OT: CO2/Km

[Roger]

For some years new cars have been tested (under artificial conditions) for carbon output but how do these figures compare to real life usage? I must confess that I have not bothered to keep detailed records of petrol consumption since the 1970s but there must be a fair number of you out there who do so do your official figures bear any relation to the overall consumption in practice?

FYI I understand that one UK gallon of petrol produces 10.4 kg of CO2 and one UK gallon of diesel 12.2 kg of CO2.

Dribble's favourite, the Toyota Prius, has an official figure of 104 gms/km which equates to 62.5 mpg and Dribble would have us believe that that is easily achievable in the real world (but then if you drive a virtual car just about anything is possible).

Back in March I happened to notice a reference in the press to the Department for Transport running a whole fleet so I put in a FOI request and promptly forgot about it. Last month I came across the acknowledgement of that request which reminded me that I had never received a reply so sent a reminder. Much to my surprise I have now got an answer part of which I reproduce below:

"The Government Car and Despatch Agency (GCDA), an executive Agency of the Department for Transport, operates a fleet 104 Toyota Prius. The Agency does monitor the fuel consumption of its vehicles. Its latest report shows that the average fuel consumption of the Toyota Prius fleet was 42.69 mpg. The worst example is an average of 32.45 mpg and the best example is an average of 51.49 mpg."

42.69 mpg is about 152 gms/Km, a far cry from 104 gms/Km.

My current car (petrol) is 213 gms/Km which is 30.5 mpg and on long trips the car computer shows consumption somewhere in the mid 30s so I wouldn't be at all surprised if my overall consumption was somewhere close to the official figure. It sure as hell isn't anywhere near 21 mpg which is where it should be if it performed as badly in comparison to the official figure as the average Prius does.

[Adrian]

Roger gurgled happily, sounding much like they were saying:

Depends how you drive.

Depends on the completeness of combustion.

[Andrew Gabriel]

I got a new Fiesta about 6 months ago, the first car I've had with an MPG indicator. That does about 42 mpg on the motorway if I'm not thinking about economic driving, and about 5mpg more if I do (and about 10 mpg more if I take it to silly extremes). From 55-70MPH, the efficiency is constant (engine efficiency improves against increased drag). If I can't keep above 55 MPH, the efficiency starts dropping off and at 30MPH it's down to somewhere around 30 mpg, and in town with traffic lights, junctions, etc, it's around 20 mpg (although driving along Euston/Marylebone road on Sunday, I couldn't get to even 20 mpg, what with stopping before each box-junction until car in front crawls past far end enough for me to fit in, before some bastard in the next lane cuts in instead).

[Steve Firth]

Both Mr Plowman and myself have observed in the past that the current fuel cycle takes no account of the state of charge/discharge in the batteries fitted to the Prius. In effect this vehicle starts the test with "extra fuel" that is not accounted for in the CO2 emissions/mpg calculation.

[dennis]

8<

It is well known that the test results are fiddled for a prius.

You start with a full battery and finish with a flat battery. The fuel needed to recharge the battery to the original state is not shown. However drivel will be along to explain the perpetual motion aspect of a Prius that mean you never use any fuel to charge the battery.

[dennis]

Take it back for repair. I have a turbo diesel Astra and it never does less than 50 mpg unless I am in a traffic queue. I frequently get more than 50 mpg if I am motorway driving.

[Roger]

The message from [e-mail] (Steve Firth) contains these words:

Unfortunately the dft doesn't appear to agree with you.

In June last year I asked them:

"Is there any truth "I cannot comment on the results of any particular vehicle, although I can tell you that the test for hybrid cars - as set out in Annex 14 of ECE Regulation 83.05, does factor in the charge level of the battery. If you would like to obtain a copy of this Regulation, we would be happy to provide you with a copy - albeit for a small charge."

Being a skinflint I didn't take the query any further.

[ARWadsworth]

Does that include any refinery/production CO2 costs or are they just the CO2 emmissions of the final product?

I believe that petrol involves more refining than diesel and so these may not be the true CO2 emmissions per gallon.

Adam

[Roger]

The message from "ARWadsworth" contains these words:

AIUI that is just the amount of CO2 you get by burning a gallon. Production and distribution would be extra. I don't know for sure but I would have thought that the more volatile fuel would be easier to refine.

A internet search brought up the following on the Total site:

"Black, sticky and foul-smelling, crude oil is a complex mixture of hydrocarbons which have to be separated by a distillation process (i.e. refined), in order to obtain usable end products.

In the separation process, there is a specific order and proportion of each product produced, which cannot be changed to respond to changing customer demand.

The first products to be separated out are the lighter distillates: the LPGs (liquefied petroleum gases) like butane and propane, the petrol for use in automobiles and the ?naphta? used for numerous derivatives in the petro-chemical industry, particularly plastics.

Next come the medium distillates, firstly kerosene for aviation fuel, then diesel oil for diesel engines and fuel oil for domestic heating.

Finally, there is the distillation of heavy products, paraffin, oils, heavy fuel for industrial heating systems and the production of electricity, resins and bitumens.

Is it possible to decide to increase the production of certain products such as diesel oil?

The answer is that whilst you can increase production of certain grades it is only by a few per cent. It can be done by converting heavy fuels into lighter products by ?cracking? them. But these conversion processes are very high in energy use and hydrogen consumption. There is also an increased cost in production which is passed on to the consumer.

There are 720 refineries around the world, with a capacity of 85.3 million barrels a day. Of these, 150 are situated in the United States,

30 in Japan and around 15 in each of the large western European nations like Italy, Germany and France."

Other than cracking heavier fuels ISTM that petrol should be cheaper to refine.

[Andy Champ]

Roger wrote: > "The Government Car and Despatch Agency (GCDA), an executive Agency of

Fascinating. That means that the average Prius is less economical than my wife's shopping-trolley-hatchback that cost a third of the price.

And that worst case they are worse than my horribly thirsty planet destroying sports car that would be paying ***knows what in road tax as a penalty - if it wasn't too old :)

And that best case they are no better than a modern diesel.

Ah well.

Andy

[ARWadsworth]

OK, thanks for the info

I watched the BBC News on a television tonight. You have to realise that I do not have a TV so it was quite a rare occassion for me.

The broadcast said that "log burning boilers do not contribute to the CO2 emmissions as the logs absorbed CO2 when they grew"

So what did coal and oil do when they were trees millions of years ago?

Sorry Roger, It is not a go at your post but a go at the mixed ways of deciding upon CO2 usage and output that will be used by political parties.

Adam

[The Natural Philosopher]

Its well known that a decent small diesel will do at lest 50% more than a Priapus on anything but urban roads. 60mpg+ seems very acvievable.

Clarkson did fairly well in his twin turbo Jaguar as well..

[The Natural Philosopher]

I dont think so. Petrol is almost a by product of diesel production allegedly. Its sold below cost apparently. In terms of the barrel of oil-> petrol rate of conversion.

[Ed Sirett]

There's something wrong with those figures. A gallon is a volume measure, diesel is somewhat denser than petrol and has a marginally greater carbon:hydrogen ratio (though both are near 1:2). Ergo there is no way that more CO2 is produced by petrol either per unit volume or unit mass burnt.

My figures would be (assuming a C:H ratio of 1:2)

Volume of 1 gallon (say 4.5 litres). Mass Petrol (0.75 x 4.5) kg = 3.4, Mass of Diesel 4.5x 0.9 kg = 4.05 Mass of Carbon is 12/14 of total. Mass of CO2 (assume no CO) is (12+16+16) kg per kg of Carbon.

So Petrol 9.7 kg /gallon. Diesel 11.6 kg/gallon.

[Ed Sirett]

Yep. I got my fill of eco-speak when doing my CG 6083. The whole (unstated) assumption of using wood is that the supply is sustainable and the source vegetation will grow back absorbing the CO2 produced in combustion. This is something of a big assumption, IMHO.

[Fred]

There are some figures here:

suggest the density of diesel is closer to 0.84 than 0.9

It's a shame that the CO2 used in cracking oil to increase octane rating of petrol is conveniently forgotten. I'm not sure what the current figures are, but it a few years ago it was generally thought to require an extra 5% of oil.

[Vortex3]

We've had a Prius for 50,000 miles.

In normal family short run/school run/shopping kind of driving it delivers

45-55 in Winter and 50-60 in summer.

Plan will be to keep the car for at least 100k miles.

To make an objective fuel comparison surely one should forget chemistry and think in terms of miles per pound, diesel being 15% more expensive than petrol.

BTW before anybody starts to shout "beardy tree hugger" my other car is a V8 and I think it's great.

D

[Bob Mannix]

Indeed but I believe it is missing the point. Toyota are extremely forward thinking and innovative. They realise that there will be a gap between affordable fossil fuel and a battery technology that can truly take the place of FF and that this gap can only be filled by hybrids of some sort. Selling the Prius at a huge loss and marketing it well (as they are) ensures they will have a huge amount of real world data on operating a hybrid. They are trying to ensure they will be market leaders when the sh*t hits the fan and they probably will.

We all know the *only* energy that goes into a Prius goes in through the fuel tank (save a tiny amount recovered from braking) and it's heavy - of course you can do better if you want overall fuel economy but you can't do any better as a test program for hybrid technology. Their losses will come out of the R&D budget, and good luck to them, and thanks to Drivel and the other customers for being public spirited enough to buy them!

[Roger]

The message from Ed Sirett contains these words:

You just had a senior moment Ed?

10.4/9.7 = 1.07 12.2/11.6 = 1.05

Not really much difference at all. Incidentally igures pulled from the net suggest petrol has a density of 737 kg/m^3 and diesel 847.

[The Natural Philosopher]

Well its probably cos diesel produces more solid carbon soot ;-)