Soot-Free Low-NO_x Aeronautical Combustor Concept: The Lean Azimuthal Flame for Kerosene Sprays

Abstract

An ultralow emission combustor concept based on “flameless oxidation” is demonstrated in this paper for aviation kerosene. Measurements of gas emissions, as well as of the size and number of nanoparticles via scanning mobility particle sizing, are carried out at the combustor outlet, revealing simultaneously soot-free and single-digit NO x levels for operation at atmospheric conditions. Such performance, achieved with direct spray injection of the fuel without any external preheating or prevaporization, is attributed to the unique mixing configuration of the combustor. The combustor consists of azimuthally arranged fuel sprays at the upstream boundary and reverse-flow air jets injected from downstream. This creates locally sequential combustion, good mixing with hot products, and a strong whirling motion that increases residence time and homogenizes the mixture. Under ideal conditions, a clean, bright-blue kerosene flame is observed, free of soot luminescence. Although soot is intermittently formed during operation around optimal conditions, high-speed imaging of the soot luminescence shows that particles are subjected to long residence times at O2-rich conditions and high temperatures, which likely promotes their oxidation. As a result, only nanoparticles in the 2–10 nm range are measured at the outlet under all tested conditions. The NO x emissions and completeness of the combustion are strongly affected by the splitting of the air flow. Numerical simulations confirm the trend observed in the experiment and provide more insight into the mixing and air dilution.

MILD Combustion and Biofuels: A Minireview

“…Despite the lower maximum temperature and higher residence times than the ones of conventional combustion processes, the effectiveness of MILD combustion in a wide range of power and power density is guaranteed, as discussed in reviews ,, and archival papers ,,, as well as in the outcomes of international research projects funded by international entities . This is also confirmed by its utilization in gas turbine (e.g., sequential combustion) or reheating furnaces as a small set of examples.…”

Recent Combustion Strategies in Gas Turbines for Propulsion and Power Generation toward a Zero-Emissions Future: Fuels, Burners, and Combustion Techniques

“…The new burner developed by researchers at Cambridge University [78] is a MILD burner. It is characterized by specific azimuthal fuel injection and an opposite air flow injection, which both emphasize the dilution of the fresh air and fuel with the hot gases (for more details, the reader is invited to refer to the work of Oliveira et al [78]). This particular burner was demonstrated to work with both methane and kerosene spray with a single digit CO and NO x production.…”

Special Issue in Memory of Professor Mário Costa

“…Five papers are included on this topic. Oliveira et al 8 demonstrate an ultralow emission combustor concept based on "flameless oxidation" for aviation kerosene. Experiments and simulations demonstrate the existence of a nominally diffusion-type kerosene system that has zero soot and produces very low levels of NO x and CO, showing a promising combustor concept for the next generation of ultralowemission aeroengines.…”