Percent vs g/Kg conversion

kevpatts

Hey,

How do I convert from the percentage value that the NCT gives for CO2 emissions to g/Kg that manufacturers advertise?

Kev

colm_mcm

You can't. They're measuring different things.

Assuming you mean emissions relating to tax.

jimgoose

The NCT readouts are parts-per-million, not per cent. And you mean g/km from the manufacturers, yes? You can't really convert that way without getting into some fairly serious chemistry and engineering!

CiniO

kevpatts wrote: »

Hey,

How do I convert from the percentage value that the NCT gives for CO2 emissions to g/Kg that manufacturers advertise?

Kev

I never heard about NCT measuring CO2 emissions.

kevpatts

okay, so I'll get to the crooks of my query then. I just did the NCT and got a CO2 reading of "0.16 vol%". How does this compare to say a new 999cc Ford Focus. Is there any way to compare?

CiniO

kevpatts wrote: »

okay, so I'll get to the crooks of my query then. I just did the NCT and got a CO2 reading of "0.16 vol%". How does this compare to say a new 999cc Ford Focus. Is there any way to compare?

You didn't.
CO2 emissions is not part of NCT test.
You couldn't possibly get any CO2 readings...

jimgoose

kevpatts wrote: »

okay, so I'll get to the crooks of my query then. I just did the NCT and got a CO2 reading of "0.16 vol%". How does this compare to say a new 999cc Ford Focus. Is there any way to compare?

No, beacuse the NCT is looking at ratios of substances (including CO, not CO2, but howsoever) within the exhaust gas, and the road-going CO2 figure is concerned mainly with fuel consumption.

PaddyFagan

kevpatts wrote: »

okay, so I'll get to the crooks of my query then. I just did the NCT and got a CO2 reading of "0.16 vol%". How does this compare to say a new 999cc Ford Focus. Is there any way to compare?

No. http://www.rac.co.uk/forum/showthread.php?12660-Converting-the-MOT-result-of-Co2-in-to-g-km

Paddy

Chimaera

kevpatts wrote: »

okay, so I'll get to the crooks of my query then. I just did the NCT and got a CO2 reading of "0.16 vol%". How does this compare to say a new 999cc Ford Focus. Is there any way to compare?

In short, no.

The CO2 emissions figure quoted for new cars (and the one that gets used for tax purposes) is based on a standardised drive cycle test carried out on a rolling road dynamometer (to simulate real world driving conditions), and gives CO2 output in g/km i.e. how much it puts out for each kilometre driven.

The NCT figure is the mass fraction of CO2 contained in the exhaust gases at the time the measurement is taken i.e. for every kilogramme of exhaust gas emitted, how much CO2 does it contain. Since the NCT is a static test done under no load, there's no convenient comparison to be made with the other value. Bear in mind that the NCT is checking to confirm that emissions are below a particular limit, not establishing what they are in absolute terms.

If you want to compare your car to another, look up the original CO2 emissions figure for the car from the manufacturer's literature.

CiniO

Chimaera wrote: »

In short, no.

The CO2 emissions figure quoted for new cars (and the one that gets used for tax purposes) is based on a standardised drive cycle test carried out on a rolling road dynamometer (to simulate real world driving conditions), and gives CO2 output in g/km i.e. how much it puts out for each kilometre driven.

The NCT figure is the mass fraction of CO2 contained in the exhaust gases at the time the measurement is taken i.e. for every kilogramme of exhaust gas emitted, how much CO2 does it contain. Since the NCT is a static test done under no load, there's no convenient comparison to be made with the other value. Bear in mind that the NCT is checking to confirm that emissions are below a particular limit, not establishing what they are in absolute terms.

If you want to compare your car to another, look up the original CO2 emissions figure for the car from the manufacturer's literature.

All corrects, except that they don't measure CO2 on NCT. They do measure CO and HC for petrol engines.
CO2 is not poisonous gas, no point in measuring it's content in exhaust fumes.

kevpatts

Thanks all.

Not easy to look up the stats for my car! 1987 BMW 316 (not i) that's been converted from leaded to unleaded. Anyone would be guessing. I'd have to get it measured.

alias no.9

kevpatts wrote: »

Thanks all.

Not easy to look up the stats for my car! 1987 BMW 316 (not i) that's been converted from leaded to unleaded. Anyone would be guessing. I'd have to get it measured.

If you can find an official fuel economy figure for it in mpg or l/100km, it can be calculated. Not sure if standardised testing for fuel economy goes back that far though. If it's for VRT you may just have to suck it up at the max rate, probably close enough to the truth anyway.

dougie-lampkin

This site claims 185 g/km for the carb'd version, putting you in the 30% VRT band. It also claims 204 g/km for the EFI version, so I'm not sure if they're both accurate.

If you've NCT'd it, I assume it's already registered, so why do you need the emissions figures? Did you VRT it recently at the max rate?