235 mpg VW

[WhiteBlue]

VW will introduce the XL1 hybrid with 235 mpg (US) next year. The engine will be a 0.8L common rail 2 cylinder turbodiesel with 48 bhp and 120 Nm torque. The electric motor will have 20 kW with 100 Nm torque and will be supplied by a 60 kg Lithium Ion battery made by Sanyo. The milage is cool.

[tok-tokkie]

With that mpg I was expecting a tiny tandem 2 seater not a fairly mainstream car like that.

[autogyro]

Now this will be a real breakthrough in electric/hybrid technology.
I had an idea that VW were keeping their powder dry.
Price will be the clincher.

[xxChrisxx]

Mpg figures for range extended hybrids always have to be taken with a pinch of salt. The figures can be cooked up to look better than real life situations. Which being fair, test duty cycles to make fuel consumption figures look better then real world too.

Typical practice is to 'not count' the battery powered milage, or choose a range that requires only a small amount of range extension.

So for e.g. if you have 100 miles EV-battery range. And a 30mpg range extender engine.

Doing 130miles, = 130mpg.
Doing 160miles = 65mpg.
etc.

[piast9]

If that range was calculated in a way presented by xxChrisxx then it is cheating, isn't it?

At first I thought that it is physically impossible to achieve such high mileage because of for example just air drag but calculations proved that I was wrong. My rough calculations for extremely sleek car with drag coefficient of 0,2 and 2 m^2 frontal area at 90 km/h showed that it needs about 56 MJ of energy to overcome the drag at the distance of 235 miles. American galon of diesel contains 160 MJ of energy.

[xxChrisxx]

If that range was calculated in a way presented by xxChrisxx then it is cheating, isn't it?

Well not really, as long as everyone uses the same method of calculating the figure and that method is transparent, you get a comparable result for hybrids.

It was just a warning that it's easy to be hoodwinked by marketing. You've just got to be careful when comparing it to figures calculated in a different way, or when comparing it to convetional engines.

[Richard]

Isn't that why we have EU defined tests for city and extended driving? Presumably the hybrid would do well in stop start city test, but drop off in the extended test?

[xxChrisxx]

Isn't that why we have EU defined tests for city and extended driving? Presumably the hybrid would do well in stop start city test, but drop off in the extended test?

Most regulatory bodys have duty cycles, but they are not really represetetive of read world driving conditions. There is work towards making a universal (EU and US basically) duty cycle that is far more representative of real world condiions. If I remember correctly the toughest by far is the cycle set by the Californian emissions people.

I'm not sure what duty cycles hybrids are put through, I don't think it's the same as conventional engines as it would be unfair. As the hybrid essentially gets the battery milage free.

Is just a case of coming up with a reliable metric for comparing hybids and non hybrids fuel consumption.

[piast9]

Well not really, as long as everyone uses the same method of calculating the figure and that method is transparent, you get a comparable result for hybrids.

It is cheating because users will not achieve anything close to the declared mileage in real life. First thought of the average buyer of such car is that such car is for example 8 times more economical than his current one.

[xxChrisxx]

Well not really, as long as everyone uses the same method of calculating the figure and that method is transparent, you get a comparable result for hybrids.

It is cheating because users will not achieve anything close to the declared mileage in real life. First thought of the average buyer of such car is that such car is for example 8 times more economical than his current one.

If they were only popping to the shops or a short commute, they'd burn no fuel, so it's far more efficient than a conventional engine (probably a lot more than 8 times). If they expect to travel 1000miles in one trip on 4 gallons, then yes they will be dissapointed.

This was the reason for my warning about broadly looking at a single figure, without knowing how it was derived.

It's not a technical way of trying to trick you (though marketing will use it for that), it's that hybids having an 'emission-free' range that makes it really hard to compare to a non hybrid with a single figure.

[piast9]

If they were only popping to the shops or a short commute, they'd burn no fuel

... until the batteries go flat. What then?

[xxChrisxx]

I'm not trying to argue with you, this is the method manufacturers are using to compare range extended hybrid fuel economy. It's as valid as any other, as long one is clear what the figure is actually describing.

[autogyro]

It means little to most people if a figure for Miles per gallon is used when one of the energy sources on the vehicle is not measured in liquid volume.
A far better comparison would be energy cost per mile broken down into the liquid and electrical components.
This would also allow simple geographical energy cost comparisons.

[Lycoming]

In and of itself, the MPG scale is somewhat misleading. It's only 1 l/100km.

[Just_a_fan]

I understand(*) the official test cycle allows for the battery to be fully charged before the test commences. This in itself will give a figure that will usually not be achieved in real world use.

(*) Heard this from someone involved in developing a hybrid system.