|The SEAT Mii Ecofuel. Click to enlarge.|
SEAT, a member of the Volkswagen Group, is expanding its Mii family with the introduction of the Mii Ecofuel, which runs on natural gas. The first model with a CNG engine to wear a SEAT badge, and making its debut at the Geneva Motor Show 2013 this coming week, the Mii Ecofuel offers average consumption of 2.9 kg CNG/100 km and CO2 emissions of 79 g/km. Given the fuel price in many countries, the running costs are approximately half those of a Mii with a gasoline engine.
The 1.0-liter, 68 PS (50 kW) engine is based on the three-cylinder gasoline unit found in the Mii with 60 PS (44 kW) and 75 PS (55 kW) outputs, but it’s been specifically developed for CNG operation. At an entry price of €12,050 (US$15,700) in Germany, the new SEAT Mii Ecofuel is also the most inexpensive CNG model on the market.
As in the gasoline-driven Mii models, the Ecofuel version features a three-cylinder spark-ignition engine with a displacement of 999 cc. In the CNG variant, the compact power unit generates its 68 PS at 6,200 rpm. The lightweight and high-revving engine reaches maximum torque of 90 N·m (66 lb-ft) at 3,000 rpm.
To achieve optimum CNG operation, the three-cylinder engine has been modified in several areas.
An increase in compression ratio from 10.5:1 to 11.5:1 improves combustion efficiency in CNG operation. Because of the higher pressures and combustion chamber temperatures, the spark plugs now have a higher ignition voltage. The lower lubrication characteristics of gaseous fuels are compensated by different valves, as well as special guides and valve seats. The cam profiles and engine control unit are also modified.
In the new SEAT Mii Ecofuel, the ECU also handles the management of the gas injector valves and the electronic gas pressure regulator. Moreover, the engine control unit uses a lambda sensor to recognize the different qualities of “low gas” and “high gas”, as they are sold on the German market in particular. When running on low gas, which has a lower calorific value due to its lower methane content, injection timing is adapted to suit.
Compared with conventional gasoline, the combustion of CNG produces around one quarter less CO2, as well as significantly less carbon-monoxide and hydrocarbons. Fine particulates or soot are not emitted at all, although unburnt residual methane has to be converted by the catalyst. For this reason, the catalytic converter is equipped with slightly different precious metals.
Despite being specifically engineered to run on CNG, the Mii Ecofuel engine can also run on unleaded gasoline. With a full CNG tank (11 kg), the Mii Ecofuel has a range of up to 240 miles (386 km); the reserve gasoline tank (10 liters) extends the range by up to 140 miles (225 km) for a total range of up to 380 miles (612 km).
A special fuel level indicator in the instrument panel informs the driver of the level in both the gas and the gasoline tank. The ranges available in both operating modes are also shown in the multi-function display.
Two CNG tanks are located beneath the vehicle floor to save space; the only difference between the Ecofuel and the gasoline models is the absence of a spare wheel well. The connector for filling up the SEAT Mii Ecofuel is located beneath the same flap as the gasoline cap.
The SEAT Mii Ecofuel’s low consumption and emissions figures are supported through standard fit fuel-saving Ecomotive Technology, including a Start/Stop system and a Brake Energy Recovery system. This is combined with a low curb weight (956 kg (2,108 lbs) without driver); good aerodynamic characteristics (cw = 0.32; frontal area = 2.07 m2); and an efficiently matched engine/transmission combination.
Initially, SEAT will introduce the Mii Ecofuel in markets such as Germany, Italy, Austria, Switzerland, the Netherlands, Sweden and the Czech Republic where there is a clear demand for CNG fueled cars and the infrastructure to support it.