Methane

20 pages, 2668 KiB

Open AccessFeature PaperArticle

Influence of Annular Flow Area and a 30-Degree Impingement Angle on Methane/Oxygen Diffusion Flame Stability

by Joshua M. Hollingshead, Makayla L. L. Ianuzzi, Alexandra C. Risha, Jeffrey D. Moore and Grant A. Risha

Methane 2025, 4(3), 16; https://doi.org/10.3390/methane4030016 - 2 Jul 2025

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Abstract

This work examined the effects of secondary annular flow area on flame stability in an experimental diffusion flame burner. The burner was composed of a horizontally mounted, rectangular chamber that utilized a retractable spark plug for ignition and an inverse coaxial injector. The primary and secondary gaseous reactants were oxygen and methane, respectively. Three injectors were assessed to have a fixed primary flow area and secondary flow impingement angle of 30 degrees with the primary flow and distinct secondary annular flow areas. Resultant flames and flame standoff distances were recorded via optical windows aligned parallel to the burner axis. Flame stability regime maps were generated based on the reactant equivalence ratio, the methane Reynolds number, and the injector secondary annular flow area. Results showed that among the injectors, the greater the secondary annular flow area with an impingement angle, the better the likelihood of generating a stable, anchored, fuel-rich diffusion flame for hydrogen production over the largest range of Reynolds numbers. As the secondary flow area decreased, stable diffusion flames transitioned from existing at highly turbulent flows to experiencing near-blowoff or no ignition under the same conditions. Secondary annular flow area significantly influences the location and range of stable, anchored methane/oxygen diffusion flames. Full article

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22 pages, 2172 KiB

Open AccessArticle

High-Precision Methane Emission Quantification Using UAVs and Open-Path Technology

by Donatello Fosco, Maurizio De Molfetta, Pietro Alexander Renzulli, Bruno Notarnicola and Francesco Astuto

Methane 2025, 4(3), 15; https://doi.org/10.3390/methane4030015 - 26 Jun 2025

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Abstract

Quantifying methane (CH₄) emissions is essential for climate change mitigation; however, current estimation methods often suffer from substantial uncertainties, particularly at the site level. This study introduces a drone-based approach for measuring CH₄ emissions using an open-path Tunable Diode Laser Absorption Spectroscopy (TDLAS) sensor mounted parallel to the ground, rather than in the traditional nadir-pointing configuration. Controlled CH₄ release experiments were conducted to evaluate the method’s accuracy, employing a modified mass-balance technique to estimate emission rates. Two wind data processing strategies were compared: a logarithmic wind profile (LW) and a constant scalar wind speed (SW). The LW approach yielded highly accurate results, with an average recovery rate of 98%, while the SW approach showed greater variability with increasing distance from the source, although it remained reliable in close proximity. The method demonstrated the ability to quantify emissions as low as 0.08 g s⁻¹ with approximately 4% error, given sufficient sampling. These findings suggest that the proposed UAV-based system is a promising, cost-effective tool for accurate CH₄ emission quantification in sectors, such as agriculture, energy, and waste management, where traditional monitoring techniques may be impractical or limited. Full article

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13 pages, 5123 KiB

Open AccessFeature PaperArticle

Biogas Purification by Intensified Absorption in a Micromixer

by Tarsida N. Wedraogo, Souhila Djerid, Jing Wu and Huai Z. Li

Methane 2025, 4(3), 14; https://doi.org/10.3390/methane4030014 - 25 Jun 2025

Viewed by 237

Abstract

Biogas is a renewable energy source produced by anaerobic digestion of organic waste. It can be upgraded to bio-methane by removing carbon dioxide, water and impurities. The present work focuses on carbon dioxide removal using both physical and chemical absorption in a micromixer. The absorption efficiency in the micromixer was studied under various conditions of co-current gas–liquid flow. With physical absorption, 25% of carbon dioxide could be removed from the biogas stream (with a liquid flowrate of 40 mL/min and a gas flowrate of 25 mL/min). In absorption with a chemical reaction, up to 88% of the carbon dioxide was eliminated with a catalyst concentration of 77.4 mol·m⁻³. In both cases, the space time was below 3 s. Liquid-side mass transfer coefficients as large as 3.5 s⁻¹ were achieved, which is at least two orders of magnitude higher than those reported in conventional absorbers. Full article

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Methane, Volume 4, Issue 3 (September 2025) – 3 articles

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