Comparing Alternative Jet Fuel Dependencies Between Combustors of Different Size and Mixing Approaches

Abstract

Analyses used to reveal fuel dependencies on lean blow out and ignition at specific operating conditions in specific combustors show inconsistent trends with each other. Such variety is however consistent with the occurrence of transitions between the governing physical phenomena as the ratios between evaporation, mixing, or chemical time scales with their respective residence times also vary with specific operating conditions and combustor geometry. It is demonstrated here that the fuel dependencies on LBO in a large, single-cup, swirl-stabilized, rich-quench-lean combustor varies with operating conditions such that a feature importance match is attained to fuel dependencies observed in a much smaller combustor at one end of the tested range, while a qualitative match to fuel dependencies observed in a lean, premixed, swirler-stabilized combustor of comparable size at the other end of the tested range. The same reference combustor, when tested at cold conditions, is shown to exhibit similar fuel dependencies on ignition performance as the much smaller combustor, when tested at both cold and warm conditions. The practical significance of these findings is that a reference rig, such as the Referee Rig, can capture fuel performance trends of proprietary industry combustors by tailoring the inlet air and fuel temperatures of the tests. It is, therefore, a trustworthy surrogate for screening and evaluating sustainable aviation fuel candidates, reducing the dependency on proprietary industrial combustors for this purpose, thereby increasing transparency within the evaluation process while also expediting the process and reducing cost and fuel volume.

Numerical Modeling of Chemical Kinetics, Spray Dynamics, and Turbulent Combustion towards Sustainable Aviation

“…In the same program, similar trends were observed during the LBO-limit and ignition tests performed on lab-scale and proprietary combustors. Data analysis by Boehm et al [84] suggested LBO figures of merit to be remarkably influenced by 20% recovered temperature (T 20 ) and density, selected as representative independent variables of evaporation and atomization, respectively. In addition, it was shown that some fuel dependencies emerge over a wide range of combustor length scales and design approaches, and similar trends can be identified for two systems operated at conditions that match ratios of characteristic timescales (e.g., evaporation-to-residence-time).…”

Perspectives on Fully Synthesized Sustainable Aviation Fuels: Direction and Opportunities

“…Although jet fuel combustion has been studied for decades, unknowns remain. For example, critical factors for altitude relight are not well characterized: atomization is a complex interplay of fuel surface tension, viscosity, density, and air temperature and pressure; fuel vapor pressure, and molecular composition are also important (Peiffer et al, 2019;Boehm et al, 2021). Research, such as the National Jet Fuels Combustion Program (Colket et al, 2016;CAAFI R&D Team, 2019), has added to the understanding of the interaction of fuel chemical composition and physical properties with combustion.…”

“…For 100% synthesized fuels, new requirements may need to be added to the specification. For example, the NJFCP suggested several characteristics as potentially critical to the safety and operability of jet fuels, such as derived cetane number (Colket et al, 2016;Stachler et al, 2020;Boehm et al, 2021). These new requirements need to be considered, researched and verified.…”