A Marelli team led by Fernando Damasceno, a specialist in ethanol-powered engines, realized they could exploit that same feedback loop to determine, indirectly, the ethanol percentage in the fuel mix. Here’s how: let’s say you are running on pure gasoline. If you hit the gas pedal and add air to the fuel mix going into the cylinders, the ECU easily calculates the amount of fuel needed to keep things “happy,” that is, to reach the stoichiometric ratio. Now suppose there’s some ethanol, in addition to gasoline, in the tank. The ethanol—whose energy density is less than gasoline’s—reduces the stoichiometric air-to-fuel ratio of the mixture, and that means you need more fuel in proportion to air to burn both completely.

But if the ECU doesn’t know how much ethanol is in the tank, how does it know what the new stoichiometric ratio is? It doesn’t, initially. The ECU keeps increasing the amount of fuel injected while it monitors the oxygen probe at the exhaust. It knows when the stoichiometric ratio has been reached when it determines there is no oxygen there. The ECU records the fuel increment and compares it to values stored in its memory, and in that way it finds that the mixture is, say, 90 percent gasoline and 10 percent ethanol. Each time fuel is added to the tank, the ECU repeats the process.

Marelli’s sensorless approach seemed promising, but still the company got nowhere with automakers. “They said it wouldn’t work,” Bonfiglioli recalls. “We had to show them our demonstration vehicles.” That was in 2000. It was only three years later that Volkswagen, in Wolfsburg, Germany, decided to give it a shot. In March 2003, using Marelli’s flex-fuel system, the automaker introduced the Gol TotalFlex, the first flex car in Brazil.

That launch, combined with the Brazilian government’s decision to give flex cars a tax break, spurred a revolution in the country’s automotive industry. Other big auto­makers rushed to announce their flex offerings, and since then, sales of flex cars have sky­rocketed. In 2003, they corresponded to only 3.5 percent of total sales; now that share has risen to nearly 90 percent. Marelli supplies its flex ECUs to Brazil’s largest automakers, including Fiat, Ford, and Volkswagen, and it has about 50 percent of that market, with the rest divided between Bosch and Delphi Corp., in Troy, Mich.

“To some extent, what’s happening in terms of cars being sold there is fairly directly attributable to the capability that Marelli’s solution has provided,” says Sharfman, the auto expert in New York City. “So if you started to have an efficient source [of ethanol] here or in some other country, I think that over time this kind of solution is going to spread.”

Flex-fuel technology has succeeded in Brazil mainly because consumers saw a chance to save money. Because ethanol comes from an agricultural product, its price varies according to crop seasons. In October 2006 in southeast Brazil, gasoline cost an average of $1.12 per liter and ethanol was $0.63. You’ll go farther on 1 L of gasoline, but in the end the cost per ­kilometer is still less with ethanol. At 1000 km (621 miles) per month, flex fuel could save the average driver around $200 per year.

“The Siena TetraFuel advances this flexibility one step further,” says Marco Antonio Saltini, director of government relations at Fiat in Brazil. “Consumers see a chance to save even more using natural gas.”

Running on natural gas, whose cost per kilometer in Brazil is less than half that of gasoline, someone who drives more than 160 km per day can recover the additional cost of the TetraFuel system in nine months to a year, saving some $1095 annually, Saltini says. He adds that implementing a natural gas system by retrofitting would cost twice as much as doing the same with the TetraFuel system.

Still, it’s a niche market. Fiat hopes to sell around 2500 Siena TetraFuel cars, currently priced at $19 124 each, this year. It’s a tiny fraction of the more than half a million vehicles that Fiat’s Brazilian unit sold in 2005. But Saltini notes that because the car can run on pure gasoline, Fiat can sell it elsewhere in Latin America. In fact, the automaker says the Siena TetraFuel should hit the Argentinean market early this year.

The TetraFuel technology has interesting possibilities in other markets as well. The European Union plans to increase the share of biofuels in transportation to 5.75 percent by 2010, and many experts see a big push toward E85, the 85 percent ethanol and 15 percent gasoline blend. The same trend is occurring in a host of other countries, including the United States, China, India, and Japan.

And don’t forget about the TetraFuel’s ace in the hole: its natural gas capability. Natural gas has historically cost less than oil, and reserves are plentiful, so it could work as another transitional fuel if gasoline prices go up. There are already more than 5 million natural-gas vehicles around the world. Argentina has a fleet of 1.5 million, and Brazil and Pakistan have more than 1 million each. Other countries investing in natural-gas cars include Iran, which has the world’s second-largest natural gas reserve; Germany, which plans to have more than 1000 natural-gas filling stations by the end of the year; and France, which has a program to let drivers fill up their natural-gas cars using home refueling units.

Marelli is discussing with other automakers the use of the technology outside Brazil, but the company declines to provide any details. Could the TetraFuel become a hit in Europe, Asia, or North America? Time will tell.

In the meantime, flex technology and ethanol could make energy production more regionalized, with countries producing biofuels where there’s arable land and favorable weather. Different fuels would be available in different places, and drivers wouldn’t have to worry about it. “The idea is to have a multifuel car that runs with the fuel it finds,” Bonfiglioli says.

“You can’t yet put water in,” he jokes. “But just wait.”