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Old 14th March 2008, 13:11   #1
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Arrow TechSpec® : Diesel Fuel and the role of Cetane in Engine performance

Ever wondered why a particular brand of Diesel fuel makes you engine Zoom wherein the other makes it fart black smoke ??

Ever wondered why your friends diesel car performs better than yours although you both use diesel from same oil company ??

After reading many discussion posts and threads. Taking many advises I finally decided to put into place this thread which will give insight and answers to questions above.

Read On...............


Diesel Fuel Quality

Fuel quality is defined by the physical property specifications given in the ASTM Standard Specification for Diesel Fuel Oils, ASTM D-975 or D-4737. Carbon residue, ash and sulfur increase engine wear and deposit formation.

Premium diesel fuels have lower specifications for these properties. Additionally, premium diesel fuels are more stable in storage than standard fuels, so the premium fuel quality you purchase won't degrade over time.


THE ATSM Worldwide Standards

The ASTM Standard Specification for Diesel Fuel Oils (D-975) states, "The cetane number requirements depend on engine design, size, nature of speed and load variations, and on starting and atmospheric conditions. Increase in cetane number over values actually required does not materially improve engine performance. Accordingly, the cetane number specified should be as low as possible to insure maximum fuel availability." This quote underscores the importance of matching engine cetane requirements with fuel cetane number.

ASTM D 4737 is a newer method and this method calculates CI using a four variable equation based on diesel's low, mid and high boiling points as well as density.

The Calculated Cetane Index by Four Variable Equation is useful for estimating ASTM cetane number when a test engine is not available for determining this property directly and when cetane improver is not used.

This also provides a means for estimating the ASTM cetane number (Test Method D 613) of distillate fuels from density and distillation recovery temperature measurements.

This specification(ASTM D 4737) is being use by most petroleum companies inIndia as a standard measure.


Specifying Diesel Fuel

Cetane number is an important measure of ignition quality, or cold-starting ability.

API gravity is an excellent indicator of heat value, which translates into fuel economy and power.

The distillation curve reflects the molecular weight distribution, with higher boiling fractions providing better lubrication, higher cetane - and more deposits.

Sulfur content is directly related to corrosion; this needs to be as low as possible.

Oxidation stability, water, and sediment content affect the storage life of the oil. For winter use, low cloud point and low temperature filter plugging point are critical to uninterrupted operation.

To ensure the best quality fuel for our diesel engines, we should follow the engine manufacturer's specifications for all these characteristics and I am afraid its not given out by manufacturers here .


What is Cetane Number?

Cetane Number is a measure of the ignition quality of a diesel fuel. It is often mistaken as a measure of fuel quality.

Cetane number is actually a measure of a fuel's ignition delay. This is the time period between the start of injection and start of combustion (ignition) of the fuel.

In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower cetane fuels.

Cetane number should not be considered alone when evaluating diesel fuel quality. API gravity, BTU content, distillation range, sulfur content, stability and flash point are also very important. In colder weather, cloud point and low temperature filter plugging point may be critical factors.


Determining Cetane Number

The optical method for determining cetane number is ASTM test D-613. This method requires the use of an industry standard test engine equipped with accepted
instrumentation and operated under specific conditions.

In this test, the engine compression ratio is varied for the test sample and reference fuels of known cetane number to obtain a fixed ignition delay. The compression ratio of the sample is bracketed by those of two reference fuels. The cetane number of the sample fuel is determined by estimating between the two reference fuel points.

Because the ASTM D-613 test is time consuming and expensive, calculated cetane index (ASTM D-976 or D-4737) is often substituted for cetane number.

The calculated cetane index is derived from the fuel's density and boiling range. While useful for estimating the cetane number of distillate fuels, this technique can not be applied to fuels containing additives that raise cetane number. These additives do not change the fuel density or distillation profile, so they do not alter the calculated cetane index.


How Does Cetane Number Affect Engine Operation?

There is no benefit to using a higher cetane number fuel than is specified by the engine's manufacturer.

Diesel fuels with cetane number lower than minimum engine requirements can cause rough engine operation.

They are more difficult to start, especially in cold weather or at high altitudes. They accelerate lube oil sludge formation. Many low cetane fuels increase engine deposits resulting in more smoke, increased exhaust emissions and greater engine wear.

Using fuels which meet engine operating requirements will improve cold starting, reduce smoke during start-up, improve fuel economy, reduce exhaust emissions, improve engine durability and reduce noise and vibration.

These engine fuel requirements are published in the Owners manual for each specific engine or vehicle, although I could not find it in my vehicle manual.

Overall fuel quality and performance depend on the ratio of parafinic and aromatic hydrocarbons, the presence of sulfur, water, bacteria, and other contaminants, and the fuel's resistance to oxidation.

The most important measures of fuel quality include API gravity, heat value (BTU content), distillation range and viscosity. Cleanliness and corrosion resistance are also important. For use in cold weather, cloud point and low emperature filter plugging point are also important.

Cetane number does not measure any of these above characteristics.


Cetane Improvers / Ignition Accelerators

Diesel fuels are blends of distillate fuels and cracked petroleum hydrocarbons. The cracked hydrocarbons are low cetane compounds, largely due to their aromatic content.

To meet the cetane number demands of most diesel engines, cetane improvers can be added to these blends. The lower cetane compounds are less responsive to these cetane improvers than the higher cetane paraffinic fuels.
  • Cetane improvers modify combustion in the engine.
  • They encourage early and uniform ignition of the fuel.
  • They discourage premature combustion and excessive rate of pressure increase in the combustion cycle.
Depending on the amount of high versus low cetane components in the base fuel, typical alkyl nitrate additive treatments can increase cetane by about 3 to 5 numbers (1:1000 ratio).
With high natural cetane premium base fuels containing a high percentage of parafins) and a 1:500 treatment ratio, cetane may increase up to a maximum of about 7 numbers.

Most cetane improvers contain alkyl nitrates which break down readily to provide additional oxygen for better combustion. They also break down and oxidize fuel in storage. This generates organic particulates, water, and sludge - all of which degrade fuel quality.

The result is often a fuel which no longer meets even minimum requirements. Because of these drawbacks, nitrate cetane improvers should not be used (if you intend to).


Now for the Cetane Specification by Oil Companies
  • Normal diesel from all brands has a Cetane number between 46 min - 48 max.
  • Premium diesel from IOC, IBP, HP, Shell etc. has a cetane number between 48 min - 52 max.
I am also aware that System D (which I use) does not help improve the Cetane number. I cannot say the same about other additives as I havent researched on them.

I was not able to find the exact Cetane number specification on HP diesel fuel on their website, but as long as the follow the standards, it should be same as others.

Sources A B C D
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Old 15th March 2008, 01:07   #2
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Quote:
Originally Posted by dadu View Post
I am also aware that System D (which I use) does not help improve the Cetane number. I cannot say the same about other additives as I havent researched on them.

sir i don't know why but i'm sure that system D makes a lot of difference as i'm using it since 2 years and i have got good results. it makes engine more smother and improves acceleration. don't know about fuel efficiency as we never measured it.



and very nicely written and informative article i must say.

Last edited by overdose14 : 15th March 2008 at 01:08.
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Old 15th March 2008, 12:28   #3
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System D is more helpful in cleaning up residue from engine and diesel pump
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Old 15th March 2008, 12:52   #4
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I think black smoke is just a way of life for diesel engines.
I have seen the best of diesel cars emit black smoke ,even a new S320CDi recently. It sure is a big turn off to see that, but i guess the upside is that the engine is discharging the unwanted deposits.

Although i havent see my car do this, i am sure it does when pressed hard.
Whats the best way to reduce the black smoke under hard acceleration? If premium diesel is the only way to reduce this, we german diesel owners are in a fix as these fuels are not approved by the company.
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Old 15th March 2008, 13:39   #5
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On the contrary IOC premium smokes more than IOC regular in Swift D, maybe the engine has been calibrated for the regular diesel
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Old 15th March 2008, 15:37   #6
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Nice article Dadu

but i still dont understand why my safari 3.0 emits lot of black smoke with premium fuels

and black smoke is almost gone since i moved to regular diesel which you claim is having less Cetane value Though i admit engine was a bit(just a bit ) more peppy when i used premium fuels

but this problem also is gone since i have started using regular diesel+System D regularly.

It will be nice to read some more discussion regarding the same facts and how we can choose the right fuel available

need more brand based discussion of your above values please.


Thanks
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Old 15th March 2008, 21:35   #7
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Quote:
Originally Posted by Sahil View Post
I think black smoke is just a way of life for diesel engines.
I have seen the best of diesel cars emit black smoke ,even a new S320CDi recently. It sure is a big turn off to see that, but i guess the upside is that the engine is discharging the unwanted deposits.

Although i havent see my car do this, i am sure it does when pressed hard.
Whats the best way to reduce the black smoke under hard acceleration? If premium diesel is the only way to reduce this, we german diesel owners are in a fix as these fuels are not approved by the company.
The biggest culprit is EGR (exhaust gas recirculation).

I am in the process of researching on pros & cons of disabling this EGR on my Laura.

I have been using Shell regular diesel all the time and am forced to use Shell premium diesel because they no longer sell regular. I know it is against what the manual says, but then I don't trust other fuels at all (billing, purity, etc.)

I wrote to Shell India for clarification, but I guess they don't check their emails :-)
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Old 16th March 2008, 14:42   #8
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The problem being two fold for determining the optimal diesel brand for ones vehicle.

- the manufacturers dont specify it in their manuals and neither do they let you know the diesel specs they used for calibrating their engines.

- The oil companies also dont provide detailed data on this although they do provide the basics.

Let me see of I can find out more on this, but cant promise anything here.
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Old 16th March 2008, 15:02   #9
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I have bought a bottle of System D for my swift vdi. Will use it in a day or two and update on the change in performance, if any
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Old 16th March 2008, 20:58   #10
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Hi ,

I use Turbojet for my scorpio . Can i get more details about System D . Can it be used in a new scorpio . Also any inputs on better quality fuel incomprsion to performance fuels from HP , BP , IBP , Shell , Reliance
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Old 24th March 2008, 12:10   #11
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Yes, you can use System D on new engines but only with Normal Diesel.

Turbojet, Xtramile and Speed Diesel are already mixed with additive from the plant.

Quote:
Originally Posted by kARTIK IYER View Post
Hi ,

I use Turbojet for my scorpio . Can i get more details about System D . Can it be used in a new scorpio . Also any inputs on better quality fuel incomprsion to performance fuels from HP , BP , IBP , Shell , Reliance
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Old 24th March 2008, 13:13   #12
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Okay, I researched some more on what everyone is speculative here i.e. which diesel from which oil companies perform better.

I read through the petroleum ministry Auto Fuel policy, I read through the technical documentation available at the various oil companies website and I read through the specifications presented by Oil experts at the various conferences across the world including papers presented by Dr Y.P. Rao, VP technical, Gulf oil and R.K. Malhotra R&D IOC.

So here the collative :

This is the Emission regulation which the Govt wants to achieve:

TechSpec® : Diesel Fuel and the role of Cetane in Engine performance-emission-roadmap.jpg


And to achieve it these the Fuel Specifications which the petroleum ministry has enforced on the Oil companies as per timelines specified above. These are defined in ISO 1460:2005 (5th Revision)

TechSpec® : Diesel Fuel and the role of Cetane in Engine performance-fuel-specifications.jpg


These are the detailed Diesel specifications.

TechSpec® : Diesel Fuel and the role of Cetane in Engine performance-diesel-specifications.jpg

Yes, you read it right the Diesel we use as per BS III has 5% diesel which will increase to 10% in 2010 as per BS IV, but this is also subject to ethanol availability.

Now this has its own problems like:
  • Blend Stability- poor and would need couplers
  • Viscosity & lubricity- lower but can be restored with lubricity improver
  • Cetane value – lower; can be restored with additives
  • Lower Energy Content& Flash Point
  • Material Compatibility and Corrosion are matters of concern for engine durability
I also read that IOC R&D has successfully developed additive package with coupler for blending of 5% ethanol in diesel. This blend meets most of the properties of diesel as per BIS except the Flash Point.

The major difference in BS IV vs BS III is the Sulphur content, the sulphur content in diesel is reduced to quite a lot. But the good part is that the Cetane number of Diesek wont change from BSIII to BS IV i.e. it will remain as CN min of 51.

So all oil companies have to adhere to these norms and as per cities and year deadline (subject to adulteration by pumps).

So your vehicle performance also depends on the fuel specification given by the manufacturer + your location, as if your vehicle is BSIII and you fill fuel apart from these 11 cities, your fuel is not able to meet the vehicle needs and also one more major factor is adulteration.

Quote:
Originally Posted by dadu View Post
The problem being two fold for determining the optimal diesel brand for ones vehicle.

- the manufacturers dont specify it in their manuals and neither do they let you know the diesel specs they used for calibrating their engines.

- The oil companies also dont provide detailed data on this although they do provide the basics.

Let me see of I can find out more on this, but cant promise anything here.
Sources : IOCL/ Google

Special thanks to the published documents by Dr Y.P. Rao, VP technical, Gulf oil and R.K. Malhotra R&D IOC.

Last edited by dadu : 24th March 2008 at 13:15.
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Old 6th April 2008, 11:31   #13
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Dadu ,

I just serviced my scorpio and have still some turbojet left in tank . i intend to put normal diesel and system D . can you help me with tips as frankly never used it and dnt want be unsure .
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Old 13th April 2008, 21:11   #14
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- 1 ml per ltr i.e. if you put 60 ltr, put 60 ml of System D, it has a measurer at the neck and levels of 10ml/ 5 ml.

- You can buy it at IBP/ BP pumps as they have marketing tieups with them.

- Better take the Fuel to the minimum you can in the tank and then do a full tank with system D, put apprx amount of system D and then ask them to fill up. Top up later if less, but it doesnt need to be very precise.
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Old 29th June 2009, 17:18   #15
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Hi,

Of late i feel that after filling Shell diesel (VM road, Bangalore) my indica is sluggish and the milege drops. this does not happen if i fill normal diesel from my regular IOC pump. Anybody else in Bangalore have experienced the same.
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