# Diesel Cetane Info



## ljgmdad (Feb 2, 2012)

Useful info:

http://dieselsite.com/prodrev/cetane.htm

Cetane number is one of the most widely-known parameters of diesel fuel. Awareness doesn't always mean understanding, and there is a danger that cetane number can be confused with cetane index. A brief explanation is in order.

A diesel engine is a compression-ignition engine. The fuel is ignited by the high-temperature, high-pressure air created in the cylinder as the piston nears the end of the compression stroke. Fuel in gasoline engines is ignited by a spark plug.

The cetane number is a measure of the ease with which diesel fuel is ignited during the compression stroke. The number is determined using a specified laboratory test engine. The cetane index, on the other hand, is calculated using an equation involving the API gravity (density) and the distillation curve of the fuel. Consequently the cetane index cannot be increased and improved by cetane-improving additives because the equation doesn't account for the amount of cetane-improving additive in the fuel. If there is nowhere to put the additive into the equation, there is no way to change the cetane index except by changing API gravity or distillation.

When injected into the combustion chamber of the cylinder, fuel must quickly mix with air then ignite with no other ignition source. The time between the beginning of fuel injection and the start of combustion is called "ignition delay." Higher cetane number fuels result in shorter ignition delay, providing improved combustion, lower combustion noise, easier cold starting, faster warm-up, less white smoke, and, in many engines, reduction of some emissions. Society of Automotive Engineers publications have reported better fuel economy and increased power as a result of increasing the cetane number with additives.

When a diesel engine was run with naturally high-cetane fuel instead of the naturally low-cetane fuel improved to the same cetane number with additives, Texaco's research demonstrated an average 4.6 percent decrease in power, with an average 4.2 percent increase in fuel consumption.

The disadvantage of natural high cetane fuel compared to "additive-improved" cetane fuel is that the former is generally less dense. This lower density, as with winterized fuel, means lower volumetric energy content, so fuel economy and power per volume of fuel is reduced. Since fuel is bought by volume, this is a direct economic loss to the customer.

The NCWM analyzed data for more than 300 diesel fuel samples. Their average cetane number was approximately 44. This is probably representative of all U.S. diesel fuels. An increase of three points in cetane number above average (an increase of seven points above the minimum ASTM specification of 40) will provide added performance in some engines.

The Engine Manufacturers Association, the American Trucking Association, the American Automobile Manufacturers Association, and the recently-announced automotive manufacturers' World-Wide Fuel Charter all stress that the cetane number for premium diesel should be well above the national average. They feel that diesel engines operate better on fuels with cetane numbers above 50.


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## BB_cuda (Nov 8, 2011)

I think we'll have to dub this guy "Sheldon" for the day ....Big bang theory character. Good stuff there Ljgmdad


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## 3ismagic# (Mar 17, 2011)

BB_cuda said:


> I think we'll have to dub this guy "Sheldon" for the day ....Big bang theory character. Good stuff there Ljgmdad


Bazinga!


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## UncleJ (May 7, 2006)

Ahh, volumetric efficiency, haven't thought about that since my hot rod days long ago. Still valid and important! I wonder what the Cetane numbers are for the CARB mandated diesel fuel sold in CA, since there is no "premium diesel" here (as far as I can determine)?:angel:


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## F32Fleet (Jul 14, 2010)

49 IIRC

Sent from my MB525 using Bimmer App


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## d geek (Nov 26, 2008)

UncleJ said:


> ...I wonder what the Cetane numbers are for the CARB mandated diesel fuel sold in CA, since there is no "premium diesel" here (as far as I can determine)?:angel:


I've looked several times and could never find a CARB requirement for elevated cetane. However, apparently the process of brewing CARB diesel does result in higher cetane numbers. Just remember that if they find a way of meeting the CARB requirements in the future and can save money by keeping the cetane lower, then you may not always be gauranteed the higher cetane number.


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## UncleJ (May 7, 2006)

49 seems like a decent number. However I also agree, if the refiners can brew it to meet the (unaccountable, omnipotent) CARB regulations at a lower cetane they will.:tsk:


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## wanderlust (Feb 19, 2012)

That actually explained a lot. It certainly explains why biodiesel does not necessarily increase fuel economy despite high cetane.


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## Axel61 (Mar 10, 2011)

just in case buy yourself and AMSOIL cetane Booster it works for me


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