diesel cetane

Question for the diesel engine experts - My owners manual (Ford 7.3) says not to use any fuel additives that have cetane, but lots of the diesel additives do have cetane.

What does cetane do and why would it be bad for a diesel engine?

Tractor related link - we have a 2 diesel tractors.

Cetane number or CN is a measurement of the combustion quality of diesel fuel during compression ignition. It is a significant expression of diesel fuel quality among a number of other measurements that determine overall diesel fuel quality......read again on the additive bottle bet it says cetane improver

Hey Nancy bamaray is right went toa school on this last week. chesk this link. We have used this in our Dodge for several years

Diesel fuel conditioner
Untitled URL Link

cetane is how fast the diesel burns during it combustion cycle. The reference is to a cetane engine buring cetane fuel.

Once cetane reaches a certain level, it is no longer a problem.

Once cetane reaches a certain level, it is no longer a problem.

Once cetane reaches a certain level, it is no longer a problem.

Most folks dont understand this. again...

Once cetane reaches a certain level, it is no longer a problem.

getting cetane higher will not help anyting.

If you are racing a diesel and need ultra high rpms out of it, your cetane number will come into play. but for a common low rpm farm tractor, cetane of normal diesel is plenty high. Usually a cetane number of 38 to 40 will be plenty fine for farm tractor and even trucks and cars...

Cetane is a measure of ignition quality of the fuel or more properly, ignition delay. IIRC the higher the number the easier the fuel will light which allows for more burn time and a cleaner burn.
I can not for the life of me imagine why Ford would discourage the use of additives with Cetane improvers unless they've simply declared war on all additives. Then again... if one looks at the things Ford did, diesel engine related, with it's pickup trucks... they could hardly be held as much of an authority on fuel.

I don't generally use additives myself because we generally have fuel of sufficient quality here that they're not needed... so I see additives mostly as a waste of money... but i don't think they're going to cause you any harm.
What can cause damage is additives with large quantities of methyl alcohol. That's not so good for rubber parts in the system...

Rod

A diesel engine run on a fuel with a lower cetane number than it was designed for will be harder to start, noisier, operate roughly and have higher emissions.
In a diesel engine, the fuel is ignited by hot air; the air is heated by compression. The fuel is injected into this hot air just before the piston reaches top center. (“Top center” is the moment when the piston has traveled into the cylinder as far as it can go, and compression is at a maximum.) Ideally, ignition should begin just as the piston reaches top center. If it does not, the entire charge of fuel may have time to become thoroughly mixed with air, and when it does ignite, the pressure rise will be much steeper than it would have been had ignition occurred earlier. So a desirable property of a diesel fuel is that it ignite quickly.

In the 1930"s the Cooperative Fuel Research committee sought a way of expressing the tendency of a diesel fuel to ignite quickly, and their work was taken up by the ASTM. A substance that ignited very quickly, cetane (n-hexadecane) was arbitrarily given a rating of 100, and a substance that was slow to ignite, alpha-methylnapthalene (later called 1-methylnapthalene), was assigned a rating of zero. Values on this scale were named “cetane numbers.”

A specially-designed engine with adjustable compression is used to determine a fuel’s cetane number. The fuel being tested is injected at 13° before top center. (This describes a particular moment in the engine’s cycle. “13°” refers to the rotation of the crankshaft.) The engine’s compression ratio is then adjusted until the fuel ignites at top center. Retaining this compression ratio, the engine is then run on various blends of cetane with 1-methylnapthalene, until a blend is found for which ignition occurs at top center. The cetane number is the percentage by volume of cetane in the mixture that has the same performance as the fuel being tested.

Ceatine is ignitions temp, not flame speed or burn time.
Of course lowering the cetane number inproves cold weather starting.

Here's more than you could WANT to know about diesel fuel...
Chevron/diesel

"Of course lowering the cetane number inproves cold weather starting. "

HUH???

Yeah, my thoughts too!

If I understand your post correctly, putting an additive with cetane in diesel fuel could raise the cetane percent and cause the fuel to combust before the piston is in the proper position.

Correct?

My reason for asking is during the unusually cold weather 2 weeks ago, I looked at additives to prevent gelling. Some of the gelling preventatives had cetane.

I didn't buy any of the ones that had cetane because the owner's manual had said not to use additives with cetane.

Nancy"s taling about her Truck.
Nancy that 7.3 was made by Interntional and has been around for a Lllong time. Cetanes about 40 will work fine and additives shouldn"t have any problems.
By the way my 1994 Ford with 7.3 has 240K miles and I am sure has had additives put in it. Runs fine

Been adding straight cetane to diesel for years. The Deutz Fahr agrofarm 100 engine needs 46 cetane and up. I buy diesel fuel from Southern States Petroleum and it's premium diesel. I don't have to add cetane now since they raised their's to 52. I've read that anything over 55 is a waste. I sell cetane to several backhoe operators and they swear by it on cold starting, less smoke and fast starts. I even add it to my dads heating oil and it gives it more BTU's per gallon and burns cleaner.

Depends which way you looki at it. I should have been clearer.
Higher octane number on gasoline raises the ignition temp.
Higher cetane number for diesel lowers the ignition temp.
Cetane rating is the inverse of octane.

RIght.... higher octane = less apt to detonate/ping. (spark ignition engine)
Higher cetane = lower ignition temp = easier cold starting.

That"s a great reference, Bob. Thanks for posting it.

Nancy,
Most of the typical diesel additives that are on the market will raise the cetane number by just a few points and while that helps cold starting there is just not enough improvement to make a huge difference in the performance in either the 7.3L Ford/Navistar or any of your farm tractors.
of cetane numbers that the fuel should have.

general motors eay the same thing about the duramaxx i used it in mine in the winter months put 150000 miles on it with no problems.
RICK

I won't often say this... but BURN THAT MANUAL. It's plain incorrect.
It would be more to your benefit,if you can find it... to buy a premium/winter blend fuel and avoid the use of alcohol based additives entirely. I know that's not so easy to do, but if you can...
Winter fuel is the standard around here from november until april and I don't need any additional additives other than whatever the refiner adds...

Rod

The gas corollary is:

Once octane reaches a certain level, its no longer a problem.

Ie if you run a normal engine, designed for 87 octane, running 92 octane does nothing for you.

Nancy,Iv run power service supplement in my 2000 7.3 Ford since 04 and never had a problem. The bottle says prevents fuel gelling to -40 below zero, equals performance of 50/50 blend no1 and no2 diesel fuels, lowers cold filter plugging point, boosts cetane up to 4 points, does not contain any alcohol, will not void engine manufactures warranty, also disperses water in diesel fuel. I also use it in my Ford diesel tractors. J

Nancy,Iv run power service supplement in my 2000 7.3 Ford since 04 and never had a problem. The bottle says prevents fuel gelling to -40 below zero, equals performance of 50/50 blend no1 and no2 diesel fuels, lowers cold filter plugging point, boosts cetane up to 4 points, does not contain any alcohol, will not void engine manufactures warranty, also disperses water in diesel fuel. I also use it in my Ford diesel tractors. J

Hello Nancy Howell,
All additives as stated, will increase the cetane level of the fuel.
The product you and I buy at the pump, is specific to where the product is sold.
In other words, it should do the job AS IS!
Under NORMAl circumstances, we need to do nothing at all. Adding a cetane booster will help only, if the region is experiencing an anusually cold weather. If you bought the fuel in Florida, and were going to Maine, you WIll need to treat the fuel for the colder climate.
Guido.

no.. cetane controlls how fast the diesel burns and limits the higher rpms of the diesel engine. If you have high enough cetane to run at 5000 rmps, and your engine will only run at 3800 rpms due to the governor or computer, adding more cetane improver will not help. a special test engine is used to determine the max rpm of the engine under the test diesel. Cetane gas is used at a reference to see if the diesel burns faster or slower. If your fuel has enough cetane to run at 5000 rpms,, it will not help to ad more cetane improver as your engine will not and can not run faster than the computer will let it run. Modern computer controlled diesels actually run the injectors so that they fire LATE in the cycle. Because of the late firing, cetane numbers become a bit more important as you need it to completly burn fast enough. Again, if your fuel is high enough, adding more cetane improver will NOT help.

cetane improvers do NOT make it start better or run better if you already have fuel at the correct level.

So bottom line, in north america is is difficult to buy diesel that is too low in cetane. And due to the uld is plenty good for engines.

However there are lots of opinions and lots of snake oil out there.

If you run a good injector cleaner through the engine every 50,000 miles and keep the filters clean and the glow plugs working with good starting batteries, you will do ok on pump diesel.

filling stations automatically convert to winter diesel early enough to protect you from gelling in ultra cold in most cases. winter diesel does not have the same horsepower as summer diesel, so they will change back to summer diesel as the weather warms up. You should not need additives as some folks run a million miles with no additives and others claim to run 200,000 miles with additives...

As I get any diesel equippment through the shop, I run a can of BG 44k injector cleaner though it. If the injectors are already clean it will do nothing. If they are dirty, you see it start quicker and run better. As I buy it by the case it cost me about $13 a can. Clean injectors will make the diesel fire quicker and complete. Make sure your air filter is cleaned a replaced every couple of years. Oil covered air filters will destroy the maf sensor in modern diesel engines so stay away from them.

Cetane and octane have little to nothing to do with flame speed. They refer to ignition temp.

Don't worry about the small cetane addition with the conditioner additives. I see a lot of Southern trucks stranded in Iowa during the cold weather. We are about on the edge of fuel blended strong enough to handle the winters. It is a GOOD idea to add a slug of power services when you travel more than a 100 miles north in cold weather.

Apparently if hinges on how well a fuel ignites under pressure.See Wikipedia for explanation and all other variables.

Hello buickanddeere,
CETANE is the ignition quality measure
of Diesel Fuel.
It WILL affect the following:
1. Cold starting.
2. Smoke emission quantity.
3. Combustion.
Guido.

Hello buickanddeere,
Low Cetane fuel has a LONG ignition delay.
High Cetane fuel has a Short ignition delay.
Low Cetane, warmer operating temp.
High Cetane, colder operatimg temp. That is why some additives will increase the Cetane level, for better cold weather startability.
Guido