Fuel for debate: gas guzzlers are an environmental hazard. Can car engineers clean up their act? (Technology/Chemistry).

1 Then: Muscle Mania

More than a century ago, in 1886, the world celebrated an invention that would transform history--the modern gasoline-powered car, developed by German engineers. "Streets were filled with horse waste," explains University of Washington engineering professor Adam Bruckner. "So when the automobile came around, it was seen as a clean alternative to the carriage." Less than half a century ago, it started to dawn on scientists that this engineering marvel, the gasoline-burning combustion engine, might be a far more dangerous environmental threat than horse manure.

Besides belching out toxic chemicals, each gallon of gas burned by a modern American car produces 20 pounds of carbon dioxide (a heat-trapping gas in Earth's atmosphere thought to cause global warming), according to the Union of Concerned Scientists. Still, that number beats C[O.sub.2] auto emissions in the 1970s, when "muscle cars" like the Chevy Camaro--small vehicles with monster engines--were the rage.

In 1970, the U.S. government passed the Clean Air Act, requiring cars to become more fuel efficient: Efficiency is measured by the number of miles a car runs per gallon of fuel (mpg). Since a car with greater efficiency uses less fuel to travel the same distance, it spews fewer pollutants into the air (see graph, above). Since the mid-'70s, C[O.sub.2] emissions from cars have been slashed nearly in half.

2 Now: Livin' Large

Leave the limo at home--the hottest celebrity wheels these days are SUVs (sport utility vehicles). And celebs aren't the only ones in the driver's seat. Today, more than 70 million SUVs cruise American highways, and the number keeps soaring. The problem: Most SUVs are inefficient gas guzzlers that only fuel atmospheric pollution.

The U.S. is the world's top gas-guzzling culprit, consuming 8 million barrels (336 million gallons) of oil daily to power cars and tracks--or two thirds of all U.S. daily oil use. Oil is a fossil fuel drilled from wells that can't be replenished, Bruckner explains: "In 50 years we'll run dry." Which means gasoline, a fuel refined (purified) from oil, will soon be in short supply.

The U.S. is also the world's single largest emitter of carbon dioxide gas (see pie chart, above left), so many scientists think one way to both save oil and curb C[O.sub.2] emissions is to make vehicles even more fuel-efficient. "We've saved 60 billion gallons of oil since fuel economy standards were set in the '70s," says David Friedman of the Union of Concerned Scientists. "I'm optimistic we'll eventually develop a technology that doesn't run on fossil fuel at all. It's too bad we need it right now."

3 Soon: Your Future Wheels?

Imagine a car without pedals or a steering wheel that handles as smoothly as a Porsche but doesn't belch a single pollutant. Impossible? The Hy-wire is General Motors' latest futuristic car design: It boasts no engine but is powered by a fuel cell, a battery-like unit that runs on hydrogen gas and emits only water--clean enough to drink (see diagram, p. 12)!

Unlike a combustion engine that uses mechanical thrust to propel a car forward, a fuel cell creates an electrical current (path on which electricity flows) to both move and control the car. The Hy-wire's steering wheel looks more like an X-box video-game controller or pushbutton controls in fighter jets, which steer planes "by wire" (with electricity). A punch of one button, and the car takes off. Push a different button and it stops.

Another feature: Fuel cells can be flat, which means engineers are free to create designs for future cars that won't need a hood to conceal a bulky combustion engine. "Cars used to look like a horse-drawn carriage," says fuel-cell expert Romesh Kumar of Argonne National Laboratory in Illinois. "We don't have to be bound by what a car looks like today."

But fuel-cell technology is still largely on the drawing board, and GM won't launch the Hy-wire until 2010. While Honda has already launched a road-ready fuel-cell prototype, its hydrogen gas must still be made using natural gas instead of renewable solar power or wind energy. And unlike gasoline, hydrogen--the lightest element on the periodic table--must be pressurized to fit in the small storage tanks on board a fuel-cell car, a potential danger. So engineers predict it will take two decades to perfect the mass manufacture of fuel-cell vehicles.

Tomorrow's Fuel: Clean and Mean

HEATWAVE Lean against the hood of any car after driving it a few miles and you'll feel like you're up against an open oven. Temperatures inside a combustion engine (also called a heat engine) can soar to thousands of degrees Fahrenheit. But the heat emitted by a fuel cell wouldn't even boil water. What gives?

"The physics of the universe sets limits to the energy you can extract from a heat engine," says Bruckner. In a combustion engine, a spark plug ignites gasoline from a fuel tank to create an explosion. But only about 20 percent of the chemical energy (energy stored in the bonds of a molecule) released in the explosion becomes mechanical energy, or energy that thrusts the car forward. The rest is lost as heat.

"There's no fire inside a fuel cell," says Bruckner. Instead, hydrogen gas is converted into electrical energy (see Fuel Cell Car, left). This electricity then flows to an electric motor, a machine that converts electricity into motion. In all, a fuel cell converts up to 50 percent of energy from hydrogen into motion instead of heat.

SADDLE UP Harnessing energy from a heat engine is kind of like trying to saddle a wild horse. That's because heat results from the increased random motion of molecules, Bruckner explains. Electrical energy from a fuel cell is easier to control--it's a stream of charged particles that follow a circuit (closed path).

Think of a fuel cell as a battery with a metal anode (negative end) and cathode (positive end) separated by a plastic membrane, says Kumar. The difference in electrical charge between the positive and negative sides is called potential (measured in volts). A battery with bigger potential produces more energy.

A single fuel cell couldn't power a hair dryer. But the 200 fuel cells in GM's Hy-wire are connected in a stack to produce a total of 125 to 200 volts--enough electric potential to power 67 hair dryers (see Fuel Cell Stack, left).

UNDER CONTROL A single hydrogen atom consists of one proton in the nucleus, or center, and one electron in orbit around the nucleus. In a fuel-cell reaction, hydrogen gas is stripped of electrons at the anode (see How Fuel Cells Work, left). The negatively charged particles then shoot through a wire circuit attracted by the positive cathode. If this battery were in a flashlight, the electricity would light the bulb. In a fuel-cell powered car, it drives the electric motor.

Next, oxygen from the air gains electrons, at the cathode. The leftover protons (positively charged hydrogen atoms) skip the circuit and pass through the plastic membrane. Once they cross over, two hydrogen protons hook up with one negatively charged oxygen atom to form water as a steamy vapor.

THINK: What is the relationship between fuel efficiency and C[O.sub.2] emissions? What might be one way the government can help curb the effects of global warming today?

FUEL CELLS:

Electric Power From Hydrogen Fuel

Hydrogen packs almost three times more energy than gasoline. Fuel cells can harness that energy for clean efficiency.

HOW FUEL CELLS WORK

1 Hydrogen gas is fed to the anode where it splits into electrons and protons.

2 Electrons exit the anode through an electrical circuit.

3 Only protons pass through the plastic membrane.

4 Oxygen combines with hydrogen protons to form water.

[ILLUSTRATION OMITTED]

AVERAGE EFFICIENCY
OF NEW VEHICLES

Miles Per Gallon (MPG)

Year

1977  15.2
1980  23.1
1985  25.4
1990  25.4
1995  24.9
2001  24.4

SOURCE: U.S. DEPT. OF TRANSPORTATION, 2002

Note: Table made from line graph.

GLOBAL C[O.sub.2] EMISSIONS: THE TOP 6 BELCHERS

Global emissions total 6,457 million metro tons. How many metric tons does the U.S. emit? One third of U.S. emissions come from vehicle exhaust. How much is that in metric tons?

REST OF THE WORLD
USA                23.2%
CHINA               8.9%
RUSSIA              6.3%
JAPAN               4.9%
INDIA               4.6%
GERMANY             3.6%

SOURCE: U.S. DEPT. OF ENERGY, 1999

Note: Table made from pie graph.

Did You Know?

* The fuel cell was invented in 1839 by amateur scientist Sir William Grove--before the first combustion engine. But the fuel cell failed to attract scientific interest because it's so much costlier to produce than the gasoline engine.

* The space program has used fuel cells since the 1960s to power electrical systems on board piloted spacecrafts such as Gemini and Apollo, and later to power the space shuttle and International Space Station.

* A fuel-cell car can accelerate faster and haul more weight than a conventional combustion engine. "You can even have a fax machine or microwave inside once electricity is on board," says David Friedman of the Union of Concerned Scientists.

* Take any car on the road today, add a fuel cell, and the fuel economy (number of miles the car can travel per gallon of gasoline) would be 2.5 to 3 times greater, says Romesh Kumar of Argonne National Laboratory.

Cross-Curricular Connection

History: Research the history of the automobile and create a timeline extending into the future. Include milestones in the progress toward a hydrogen-powered car.

Critical Thinking: Research and write a short position paper on why Americans should or should not drive large vehicles like SUVs. Present your arguments in a crass debate.

Resources

Airhead, a Web site that promotes environmental-impact awareness, has an emissions calculator, to tally your own contribution to global C[O.sub.2] emissions: www.airhead.org/

A recent article in Time magazine presents the heated national debate over SUVs: "Why SUVs are all the Rage," by John Cloud, Time, February 24, 2003

Students can compute the gas mileage of their family's vehicles and learn more about how to save gasoline at: www.fueleconomy.gov/