Most Fuel-efficient Gasoline Car Hits Japanese Market

Jul 10, 2014
Takashi Takada, Nikkei Automotive Technology
The new Mira e:S is the most fuel efficient gasoline vehicle.
The new Mira e:S is the most fuel efficient gasoline vehicle.
[Click to enlarge image]
Dual injectors were employed to prevent knocking and realize a high combustion stability.
Dual injectors were employed to prevent knocking and realize a high combustion stability.
[Click to enlarge image]

Daihatsu Motor Co Ltd announced that it has partially remodeled its "Mira e:S" light car and released it July 9, 2014, in Japan.

The most distinguished feature of the vehicle is its high fuel efficiency of 35.2km/L (approx 82.8mpg) under the JC08 test mode, which is higher than the fuel efficiency of any other gasoline vehicle. The price of the two-wheel-drive (front-wheel-drive) model is ¥766,200-1,213,700 (approx US$7,533-11,933), and that of the four-wheel-drive model is ¥1,018,200-1,316,500 (including tax).

To improve fuel efficiency, Daihatsu increased the compression ratio of the engine from 11.3 to 12.2. In addition, it changed the shape of the intake port to strength the vortex flow (tumble) of the air-fuel mixture and employed a spark plug with a high ignition performance to enlarge fire at the early phase of ignition.

To prevent knocking (abnormal combustion) caused by the increased compression ratio, Daihatsu employed dual injectors and the Atkinson cycle, which is used for hybrid electric vehicles (HEVs). The dual injectors and the Atkinson cycle realized a combustion stability (the reduction of fuel particle size) and the reduction of pumping loss, respectively.

Moreover, the company reduced the amount of energy regenerated during acceleration and constant speed running and increased the amount of energy generated during deceleration, reducing engine load and improving fuel efficiency.

Before the development of the new vehicle, the most fuel efficient gasoline vehicle was Suzuki Motor Corp's "Alto Eco" light car with a fuel efficiency of 35.0km/L. With the partial improvement, the fuel efficiency of the new Mira e:S is 0.2km/L higher than that.