There is a basic relationship between engine reliability and quality of fuel oil and lubricating oil.
Introduction - Hand in hand with new secondary refinery processes, which have developed during the last decades, new engine problems have emerged. It is, unfortunately, a proven fact of life that the end users often have to “pay” for technological advances, until all the links in the chain have adapted to the new parameters.
The significance of fuel oil quality in relation to the condition of an engine is obvious. But this will always have to be considered taking into account the complex system of the main parameters, such as engine/turbocharger specifications, load parameters (high/low), environment, filters, purifying systems, quality of the lubricating oil and the qualifications of the operating engineer. It is not the intention to expand on all the aforementioned aspects in this blog, but mainly to highlight the basic relation between engine reliability and quality of fuel oil/lubricating oil.
Trilateral interplay - In any particular engine installation the choice of lubricating oil must not only satisfy the requirements of the engine design, condition and load, but also requirements put forward by the quality of the fuel oil. This may be described by a trilateral interplay involving the lubricating oil, the fuel oil and the engine.
Trouble-free engine management requires each of these three elements to have both design and quality within certain limits. Exceeding these limits may lead to reduced service intervals or, in the worst case, serious engine damage.
Lubricating oils can vary both in quality and characteristics, but most engine manufacturers attempt to avoid these problems by extensively testing different types of lubricating oils during shop trials.
It is generally agreed that the fuel oil, which is the third element in this interplay, has the most influence and the biggest variation in terms of quality and properties.
The continuous development of refinery processes during the last decade has resulted in changes in the characteristics of both distillates and heavy fuel oils.
Increased demands with respect to environmental issues have also resulted in changes, in particular for the lighter distillates.
Possibly, a high quality grade of lubricating oil may prevent the negative effects of unwanted fuel oil properties and secure satisfactory engine performance.
Even with a high quality grade lubricating oil, the risk of experiencing problems with low-quality fuel oils is high, particularly in combination with certain load conditions.
The interplay involving fuel oil, lubricating oil and the engine can be illustrated as in the below table.
The areas of concern mentioned in the illustration above may (hopefully) not materialize very often, but, if they do, they will cause serious problems.
Very often these problems may be traced directly back to unwanted fuel oil characteristics, but in some cases they are due to inappropriate adjustment of the properties of the lubricating oil to the characteristics of the fuel oil.
Off-spec bunkers - A major concern related to marine fuel oil is the receipt of off-spec bunkers. Although this blog does not deal specifically with this issue, the areas of concern mentioned above are also applicable to off-spec bunkers problems.
The importance of proper fuel oil sampling and analysis procedures can not be over-emphasised.