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SEAT introducing natural gas Mii Ecofuel with 79 g/km CO2

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.



It appears that the price for the petrol version in Germany is 8,890-9,700 Euros:

That gives some idea of the CNG premium.
Higher mileage drivers are going to save the ~2,000 Euros premium on fuel in a pretty short time.

Account Deleted

The price in Germany for the basic up! is 10,000 EUR with the bi-fuel natural gas option it is 13,000 EUR. So the premium is 3000 EUR or 30%. Larger more expensive cars needs larger motors and they maintain that 30% premium. You still need to drive a lot to justify the premium. A rough rule is that you would spend 6000 EUR to drive the same distance on natural gas as you can drive spending 9000 euro on gasoline. So in order to make up for the premium you need to drive 166,154 kilometer (=(9000/1.3)*24) assuming one liter of gasoline cost 1.3 EUR and you can drive 24 km per liter in the up!

The natural gas option makes most sense for those who drives a lot like taxies. However, the most important thing would be to get trucks and commercial ships to use natural gas instead of oil. That would really help reduce air pollution on this planet. Globally you could save 4 million barrels per day for ships and an additional up to 8 million barrels per day for trucks and other heavy duty vehicles.

Prices see


This is a SEAT, not the VW Up, and so the base price is lower.
Whilst it is true that the price of larger cars, or more accurately larger engined cars, would cost more to have the NG version there is no reason why the differential should stay at 30% on the cost of the total vehicle.
Admittedly at present there is a substantial NG premium, but that is what the use of the MQB platform is meant to address.

You aren't going to get 24 miles/litre from the Up or the Mii using petrol or NG, and (=(9000/1.3)*24) is 72,000, not 166,154

Using a more realistic 18km/litre to include short city driving runs and winter weather etc then you come out to around 54,000km or so.

That is 33,480 miles.

For someone who uses a car a lot that is less than two years driving.

That sounds like a pretty good pay back time to me.


Everybody's talking about the "payback time" based on fuel cost differences but that's not the target market of this car. This is a car for those who don't mind paying more to reduce their CO2 emissions, so the comparison should be made between g/km of the alternatives.


@al vin:
I'm not sure where you get that idea from.
Using natural gas or LPG here in the UK is a perfectly sensible economic choice for high mileage drivers who couldn't give a stuff for CO2 emissions.

Account Deleted

Davemart I said km not miles and (=(9000/1.3)*24) is 166,154. The Seat and the Up are identical apart for the batch and some minor unimportant things. I found the basic Seat price it is 9000 EUR and the gas version is 12000 EUR so the premium is still 3000 EUR but now 33% relative speaking not 30% as for the up.

Account Deleted

Seat price


I messed up in looking at your figures, but those you are using are out.
I have already given the price of the Seat Mii, which as you now say starts at around 9,000 Euros.

Petrol in Germany is not 1.3 Euros/litre, but:
That is £1.358/litre, or at 1.15Euros/pound 1.56 Euros/litre

The Seat Mii does not get 24 kilometres/litre:

Taking that as 60 miles per imperial gallon, 4.5 litres that is 13.3 miles per litre, or 21.5km/litre
So, 9000/1.56*21.5 = 124,038km or 76,903 miles

That is around 4 years in commercial use.

And that is for a tiny, ultra economical car.

Much of the cost of NG is in the pressurised tank, which of course is more economic in larger sizes as the external area increases far less than the volume.

So there is by no means a fixed percentage premium for NG as you suggest, it is just that this comparatively cheap version is the first one VW have rolled out, and NG versions of the Golf etc are coming, which on the MQB platform will be able to have a very restricted premium increment.

So in Europe at least with expensive petrol the economics of NG vehicles look good for people who travel long distances per year.


I was not explicit in the point I was trying to make.
If, as I suggest, the incremental cost of NG does not rise proportionally as the vehicle size and petrol consumption increases, then the economics of more gas-guzzling cars switching to NG will be even better, as common sense suggests they might.
Cars which use a lot of fuel, and vans etc, are the ones which stand to gain most from reasonably prices NG versions.


Isn't the smallest Prius C at about ($19K - $2.5K subsidies - $16.5) a better buy?


Davemart, when I said "This is a car for those who don't mind paying more to reduce their CO2 emissions" I meant they didn't mind paying more for the car. And as VW is putting the car's g/km up front instead of its km/$ I assume that's their target market.


I dunno about the comparisons with the Prius.
I haven't run a cost analysis ( I am not being funny, it used to be my job ;-)) and we are talking in general terms, not even being really specific about which country we are talking about!
In general though, this sort of drive train, if you are a high mileage driver, can make sense in Europe, where petrol is expensive.
I have done a rough analysis of the costs of LPG conversions, which is what we use in the UK rather than NG, and that makes sense particularly for drivers of bigger cars for drivers who go more than around 12,000 miles a year.

I doubt that NG makes sense in the US at the moment, with petrol prices low compared to Europe, even though NG is also cheap.
The cost of NG cars is also high in the US, as the market for them is very immature.

What we have is the new costs on a small car from the VW group, which is the first they have produced using new platforms which were designed from the outset to allow a host of different drive trains including natural gas.

No one is going to shop a Prius against the far smaller Mii.
We will be able to do a sensible comparison when VW bring out their version of the Golf using NG on the new MQB platform, as people might cross shop those.

From the VW group alone we are going to have a host of drive train alternatives to be weighed up against each other.

Al vin:
Fair enough. I thought you were talking about total cost of ownership.


If you want to see real mileage figures, you can look on

There are already two Seat Mii Ecofuel drivers with an average fuel consumption of 3,5 kg/100 km, whereas the gasoline version has a fuel consumption of about 5,3 l/100 km.

That means fuel costs of about 4 €/100 km instead of 8 €/100 km.

I´ve got a Daihatsu Cuore, with really economical driving it can realize less than 4 l/100 km, which means fuel costs of about 6 €/100 km in Germany.

So the VW Up!/Seat Mii (same car, only badge-engineering) is current by far the cheapest solution to drive a car running on fossil fuels.


DM...I referred to the very small Hybrid Prius C and not the Prius III. It may not be as small as the Seat, but it may be the smallest car Americans would drive?


That confirms my argument that, at least for higher mileage drivers, this is economic at European fuel prices.


I have not seen the Prius C, so don't know what VW car it will compare with.
There will likely be NG versions of both the Polo and the Golf though, which should provide good comparisons.


I'd love to have one of these! I've been paying around 3.75 per gallon for my car And I'd love a way to start saving. At ~15k it's not too expensive either. The only problems is that there aren't many cng fueling stations around my house. I'm hoping they start to build more.

for anyone interested, this is a map of cng stations in the U.S I've been looking at. There are few and far between.

Roger Pham

Now, this a real Volkswagen (people's car). Synthetic methane can be used in place of NG. Synthetic methane can be made from gasification or pyrolysis of waste biomass. Renewable-energy H2 can be added to the biomass gasification process to double the yield of methane per unit of waste biomass, in order to utilize the excess energy of solar and wind energy collectors. Along with BEV's and FCV's, CNGV's can accelerate the transition toward independency from fossil fuels. Larger CNGV's should be hybridized (HEV) in order to reduce the energy footprint.


DM...the Toyota Hybrid Prius C (at $19,080 - subsidies) is based on the Toyota Yaris LE 5-door @ 16,430. The internal volume is about 87.4 cu. ft.

It is close to the Honda Fit is size etc.

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