Lean Blowoff Limits and Emissions Measurements in a Lean Premixed Prevaporized Combustor with Variable Reactant Inhomogeneity

Lean premixed prevaporized (LPP) combustor designs and sustainable aviation fuels (SAF) show great promise for the development of next-generation low-emission civil supersonic transport (CST) aircraft engines. In this work, exhaust emissions sampling and optical diagnostic measurements were conducted in an LPP model combustor with variable reactant inhomogeneity. The LPP combustor features a novel premixer design, which facilitates control of the level of fuel vaporization and fuel-air mixedness entering the combustor. Measurements of lean blowoff (LBO) limits and gaseous emissions trends were obtained through the optically accessible combustor liner and custom exhaust sampling probe. The combustor was operated at elevated temperature (700 K) and pressure (9 bar) conditions to simulate the combustor inlet conditions of CST aircraft engines. A conventional Jet A fuel was used as the baseline fuel, to which a SAF was compared. Results show that a moderate level of prevaporization and premixing was sufficient to properly stabilize the premixed main flames. With reduced prevaporization and premixing, the main flames did not properly stabilize and NOx emissions were increased. With improved prevaporization and premixing, NOx emissions were reduced but LBO limits were also altered, with the trend depending on fuel type. Such trends aligned with measured fuel effects on prevaporization, suggesting that both fuels benefited (in terms of LBO limits) from an intermediate level of prevaporization and premixing. For all levels of reactant inhomogeneity, emissions indexes of NOx remained below 10 g per kg fuel burned across the range of test conditions. These measurements highlight the trends and tradeoffs of combustor stability and emissions with varying reactant inhomogeneity, as well as the effectiveness of LPP combustion at minimizing NOx emissions. In addition, the optical diagnostic data represents a large database with potential for CFD model development and validation in a non-proprietary LPP combustor geometry.