59203 - A Numerical Study on the Influence of Hydrogen Addition on Soot Formation in a Laminar Aviation Kerosene (Jet A1) Flame at Elevated Pressures 

The soot emission standards for aircraft engines are becoming increasingly restrictive, and the hydrogen addition on aviation fuels to reduce soot emission have received increased attention recently. Previous studies have validated the feasibility of hydrogen addition on aero-engine combustor and analyzed the benefit of hydrogen addition in practical application. A numerical investigation of the effect of hydrogen addition on soot formation in a laminar aviation kerosene (Jet A1) flame at elevated pressure condition was conducted to obtain a more fundamental understanding of the reason of less soot formation by hydrogen addition.

The particle population balance equation (PBE) describing the soot aerosol dynamics was solved by fixed sectional method to obtain detailed soot formation modelling. The kinetic mechanism of Jet A1 is the popular surrogate mechanism (Dagaut et al. 2014) containing the large PAH growth (Saffaripour et al. 2014). The above modelling method that has been validated in literature was then used to simulate the soot formation of kerosene-air, (kerosene+hydrogen)-air, and (kerosene+helium)-air coflow laminar flame. The helium was chosen as an additive since it has a dilution effect similar to that of hydrogen and is chemically inert. The volume fraction of hydrogen and helium in the fuel stream changed from 0 to 24% and 0 to 30%, respectively. The pressure changed from 1 to 6 atm.

The soot production of (kerosene+hydrogen)-air flame is smaller than that of (kerosene+helium)-air flame in atmosphere, indicating that the hydrogen addition to the fuel in a kerosene-air diffusion flame suppresses soot formation not only through the dilution effect but also the chemistry effect. The soot volume fraction and primary particle diameter of (kerosene+hydrogen)-air flame is smaller than that of kerosene-air flame in atmosphere. The reason from the chemistry aspect is that the hydrogen addition effectively suppresses the soot precursor (large poly-aromatic hydrocarbon) formation, which weakens the soot nucleation and soot growth process. Meanwhile, the height of (kerosene+hydrogen)-air laminar flame is smaller than that of kerosene-air laminar flame, which maybe caused by the short ignition delay time by hydrogen addition showed in the closed homogeneous reaction. The soot production of kerosene-air flame dramatically increases with the increase of pressure since the high pressure promotes the soot precursors formation. The soot production of (kerosene+hydrogen)-air flame in the high pressure condition also realizes remarkable reduction since the high pressure enhances the chemical inhibiting effect of hydrogen addition.