Sustainable Aviation Fuels Approval Streamlining: Auxiliary Power Unit Lean Blowout Testing

Peiffer, Erin; Heyne, Joshua S.; Colket, Meredith B.

doi:10.2514/1.j058348

Cited by 24 publications

(11 citation statements)

References 18 publications

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“…The random forest statistical analysis approach used in this work has been described previously (Peiffer et al, 2019;Colborn et al, 2020). In summary, the method employs random sampling and replacement to decrease overfitting and allows for one dependent variable (e.g., LBO or ignition performance) to be evaluated against multiple independent variables (e.g., fuel properties) (Hastie et al, 2008).…”

Section: Discussionmentioning

confidence: 99%

“…APUs are small gas turbine engines that are used to provide power to spoolup the main engine during starter-assisted air starts. APUs are particularly sensitive to the physical properties that influence atomization and vaporization (Peiffer et al, 2019) because of their small volume, and corresponding low combustor residence time (τ cmb ρ air V cmb /W air ). The 131-9 combustor is swirl-stabilized and relies on a rich-quench-lean combustion process, like many of the much-larger, main engine combustors.…”

Section: Apu-cr Experimentsmentioning

confidence: 99%

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

2021

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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.

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Section: Discussionmentioning

confidence: 99%

Section: Apu-cr Experimentsmentioning

confidence: 99%

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

2021

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“…Surrogates that mimic jet fuel properties have been used historically to understand combustion phenomena, while here we report potentially worst case fuel compositions. Previous efforts from the NJFCP program have shown that certain fuel properties (σ, µ, and ρ) have more of an impact on predicting ignition probabilities [14,15,30]. SAF approval could benefit from the manipulation instead of mimicking surrogate properties to illustrate the complex physical competition of properties.…”

Section: Discussionmentioning

confidence: 99%

“…Recent random forest regression (RFR) results on LBO of SAFs in four combustor rigs showed that derived cetane number (DCN) is the most significant feature importance in both the Referee Rig and toroidal jet-stirred reactor at elevated temperatures, and the second most significant feature importance in the Sheffield rig [13,14]. These three rigs show the dominance of chemical timescales near LBO, where chemical timescales are a function of the fuel chemical properties and accompanying thermodynamic conditions.…”

Section: Introductionmentioning

confidence: 99%

“…These three rigs show the dominance of chemical timescales near LBO, where chemical timescales are a function of the fuel chemical properties and accompanying thermodynamic conditions. However, experiments using the Honeywell auxiliary power unit (APU) show no sign of DCN affecting LBO [14]. Lack of a swirler and presence of a small pressure atomizer contribute to this difference and enhance the dominance of evaporative timescales near LBO, where evaporative timescales are a function of physical fuel properties and distillate properties.…”

Section: Introductionmentioning

confidence: 99%

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Orthogonal Reference Surrogate Fuels for Operability Testing

2020

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The approval and evaluation process for sustainable aviation fuels (SAF) via ASTM D4054 is both cost- and volume-intensive, namely due to engine operability testing under severe conditions. Engine operability tests of combustor under figures of merit (FOM) limit phenomena are the fuel effects on lean blowout, high-altitude relight, and cold-start ignition. One method to increase confidence and reduce volume in tiered testing is to use surrogate fuels for manipulation of properties. Key fuel performance properties (surface tension, viscosity, density) for cold-start ignition was determined prior to this study. Prior work regarding this FOM has not considered the combination of these properties. A surface tension blending rule was validated and incorporated into the jet fuel blend optimizer (JudO). A generalized surrogate calculator for N-dimensional surrogate components and features was developed. Jet fuel surrogates developed in this study were a mixture of conventional and sustainable aviation fuels instead of pure components. These surrogates suggested to be tested in this study could illuminate near worst-case effects for sustainable aviation fuel in a given configuration/rig. With those scenarios tested, we can further understand the influence on the key properties relative to cold-start ignition. This work and supporting experimental evidence could potentially lower the barrier for SAF approval processes.

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