PHOTO: Fiat

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.