Don't I know it - I remember reading an article (a little while ago, admittedly) where the best anyone could come up with was to impinge hydrogen onto pellets, which were fed into your tank and gently heated to get the hydrogen off. I think acceptable mileages could be achieved that way, but they couldn't explain how to get the 'dead' pellets out easily!

Then of course there's the issue of the provenance of the hydrogen... Steam reformation of methane? That's sustainable!

I meant isn't as simple as they would make us believe btw.

There's also a school of thought that wants to use nuclear/renewable electricity to generate hydrogen to make ethanol rather than the primary and secondary bio-ethanol routes. Seems like hard work to me.

I meant isn't as simple as they would make us believe btw.

I guessed that! :P

There's also a school of thought that wants to use nuclear/renewable electricity to generate hydrogen to make ethanol rather than the primary and secondary bio-ethanol routes. Seems like hard work to me.

I'm sure a simple energy balance would put paid to that idea. A mix of nuclear and renewables would be OK to supply everyone's kettles, but my money's on microbiotic production to keep our motors running...

Don't understand the density thing.....

Diesel engines are generally more efficient because of the combustion cycle when compared to petrol spark ignition. Diesel is able to run at very high Air to Fuel Ratio's (AFR) whereas petrol spark ignition has to run pretty close to 14.7:1 AFR all the time. Most of the time you drive at very small part load cycles which is when disesel engines are very efficent..

I did say that the difference in density is only PART of the reason that diesel engines are more economical. Here is why/how

Someone has used the term "stoichemetric" - for our purposes this is very simply the theoretical mass of oxygen required to burn a certain amount of fuel.

The approx average molecule of diesel is C12H26 molecular weight is 170 - every 12g of carbon needs 32g of oxygen to burn completely, every 2g of hydrogen needs 16g of oxygen to burn completely

So 170g of diesel needs 592g oxygen (12x32=384 plus 26/2x16=208 )

The stoichemetric ratio for diesel is 170:592 = 1:3.48

NB that is oxygen not air; because air is 21% oxygen the ratio for air is 1:16.58

In simple terms the formula is

diesel + oxygen => carbon dioxide + water + ENERGY

(NB this is a much simplified version of the combustion process - the other constituents of air get involved, diesel is a complex mixture with impurities, you need to add some excess air to ensure complete combustion, you never get 100% efficient combustion, etc etc)

If you haven't got bored and buggered off by now you will see that all these calculations use mass not volume. Engine management systems meter stuff by volume cos it's easier than using mass but the volumes are calculated to give the required mass of oxygen and fuel. That is why you have air and fuel temperature sensors in the management system because air and fuel expand/contract with changing temperatures so you need to adjust the volumes being delivered to get the correct mass.

Finally my point

Because diesel is denser than petrol and you buy fuel by volume not by weight, you get more carbon and hydrogen for your money and so get more energy per litre from diesel than petrol.

BOOOOO! - Is anybody still there

Oh yeah - before you ask - if it ain't already obvious - I'm a chemist

Oh yeah - before you ask - if it ain't already obvious - I'm a chemist

Shame you can't spell STOICHIOMETRIC, then! :P

Still more fun in a petrol..., and I don't think that can be equated:rolleyes:

Petrol engines create a lot of heat compared to a diesel. When i open the bonnet on my TFSI this wave of heat hits you unlike the diesel. That heat is wasted energy whereas the diesel makes more work of it's energy hence less heat and wasted fuel.

Oh yeah - before you ask - if it ain't already obvious - I'm a chemist

I'd have never have guessed

PS. I hope you don't regurgitate this stuff at dinner parties!

I'd have never have guessed

PS. I hope you don't regurgitate this stuff at dinner parties!

Chemists are infamous drinkers

Shame you can't spell STOICHIOMETRIC, then! :P

errmmm... mumble mumble mumble

ah yes!

Jus testin yoo chaps to sea hoo woz awaik and hoo cud spel

You may have noticed I did it again there but you have to look really hard this time.

I'd have never have guessed

PS. I hope you don't regurgitate this stuff at dinner parties!

Never get invited - I've often wondered why. :(

Never get invited - I've often wondered why. :(

As part of a project I worked on some years ago I had to interview an embalmer in a funeral directors. After discussing the various funtions of his job I said (a bit tongue in cheek) that he must be a popular dinner party guest - his reply was the same as yours - "I never get invitied"

I cannot find the article on autoexpress but I have seen a post about diesel rising to £2.30 per litre by next June, I have also heard my fleet operations manager moaning about it at work!!

this one?

I cannot find the article on autoexpress but I have seen a post about diesel rising to £2.30 per litre by next June, I have also heard my fleet operations manager moaning about it at work!!

"it was suggested to him that diesel will rise to £2 a litre....."

WTF??!?!?

No explanation or evidence for this theory.

I can suggest to you that it will be £3 a litre next wednesday but that doesn't make it true

"it was suggested to him that diesel will rise to £2 a litre....."

WTF??!?!?

No explanation or evidence for this theory.

I can suggest to you that it will be £3 a litre next wednesday but that doesn't make it true

In the AutoExpress article they're blaming the super-tankers which are going to start using a diesel mix to cut sulphur emissions.

DUTY IS EXACTLY THE SAME ON DIESEL AND UNLEADED

Shouting or not, you are wrong!!!!

2007 fuel duty (as of 1 October 2007) in the United Kingdom is:

• 50.35 pence per litre for ultra-low sulphur unleaded petrol/diesel
  
• 53.65 pence per litre for conventional unleaded petrol
  
• 56.94 pence per litre for conventional diesel
  
• 30.35 pence per litre for bio-diesel and bio ethanol - low tax to encourage consumer conversion
  
• 16.49 pence per kg for gas other than natural gas (LPG)
  
• 13.70 pence per kg for natural gas used as road fuel.
  
• 9.69 pence per litre for rebated gas oil (red diesel)
  
• 9.29 pence per litre for rebated fuel oil

So Diesel is 3.3p per litre more - that makes it NOT THE SAME!! Only if you are describing ultra-low sulphur fuels is the duty the same

I thought the ultra-low sulphur diesel/petrol is the normal stuff in the pumps??

Ministerial statement in July 2007 (before the fuel duty rises later in the year)

The Motor Fuel (Composition and Content) (Amendment) Regulations (SI 2007/1608) issued by the Department for Transport require oil suppliers to supply sulphur-free diesel (SFD) to garage forecourts from 4 December 2007. While the current duty rate on both ULSD and SFD is 48.35p per litre, mixtures of the two fuels meet neither definition, and are liable to the heavy oil duty rate (currently 54.68 ppl).

In the transitional period before and after the DFT regulations come into force, there may be occasions when ULSD and SFD need to be mixed, and the high rate of duty may act as a disincentive for the industry to supply SFD. The provisions will remove the density and distillation requirements from the ULSD definition, so that mixtures of ULSD and SFD will meet the ULSD definition. Bringing forward the deregulatory changes to the definition of ULSD will ensure the smooth changeover from ULSD to SFD

So more confusion? I am unsure of exactly what fuels on forecourts are ULSD and SFD, though two different diesels are often available, and these are standard and a more expensive one.......

Are the comparisons here not a bit off?

Do all (or most) VAG petrol engines not require super? that's only a couple of pennies cheaper than diesel.

Are the comparisons here not a bit off?

Do all (or most) VAG petrol engines not require super? that's only a couple of pennies cheaper than diesel.

I was thinking that as well. Not sure about all petrol engines, but thought it was definitely required in the VRS?

Shouting or not, you are wrong!!!!

2007 fuel duty (as of 1 October 2007) in the United Kingdom is:

• 50.35 pence per litre for ultra-low sulphur unleaded petrol/diesel
  
• 53.65 pence per litre for conventional unleaded petrol
  
• 56.94 pence per litre for conventional diesel
  
• 30.35 pence per litre for bio-diesel and bio ethanol - low tax to encourage consumer conversion
  
• 16.49 pence per kg for gas other than natural gas (LPG)
  
• 13.70 pence per kg for natural gas used as road fuel.
  
• 9.69 pence per litre for rebated gas oil (red diesel)
  
• 9.29 pence per litre for rebated fuel oil

So Diesel is 3.3p per litre more - that makes it NOT THE SAME!! Only if you are describing ultra-low sulphur fuels is the duty the same

Given that the only type you can buy at the pumps is ultra low sulphur diesel and has been for quite some time.......

Are the comparisons here not a bit off?

Do all (or most) VAG petrol engines not require super? that's only a couple of pennies cheaper than diesel.

I was thinking that as well. Not sure about all petrol engines, but thought it was definitely required in the VRS?

Really??

My ST produces it's 220 odd horses on normal 95ron stuff

VAG say that you should use super for the best results in the FSI engines.

I don't know if the quoted power outputs are on regular or super though.

Anyone know for sure?

I might start chucking red diesel in mine, I think the fine won't be as much as paying for the convential stuff overtime.

I might start chucking red diesel in mine, I think the fine won't be as much as paying for the convential stuff overtime.

Yes it will because they make you pay back tax to the mileage where it could be proved you had not.

Maybe last MOT, maybe from when the car was new, plus a fine and possible criminal charges.

If you were going to be trying that it would be veggi oil IMHO in an old IDI derv.