Thread: Diesel and Cetane - 'premium' diesels

Originally Posted by Disomania

Right, Here's hoping I can get a simple and easy to understand answer.

Recently we've started to get "Vortex Premium" diesel at a couple of the clatex outlets. They charge a 5 - 10c premium for this stuff.

The advertising blurb says it cleans the injectors and has a higher cetane rating than 'standard' diesel.

Can somebody, an industrial chemist who speaks plain English, please enlighten me on what's what with this stuff?

I have read that the higher cetane means it SHOULD (escape word) burn more evenly than the lower cetane fuel, and if it has additives to clean, should do that.

BUT - Is it all just hype or will there be an advantage? Unlike the 98 octane petrol, there are NO claims of better mileage, just a better, cleaner burn.

It's not like the timing can be changed on a Diesel or can it? On a petrol, its a matter of timing the spark, on a diesel how would you do it?

Funny, I was talking to a former student who works at a refinery about just that this morning.

She said that their product has a chemical added to increase the cetane. This is added at the tanker terminal to standard diesel, not at the refinery.

I also found this:

BP Ultimate Diesel (10ppm sulphur)has a guaranteed cetane rating minimum of 50
The ULS (10ppm sulphur) Diesel has a guaranteed cetane rating minimum of 48

BP claims typical cetane of 55-60 for ultimate compared to typical of 51 for normal. Theoretically, higher cetane ratings alter combustion and are meant to result in reduced diesel clatter.

I assume the other brands are the same deal.

If you have an EFI diesel it may be able to optimise your engine's operation to make better use of the slight increase in cetane. If you have a mechanical injection diesel (Tdi, isuzu, etc), then I doubt you will notice a difference.

EDIT: This is a good explanation from wikipedia of what cetane number means:

Cetane is an un-branched open chain alkane molecule that ignites very easily under compression, so it was assigned a cetane number of 100, while alpha-methyl napthalene was assigned a cetane number of 15 . All other hydrocarbons in diesel fuel are indexed to cetane as to how well they ignite under compression. The cetane number therefore measures how quickly the fuel starts to burn (auto-ignites) under diesel engine conditions. Since there are hundreds of components in diesel fuel, with each having a different cetane quality, the overall cetane number of the diesel is the average cetane quality of all the components. There is very little actual cetane in diesel fuel.

The minimum cetane number of fuel will be specified by the manufacturer to be the minimum required for reliable starting and running. Above this, increases in the number only have a very minor influence on the effective timing, as this is mainly affected by airflow and fuel/air mixing within the combustion chamber. To quote Ricardo "...neither the power output nor the efficiency of the engine are affected appreciably by variations in the cetane number, even over a very wide range". I doubt that even EFI engines are influenced significantly by changes in cetane number, and probably a lot less than by other characterists of the premium fuel such as its viscosity, solvent ability for injector deposits, lubricity, etc.

And all fuels marketed as diesel in Australia must meet minimum standards, which are adequate for most engines on the market.

John

I think I've read something similar about cetane somewhere, but it's a bit of a black art.


Seems the only real claim from the people making this premium diesel is for emissions/cleaning. I've just put a tank in the D4 to see how it goes, and will do a few tanks of this, then go back to the 'old' style and see if I notice a difference. I'm guessing it will not be much as there don't seem to be any claims of better fuel consumption.

Thanks gents.

BP Ultimate, at least here in W of A, isn't currently available apparently due to some kind of supply issue. Its been plastered all over the bowsers that usually tote it. I've had my TD5 since late December and I'm still waiting to try it out and see if it makes any difference apart from emptying my pocket a bit more.

Went thru this with PULP in the Rangie using Ultimate. It did make it run a fair bit smoother, but really the power didn't dent the back of my seat any more, just felt a bit better down lower.

However, after using it for so long and with the overall cost of it these days, I went back to std ULP and it actually felt like it revved a bit better and faster.
As the Rangie is only a 8.13:1 CR, it really didn't make use of the higher octane rating and I would hazard a guess and say with Ultimate diesel, its probably not going to be much different.
Even common rail diesels still have a varying range of compression ratios and ..... pardon the pun.... ultimately.... this has more of an affect on the combustion than varying the cetane rating. It may well be felt more in a 21:1 CR than a TD5 which is about 18:1.

As said before, in an inline or rotary style pump on a direct injection, its really not going to make difference with the power, but it may smoke less when you stand on it and feel slightly smoother or quieter. On a precom diesel, I really wouldnt worry about it. Save you 10c a litre and by a bigger turbo!!

Cheers

Andrew

we have been learning about fuels and oils this week at school,i will have to upload the handouts they are very good

i will upload them tomorrow