Soot-Free Low-NO<sub><i>x</i></sub> Aeronautical Combustor Concept: The Lean Azimuthal Flame for Kerosene Sprays
Pedro M. de Oliveira, Daniel Fredrich, Gianluigi De Falco, Ingrid El Helou, Andrea D’Anna, Andrea Giusti, Epaminondas Mastorakos
Abstract
An ultralow emission combustor concept based on\n“flameless oxidation” is demonstrated in this paper for aviation\nkerosene. Measurements of gas emissions, as well as of the size and\nnumber of nanoparticles via scanning mobility particle sizing, are\ncarried out at the combustor outlet, revealing simultaneously sootfree\nand single-digit NOx levels for operation at atmospheric\nconditions. Such performance, achieved with direct spray injection\nof the fuel without any external preheating or prevaporization, is\nattributed to the unique mixing configuration of the combustor.\nThe combustor consists of azimuthally arranged fuel sprays at the\nupstream boundary and reverse-flow air jets injected from\ndownstream. This creates locally sequential combustion, good\nmixing with hot products, and a strong whirling motion that\nincreases residence time and homogenizes the mixture. Under ideal conditions, a clean, bright-blue kerosene flame is observed, free\nof soot luminescence. Although soot is intermittently formed during operation around optimal conditions, high-speed imaging of the\nsoot luminescence shows that particles are subjected to long residence times at O2-rich conditions and high temperatures, which\nlikely promotes their oxidation. As a result, only nanoparticles in the 2−10 nm range are measured at the outlet under all tested\nconditions. The NOx emissions and completeness of the combustion are strongly affected by the splitting of the air flow. Numerical\nsimulations confirm the trend observed in the experiment and provide more insight into the mixing and air dilution.