Environment: ENEA, biofuels in aviation reduce up to 40% jet engine pollution

For the first time in Italy a mixture of biofuel and kerosene was tested on a military jet, showing a reduction of up to 40% of polluting emissions, as shown by a study published in the international journal Toxics, which also investigated the overall impact of these new aviation fuels on health and the environment. The study was conducted by an ENEA team in collaboration with the Italian Air Force, as part of a cooperation agreement on the use of biofuels in aviation, which also involves the Cnr and the Ministry of the Environment and Energy Security.

The tests were conducted on two different mixtures containing 13% and 17% biofuel respectively during several aircraft ground tests at the Experimental and Space Aviation Division (DASAS) of the Pratica di Mare military airport, near Rome. "In our mobile laboratory we calculated the emission values by type of fuels, which represent the concentration of pollutant in the aircraft's exhaust gases in relation to the quantity of fuel burned", explained Antonella Malaguti, researcher at the ENEA Laboratory of Atmospheric Pollution at the Bologna Research Center. “The two biofuel mixtures showed an overall average reduction of 20% - up to 40% at medium regimes - in black carbon emissions, i.e. elemental carbon; at the same time, we found an increase of up to 30% in nitrogen dioxide and total particles emitted, particularly nanoparticles[1]", said Malaguti.

“The novelty of this study lies in the evaluation of potential biological responses of the human lung to combustion products, through direct exposure of an in vitro model of bronchial cells to both fossil fuels emissions and the two biofuel mixtures. This test, together with the calculation of the the lung dose, opens important scenarios for determining the potential risk for humans", pointed out Maurizio Gualtieri, researcher at ENEA at the time of the study and currently at the Milan-Bicocca University. “Furthermore – continued Gualtieri – the test campaign highlighted a greater deposition of fine and ultrafine particles (i.e. with a diameter of less than 100 nanometres), both in the cellular system and the lungs, even if this increase should not be ascribed primarily to the bio component of fuel blends[2]”.

The biological results showed an increased antioxidant response of the cells, quantified through the expression of the HO-1 gene (emissions from traditional fuel combustion have slightly greater effects than those from the new biofuels). By analyzing the response of the cells one hour after the end of the exposure, the activation of the antioxidant response increased considerably. “The data reported in the article refer only to biofuels but the same can be said for traditional fuel. This increased response suggests that emissions exposure triggers acute oxidative cellular stress which, combined with lung deposition data, ring a warning bell on the effects of repeated exposure to these emissions over time", Malaguti and Gualtieri said.

The outcomes of the test campaign and the experimentations are a notable step forward in the study to mitigate the impact of aviation on climate change, one of the sectors most interested in the impact of emissions and which is increasingly attracting the interest of the international community and the world of research. “Reducing aviation's climate impact requires a great effort in the development and testing of renewable fuels to partially or totally replace fossil fuels, keeping in mind the potential effects on human health, as shown by our study”, concluded Malaguti and Gualtieri.

[1]  During the combustion tests at medium engine regimes (50% RPM), in fact, the elemental carbon emissions per kilogram of mixture were equal to 199 mgC/Kg (-40%) compared to 312 mgC/Kg of fossil fuels alone; NO2 emissions per kilogram of mixture were equal to 2460 mg/Kg (+30%) compared to 1867 mg/Kg of fossil fuels alone; the number of particles emitted was respectively 1.4x1016/Kg compared to 6.4x1015/Kg for fossil fuels alone.

[2] During the tests, the bio fuel (HEFA) was mixed with a kerosene of fossil origin in the Jet A-1 fuels category, which can have a variable concentration of sulphur, as long as it is lower than 0.3 ppm. Further analyses following the tests showed an increase of this element, still below the limit value. In fact, the kerosene used for the first tests had a sulfur concentration of less than 0.08ppm while that used for the bio mixtures had a sulfur content higher than 0.11ppm. The bio fuel showed a sulfur concentration well below 0.002ppm.