Fiat Siena Tetrafuel Offers FlexFuel Times Four

When it comes to flex-fuel vehicles, Brazil is leading the way. Brazilian motorists with flex-fuel vehicles — that's virtually all newer models — can use any blend from 100 percent gasoline to pure alcohol. All Brazilian gasoline is now blended with 25 percent ethanol and Brazilian fueling stations still offer 100 percent ethanol for the older alcohol-only vehicles. Models that can also run on natural gas are also becoming available.

With all these fuel alternatives at play, you'd think that someone would find a way to capitalize on the trend. That's now a reality as Fiat has begun selling the world's first production vehicle that can run on all four fuels — compressed natural gas (CNG), gasoline, pure ethanol (E100), and E25 ethanol/gasoline blend.

A single Electronic Control Unit developed by Magneti Marelli selects the fuel automatically depending on driving conditions. For economy reasons, natural gas is the default fuel. Because of CNG's lower energy content, when the ECU detects a need for more torque for acceleration or hill climbing, the system automatically switches to a liquid fuel. It switches back to CNG when it again is determined as the appropriate fuel. The system also reverts to liquid fuels automatically if natural gas pressure drops below 150 psi.

The Siena Tetrafuel's 1.4-liter engine was modified with an integrated injection manifold featuring a natural gas common rail with four injectors, new cylinder heads, tubes, and valves. The base of the trunk was reinforced to handle the added weight of the natural gas cylinders, which hold 6.5 cubic meters of gas. Also, the suspension and brakes were modified to retain the same performance and characteristics of the standard model.

A digital display alerts the driver of a low level of CNG, the level of pressure in the cylinders, external temperature, and any potential damage to the system. The system also warns when liquid fuel levels drop below 4 percent of capacity since liquid fuel is required to cold-start the engine.

The Fiat Siena 1.4 Tetrafuel is proving very popular with Brazilians. Over 700 are being sold monthly, a figure some 350 percent higher than original sales projections.