Multi-stage water separator protects modern diesel injection systems in commercial vehicles

Modern diesel engines deliver hugely enhanced performance and a significant improvement in efficiency in terms of emissions behaviour and fuel consumption. In order to achieve such improvements, modern common rail injection systems operate at injection pressures exceeding 2,500 bar. These ever higher injection pressures place increasing demands with regard to the separation of water contained in diesel fuel.

Structure of three-stage water separator for diesel fuel

Ludwigsburg/Hanover, 23 September 2014 - Water enters the fuel tank and diesel fuel in a number of ways: substandard fuel with a high water content can be a possible cause, as can misfuelling or the ingress of water via the fuel tank ventilation or condensation. The consequences include corrosion and cavitation on injectors, valves and the injection pump – which can ultimately lead to a system failure. Moreover, free water can cause microbiological growth and corrosion processes which frequently lead to premature blockage of the fuel filter or pitting corrosion of the filter housing.

Today, commercial vehicle engines are developed for global use. Modern fuel filter systems must therefore meet a variety of demands in terms of fuel quality, contamination, water content and use with regard to their filtration and separation requirements.

In the past, single-stage concepts were sufficient to meet the requirements for water separation efficiency. For this purpose, the filter element was equipped with a water barrier layer on the flow side. However, this concept is no longer adequate for pressure side filter operation or for the use of modern low-supher fuels, which contain biofuels and have a high additive content, in order to effectively protect the injection system from damage.

If water from the fuel tank enters into the fuel circuit, it is broken up into small droplets in the low-pressure fuel pump. After several fuel cycles, droplets measuring d3.50 < 4 µm – i.e. less than 1/10 the diameter of a hair – may form. A stable fuel/water emulsion then forms, which does not separate, even over several days.

Separating small droplets presents a challenge for fuel filter systems: filter elements that are based on a water repellent effect on the flow side of the filter cannot ensure water separation in the long term. The small droplets are not separated at the surface but, owing to their size, are forced through the pores of the filter medium. The hydrophobic properties are impaired to such an extent, particularly by additive components in biofuel and separated impurities, that the water separation capability is completely lost over the service life of the filter.

In order to ensure reliable water separation over the service life of the filter element, MANN+HUMMEL has developed a three-stage filtration concept which is used in the latest filtration modules.

With this concept, the fuel flows from the outside to the inside of the filter element. In the first stage, solid particles are filtered out by the filter medium. It is crucial that the coalescer and the hydrophobic fabric are not contaminated by particles. The coalescer then retains the water droplets and combines them to form much larger drops. In the third stage, the hydrophobic screen fabric prevents the drops from following the fuel into the injection system. This is a principle that works thanks to the tailored development of the fuel filter element. The separated water itself is collected in the filtration module, detected there and emptied out either manually or automatically. Thanks to the high water separation efficiencies that can be achieved, the injection systems and commercial vehicle engines are thus reliably protected.

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Press images:           Structure of three-stage water separator for diesel fuel

Image can be reprinted free of charge for editorial purposes.

Press contact:          Miriam Teige
                                       Tel.:   +49 (0) 7141 98-2583
                                       E-mail: miriam.teige@mann-hummel.com

The MANN+HUMMEL Group is a leading global expert for filtration solutions and development partner and original equipment supplier to the international automotive and mechanical engineering industries. Employing 15,231 people at around 60 locations worldwide, the company achieved turnover of about 2.68 billion euros in 2013. The group’s product portfolio includes air filter systems, intake manifold systems, liquid filter systems, cabin filters and plastic sound components (known as 'symposers'), as well as filter elements for vehicle servicing and repair. For general engineering, process engineering and industrial manufacturing sectors the company’s product range includes industrial filters, a series of products to reduce carbon emission levels in diesel engines, membrane filters for water filtration and filter systems.