HFRR

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Principle of the HFRR measurement

The HFRR value ( engl. High frequency reciprocating rig) is a measure of the lubricity of diesel fuels or fuel oil sulfur EL. Due to the introduction of low-sulfur diesel (EL heating oil), the lubricity of which is considerably worse than that of fuel containing sulfur despite the same density and viscosity and which has led to a significantly increased frequency of damage in fuel-lubricated diesel injection pumps (fuel pumps), the HFRR value in research and Development of engine technology gained in importance. Since parts of the injection pump in diesel engines are only lubricated by the fuel itself, precise knowledge of the lubricity of the fuel is necessary. A description of density and viscosity alone is not sufficient. A measuring method was developed with which the lubricity can be measured easily and repeatedly.

Measurement method

A steel ball with a diameter of 6 mm is clamped in a holder and pressed onto a steel plate of defined hardness and surface roughness with a force of 2 Newtons . The holder grinds the ball over the plate with a frequency of 50 Hz and a horizontal oscillation path of 1 mm. The ball slides back and forth on the plate in a liquid bath (at 60 ° C) made of the fuel to be tested. The amount of liquid is 2 milliliters in a bath with the surface of 6 cm². The test takes 75 minutes.

The movement creates a so-called wear cap on the ball , an approximately circular flattening; sometimes the smallest and largest diameter is also specified. The diameter of this wear cap in µm is the HFRR value. A smaller value indicates better lubricity. Due to the spherical shape of the test body, the wear is not linear. In the event of poor lubrication, a larger wear cap results, which leads to a lower surface pressure between the steel ball and steel plate. Thus, under the same conditions, the value for poorly lubricating liquids does not become greater to the extent that the lubricity has actually decreased.

Examples of the lubricity of common fuels

  • Biodiesel fuel (Europe, according to standard EN 14214): approx. 320 µm
  • Diesel fuel (Europe, according to DIN EN 590): <460 µm
  • Low-sulfur heating oil EL (Germany, according to DIN 51603-1): <460 µm
  • Diesel fuel (USA, according to ASTM -D975): 550 - 600 µm

literature

  • Karl-Heinz Dietsche, Thomas Jäger; Robert Bosch GmbH: Automotive paperback. 25th edition. Friedr. Vieweg & Sohn Verlag, Wiesbaden 2003, ISBN 3-528-23876-3 .

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