Cetain ratings ?? - PeachParts Mercedes-Benz Forum

truckinik · #1 04-01-2007, 02:26 AM

Hey, do any of you guys know anything about cetain ratings, for diesel fuel? Aparently it's the same as Octain, for gas...Anyone know more about it ??

H-townbenzoboy · #2 04-01-2007, 02:49 AM

It's CETANE, and this is its definition from a Chevron booklet on diesel fuels.

Quote:

"CETANE NUMBER
Cetane Number is a measure of how readily the fuel starts to burn (autoignites) under diesel engine conditions. A fuel with a high cetane number starts to burn shortly after it is injected into the cylinder; it has a short ignition delay period. Conversely, a fuel with a low cetane number resists autoignition and has a longer ignition delay period. Although the cetane number of a fuel is assumed to predict its ignition delay in any engine, the actual delay represented by the cetane number is valid only for the single cylinder engine in which it was measured. The fuel's performance in other engines may differ.
A fuel's ignition delay is determined by its chemistry. In a warm engine, the delay is independent of the physical characteristics of the fuel, like volatility and viscosity. (The cetane index correlations utilize density and distillation temperature properties to estimate cetane number, but these properties are being used as indirect indicators of fuel chemistry, not as direct variables.)
Cetane numbers apply only to distillate fuels; they are not measured for fuels containing petroleum resid (marine fuels)."

Robert W. Roe · #3 04-01-2007, 02:56 AM

I for one have not seen a cetane sticker on a diesel pump in many years.
I have seen 40 and 45 way back when; I'm not sure what ratings the new ULSD (ultra low sulfur diesel) has.

truckinik · #4 04-01-2007, 02:57 AM

Quote:

Originally Posted by H-townbenzoboy

It's CETANE, and this is its definition from a Chevron booklet on diesel fuels.

Wow, thanks for the education, on Cetane. I didn't know if it was a really big deal or not..Now I know a bit more about it.
Could this be why, my Freightliner, runs better, even with a higher water content in the fuel when it's warm/hot, than it does, when I first start it up. It burns off the water, a lot easier, when the engine is burning the fuel a lot better, too? It just steams the water, instead of it hanging around..?

Honus · #5 04-01-2007, 10:45 AM

In Northern Virginia, as far as I can tell, almost all of the stations are selling 40 cetane diesel. BP used to sell 45 cetane. My 1985 300D ran quieter, smoother, maybe with more power on the 45 cetane than it does on the 40.

There is a BP in Tysons Corner that sells 50 cetane. At $2.99 per gallon, it's pricey, but it makes my car run great.

Honus · #6 04-01-2007, 10:49 AM

Quote:

Originally Posted by truckinik

Wow, thanks for the education, on Cetane. I didn't know if it was a really big deal or not..Now I know a bit more about it.
Could this be why, my Freightliner, runs better, even with a higher water content in the fuel when it's warm/hot, than it does, when I first start it up. It burns off the water, a lot easier, when the engine is burning the fuel a lot better, too? It just steams the water, instead of it hanging around..?

Why does your fuel have water in it?

truckinik · #7 04-03-2007, 03:32 PM

Yes, with a fuel system as large as it is, on these trucks, there's always a certain "Acceptable' amount of water, in the fuel. I was simply inquiring about Cetane, for educational purposes though. I use different additives in my diesel, to reduce water, as much as humanly possible, and occasionally open the bottom plug on my fuel tanks with a full tank. I just let it drain, until fuel comes out, and plug it up. The water sinks to the bottom, so this is very easy, and not an environmental threat, in most cases. You can see when the fuel is coming, and plug it up easily. I do this about twice a season. I also run a water seperator filter, in the trucks. They come with it from the factory, and the filter mount, has a petcock on the bottom also.

Larry Delor · #8 04-03-2007, 07:02 PM

I would think that a contributing factor to your truck running better when it is hot than at start up, is because everything is fairly sloppy when it is cold and therefore compression is a little reduced. From what I understand, the slop is necessary, because of the extreme temps in the combustion chamber (heat make the metal expand).

ok ok, I know "slop" isn't a technical term, and it's not really slop, it's more generous tolerances.

truckinik · #9 04-03-2007, 07:10 PM

Quote:

Originally Posted by Larry Delor

I would think that a contributing factor to your truck running better when it is hot than at start up, is because everything is fairly sloppy when it is cold and therefore compression is a little reduced. From what I understand, the slop is necessary, because of the extreme temps in the combustion chamber (heat make the metal expand).

ok ok, I know "slop" isn't a technical term, and it's not really slop, it's more generous tolerances.

Understood, Thanks.

300SD81 · #10 04-03-2007, 07:15 PM

Why do we never see multiple centane ratings at gas stations? Its always 3 grades of gas + diesel... Never 3 different diesels...

Larry Delor · #11 04-03-2007, 09:59 PM

I think maybe it's because Diesel users have always been some sort of red-headed stepchildren. For many years, the majority of Diesel users were trucks and heavy equipment - stuff that nobody really cared about, plus it's not like somebody was trying to "hot-rod" their front-end loader. Bolting a "T" on an 8V92 was about it. The few cars that used diesel, were of no significance to anybody but the owners of said cars, and they typically didn't buy a diesel for its 0-60 time

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