Mercedes Benz OVERSTATING fuel consumption

Ultrasonic

sh0597 wrote: »

The fairest way to tax CO2 production is to increase fuel duty. The present system is imperfect for a few obvious reasons.

I agree. Not just because it would reflect what cars are actually capable of, but also because it would be affected by how economcially people drive. But whilst this would be the most accurate way of taxing on the basis of CO2 production, it is a slightly different question whether it would be the best way to minimise CO2 emissions, which at least should be the reason for taxing higher CO2 emissions more. My guess is that the current system is probably more effective for this.

Ultrasonic

uniqu3 wrote: »

Easy test:
20+ year old Citroen AX diesel - 60+ mpg
New Fiesta 1.6TDCi - 60+ mpg

The Citroen AX will output closer to double the CO2 emissions of the fiesta.

Could you explain why that would be the case, and ideally provide a reference to back that claim up? I'm sceptical it is true to be perfectly honest, but I'm open to be being proved wrong.

Joe_Horner

uniqu3 wrote: »

At which point the whole system would become unfair and the motor industry would be severely disadvantaged.

Easy test:
20+ year old Citroen AX diesel - 60+ mpg
New Fiesta 1.6TDCi - 60+ mpg


The Citroen AX will output closer to double the CO2 emissions of the fiesta. There's plenty of further comparisons to be made, but essentially it would be a massively unfair system. CO2 emissions are based on much more than MPG,

Err, no they're not. CO2 emissions is exactly related to fuel consumption for a given fuel because a given volume of fuel will produce a given volume of CO2 when it's completely burnt.

For average petrol, completely burning 1 litre of petrol will produce about 2300 grams of CO2. For diesel that figure is about 2650g per litre burnt.

It doesn't matter whether you burn it in a Fiesta, an AX, a Moggie Minor, or by pouring it on the ground and throwing a match in because the amount of CO2 produced is determined by the number of carbon atoms in the fuel burnt and nothing else. It's basic chemistry.

Any car doing, say, 60mpg, will use approx 0.0471 litres of fuel to travel 1 km - regardless of what engine it has - because two cars doing the same MPG will use the same amount of fuel to travel the same distance.

Burning that 0.0471 l of fuel will produce (for petrol) 0.0471 x 2300 = 108g of CO2 or (for diesel) 125g of CO2 because that's the amount of CO2 that chemistry says will be made by burning that much of those fuels.

In practice. older "dirtier" engines will actually produce very slightly less CO2 than a modern one at the same fuel consumption because older dirtier engines tend to let more of the fuel escape down the exhaust as unburnt hydrocarbons




eta: as for VEd and insurance, you obviously haven't caught up with the fact that you no lnger need insurance to buy VED because they don't check anymore.

uniqu3

Ultrasonic wrote: »

Could you explain why that would be the case, and ideally provide a reference to back that claim up? I'm sceptical it is true to be perfectly honest, but I'm open to be being proved wrong.

Predominantly it's down to aftertreatment. Modern vehicles are built on a variety of carbon-reducing aftertreatments including, but not limited to, EGR systems, EGT Measurements, DPFs and Catalytic Converters. There are already massive improvements in existence in the industry for these, but they're either not cost effective or developed enough for production quite yet.

An older car may return the same amount of MPG, but won't include aftertreatment systems which are responsible for the reduction in Carbon Dioxide emissions in vehicles.

The thing about CO2 is that it isn't harmful - there are far worse things that produce CO2. There's a cycle involved where us fleshy creatures (people, animals etc.) inhale the air and exhale around 5% more CO2 (and the same amount less oxygen). Trees do this the other way around mostly. Therefore, deforestation contributes more to the problem than cars, and the production of meat probably even more so.

The issues with exhaust gases are the particulates and carbon monoxide more than anything.


The only fair way to ever tax cars would be on a variable system whereby tax was tailored to an individual by means of testing the range of CO2 produced in each car and applying a class that way. Can't see that working though, due to the factors/costs.


Quick Edit: Left out a little bit about forthcoming technology for reducing warm-up cycles in IC engines, thus reducing CO2 further. I could be pedantic and add that MPG is only relevant when moving, so a stationary vehicle would do 0mpg and produced less CO2 than a moving vehicle in most situations; thus MPG is not exclusively relevant to CO2 emissions.

uniqu3

Joe_Horner wrote: »

Err, no they're not. CO2 emissions is exactly related to fuel consumption for a given fuel because a given volume of fuel will produce a given volume of CO2 when it's completely burnt.

For average petrol, completely burning 1 litre of petrol will produce about 2300 grams of CO2. For diesel that figure is about 2650g per litre burnt.

It doesn't matter whether you burn it in a Fiesta, an AX, a Moggie Minor, or by pouring it on the ground and throwing a match in because the amount of CO2 produced is determined by the number of carbon atoms in the fuel burnt and nothing else. It's basic chemistry.

Any car doing, say, 60mpg, will use approx 0.0471 litres of fuel to travel 1 km - regardless of what engine it has - because two cars doing the same MPG will use the same amount of fuel to travel the same distance.

Burning that 0.0471 l of fuel will produce (for petrol) 0.0471 x 2300 = 108g of CO2 or (for diesel) 125g of CO2 because that's the amount of CO2 that chemistry says will be made by burning that much of those fuels.

In practice. older "dirtier" engines will actually produce very slightly less CO2 than a modern one at the same fuel consumption because older dirtier engines tend to let more of the fuel escape down the exhaust as unburnt hydrocarbons




eta: as for VEd and insurance, you obviously haven't caught up with the fact that you no lnger need insurance to buy VED because they don't check anymore.

You're quite incorrect. For the first part, see my post on aftertreaments above.

For the second part, leave your car either:

a) Taxed, but uninsured, or;
b) Insured but un-taxed.

I'll wait for the thread complaining about the penalties.

JustinR1979

uniqu3 wrote: »

You're quite incorrect. For the first part, see my post on aftertreaments.

I did wonder why dpf's and cats etc were fitted if they didn't lower emissions.

uniqu3

JustinR1979 wrote: »

I did wonder why dpf's and cats etc were fitted if they didn't lower emissions.

In a way, a DPF is a knock on effect from an EGR. The theory behind EGR systems is that they reintroduce incomplete combustion and the engine reduces the 'fresh' fuel to allow for the little extra that's recycled. This produces particulates, hence the DPF then reduces these nastiest from entering the air. It's not exclusively for that reason, but it's a large factor.

Older EGRs were reasonably useless, but the drive for further reduction in emissions has steadily lead to some very clever systems that we'll be seeing soon in 2015 and 2016 variants across the board.

Bit on the improvement in CO2 since 2000 is on this site:

http://www.smmt.co.uk/co2report/#responsiveTabs1

JustinR1979

I know on the early Vaux ecotecs the egr seemed to be a backward step, just clogs everything up with crap.
Just more and more junk to go wrong.

Joe_Horner

uniqu3 wrote: »

You're quite incorrect. For the first part, see my post on aftertreaments above.

For the second part, leave your car either:

a) Taxed, but uninsured, or;
b) Insured but un-taxed.

I'll wait for the thread complaining about the penalties.

Wrong again.

Catalytic converters slightly increase CO2 emissions by converting carbon MONoxide (CO) into CO2. They also burn off any unburnt fuel, again creating more CO2.

EGR is a method for reducing nitrous oxide emissions by reducing burn temperatures, and has nothing at all to do with carbon compounds of any kind.

DPFs remove solid carbon (soot) particles which are nothing to do with CO2 until they're burnt off by a regeneration cycle, at which point they produce more CO2 than just letting the solid carbon settle unburnt on the roadside and surrounding buildings.

Please, if you're going to try and argue "green" then at least learn the difference between the chemicals involved!

As for the VED and insurance, the only effect that VED used to have on insurance (and one of the reasons given for keeping it) was that you had to show the insurance in order to buy the VED.

That's no longer considered neccessary and the penalties you mention will arise from ANPR or database checks, not from having or not having VED.

uniqu3

JustinR1979 wrote: »

I know on the early Vaux ecotecs the egr seemed to be a backward step, just clogs everything up with crap.
Just more and more junk to go wrong.

It's not so bad the more the technology improves - the reliability of systems is improving as it's in a manufacturers best interest to reduce warranty spend by improving the systems. The Vauxhall ones were crap though.

I had a presentation by T.Rad recently and you'd laugh if you saw the comparison in size of their new tech EGRs to the little things you used to get on the old Vauxhalls.