In collaboration with the Federal Office of Civil Aviation (FOCA), the Swiss Air Force and the Paul Scherrer Institute (PSI), researchers from the ZHAW Center for Aviation measured the pollutant emissions of the Federal Council jet both when using conventional kerosene and when using a mixture with sustainable fuel as part of the AGEAIR II project. The aim was to thereby enable a comparison of the pollutant values.
In addition to civil aviation, Switzerland's military aviation should also reduce its fuel emissions. To this end, sustainable fuel, e.g. HEFA fuel (Hydroprocessed Esters and Fatty Acids), is to be mixed with conventional paraffin in the future. HEFA fuel is produced from waste products such as cooking oil and animal fats. By the end of the year, the Swiss Armed Forces plan to use a paraffin mix that contains a proportion of two per cent sustainable fuel. The background to this is also a requirement of the European Union, which stipulates that the admixture of sustainable fuels be gradually increased to 70 per cent by 2050.
In addition to reducing CO2, the use of sustainable fuel is also intended to reduce emissions of particulate matter that is harmful to health, such as soot particles. To this end, emission measurements were carried out at the military airport in Payerne on a Federal Council jet, a 20-year-old Cessna 560 XL Citation Excel, under the direction of the FOCA. The team led by ZHAW researchers Lukas Durdina and Julien Anet was responsible for the test plan and the evaluation of the results. "For the measurements we used our mobile emission measurement system SMARTEMIS, the exhaust probe was provided by the FOCA and the air force supplied the fuels and the jet for the measurements," explains Lukas Durdina, who researches aircraft engine emissions at ZAV. At the beginning of the test series, the ZHAW team, together with staff from the Paul Scherrer Institute (PSI), carried out measurements with conventional fuel; on the second day of testing, they mixed it with 30 per cent HEFA fuel.
Surprising results
Given the preliminary measurement results, however, the ZHAW team was surprised. "The admixture of 30 per cent HEFA fuel reduced particulate emissions much less than expected; they were only about 20 per cent below the value with conventional fuel," Lukas Durdina summarises the results. In comparable tests with larger aircraft, the reduction in particulate matter was noticeably greater. The exact reasons for this still need to be investigated. As part of a follow-up project, new measurements are planned with the same jet, "but this time under different climatic conditions and with different fuel mixtures," says ZHAW researcher Lukas Durdina.
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