FO / MDO ANALYSIS INTERPRETATION

Recently  my colleagues  and myself were carrying out an investigation on a vessel ( not under our management , on pre purchase inspetion), on their constant liner damages. the very fist doubts went into the fuel quality, so we have checked fuel analysis report, couple of large quantity bunkers were even though under specification but beyond engine manufacturers limit. so Naturally we have asked CE about the precautions taken , the reply was horrific and never expected from such a senior Chief Engineer. believe me he was having more than 15 years (actual) experience onboard in the rank.

CE version 

I have received the analysis report and the symbol was thumbs up in Green and I used the fuel and didn't check much details.

I have put the above not to hurt anybody's ego but I have understand that most of the engineers are not keen to check the  Analysis report , may be it is taking a back seat think that owners / managers office to send a conclusive comment in a form a capsule.


Before that analysis report indications like thumbs up / green signal all depends on whether the fuel is complying with the ISO 8217 standards. As most of us aware there are different limits for Iso 8217: 2005; ISO8217:2010 etc... to the latest ISO8217:2017  but unfortunately in a very competitive market like ours, most of us  still using 2005 standards. The owners finding it difficult to impose 2010 or better standards in the charter party agreement. The aforementioned is beyond our reach , hence we look into the vital parts of analysis report.

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Density and API Gravity – Fuel is sold by weight; therefore, density must be known to determine the volume of fuel received. 

what we have observed recently , there is a difference of around 0.3 to 0.6 % lower in density as per analysis, which translates into a loss of around 3 to 6 MT in 1000 MT of bunker intake. This is commercial issue , but below is the major one in engineers point of view.

Density must also be determined for selecting the correct size gravity disc for the purifiers and for the determination of calorific value of fuel. so the gravity disc to be arranged for a conventional purifier as per nomogram chart from the instruction manual.

Viscosity – Fuel grades are based on viscosity. High viscosity fuels are generally less expensive than lower viscosity fuels; however, high viscosity fuels will require pre-heating prior to centrifuging and fuel injection in order to lower the viscosity.  Viscosity testing determines the preheating temperature required.  Recent trend shows there is a slight hike in the viscosity from the Argentinian / Singapore / Houston bunkers. but not of a higher percentage, for eg: for RMG grade the limit is 380 and the max observed till now is 394 Cst

Water – Fuel with a high water content will burn less efficiently.  The presence of salt water in fuel will cause many other problems.  Presence of water also reduces the calorific value of the fuel.

The water can be removed by settling and by effective purification . The age old practice of draining comes a vital part in removing water.

Carbon residue- It does not represent  combustion conditions in an engine. It gives an indication of the amount of hydrocarbons in the fuel which have difficult combustion characteristics.A high carbon residue will increase the likelihood of deposit formation.

Sulfur – High sulfur represents a loss of fuel efficiency and may cause corrosion.  Very low sulfur is also not recommended where cylinder lubrication is used.

The values are very vital , according to the sulphur cont the HMI index  / the grade of Cylinder oil to be changed. In ME series of engine the sulfur % to be fed as soon as the fuel is into the use.

Ash – Sodium, Vanadium, and catalytic fines are incombustible impurities found in fuel oil.  After carbon residue is determined, the remaining sample is heated to extremely high temperatures to burn off all combustible matter.  The ash that remains is weighed and compared to the original mass of the sample to determine a percentage.In short it is the heavy metal content in the fuel.  

A high ash content may lead to deposits, excessive wear, and corrosion.

The ash content can not  be  fully removed by settling and by purification, but a constant effort will reduce the contents.

Vanadium and Sodium – These two incombustible impurities found in ash are particularly hazardous if excessive.  Ashes from these elements lead to high-temperature corrosion on exhaust valves, particularly when they are in the ratio of 3 parts vanadium to 1 part sodium.

This has to be read in conjunction with  ME engines Exhaust valve burn outs. for 500 mm bore engine the normal burn out is 8 mm , but recently noted from various licensees that the burn out is more than 14 mm for engines done 14000 hours ( overhaul interval is 16000 hours) , hence MAN introduced a new inspection period of 6000 hours. Initial informations are leading to slow speed operation leading to high exhaust valve spindle temperature and the presence of Vanadium and Sodium in the lethal combination of 3:1

Only Remedy Purification and purification only.

Aluminum and Silicon – CATFINES. These two elements indicate aluminosilicates remaining after catalytic cracking.  Aluminosilicates in fuel are a cause of wear in cylinders and high pressure fuel system components.  Silicon may also indicate dirt or sand in the fuel.

In order to avoid abrasive wear of fuel pumps, injectors and cylinder liners the maximum limit for Al+Si defined in ISO 8217:2010 is 60 mg/kg for RMG and RMK category fuels.

Having said that please find below chart from various engine manufacturers.

The above chart underlines the importance of effective purification, as there is no other safeguards for the operators pertaining to this matter.

CCAI (Calculated Carbon Aromaticity Index) – This is a calculated figure indicative of the ignition quality of the fuel. Values above 870 are not recommended for most types of engines.

Pour point- It is the lowest temperature at which a fuel will continue to flow when it is cooled under specified standard conditions. Contrary to straight run heavy fuels (pour point typically in the +20°C range), bunker fuels from a complex refinery generally have pour points below 0°C (range –10 to –20°C). This is because bunker fuel tanks are usually not completely heated

— only before the fuel transfer pump. This can lead to problems if a vessel receives high pour straight run bunker fuel. For distillate marine diesel, the cold temperature behavior is controlled in ISO 8217 by a pour point maximum. 

The above are the normal figures earlier an engineer concentrated. now we will discuss about some of other parameters.

Acid Number- All fuels have a naturally occurring acid number, however fuels with high acid numbers arising from acidic compounds can cause accelerated damage to large diesel engines, especially the fuel injection equipment. However, fuels manufactured from naphthenic crudes can have an acid number exceeding the maximum specified in ISO 8217:2010

TAN (Total Acid Number) = 2.5 mg KOH/g

SAN (Strong Acid Number) = 0 mg KOH/g

But from the experience noted that if TAN is around 0.8 mg KOH / g, better to Carry out the presence of external acidic compounds (ex Fatty acids) is known to have caused accelerated damage to the fuel injection equipment of the marine diesel engines. some companies have reduced the limit to 0.4 mg KOH / g

Net Specific Energy - The net specific energy needed to be inputted into the MOP  to have a better injection and timing lag adjustment in ME series of Engine.

if the net energy is not included properly then the fuel injection offset won't be proper , then PMI load and actual engine load will be total different.

Now Let's Look into the Distllate fuel items.

Lubricity-  The limit corrected wear scar diameter (wsd1.4) at 60°C is 520 . as the Scar diameter more the lubricity will be less. please find below a sample picture for a comparison study. it is always better to add lubricity Improver.

Pour Point - there should be two pour points in winter and in summer, Marine diesels with a high content of heavier n-paraffins require vigilance if wide temperature changes are expected. (Wax settling can occur, even when the pour point specification is met (-6 Degree Celcius) . But be careful , there may be suppliers using pour point depressants, hence the Cloud Point and CFPP is very much important.

Cloud Point- is the temperature at which paraffin, which is naturally present in diesel fuel, begins to form cloudy wax crystals. When the fuel temperature reaches the cloud point, these wax crystals flowing with the fuel coat the filter element and quickly reduce the fuel flow, starving the engine, the limit is -16 Degree.

CFPP- The CFPP  (Cold Filter Plugging point) is the lowest temperature at which fuel will still flow through a specific filter. Without a wax modifier, a fuel's CFPP is generally around 3°C below the CP

Oxidation Stability- Degradation of distillate fuels by oxidation can cause fuel stability problems. Unstable distillate fuels can form insoluble organic particles which may clog fuel filters , cause wear and contribute to injector deposits. 

Current supply logistics make it almost inevitable that marine distillate fuels can contain bio-derived material, i.e., fatty acid methyl esters (FAME), that can impact the oxidation stability of the fuel and it can cause accelerated wear on the fuel oil . The FAME qualitative should be less than 0.5 % V/V

Viscosity - The limit value is 6 , but normally found between 2 to 3 , additive to be used to increase the viscosity.

No Need to mention about the sulphur content , which is one of the major limiting criteria of the fuel.

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