Lean Blowoff in a Toroidal Jet-Stirred Reactor: Implications for Alternative Fuel Approval and Potential Mechanisms for Autoignition and Extinction

Abstract

Sustainable aviation fuels (SAFs) have been identified as a method to reduce the aviation sector's environmental impact through carbon mitigation. Current certification processes of potential, viable SAFs require labor cost intensive assessments with investigation into combustor performance parameters related to fuel effects such as lean blowoff (LBO) where there exists the competition between multiphase physics and chemical kinetics of the fuel. Recent efforts show LBO effectively scales with the evaporative, mixing, and chemical time scales of a given combustor. Here, a toroidal jet-stirred reactor (TJSR), an experimental configuration meant to emulate perfectly stirred reactor (PSR) studies, is used to study the effects of fuel chemistry physical time scales on LBO while mitigating and minimizing the effects of evaporation mixing, respectively. For this investigation, six fuels/fuel mixtures spanning a range of derived cetane number (DCN) were evaluated in a lean premixed, prevaporized environment with engine relevant characteristics such as recirculation inlet temperature residence times (P = ∼1 atm, T = 460 K, τ = 5.5−6.5 ms). Gas phase emissions sampled within the reactor were measured with a Fourier transform infrared spectrometer to gain insight into relevant trends in species production for varying fuels as leaner conditions were approached. LBO in the TJSR was correlated with the parameters of the DCN and radical index, an indicator of OH production, signifying competition between the chemical processes of autoignition and extinction, respectively; these observations deviate from the established PSR theory for ignition extinction physics. However, the emergence of these correlations in the TJSR experiment support the importance of low temperature chemistry and flame robustness. A physical time scale approach to LBO is applied to the current experiment to elucidate the competition of autoignition and extinction phenomena. Knowledge of the physical LBO time scales and their relationship to chemical fuel properties suggest that the holistic LBO time scale may be viable as a preliminary screening metric for SAF certification.

Trends and emerging research directions of sustainable aviation: A bibliometric analysis

“…His studies were published between 2019 and 2023 [ 73 ]. Heyne, studying on energy and fuels, engineering, chemistry, thermodynamics and physics [ 74 ], examined mostly on production of sustainable aviation fuel and its use in aviation [ [75] , [76] , [77] , [78] , [79] , [80] , [81] , [82] , [83] , [84] , [85] , [86] ].…”

Perspectives on Fully Synthesized Sustainable Aviation Fuels: Direction and Opportunities

“…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.…”

Orthogonal Reference Surrogate Fuels for Operability Testing

“…This specification ensures the safe usage, fungibility, performance, and compatibility of the SAF under standard usage and severe operability conditions. Specifically, Tier 3 engine operability tests focus on fuel effects under the so-called figure-of-merit (FOM) limit phenomena, namely, lean blowout (LBO), high-altitude relight, and cold-start ignition [6][7][8]. Because of the broad range of potential physical and chemical properties of a new SAF, extensive combustor testing is needed to overcome uncertainty and ensure safety for FOM operability issues.…”