By Benesh Ben Shimon

CTO 

 

 


 

Ever since the advent of diesel fuel systems, water has been destroying their delicate, costly and high-tech components. The most common forms of damage are:

  • Corrosion: water combines with diesel additives to form acid. This corrodes/oxidizes both ferrous and non-ferrous metal components.
  • Rust: steel oxidation results in the formation of rust. This eventually migrates into the delicate sealing surfaces of moving components, scratching them and irreversibly damaging their function.
  • H2S acid: water combines with fuel degradation substances to form H2S, which will etch/eat the metal surfaces. 

H2S acid                                  Rust

      • Pitting: micro water droplets squeezed onto metal surfaces attack the delicate and fine surface finishing, leaving it rough and fatally damaged.
      • Hydrogen embrittlement: water molecules highly pressed into micro cracks in the metallic surfaces will decompose and release hydrogen to create embrittlement of the steel.
      • Molecular migration: in the presence of polar water molecules, the polar molecules of diesel’s additives will abandon the fuel and attach to the water. This enhances the creation of "soft solid" material, which will clog filters as well as other calibrated orifices and passages in the fuel system.
      • Microbiological stability: presence of water/oxygen and heat are all that organisms need to develop and survive. Bacteria and fungus create slimes/deposits, which will affect the diesel fuel composition and block venting passages in the fuel tank of the vehicle.

 

  • Fuel power: water droplets will enhance the formation of acid, gums and sediments known as "fuel degradation substances". These cause the diesel fuel to lose its caloric value and, therefore, affect its energy generation level.

What is the nature of water in diesel fuel?

  • Every diesel fuel contains a certain amount of water. It is important to distinguish between dissolved and undissolved water droplets.
  • The dissolved water droplets are part of the diesel fuel and will generally not harm anything related to the fuel system. However, once over the range of saturation level, water will exist as undissolved droplets ("free water") in the fuel. These undissolved droplets are of the major cause of wear and failure in diesel fuel systems.

What has been done about it?

  • Separation and elimination of undissolved water from diesel fuel became an essential concern with the advent of the first successful common rail injection systems in diesel engines in the mid 1990s.
  • Diverse systems for water removal exist in the market, and they vary according to engine size and power. There are "in filter" mechanisms for coalescing the droplets and draining them periodically, or larger units of multi-separators in big engines. 

Fig 1: Diesel Filters with water separation

 

  • More recently, the implementation of diesel systems in passenger car engines as small as 1 liter in volume that also comprise turbo systems, together with the environmental regulations for emission levels, have made the task of water separation a major concern for engine designers and manufacturers.

Fig 2: Basic Diesel Fuel system

 

  • For this reason, the ISO committee adopted a new revised and updated version of the ISO 16332 standard for the testing, comparing and determining of water separation efficiency. 

 

"ISO 16332-2016, Diesel engines – Fuel filter – Method for evaluating fuel/water separation efficiency":

  • This standard did much to establish normalized methods and testing liquid that would allow comparable testing of water separation efficiencies of diesel filters and/or water separators.
  • The new criteria for testing the filters with water droplets as small as 10 µm reflects the importance of this matter, and has imposed the following technical challenges: 

- Reliable generation of 10 µm water droplets.
- Reliable known and controlled distribution of those droplets in the fuel.
- Precise measurements of differential pressures, flow rate and water concentration levels.

Fig 3: The Interfacial Tension meter

Fig 4: The Karl Fischer titration method 

   

 

A.L. Group’s response:

  • Looking ahead to the ISO/DIS 16332 of 2016, A.L. Group has introduced an advanced test bench to the laboratory at its HQ. This has been built to full compliancy with the standard.
  • Engineers who are concerned with this issue will be interested to know that this test bench’s software can be programmed to electronically generate water droplets of any size between 10 µm to 300 µm.  This supersedes the previous technology of using "calibrated orifice plates” and numerous curves of differential pressure vs. orifice diameters vs. flow rates vs. liquid type.
  • This test bench is currently unique and, indeed, a remarkable innovation for the diesel filters testing market. It was made possible thanks to IFTS France’s patented invention, the Electronic Droplets Generator (EDGE).
  • This test bench will enable A.L. Group’s engineers to study in-depth and find efficient applicable solutions for customers in the field of water separation in diesel filters.

Fig 5:  The Test Bench