Winner: The Omnivorous Engine

Brazilian fuel control system lets cars run on gasoline,ethanol, and natural gas

11 min read
Winner: The Omnivorous Engine
Illustration: Sean McCabe; Original Photo: Rrenata Ursaia

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Illustration: Sean McCabe; Original Photo: Rrenata Ursaia
Silverio Bonfiglioli of Magneti Marelli in Brazil

The hot asphalt of the test track stretches ahead. I stomp on the accelerator of the Fiat Siena and shift swiftly through the gears. The engine roars, the wind whooshes. A flock of quero-quero birds lazing nearby in the scorching Brazilian sun shriek in protest.

You’d never know it by looking at this peppy white sedan—or even by driving it—but it is one special little vehicle. When it comes to fuel, it is the most flexible car on earth. The Siena carries both natural gas and a mixture of gasoline and ethanol. It will burn the natural gas—the cheapest car fuel in Brazil—while cruising, and it will switch on the fly to the liquid fuel mix whenever it needs more power, for example, when passing another car or going up a hill.

And here’s the best part: you can put any mixture of gasoline and ethanol into its tank—from 100 percent gasoline and no ethanol to 100 percent ethanol and no gasoline. The engine automatically adjusts its ignition timing and the quantity of fuel injected into the cylinders on each cycle to get the most power out of whatever mixture you’ve got while keeping emissions under control.

Cars that can use different mixes of gasoline and alcohol have been around for years. And vehicles that let the driver switch between natural gas and gasoline aren’t new, either. But one car that can do both—switching automatically between the fuels and adjusting its engine to suit an arbitrary gasoline-alcohol mix—that’s very new indeed.

“The concept is very powerful, and it certainly is portable,” says William L. Sharfman, an automotive expert and principal of Sharfman & Co., a strategic consulting firm in New York City. “Once you have the concept, it’s probably applicable to other kinds of fuel.”

As concerns about high oil prices and greenhouse-gas emissions drive legislation that is pushing demand for such alternative fuels as ethanol to record levels in many countries, the allure of such an engine isn’t hard to fathom. Sitting next to me, in the passenger seat of the Siena, automotive engineer Alfredo Silvio Castelli considers the many fuel mixtures taking hold around the world and asks, “Why choose one if you can have all of them?”

Castelli is the head of the experimental laboratory here at the Brazilian unit of Magneti Marelli, in Hortolândia, an hour and a half drive from São Paulo. Marelli, a 4 billion subsidiary of the Fiat Group, is one of the world’s largest manufacturers of automotive systems, supplying fuel-­injection modules, robotized gearboxes, and onboard electronics to automakers and racing teams worldwide. Headquartered in Milan, Marelli has industrial and R&D facilities in 15 other countries, and it was a team of the company’s engineers here in Brazil that created the engine controller that lets the Siena run on multiple fuels.

Fiat recently began selling, in Brazil only, a version of the Siena with Marelli’s system. The car’s 1.4-liter, four-cylinder engine has one set of injectors for the ­liquid fuel and another for the natural gas. The liquids are stored in a 48-L conventional tank, the compressed natural gas in two 6.5-cubic-meter cylinders in the trunk. Marelli calls the system TetraFuel; it’s a reference to the fact that it can run on pure gasoline, pure ethanol, gasohol (in Brazil, a gasoline mix with 20 percent ethanol), or straight natural gas.

Marelli says that the TetraFuel system lets an average driver cut fuel expenses by 25 percent to 40 percent compared with an ordinary gasoline-powered car. Of course, the savings depend on the relative costs of ethanol and natural gas—both of which, as it happens, have been high in North America and Europe lately. Reductions in carbon dioxide, however, are independent of market forces. According to tests Marelli conducted, a TetraFuel car running on etha­nol emits, on average, 12 percent less CO2 than when it runs on gasoline; with natural gas, the reduction reaches 24 percent.

Still, the question hangs like a mid­afternoon haze over São Paulo: In an automotive sector that seems increasingly convinced that its future is in hybrids, electrics, and even fuel-cell cars, is there room for an alt-fuel vehicle whose technological breakthroughs are all in software and electronics rather than in batteries and ionic membranes?

Without a doubt, the economics are enticing. Consumers could be liberated from dependence on a single fuel and its price oscillations. Ethanol, natural gas, and other alternative fuels could become more attractive despite their much smaller distribution networks, because drivers would know they could always turn to gasoline if they found themselves in a place where they couldn’t get the other options.

Put it all together and multifuel technology starts looking like a bridge from petroleum to other possible technologies and fuels, such as bioethanol from cellulose waste. And it would let automakers keep making internal combustion engines, something they’ve gotten very good at during the past century.

Taking stock of the various electric and partially electric drivetrains that now dominate automotive R&D, Silverio Bonfiglioli, president and CEO of Marelli’s power-train division for North and South America, says, “Those are alternatives, sure. But not for now. The alternatives available today at low cost and large scale are biofuels: ethanol and biodiesel.”

Back at the experimental lab in Hortolândia, Castelli pops open the hood of the Siena and points to a metal box the size of a paperback book sitting next to the motor. Inside the box is the engine control unit. This ECU has the same basic hardware—a 16-bit microcontroller, some memory, and some communications interfaces—found in the ECUs churned out by the millions for cars around the world.

“This is the brain of the whole thing,” Castelli says, showing me the ECU’s circuit board, which Marelli produces in a facility nearby. “All cars have one of these today. What changes is what goes inside—the intelligence you put in.”

The intelligence, in this case, is defined by the ECU software that is created. In other words, the heart of Marelli’s TetraFuel technology is not some souped-up fuel injector or breakthrough in combustion chamber design. It’s just code running on the microcontroller under the hood.

That fact may explain the almost surgical cleanliness of the Hortolândia lab. Inside the white-tiled facility, engineers in lab coats stare at computer screens flashing real-time data from engines wrapped in wires and sensors. The engines sit inside soundproof chambers with precisely controlled temperature and pressure. You’d be hard-pressed to find a greasy screwdriver, let alone a mechanic, under a car.

Automotive research labs have evolved along with the engines they create. Over the years, internal combustion engines have required increasingly sophisticated control units. The smarter ECUs are necessary to burn the fuel efficiently and smoothly, which in turn yields optimum engine performance at acceptable fuel economy and tailpipe emission levels.

An ECU commands an engine’s operation in a series of steps. First it measures how much air is going into the cylinders when you press down on the gas pedal, which, its name notwithstanding, actually regulates the flow of air into the engine. “As you change the accelerator position, you’ve changed air flow and you need an increase in the amount of fuel to keep everything happy,” says Lee Dodge, a staff scientist at the Southwest Research Institute in San Antonio. By “happy,” Dodge means complete combustion, in which “you use up all the fuel and all the air,” releasing maximum heat, he says.

This combustion sweet spot is called the stoichiometric ratio. For gasoline, you want the ratio of air mass to fuel mass to be 14.6 to 1, while for pure ethanol the ratio is 9 to 1; for gasoline-ethanol mixtures, you need intermediate ratios. The ECU calculates how much fuel it needs to inject based on this air-fuel proportion.

Next, the ECU activates a spark plug to burn the air and fuel mixed in the combustion chamber. The expanding gases push the piston down, moving the crankshaft, which rotates the car’s wheels. Burning your mixture at the right instant is crucial for good engine operation. Spark the mixture too late or too early and you’ll waste power and stress the engine. To calculate the optimal timing, the ECU considers what fuel is in the tank—ethanol requires a slightly earlier spark than gasoline—as well as the engine’s rotational speed and load.

To make sure the engine works well whether you’re cruising in a coastal town or hauling a trailer up a mountain, the ECU monitors the air intake pressure, gear position, crankshaft speed, atmospheric pressure, ambient temperature, and a myriad of other vehicular and environmental parameters. It is constantly tweaking the injection and ignition settings, trying to keep the engine running on the stoichiometric operating point. One of the greatest benefits of this ECU strategy is in limiting tailpipe emissions: a car’s catalytic converter reduces emissions drastically, but only if the exhaust gases passing through it are the products of complete combustion.

ECUs need to be programmed for each vehicle. The controller developed by Marelli is different from those of other flex cars because it accommodates all fuels automatically. It can handle pure gasoline, a fuel that other Brazilian flex cars can’t burn, because 100 percent gasoline is not sold anymore in Brazil. It can also handle pure ethanol, a fuel that flex cars in the United States can’t use, because they function only with mixes containing up to 85 percent ethanol. The same Marelli ECU also controls the use of natural gas, whereas previous bifuel cars—most of them retrofitted—normally use two ECUs, requiring drivers to manually switch between fuels.

Marelli’s TetraFuel ECU precisely adjusts the engine during transitions between the gasoline-ethanol mix and natural gas so that the driver doesn’t feel an abrupt change. When I test-drove the Siena last year, I knew the vehicle was changing fuels only because of some colored LEDs that Marelli engineers had installed on the dashboard. “This is the beauty of our system: it knows what fuel to use,” bragged Castelli, my test-drive host. “You don’t have to worry about that. The software worries about it for you.”

Brazil has a long history of ethanol production. In 1973, after the world went through its first big oil convulsion, Brazil’s military dictatorship decreed that the country would begin seeking alternatives to petroleum. The government implemented a program called Proálcool to subsidize the production of sugarcane ethanol, and by the mid-1980s nearly 95 percent of new vehicles sold in Brazil ran on pure ethanol only.

But then, in 1989, ethanol disappeared from filling stations. Sugar prices had soared on the international market, and Brazilian mills shifted production from ethanol to sugar. As a result of that shortage and as gasoline prices stabilized, sales of ethanol cars plunged to less than 1 percent in the early 1990s. After less than a decade, the Proálcool program was nearly defunct.

Ethanol, however, didn’t disappear from Brazil. Although hardly any new ethanol cars were sold, the existing fleet was out there, and it needed fuel. In fact, after the ethanol crisis passed, the fuel returned to the market. And to stretch it out, Brazil began blending it with gasoline.

The blending was fixed at 20 to 25 percent ethanol. But if a car could run with that mixture, why not with other proportions? Why not make a car with that flexibility? That was the question that the Brazilian units of Marelli and its German rival, Robert Bosch, began asking.

Research on such flexible-fuel vehicles dates back to the late 1980s. In the United States and Europe, the studies were based on a physical sensor capable of measuring the level of methanol, and later ethanol, blended with gasoline. Using that sensor, Bosch engineers in Brazil developed a prototype flex vehicle that ran on any blend of gasoline and ethanol available there (ethanol in Brazil contains a fraction of water). The problem was that the sensor alone cost US $100, and when Bosch showed the car to General Motors, Volkswagen, and Fiat, none committed to it.

Meanwhile, at Marelli, engineers were striving for a technology that would work for the most affordable cars in the Brazilian market, and so they needed a solution that didn’t depend on the expensive, unique sensor. The breakthrough came when the engineers figured out they could reliably and accurately calculate the ethanol content of the fuel using software and existing sensors in the car.

The key component in this approach is an oxygen probe that sits at the engine’s exhaust manifold. Its function is to sense the amount of residual oxygen after combustion, a measurement that helps the ECU fine-tune the air-fuel mixture. If it detects, say, too much oxygen in the exhaust, the ECU increases the fuel going into the cylinders. It then checks the oxygen level again, repeating the process every few milliseconds until the mixture is precisely adjusted to the stoichiometric ratio.

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.”

To Probe Further

For more on Magneti Marelli’s flexible fuel technologies, visit

A technical discussion of flex engines and their reduction in CO2 emissions is at

To learn more about engine control units, see “Automotive Engine Control and Hybrid Systems: Challenges and Opportunities,” by Andrea Balluchi et al., in Proceedings of the IEEE, Vol. 88, issue 7, July 2000, at

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