No abstract

The application of fuels from renewable sources ("alternative fuels") in aviation is important for the reduction of anthropogenic carbon dioxide emissions, but may also attribute to reduced release of particles from jet engines. The present experiment describes ground-based measurements in the framework of the ECLIF (Emission and Climate Impact of Alternative Fuels) campaign using an Airbus A320 (V2527-A5 engines) burning six fuels of chemically different composition. Two reference Jet A-1 with slightly different chemical parameters were applied and further used in combination with a Fischer-Tropsch synthetic paraffinic kerosene (FT-SPK) to prepare three semi synthetic jet fuels (SSJF) of different aromatic content. In addition, one commercially available fully synthetic jet fuel (FSJF) featured the lowest aromatic content of the fuel selection. Neither the release of nitrogen oxide or carbon monoxide was significantly affected by the different fuel composition. The measured particle emission indices showed a reduction up to 50% (number) and 70% (mass) for two alternative jet fuels (FSJF, SSJF2) at low power settings in comparison to the reference fuels. The reduction is less pronounced at higher operating conditions but the release of particle number and particle mass is still significantly lower for the alternative fuels than for both reference fuels. The observed correlation between emitted particle mass and fuel aromatics is not strict. Here, the H/C ratio is a better indicator for soot emission.

In the last years, several alternative aviation jet fuels have been approved as a response to worldwide concerns on adverse environmental effects of greenhouse gas emissions. However, comprehensive emissions studies are not part of the approval process. When burning a jet fuel, the exhaust gases are a mixture of gaseous specious including aromatics and non-gaseous species, particles, and soot. In addition, these species may affect the growth and lifetime of contrails known to be of influence on the climate due to their radiative forcing. Within this context, the use of synthetic aviation fuels may offer several advantages, going beyond reduced CO 2 emissions. These issues were addressed by studying the combustion of synthetic jet fuels taking into account their individual composition. An overview of what is known on their emission pattern was presented. Mostly, the same general trends were reported for the emissions of interest, for the fuels considered and at the power settings selected, with no adverse emissions effects. In particular, less soot particle emissions were reported, in mass and in number concentration, for GtL, HEFA, and farnesane. Moreover, a strong link between the amount and type of aromatics content of a jet fuel and soot emissions was observed.

Particle size distribution functions (PSDF) and mean particle sizes have been determined in a laminar premixed ethylene/air flame with three different experimental approaches: photo-ionization mass spectrometry (PIMS), scanning mobility particle sizing (SMPS), and laser-induced incandescence (LII). The main goal of this investigation was the crossvalidation of these three methods used at our institute for the determination of particle sizes in a great variety of flames or exhaust gases. We found good agreement between the three methods in the ranges where they are comparable as well as a complementary behavior for the different size ranges. PIMS and SMPS are able to measure the particle size distribution functions with good resolution. PIMS is favorable in detecting the smallest particles (<6 nm) and thereby able to detect even bimodal distributions of the soot precursor particles. SMPS and LII are suitable in the mid-and upper range of the particle sizes (>2 nm and >3 nm, respectively). LII offers the particular advantage of being a non-intrusive method. This makes it applicable in extreme environments, such as high pressure flames, as well as in very sensitive flames because no probe is needed.

We present a simple method for comparing particle size measurements, obtained with laser-induced incandescence (LII) and a scanning mobility particle sizer (SMPS) in a premixed laminar sooting flame. A quartz cell was installed in line with the SMPS probe to allow LII measurements within the SMPS sample line. In this configuration, the LII and SMPS measurements gave similar results in terms of mean particle size. After the probe, the soot particles appear to be made of tight compact particles. In addition, with this experimental configuration, the influence of the probe in the flame is studied for different particle size ranges by applying LII before and after the probe. Application of SMPS with and without LII in the quartz cell shows that laser heating during LII measurements has an influence on the soot particle size distribution. The method could be used to improve probe sampling of particulate matter in reactive fields as well as to validate the interpretation of relevant physical mechanisms involved in the LII process.