Diesel bug: early detection

Dag Pike

The fuel systems on modern diesel engines that have common rail injection systems are increasingly sensitive to contamination of the fuel, especially with low sulphur fuels. - See more at: http://www.maritimejournal.com/news101/power-and-propulsion/diesel-bug-early-detection#sthash.sjRWUkBV.dpuf

Water in the fuel is relatively easy to remove simply by draining any water from the fuel filter’s separator but there can be a growing problem with what is known as the 'diesel bug, a microbial contamination that can lead to serious fuel blockages that can be challenging to clear.

There are a number of different types of micro-organisms that can grow in certain types of fuel. The biggest problem is presented by a filamentous fungus called Hormoconis resinae, (H Res) which was previously called Cladosporium resinae, and which is more commonly referred to as the diesel bug. H Res is a fungus that thrives in diesel fuel and it requires only a minimal amount of water content in the fuel to grow and will cause filter blockages, component failure and tank corrosion if left unchecked. Bacteria and other types of fungi, particularly some yeasts can also cause problems in fuel tanks, usually acting as a consortium.

Previously it was necessary to send a fuel sample for laboratory testing in order to detect the diesel bug and this could take several days for the results to return. Now British company Conidia has developed a testing system that can give results in a matter of minutes. The objective of this test is to provide rapid screening of fuel samples, giving a quick and accurate assessment of H Res, bacteria & other fungi including yeasts in the fuel tank. This test is unlike current growth-based tests which require a minimum of 72 hours to provide any results after actively growing any fungi present in the fuel sample.

The test measures the amount of active growth in the sample and provides an indication of the actions that are required and alert levels. The new system developed by Conidia provides a more accurate fungi measurement system than the old colony forming unit (CFU) count. It comprises a simple paddle that is the test strip which is simply immersed into a fuel sample. This provides results based on a traffic light scenario. If there is negligible contamination the test strip shows green, if there is moderate contamination then it shows amber and a red colour is an indication of heavy contamination.

Six test devices are included in each test package with three of these having cut off test levels that are derived from IATA guidance which means that microbes have established themselves as a consortium and a fuel treatment is required. The other three of the devices tests for higher levels where the microbes are growing so rapidly, or have been growing for a long time that they may be causing damage to the structure of the tank or are likely to cause filter blockage and component failure and a tank clean and fuel treatment are required.

Six test devices are included in each Conidia test package