CCAI related bunker issues

In these days of burning residual fuels in our ships, various types of fuel related problems occur. These can, while being evident, be a considerable 'pain in the neck' for the engine crew and for the operator of the vessel. Hence, the measures to be taken from the owner's side to avoid these hick-ups are to specify as appropriate as possible the grade of fuel required for 'his' engine. And in case of a dispute, to be a subscriber to a recognized fuel analyzing scheme. Sampling procedures for receiving fuel should be accepted by all involved parties.

Let us dwell for a moment on the issue of ordering bunkers and the specification that normally is submitted to ensure the correct grade is received on board. A number of parameters are normally mentioned, such as; density max, viscosity max, sulphur max, poue point etc. There is however a parameter rarely being mentioned in these specifications and that is the CCAI, Calculated Carbon Aromaticity Index, which gives a value on the Ignition Quality for residual fuels, since these grades cannot be verified by methods used for distillates, i.e. Diesel Index, Cetane Index and Cetane Number.

Accepted method for determination of the ignition quality of residual fuels is currently not available. It has, however, been empirically established that there is a relationship between the density, the viscosity and the ignition performance and the Shell-developed CCAI is the one presently most accepted for indicating ignition delay, although there is also a BP- developed Calculated Ignition Index (CII). CCAI gives an idea of how much the ignition is delayed, the higher the index, the longer the delay. The CCAI can be determined, with limited accuracy, by the enclosed nomogram AAAA

The combustion starts with a short delay already when a small amount of the fuel has been injected and therefore the remaining quantity injected burns in a controlled manner. If,however, the delay is long, a large amount is injected before the combustion starts,producing a quick and violent raise of pressure. This produces the characteristic"diesel knock". The problem is generally related to medium speed diesel engines when burning blended fuels less than 220 cSt. and problems seems to appear in the CCAI-span 850-890. See enclosed diagram BBBB If it is required (necessary) to operate the engine within this span the stresses on the engine components might increase considerably and special attention should be paid to:

0  Connecting rod big-end and bearing shells.

0   Main bearing shells

0  Pistons(particularly composite pistons)

0  Piston rings and liners

0  Cylinder head with studs and gaskets

0  Tie bolts

0  Intake and exhaust valves

To alleviate the effect of the ignition delay, the ambition should be to keep the engine load within 50 - 85 % and to maintain the inlet air temperature  as high  as practically possible and through pre-heating prior start-up(the CCAI problems  are accentuated on a cooler engine, hence a known  scenario is the vessel makes it to port but the engine can not be restarted upon departure due to fouled/clogged piston rings, poppet valves and turbocharger).With the violent increase of combustion pressure, when operating on fuels delaying the ignition, the rate of blow-by will increase and it goes without saying that the lub.oil quality must be optimal to cope with the additional load imposed on the bearings.

So, by way of conclusion, if the shipowner is operating engines which  are sensitive to ignition quality he would  be wise to order fuels with a CCAI limit or to set density and viscosity limits which will control the CCAI.

Special care to CCAI is needed when a ship is forced to use low viscosity fuels (below

180 cSt), due to heating limitations. If the density of these fuels is high the CCAI will be too high and ignition problems may be encountered.

ISO Viscosity Grades

Certainly! ISO Viscosity Grades play a crucial role in the world of lubrication. Let’s dive into it.

What are ISO Viscosity Grades?

• ISO Viscosity Grades, also known as ISO VG, provide a standardized method for classifying industrial liquid lubricants based on their viscosity. These grades help lubricant suppliers, equipment designers, and users communicate effectively about lubricant requirements.
• The ISO VG system ensures consistency by defining viscosity ranges for each grade. The midpoint of each range represents the nominal viscosity value, and the actual viscosity of a lubricant can vary by ±10% from this midpoint.

Understanding Viscosity:

• Viscosity measures an oil’s resistance to flow (shear stress) under specific conditions. It reflects how well the oil stays put when subjected to mechanical forces.
• Imagine a water-skier cutting through water. Water has a viscosity of 1 centistoke (cSt), which is at the lower end of the viscosity scale. If the skier were skiing on a lake of SAE 90/ISO 220 gear oil, the spray generated would be considerably less because the oil resists the ski’s force more effectively.

Absolute Viscosity:

• Absolute viscosity (also called dynamic viscosity) is a measure of how a fluid behaves under pressure. It is expressed in centipoises (cP). Machine designers are interested in this property, especially for pressurized hydraulic lines.

ISO Viscosity Grade Numbers:

• Each ISO viscosity grade corresponds to a specific viscosity bracket. For example:
  • ISO VG 32 relates to a viscosity bracket of 28.8 to 35.2 mm²/s, with a midpoint of 32.0 mm²/s.
  • The ISO VG system covers a wide range of viscosities, allowing users to select the right lubricant for their equipment.

In summary, ISO Viscosity Grades provide a common language for lubrication professionals, ensuring clear communication and effective lubricant selection.

This classification defines 20 viscosity grades in the range of 2 to 3200 square millimeters per second (1 mm2/s = equals 1 cSt) at 40ºC (104ºF). For petroleum-based liquids, this covers approximately the range from kerosene to cylinder oils.

Each viscosity grade is designated by the nearest whole number to its midpoint kinematic viscosity in mm2/s at 40ºC (104ºF), and a range of +/- 10 percent of this value is permitted. The 20 viscosity grades with the limits appropriate to each are listed in Table 1.

The classification is based on the principle that the midpoint (nominal) kinematic viscosity of each grade should be approximately 50 percent greater than that of the preceding one. The division of each decade into six equal logarithmic steps provides such a system and permits a uniform progression from decade to decade. The logarithmic series has been rounded off for the sake of simplicity. Even so, the maximum deviation for the midpoint viscosities from the logarithmic series is 2.2 percent.

Table 2 pulls together some popular viscosity measurement methods into one table. If the practitioner is comfortable with one particular measure but would like to see the correlating viscosity range in another measure, all he must to do is place a straight horizontal line through his chosen viscosity type and see its correlation within the other types of measures.

While it is true that some viscosity grades will be left out of the mix as companies move toward adopting the ISO designation, it is not necessary that the users of those products have to move away from them. Further, there is no intention to offer quality definition of lubricants with this scale. That a product has an ISO VG number associated with it has no bearing on its performance characteristics.

The ISO designation has been under development since 1975. The most recent release in 1992 (ISO 3448) contains 20 gradients. This covers nearly every type of application that the lubricant practitioner can expect to encounter. The lubricant manufacturing community has accepted the recommended ISO gradients and has devoted appreciable effort and energy to conform to the new grading approach with old and new products.

It is unlikely that all of us who learned about the use of oil from our mentors or friends under the hood of a car will ever abandon the SAE grading system. We don’t have to. At least for automotive oils, we can expect to continue to see the 10- 20- 30- 40- 50- values used. It is likely, however, that in the industrial lubrication world there will be more ISO dependence in the future.

Class of insulation

Certainly! Let’s explore the different classes of electrical insulation based on their temperature capabilities:

1. Class-Y Insulation (Up to 90°C):

   • Class-Y insulations can withstand temperatures of up to 90°C. They are typically made of materials like cotton, silk, or paper.

2. Class-A Insulation (Up to 105°C):

   • Class-A insulations can handle temperatures up to 105°C. They are made of reinforced Class-Y materials impregnated with varnish or insulation oil.

3. Class-E Insulation (Up to 120°C):

   • Class-E insulations can withstand temperatures up to 120°C.

4. Class-B Insulation (Up to 130°C):

   • Class-B insulations can handle temperatures up to 130°C. They consist of inorganic material hardened with adhesives and were the first insulators to use this structure.

5. Class-F Insulation (Up to 155°C):

   • Class-F insulation can withstand temperatures up to 155°C. Examples include materials upgraded from Class-B with adhesives, silicone, and alkyd-resin varnish of higher thermal endurance.

6. Class-H Insulation (Up to 180°C):

   • Class-H insulations can handle temperatures up to 180°C. They are made of inorganic material glued with silicone resin or equivalent adhesives.

7. Class-C Insulation (Up to 180°C or Higher):

   • Class-C insulations withstand temperatures up to 180°C or higher. They are typically composed of 100% inorganic material.

In summary, electrical insulation is classified based on its maximum allowable temperature. By using insulating materials with higher thermal endurance, the size of electrical machines can be minimized.

Reference:

1: https://electricalbaba.com/electrical-insulation-classes/ “Electrical Insulation Classes - Electrical Concepts” 

2: https://en.wikipedia.org/wiki/Insulation_system “Insulation system - Wikipedia” 

3: https://www.electricalvolt.com/electrical-insulation-classes-classification-of-insulating-materials/ “Electrical Insulation Classes | Classification of Insulating Materials”