New test facility: How cold can fuel for diesel engines get?

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Left: Fuel flocculates in extreme cold. Right: The new test facility
Left: Fuel flocculates in extreme cold. Right: The new test facility
In extreme cold, fuels can no longer be used - but how do you measure the possible minimum temperature? A test facility has now been developed for this purpose at the Vienna University of Technology.

When it gets too cold, the car won’t start. Certain components of fuels can precipitate at low temperatures, the fuel becomes cloudy and can no longer be used. Kerosenes in fuels in particular can form small flakes when it is very cold.

This has been known for a long time - but until now there was no standardized test method that could be used to get to the bottom of the cold resistance of fuels in real operation with scientific precision. Together with partner companies from research and industry, the Vienna University of Technology has therefore now developed a climate-controlled test rig that can be used to reliably test fuels together with the tank and pipe system for winter suitability. The test rig is suitable for a wide variety of fuels - from ordinary diesel, to diesel made from recycled cooking oil, to e-fuels or special new aviation fuels based on biowaste.

So far no simple, uniform test method

The need for a new, reliable test rig for fuels had already become apparent as part of another project: The German Scientific Society for Sustainable Energy Sources, Mobility and Carbon Cycles (DGMK) joined forces with various automotive companies and fuel manufacturers to investigate the influence of fuel and vehicle technology on the winter resistance of current diesel vehicles.

-It became clear that the different project teams operate completely different test facilities for investigating fuels," says Bernhard Geringer from the Institute of Vehicle Drivetrains and Automotive Engineering at the Vienna University of Technology. -The tests are not all equally realistic and thus do not produce the same results. So the importance of developing a uniform test rig and procedure was recognized.-.

A suitable test system has now been developed and set up at the Vienna University of Technology: It is air-conditioned and can be cooled down to a temperature of -45 °C. The system contains the part of the vehicle that is crucial for evaluating winter resistance, namely the low-pressure fuel system. -We tested a wide variety of test fuels and measured the temperatures, pressures and flow rates in the fuel system-, explains Bernhard Geringer. If the test is passed, another test is carried out at a lower temperature. The lowest temperature with a positive test result is considered the operating limit for the fuel.

Reproducible and reliable

The test rig method has been extensively studied and compared with test results obtained on real complete vehicles - the two methods agree well with each other. -We were also able to show that the results are well reproducible, and that different test stands using this technology also deliver results that compare well with each other," says Bernhard Geringer.

This enabled the goal to be achieved - namely to develop a time- and cost-saving measurement method so that a complete air-conditioned vehicle test rig is not required to test the winter resistance of a fuel, but instead the fuel only has to be tested on the relevant vehicle systems.