环形系统的燃烧不稳定性：具有相似特性的液体燃料可导致显著不同行为的证据

IF 6.2 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame Pub Date : 2025-06-03 DOI:10.1016/j.combustflame.2025.114235

Véranika Latour, Daniel Durox, Antoine Renaud, Sébastien Candel

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引用次数: 0

摘要

向使用可持续航空燃料的过渡需要了解燃料成分对燃烧特性的影响，以确保现有或新的飞机发动机的安全可操作性。在saf的使用所带来的诸多问题和挑战中，燃烧系统的动力学行为问题需要特别关注。众所周知，燃烧动力学现象取决于火焰对入射扰动的响应以及燃烧与系统声模态的可能耦合。本文拟通过比较物理和热化学性质相近但化学动力学特性不同的庚烷和异辛烷两种燃料的动力学特性，揭示化学特性对这一问题的影响。这暂时与庚烷和异辛烷的十六烷数有明显的不同有关。这些数字通常用来表征自燃延迟和自燃温度。本文建议它们也可以作为一种指标，根据它们的动力学行为对不同的燃料进行分类。利用实验室规模的环形燃烧室MICCA，发现这两种燃料的燃烧动力学有显著差异，庚烷的不稳定区域比异辛烷更宽，极限环振荡幅值更高。实验观察是通过在单扇区配置SICCA中收集火焰动力学数据以及在极限环下MICCA中同时记录压力和光电倍增管来解释的。实验数据表明，两种燃料的FDF相值主要不同，异辛烷的FDF相值随振荡幅度的增加而显著降低。收集到的数据，结合分析框架，用于确定增长率和走向极限环的轨迹。这使得对实验观测结果的解释成为可能，并表明用异辛烷操作的MICCA中的不稳定点完全是非线性的，突出了燃烧系统热声行为的振幅相演化的重要性。本研究通过比较物理性质相近但化学性质不同的两种燃料（庚烷和异辛烷），揭示了化学反应性对方位燃烧不稳定性的影响。由此推断，十六烷值（庚烷和异辛烷的十六烷值有显著差异）可以作为区分不同燃料动力学行为的指标。在两个不同的试验台（环形燃烧室和单扇形燃烧室）收集的实验数据用于比较两种燃料的动态行为并解释所观察到的差异。然后在环形燃烧室MICCA中收集高振幅水平的火焰动力学数据，采用依赖喷油器分级的原始实验程序。结果揭示了FDF相与异辛烷调制幅值的有趣行为，解释了两种燃料之间观察到的动力学差异。通过考虑模型问题中增益和相位演变与振荡幅度的综合影响，这些发现得到了推广。这个问题的目的是在尽可能简单的框架中展示增益和相位变化的影响，并证明所观察到的极限环可以由线性不稳定的系统或线性稳定但非线性不稳定的系统达到。通过初步强调十六烷数与两种燃料的动力学行为差异及其对燃烧不稳定性的影响之间的联系，这项工作具有重要意义，因为它强调，在没有验证它们不会改变燃烧器的可操作性，特别是不会引起不希望的振荡之前，不应引入新燃料（SAFs）。

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Combustion instabilities in annular systems: Evidence that liquid fuels with similar characteristics can lead to notably different behaviors

The transition towards the use of sustainable aviation fuels (SAFs) requires the understanding of the effects of fuel composition on combustion properties in order to ensure the safe operability of the existing or new aircraft engines. Among the many concerns and challenges raised by the use of SAFs, the question of the dynamical behavior of the combustion systems requires specific attention. It is known that combustion dynamics phenomena depend on the flames’ response to incoming disturbances and on the possible coupling of combustion with the acoustic modes of the system. This work proposes to shed light on the effects of chemical characteristics on this issue by comparing the dynamical properties of heptane and iso-octane, two fuels featuring close physical and thermochemical properties, but presenting different chemical kinetics characteristics. This is tentatively linked to the cetane numbers of heptane and iso-octane which are notably different. These numbers are generally used to characterize the auto-ignition delay and auto-ignition temperature. It is here suggested that they might also be used as an index to categorize different fuels with respect to their dynamical behavior. Using the laboratory-scale annular combustor MICCA, it is shown that these two fuels induce significantly different combustion dynamics, with a broader unstable region and higher limit cycle oscillation amplitudes for heptane than iso-octane. Experimental observations are interpreted by gathering flame dynamics data in the single-sector configuration SICCA and from simultaneous pressure and photomultiplier recordings in MICCA operating at limit cycle. Experimental data show that the two fuels differ mainly by their FDF phase values and iso-octane presents a significant decrease in the FDF phase with the oscillation amplitude. The collected data, combined with an analytical framework, are used to determine growth rates and trajectories towards limit cycle. This enables the interpretation of the experimental observations and indicates that the unstable points in MICCA operated with iso-octane are exclusively of nonlinear nature, highlighting the importance of a phase evolution with amplitude on the thermoacoustic behavior of a combustion system.

Novelty and significance statement

This study shows the effects of chemical reactivity on azimuthal combustion instabilities by comparing two fuels (heptane and iso-octane) featuring close physical properties but different chemical characteristics. It is here inferred that the cetane numbers (which are significantly different for heptane and iso-octane) might be used as an index to distinguish different fuels with respect to their dynamical behaviors. The experimental data collected in two different test rigs (an annular combustor and a single-sector setup) are used to compare the dynamical behavior of the two fuels and interpret the differences observed. Flame dynamics data are then collected at high amplitude levels in the annular combustor MICCA with an original experimental procedure relying on injector staging. The results reveal an interesting behavior of the FDF phase with the modulation amplitude for iso-octane, explaining the difference in dynamics observed between the two fuels. These findings are generalized by considering the combined effects of gain and phase evolutions with the oscillation amplitude in a model problem. This problem is meant to exhibit in the simplest possible framework the effects of variations in gain and phase and demonstrate that the limit cycle observed may be reached by a system that is linearly unstable or by a system that is linearly stable but nonlinearly unstable.

By tentatively highlighting the link between the cetane number and the difference in dynamical behavior of two fuels and its impact on combustion instabilities, this work is significant because it stresses that new fuels (SAFs) should not be introduced without verification that they do not change the combustor operability and, in particular, do not give rise to undesirable oscillations.

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来源期刊

Combustion and Flame 工程技术-工程：化工

CiteScore

9.50

自引率

20.50%

发文量

631

审稿时长

3.8 months

期刊介绍： The mission of the journal is to publish high quality work from experimental, theoretical, and computational investigations on the fundamentals of combustion phenomena and closely allied matters. While submissions in all pertinent areas are welcomed, past and recent focus of the journal has been on: Development and validation of reaction kinetics, reduction of reaction mechanisms and modeling of combustion systems, including: Conventional, alternative and surrogate fuels; Pollutants; Particulate and aerosol formation and abatement; Heterogeneous processes. Experimental, theoretical, and computational studies of laminar and turbulent combustion phenomena, including: Premixed and non-premixed flames; Ignition and extinction phenomena; Flame propagation; Flame structure; Instabilities and swirl; Flame spread; Multi-phase reactants. Advances in diagnostic and computational methods in combustion, including: Measurement and simulation of scalar and vector properties; Novel techniques; State-of-the art applications. Fundamental investigations of combustion technologies and systems, including: Internal combustion engines; Gas turbines; Small- and large-scale stationary combustion and power generation; Catalytic combustion; Combustion synthesis; Combustion under extreme conditions; New concepts.