how is C02 ouput calculated??

[ckember]

I have been thinking abou the latest C02 ouput figures published by manufacturers that have a KERS system and the ability to power off the engine when stationary. ie, most new BMW's.

Is the figure quoted for C02 taking these new technologies into account so the average c02 output is reduced? or is the figure the real c02 ouput of the engine?

I ask because when you get your car MOT'd and they leave it running for 20minutes with the gas analyzer up the tail pipe what reading will it give? or will the engine shutdown because it thinks it is in traffic?

 

[Bobby Dazzler]

CO2 output used for VED classifications is based upon the output over a distance of one kilometre. Sort of a theoretical value though, as that would be based on a standard set driving pattern used for all calculated C02 output cars.

Presumably they'll need to overide stop/start to actually measure instantaneous output for the MOT, and you would expect that to give a different reading to that used for the VED classification.

 

[verytalldave]

A few people told me than CO2 emission levels are directly linked to a cars "average" fuel consumption. I cant quite see how this can be, so I remain to be convinced.

 

[recycled]

MOT does not measure CO2.

 

[Mactech]

Some useful stuff here:

http://www.vcacarfueldata.org.uk/information/emissions-testing.asp

 

[x332race]

From Telegraph Article

The EU emissions test

All these statistics are based on fuel consumption figures from the Vehicle Certification Agency (VCA), which are derived from an EU test procedure prescribed by an amended EU directive and known as the New European Drive Cycle.

This involves a 19.6-minute test in two parts: the Urban cycle, a series of 12 starts and stops at an average of 12mph and never exceeding 31mph, and the Extra Urban cycle, a faster single sequence of acceleration, deceleration and steady-speed driving, never exceeding 75mph. An average of the two parts, weighted by their respective distances, gives the EU Combined fuel consumption and CO2 emissions figures.

It's a very precise test, carried out on a rolling road in a laboratory at exactly 20C. It doesn't measure fuel used, but analyses exhaust gases and calculates back for fuel usage and the closely related carbon dioxide emissions. Strangely, car manufacturers are allowed to conduct their own tests, which seems a bit like being asked to mark your own exam paper.

The driving is actually done by computer-controlled robots, which press the throttle by the precise amount required to get the car to the prescribed speeds; in fact, they are allowed to slightly undershoot those speeds as a percentage deviation. The car's air-conditioning, heater, lights and radio are not used; there's no headwind; the imaginary road is flat and empty; the ambient temperature is that of a warm summer's evening.

It's also a complete fiction, more worthy of HE Bates' Darling Buds of May than the average winter crawl around the M25 with wipers scraping at the windscreen. Even the "worst-case" Urban cycle figure that we quote in Telegraph Motoring first drives is seldom an accurate indicator, and the Combined figure on which CO2 emission data is based is no more an indication of your real-world fuel consumption than a reading from a gipsy's tea leaves would be.

And it's not just us saying so; even the VCA agrees. "The fuel consumption achieved on the road is unlikely to be the same as the official test results," it declares, adding that the same car in exactly the same conditions might not give the same results, either. What Car? magazine, which is part-sponsoring the DfT's initiative, holds the same view.

"The figures are deeply flawed," says editor-in-chief Steve Fowler. "They are completely unrepresentative of our normal driving." In the past, no magazine has done more than What Car? to point this out to its readers, so it seems strange that it is now associating itself with the results.

The justification for such fantasy fuel consumption figures is the mantra of repeatability and consistency. "They're all we've got, and the closest thing to a level playing field until they revise the tests," says Fowler. Ford of Europe's chief powertrain engineer, Tim Howard, declares, "There is no silver-bullet cycle test."

Yet these flawed and highly variable CO2 figures will determine the taxes and other charges you pay, the amount your company can write down against the capital cost of your car and the sum it can claim against leasing costs.

 

[cjab98]

A few people told me than CO2 emission levels are directly linked to a cars "average" fuel consumption. I cant quite see how this can be, so I remain to be convinced.

Petrol is mostly made of Carbon and Hydrogen molecules, when mixed with the oxygen in the air the combustion process gives you CO2 and H2O (water). There will be other emissions too (like carbon monoxide CO), but it is minimal compared to the CO2 emissions, so CO2 emissions can be closely linked to fuel consumption.
You can't directly compare diesel and petrol fuel consumtion and CO2 though, as diesel is much denser the CO2 output will be higher for the same volume of fuel burned.

 

[Dieselman]

You can't directly compare diesel and petrol fuel consumtion and CO2 though, as diesel is much denser the CO2 output will be higher for the same volume of fuel burned.

15% extra.
petrol gives 10.6 kg per gallon of fuel burned, diesel gives 12.2kg per gallon.

 

[Dieselman]

A few people told me than CO2 emission levels are directly linked to a cars "average" fuel consumption. I cant quite see how this can be, so I remain to be convinced.

So how do you think it works.? I take it you have an idea otherwise you wouldn't be sceptical.

I'm not going to try to convince you the link is valid, but it is....

 

[ckember]

MOT does not measure CO2.

i know it measures the c0 level which also leads to c02 when it leaves the exhaust so it is indirectly part of the test

 

[x332race]

Information regarding MOT emissions test here

Note that the MOT test only measures Carbon monoxide (CO) and hydrocarbons (HC) in exhaust. Any Carbon monoxide coming out of the exhaust bears no relation to Carbon dioxide emissions.

 

[st4]

Co2 output has to me compatible to the cars fuel consumption as burning fuel produces co2 + h20. Assuming complete combustion the co2 output would be directly proportional to the fuel used. Diesel produces more per gallon as its denser than petrol, ergo there are more carbon atoms per gallon in deisel than petrol.

 

[x332race]

Co2 output has to me compatible to the cars fuel consumption as burning fuel produces co2 + h20. Assuming complete combustion the co2 output would be directly proportional to the fuel used. Diesel produces more per gallon as its denser than petrol, ergo there are more carbon atoms per gallon in deisel than petrol.

***, i've got to agree with you on that basically.