[debuda]

While most issues have been addressed in this thread, I decided to sum them up and write one comprehensive post to allay fears of all BS-4 automobile owners regarding use of BS-6 fuel in their vehicles.

The fuels used in internal combustion engines need to possess several properties, one of which is lubricity. As the term implies, lubricity is the ability of the fuel to provide lubrication. Certain components in an engine’s fuel system such as fuel pumps and injectors have moving parts made of metals, alloys, ceramics or composite materials which rub against each other and without proper lubrication would get damaged or wear out quickly. Since no additional lubrication (say, by lubricating oil) can be provided to these rubbing parts, the fuel itself has to work as a lubricant.

There is a misconception that sulfur is what provides the lubricity to fuel oil, but that idea is only indirectly correct. Although the sulfur does contribute somewhat to lubricity, the lower lubricity level of low sulfur fuel is more a by-product of the refinery processes used for desulfurization. During the desulfurization process hydrogen gas is introduced to the crude under extreme temperatures and pressures. The hydrogen combines with the sulfur to form hydrogen sulfides which are removed. Unfortunately, during desulfurization, critical polar and organic aromatic compounds innate to the fuel and identified as responsible for imparting significant lubricity quality, are destroyed under the necessarily intense operating conditions. The resulting yield is a satisfactory low sulfur diesel fuel, but also one that is unsatisfactorily low in lubricity.

Since diesel fuel pumps operate at much higher pressures than their petrol counterparts, the lubricity requirements for diesel fuels are generally more stringent than for petrol. In fact, lubricity has not been known to be a quality issue for multipoint port injected spark ignition engine fuels.

Prior to 1996, the limit of sulfur content in fuel was 10,000 ppm (parts per million) in India. This was reduced to 5,000 ppm in 1996 and 2,500 ppm in 1998. BS-2 brought it further down to 500 and BS-3 to 350. With the introduction of BS-4 (in 2010 for selected cities only and in 2017 all over India) the permissible sulfur content was drastically reduced to 50 ppm. And the latest BS-6 mandates further reduction to 10 ppm.

Since the mandatory reductions in sulfur content started a long time ago in India and even earlier in advanced countries, scientists and engineers have been working to find solutions to the problem of low lubricity for at least 20 years. Several solutions have been arrived at which include the use of better and more wear resistant materials in fuel system components, use of special fuel additives and the blending of diesel with biodiesel.

Use of special fuel additives by the refinery itself has been found to be a very cost-effective solution. Mono-acid additives are the most effective, requiring addition at low levels, while amide and ester additives need to be mixed in at slightly higher levels. Whichever additive a fuel refiner chooses, the main point is that they can restore fuel lubricity to necessary legal levels without compromising vehicle emissions.

The most reassuring thing about BS specifications is that they mandate that the lubricity of fuel supplied in the market meets a minimum benchmark. BS-4 mandated diesel lubricity of 460 microns and BS-6 also mandates the same (460 microns). In other words, oil companies are duty bound to ensure that the lubricity of BS-6 diesel is same as that of BS-4 diesel, if not better. So the doubts in the minds of the lay public about the imaginary ill effects of using BS-6 diesel in BS-4 cars is entirely misplaced.

Let me end this longish post by explaining how lubricity of fuel is measured quantitatively and what is meant by this number ‘460 microns’. Lubricity of a substance is not a material property, and cannot be measured directly. But it can be measured indirectly by determining how much wear is caused to a surface by rubbing with a wear-inducing object while remaining submerged in the fuel. HFRR (high frequency reciprocating rig) is recognized as the standard testing method used to measure diesel fuel's lubricity by the ASTM (American Society of Testing and Materials). Lubricity corresponds to the width of the wear scar (in microns) where the two pieces of metal rub against each other while being submerged in the test fuel. In this case, it is a ball bearing that wears on a plate or disc under a standard test load. This is why the smaller the number, better is the lubricity. The less the wear scar or scrape width, the better lubrication of the fuel. As you can imagine, this is done under some very specific parameters in order to make sure the test is as consistent as possible. Even heat and humidity are controlled during this test. The resulting number or scar is examined under a microscope in order to do the measurements.

BS-4 and BS-6 both mandate that the lubricity of automotive diesel fuel will be 460 microns (Max). In other words, the HFRR test conducted at 60 deg C should not result in a scar wider than 460 microns.

So one may go ahead and fill BS-6 fuel in BS-4 cars without any reservations.

[locusjag]

^ And why is it that our print automotive journalists had weaved a scare story of decreased lubricity of BS 6 diesel and failing injectors?

Our forum members have so far shared a lot in this thread - synthetic lubricity additives, the exact friction induced shear micron size of the additives etc.

Should I chalk it down to lack of sufficient automotive knowledge on the part of our mainstream journalists...or worse - an elaborate scheme in collusion with Automobile OEMs to scare car owners into buying BS6 cars?

[comfortablynumb]

Originally Posted by debuda

So one may go ahead and fill BS-6 fuel in BS-4 cars without any reservations.

Thank you very much for this post debuda!

I hope your explanation would apply to BS3 vehicles too (as I have one - Feb 2010 mfg'ed), and that I can safely put my paranoia about this topic on the back burner now

Cheers,
Vikram

[vsrivatsa]

Originally Posted by debuda

In other words, oil companies are duty bound to ensure that the lubricity of BS-6 diesel is same as that of BS-4 diesel, if not better. So the doubts in the minds of the lay public about the imaginary ill effects of using BS-6 diesel in BS-4 cars is entirely misplaced.

So one may go ahead and fill BS-6 fuel in BS-4 cars without any reservations.

Wow, this post made my day and put all my worries to rest Thanks a lot for the detailed explanation and clarification - have not found such comprehensive information on this important topic anywhere till date.

[Reinhard]

Originally Posted by debuda

So one may go ahead and fill BS-6 fuel in BS-4 cars without any reservations.

Thanks a ton debuda for the detailed informative post. This was the exact thought with which I took the decision to go for a BSIV car in August. Had read about the lubricity somewhere years ago and thought it would have to stand. Your post reaffirms it!

Also - I was using a BSIV 1.3 MJD for years with BSIII fuel all over Maharashtra's non-metro areas & it went absolutely fine for 9 years. Not a single injector cleaning even!

Originally Posted by comfortablynumb

I hope your explanation would apply to BS3 vehicles too (as I have one - Feb 2010 mfg'ed), and that I can safely put my paranoia about this topic on the back burner now

Well I think it will apply. Already you have been using BSIV diesel in BSIII engine without issue. Viscosity remaining unchanged - would mean BSVI will also work just the same. Enjoy your mighty muscular .

[mahadev_kc]

Originally Posted by debuda

So one may go ahead and fill BS-6 fuel in BS-4 cars without any reservations.

Thanks a lot for the valuable information. All worries are put to rest on using BS6 fuels on BS4 vehicles.

[Natt1948]

Thanks a ton, Debuda this clears my doubt on BS 4 engines. We have a Duster 2016 model and we're concerned about its long term running on BS 6 fuel. Now I guess we can relax a bit.

[gopi_rm]

Without any technical arguments, I would say BS6 diesel/petrol would not harm BS4 combustion engines because I see in Germany hundreds of Euro 4/3 cars running on normal fuel available in the fuel station which would Euro 6 conform fuel.
I hope I am not missing something here. Please correct me if so.

[adwaith]

Apologies for the noob question!

Will there be any effect if BS4 fuel is inadvertently filled in a BS6 vehicle?

[vrprabhu]

Originally Posted by gopi_rm

... would say BS6 diesel/petrol would not harm BS4 combustion engines because I see in Germany hundreds of Euro 4/3 cars running on normal fuel available in the fuel station which would Euro 6 conform fuel....

Six months since BS-VI fuel dispensation started - and used in my 10+ year old car, with 1,000+ km covered.

So far (touch wood) haven't seen any drastic difference in performance.

I did use fuel additive once (posted here - https://www.team-bhp.com/forum/techn...ml#post4857128 (The Fuel Additives Thread) ), and am attributing the perceived smoothness to the additive than the fuel....

How has been the experience of other (older car) owners?

From the lack of posts here - or anywhere else, for that matter - things appear to be hunky-dory with BS-VI petrol & diesel, but for the increased cost being shelled out a tiny sacrifice towards a cleaner environment?

[tirumalavoleti]

Thanks debuda for summing it up nicely. Below link also has the same information:

https://www.autocarindia.com/advice/...s6-fuel-416743


Now it has been 6 months since India started using BS6 diesel and no issues reported so far for BS4 diesel vehicles.

Any of our members have any issues or suggestions, please post here for others to take care

[IndigoXLGrandDi]

Originally Posted by adwaith

Apologies for the noob question!

Will there be any effect if BS4 fuel is inadvertently filled in a BS6 vehicle?

This is not a noob one.
I second this question.

Not all the Fuel Pumps in Rural Areas sell BS6 Compliant Fuels. What if One buys BS6 vehicle and unknowingly fills BS4 Fuel in Rural Area.

So how will the BS4 Fuel affect the BS6 Fuel System of the Vehicle?

[pious_devil]

Originally Posted by IndigoXLGrandDi

This is not a noob one.
I second this question.

Not all the Fuel Pumps in Rural Areas sell BS6 Compliant Fuels. What if One buys BS6 vehicle and unknowingly fills BS4 Fuel in Rural Area.

So how will the BS4 Fuel affect the BS6 Fuel System of the Vehicle?

if its one off cases it wont be a problem. However in the long run if only BS4 fuel is used in BS6 engines , its going to impact the exhaust after treatment system especially the DPF ( Diesel Particulate Filter ) and its re-generation system due to high soot.

[mtnrajdeep]

Originally Posted by IndigoXLGrandDi

Not all the Fuel Pumps in Rural Areas sell BS6 Compliant Fuels. What if One buys BS6 vehicle and unknowingly fills BS4 Fuel in Rural Area.

So how will the BS4 Fuel affect the BS6 Fuel System of the Vehicle?

How can this situation arise? I thought that after the Supreme Court mandate, the entire country transitioned to BS6 fuel. Where will these fuel pumps get the BS4 fuel from, if the supply from the refinery itself isn't being done?

[adi58]

Has anyone tried the Wurth Diesel Additive? It seems it is designed for low-sulphur fuel. Can this benefit BS4 Diesel engines as against BS6 low sulphur fuel?