in high-temperature electronics.
Many groups are keeping a sharp eye on MIT's research into fingertip jet engines. The US Army, for instance, is concerned about the weight of batteries that its soldiers must carry in the field. In 1994, the Army gave MIT US$5 million to forge ahead with research.
Batteries are not the only potential application for microturbines. With the right design, they could power the flight of small objects around the yard or house. If you want your keys, they would come to you. You wouldn't have to weigh down your pockets; just ask your belongings to trail after you, 20 feet in the air, until you need your wallet or compact. The device might also set back mugging, at least until the criminals develop their own technoraptors that could swoop down and seize wallets on the fly.
Practical application of these projects may be years away. The scientific investigation is still exploratory, and many kinks must be worked out. But one thing is certain: the demand for increased battery potency is so great that research is likely to be carried through, no matter how protracted or costly.
