View Full Version : How to raise the cetane number

08-02-2001, 11:25 AM
One way to reduce the ping sound is retard the timing but is there a chemical what you could mix in with the fuel to raise the cetane number.

Dave UK
08-02-2001, 01:20 PM
Check out the pacific biodiesel test data at

UK BS EN 590 diesel has a minimum CN of 48
US ASTM allows 40 minimum
DIN 51606 minimum 49

But as the Pacific table shows, biodiesel can be as high as 54.
This high cetane is one reason the fuel burns more cleanly than other diesel fuels.

[This message was edited by Dave UK on 02 August 2001 at 09:42 AM.]

08-02-2001, 02:15 PM
Methanol in biodiesel lowers the cetane rating. I have found it can cause rough running.

08-02-2001, 02:45 PM
I should add that if you are washing the biodiesel to get out soap you will also wash out the methanol.

08-02-2001, 05:18 PM
I use Amsoil Cetane Boost. Lots of other companies make it as well.


I asked an organic chemist (and diesel afficianado) if cetane boost will work with biodiesel or if it is formulated specifically for petrodiesel. He said it will work fine with biodiesel.

P.S. I am NOT an Amsoil dealer.

[This message was edited by Dante on 06 August 2001 at 12:54 PM.]

08-05-2001, 03:27 AM
But why would you want to raise the cetane value of biodiesel when it is already substantially higher than distillate?

Veggie Pup
08-05-2001, 03:57 AM
I know of no current production compression-ignition engine that can benefit from a cetane rating of over 50. Well-made biodiesel will have a cetane rating of 49 or higher. Why would anyone want to add a cetane booster?


08-06-2001, 04:54 PM
World energy doesn't post cetane data except as an "example." Cetane can and does vary from batch to batch. If your vehicle's performance does not suggest low cetane or if testing shows acceptable cetane, then of course you would not want to boost it--that would be a waste of money.

On the other hand, my car hesitates slightly on starting with my current supply of biodiesel but does not hesitate whatsoever on petrodiesel. The manufacturer told another user that this ASTM certified biodiesel (from WVO) tested at 40 cetane and 1.5 oz. cetane boost in a ~15 gallon tank makes the hesitation go away.

Since I don't make my own biodiesel, I will be switching to World Energy when it becomes available in Seattle.

Dave UK
08-08-2001, 10:08 AM
I've had the same thing happen with my TDI's. From cold, they take a turn or two to start on bio, but fire instantly on petro. However it's never caused a problem.

I think this slight hesitance is nothing to do with cetane. I think the heavier viscosity of bio means the engine needs a turn or two to get a good "squirt" (tech term http://biodiesel.infopop.cc/groupee_common/emoticons/icon_smile.gif ) from the injectors.

The engine has a smoother more tingly sound on bio which is what you'd expect from a more consistent higher cetane fuel. It ignites more quickly and evenly than the petro.

A test with pre warmed bio to give exactly the same fluidity as petro at ambient would prove it one way or the other.

08-08-2001, 12:39 PM
Dave, you seem to be very knowlegable on the subject generally, and I was wondering how you go about paying the exise duty to the government?--or is the fuel only used off road?--I would like to go legal, and need to know the format of payment before I go ahead and broach the subject with the authorities! I know that SVO attracts the same duty (46p), but Im thinking of experiment with used stuff from local chippies--It would still be cheaper than DERV!
Thanks in advance

08-08-2001, 03:03 PM
In my specific case, when the other person using my fuel supplier said the fuel tested at 40 cetane, I said "That can't be right. They must be referring to the ASTM minimum of 40 cetane." As a result, the other person using the fuel went back to the manufacturer and the manufacturer said the 40 cetane number was the result of testing. It still does not sound right to me, but I am still changing suppliers.

The primary non-environmental reason I am using biodiesel in my VW TDI is biodiesel is can be the best diesel fuel available in the US--better cetane and lubricity, lower particulate emissions (easier on the egr and intake systems and catalytic converter) and solvent (helps keep fuel system clean). However, all biodiesel in not created equal.

The addition of cetane boost mitigated the hesitation I mentioned, but you shouldn't need to add cetane boost to biodiesel. If you do, then IMO there's something wrong with the biodiesel.

Dave UK
08-09-2001, 08:17 AM
Dante, I think you are right. Biodiesel's cetane is largely determined by its chemical make up and oxygen content. I'm surprised thay can make it with such a low cetane.

Oddly, the stuff which many folk think makes poor biodiesel (tallow) actually gives a better energy value (more dense), the snag is it's gelling problems.

On the tax issue write to you local Customs & Excise and ask how you register as an alternative fuels manufacturer. When it all comes through you state on the return how much fuel has been used and pay the excise tax accordingly. They don't (yet) come and physically measure your fuel output.

[This message was edited by Dave UK on 09 August 2001 at 10:17 AM.]

08-09-2001, 09:24 AM
If you really wish to be legal don't forget your carriers licence(£126 for 1st 3 years)and your customer/proccessors licence from Environment Agency(this ones alittle more complicated). You may find that HM C&E require a detailed desription of your equipment etc.
Sounds like fun, don't you think


06-15-2006, 06:30 PM
[QUOTE]Originally posted by Guest:
One way to reduce the ping sound is retard the timing but is there a chemical what you could mix in with the fuel to raise the cetane number.[/QUOTE