MDPI - Publisher of Open Access Journals

14 pages, 4100 KB

Open AccessArticle

The Propagation Characteristics of Turbulent Expanding Flames of Methane/Hydrogen Blending Gas

by Haoran Zhao, Chunmiao Yuan, Gang Li and Fuchao Tian

Energies 2024, 17(23), 5997; https://doi.org/10.3390/en17235997 - 28 Nov 2024

Cited by 3 | Viewed by 999

In the present study, the effect of hydrogen addition on turbulent flame propagation characteristics is investigated in a fan-stirred combustion chamber. The turbulent burning velocities of methane/hydrogen mixture are determined over a wide range of hydrogen fractions, and four classical unified scaling models (the Zimont model, Gulder model, Schmidt model, and Peters model) are evaluated by the experimental data. The acceleration onset, cellular structure, and acceleration exponent of turbulent expanding flames are determined, and an empirical model of turbulent flame acceleration is proposed. The results indicate that turbulent burning velocity increases nonlinearly with the hydrogen addition, which is similar to that of laminar burning velocity. Turbulent flame acceleration weakens with the hydrogen addition, which is different from that of laminar flame acceleration. Turbulent flame acceleration is dominated by turbulent stretch, and flame intrinsic instability is negligible. Turbulent stretch reduces with hydrogen addition, because the interaction duration between turbulent vortexes and flamelets is shortened. The relative data and conclusions can provide useful reference for the model optimization and risk assessment of hydrogen-enriched gas explosion. Full article

(This article belongs to the Special Issue Storage, Transportation and Use of Hydrogen-Rich Fuel)

► Show Figures

Figure 1

11 pages, 11677 KB

Open AccessArticle

Mechanism of Spontaneous Acceleration of Slow Flame in Channel

by Andrey Yarkov, Ivan Yakovenko and Alexey Kiverin

Fire 2024, 7(10), 362; https://doi.org/10.3390/fire7100362 - 10 Oct 2024

Cited by 1 | Viewed by 1239

Abstract

This paper is devoted to the numerical analysis of the spontaneous acceleration of a slow flame in a semi-closed channel. In particular, the flow development in the channel ahead of the propagating flame is analyzed. The applied detailed numerical model allows the clear observation of all features intrinsic to the reacting flow evolution in the channel, including the formation of perturbations on the scale of the boundary layer and their further development. In all considered cases, perturbations of the boundary layer emerge in the early stages of flame acceleration and decay afterward. The flow stabilizes more rapidly in a narrow channel, where the velocity profile is close to the Poiseuille profile. At the same time, the compression waves generated in the reaction zone travel along the channel. The interaction between compression waves in the area of combustion products can lead to the formation of shock waves. The effect of shock waves on the flow in the fresh mixture causes an increase in the flame area and a corresponding flame acceleration. In addition, shock waves trigger boundary-layer instability in wide channels. The perturbations of the boundary layer grow and evolve into vortexes, while further vortex–flame interaction leads to significant flame acceleration. Full article

(This article belongs to the Special Issue Impacts of Combustion and Thermo-Chemistry)

► Show Figures

Figure 1

16 pages, 5933 KB

Open AccessEditor’s ChoiceArticle

Learning Flame Evolution Operator under Hybrid Darrieus Landau and Diffusive Thermal Instability

by Rixin Yu, Erdzan Hodzic and Karl-Johan Nogenmyr

Energies 2024, 17(13), 3097; https://doi.org/10.3390/en17133097 - 23 Jun 2024

Cited by 1 | Viewed by 1525

Abstract

Recent advancements in the integration of artificial intelligence (AI) and machine learning (ML) with physical sciences have led to significant progress in addressing complex phenomena governed by nonlinear partial differential equations (PDEs). This paper explores the application of novel operator learning methodologies to unravel the intricate dynamics of flame instability, particularly focusing on hybrid instabilities arising from the coexistence of Darrieus–Landau (DL) and Diffusive–Thermal (DT) mechanisms. Training datasets encompass a wide range of parameter configurations, enabling the learning of parametric solution advancement operators using techniques such as parametric Fourier Neural Operator (pFNO) and parametric convolutional neural networks (pCNNs). Results demonstrate the efficacy of these methods in accurately predicting short-term and long-term flame evolution across diverse parameter regimes, capturing the characteristic behaviors of pure and blended instabilities. Comparative analyses reveal pFNO as the most accurate model for learning short-term solutions, while all models exhibit robust performance in capturing the nuanced dynamics of flame evolution. This research contributes to the development of robust modeling frameworks for understanding and controlling complex physical processes governed by nonlinear PDEs. Full article

(This article belongs to the Special Issue Towards Climate Neutral Thermochemical Energy Conversion)

► Show Figures

Figure 1

22 pages, 8677 KB

Open AccessArticle

Analysis of Pressure Fluctuation Characteristics of Central Swirl Combustors Based on Empirical Mode Decomposition

by Xuhuai Wang, Xiang Zhang, Chen Yang, Hao Li and Yong Liu

Sensors 2022, 22(15), 5615; https://doi.org/10.3390/s22155615 - 27 Jul 2022

Cited by 3 | Viewed by 1878

Abstract

In order to study the characteristics of pressure fluctuation during unstable combustion, experimental studies had been conducted on the mechanism model of the swirl combustor and the industrial swirl combustor. The signal of dynamic pressure, heat release rate, and the high-speed flame image in the two combustors were synchronously collected by using dynamic pressure sensors, a photoelectric sensor, and a high-speed camera under normal temperature and pressure. After empirical mode decomposition of the dynamic pressure signal, several intrinsic mode functions were obtained. It was found that the pressure pulsation energy is concentrated in the first three order intrinsic mode function. Through fast Fourier transform spectrum calculation, it was found that the first three order intrinsic mode function pulsation can characterize the changes of heat release rate and air flow pulsation under cold state and flame instability. It showed that the decomposition of the dynamic pressure in the combustor by this method can obtain the main physical processes in its connotation, and provide data processing methods for the induction mechanism of oscillating combustion and combustion diagnosis in an industrial combustor test. Full article

(This article belongs to the Section Physical Sensors)

► Show Figures

Figure 1

8 pages, 1625 KB

Open AccessArticle

An Elementary Model for a Self-Accelerating Outward Propagating Flame Subject to the Rayleigh–Taylor Instability: Transition to Detonation

by Leonid Kagan and Gregory Sivashinsky

Fluids 2020, 5(4), 196; https://doi.org/10.3390/fluids5040196 - 31 Oct 2020

Cited by 5 | Viewed by 2191

Abstract

Within the Boussinesq approximation, an elementary model for the deflagration-to-detonation transition triggered by self-acceleration of an expanding flame is formulated and explored. The self-acceleration is sustained by the intrinsic Rayleigh–Taylor instability until the Deshaies–Joulin deflagrability threshold is reached, followed by an abrupt transition to detonation. Emergence of the threshold is caused by positive feedback between the accelerating flame and the flame-driven pressure shock that results in the thermal runaway when the flame speed reaches a critical level. The model offers a simple mechanism that may be responsible for the transition to detonation in thermonuclear supernovae. Full article

(This article belongs to the Special Issue Analytical and Computational Fluid Dynamics of Combustion and Fires [dedicated to Prof. Vitaly Bychkov (1968–2015) of Umea University, Sweden])

► Show Figures

Figure 1

16 pages, 9456 KB

Open AccessArticle

Study on the Effect of Flame Instability on the Flame Structural Characteristics of Hydrogen/Air Mixtures Based on the Fast Fourier Transform

by Fu-Sheng Li, Guo-Xiu Li, Yan-Huan Jiang, Hong-Meng Li and Zuo-Yu Sun

Energies 2017, 10(5), 678; https://doi.org/10.3390/en10050678 - 12 May 2017

Cited by 20 | Viewed by 4902

Abstract

In this study, the effect of flame intrinsic instability on the flame structural characteristics of hydrogen/air mixtures premixed at various equivalence ratios were experimentally investigated from the macroscopic and microscopic perspectives, respectively. The correlation degree and the relative deformation degree were defined to quantitatively study the global flame structural characteristics. Peak detection was used to capture the characteristic length of the flame and fast Fourier transform was adopted to study the components of the fluctuation of the flame front. The results show that with the development of flames, the wrinkles in the flame front increase and the correlation degree of the flame decreases. The relative deformation degree of the flame first decreases and then increases. When the equivalence ratio is 0.6, the average characteristic length initially exhibits an increasing trend, followed by a decreasing trend. The average characteristic length scale gradually increases, and the growth rate gradually decreases when the equivalence ratio ranges from 0.70 to 0.99. With the increase in the wavenumber, the amplitude of the corresponding disturbance exhibited an increasing trend followed by a decreasing one. With the development of the flame, the maximum amplitude of the disturbance shows a reverse trend, i.e., first decreasing and then increasing. The disturbances with smaller wavelengths could be further developed. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

► Show Figures

Figure 1

17 pages, 1346 KB

Open AccessArticle

Research on Cellular Instabilities of Lean Premixed Syngas Flames under Various Hydrogen Fractions Using a Constant Volume Vessel

by Hong-Meng Li, Guo-Xiu Li, Zuo-Yu Sun, Yue Zhai and Zi-Hang Zhou

Energies 2014, 7(7), 4710-4726; https://doi.org/10.3390/en7074710 - 22 Jul 2014

Cited by 15 | Viewed by 6720

Abstract

An experimental study of the intrinsic instabilities of H₂/CO lean (φ = 0.4 to φ = 1.0) premixed flames at different hydrogen fractions ranging from 0% to 100% at elevated pressure and room temperature was performed in a constant volume vessel using a Schlieren system. The unstretched laminar burning velocities were compared with data from the previous literature and simulated results. The results indicate that excellent agreements are obtained. The cellular instabilities of syngas-air flames were discussed and critical flame radii were measured. When hydrogen fractions are above 50%, the flame tends to be more stable as the equivalence ratio increases; however, the instability increases for flames of lower hydrogen fractions. For the premixed syngas flame with hydrogen fractions greater than 50%, the decline in cellular instabilities induced by the increase in equivalence ratio can be attributed to a reduction of diffusive-thermal instabilities rather than increased hydrodynamic instabilities. For premixed syngas flames with hydrogen fractions lower than 50%, as the equivalence ratio increases, the cellular instabilities become more evident because the enhanced hydrodynamic instabilities become the dominant effect. For premixed syngas flames, the enhancement of cellular instabilities induced by the increase in hydrogen fraction is the result of both increasing diffusive-thermal and hydrodynamic instabilities. Full article

► Show Figures

Figure 1

Search Results (7)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI

Saved Queries

Search Filter Reset All

Years

Feature Papers

Subjects

Journals

Article Types

Countries / Regions

Search Results (7)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI