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Processes
Special Issues
Experiments and Diagnostics in Reacting Flows
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Experiments and Diagnostics in Reacting Flows

A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Energy Systems".

Deadline for manuscript submissions: closed (31 December 2025) | Viewed by 2064

Special Issue Editor

Dr. Tao Li

E-Mail Website
Guest Editor
Department of Mechanical Engineering, Reactive Flows and Diagnostics, Technical University of Darmstadt, Otto-Berndt-Str. 3, 64287 Darmstadt, Germany
Interests: laser combustion diagnostics; ammonia and hydrogen; turbulent combustion; solid fuels; CCS; metal combustion and nanoparticles
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

We are pleased to announce a Special Issue dedicated to the latest advancements in experiments and diagnostics in reacting flows. This Special Issue aims to showcase cutting-edge research in the field of combustion science, with a focus on innovative experimental techniques and diagnostic methods.

Key topics of interest for this Special Issue include, but are not limited to, the following:

  • The development and application of optical diagnostics
  • Experiments on laminar and turbulent flames
  • Coal and biomass combustion
  • Oxidation and reduction of metal fuels
  • Combustion of ammonia, hydrogen, and fuel blends
  • Diagnostics for harsh environments
  • Engine- and gas turbine-relevant processes
  • Near-surface and catalytic processes
  • Emission measurements and treatments
  • Novel concepts and devices.

We invite researchers from academia, industry, and government laboratories to contribute original research articles, review papers, and short communications that present novel experimental methodologies, groundbreaking findings, and significant advancements in the understanding of reacting flows. Submissions employing state-of-the-art experimental techniques, such as laser diagnostics, optical imaging, spectroscopic analysis, and advanced measurement technologies, are particularly encouraged.

The aim of this Special Issue is to foster interdisciplinary discussions, promote knowledge exchange, and facilitate collaborations among researchers working around the world in the broad field of combustion science. We welcome contributions from experts across various disciplines, including chemical engineering, mechanical engineering, aerospace engineering, physics, and chemistry.

Dr. Tao Li
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • laser diagnostics
  • thermo-chemcial process
  • combustion
  • flame

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Published Papers (2 papers)

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Research

39 pages, 10403 KB  
Article
High-Temperature Degradation of Hastelloy C276 in Methane and 99% Cracked Ammonia Combustion: Surface Analysis and Mechanical Property Evolution at 4 Bar
by Mustafa Alnaeli, Burak Goktepe, Steven Morris and Agustin Valera-Medina
Processes 2026, 14(2), 235; https://doi.org/10.3390/pr14020235 - 9 Jan 2026
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Abstract
This study examines the high-temperature degradation of Hastelloy C276, a corrosion-resistant nickel-based alloy, during exposure to combustion products generated by methane and 99% cracked ammonia. Using a high-pressure optical combustor (HPOC) at 4 bar and exhaust temperatures of 815–860 °C, standard tensile specimens [...] Read more.
This study examines the high-temperature degradation of Hastelloy C276, a corrosion-resistant nickel-based alloy, during exposure to combustion products generated by methane and 99% cracked ammonia. Using a high-pressure optical combustor (HPOC) at 4 bar and exhaust temperatures of 815–860 °C, standard tensile specimens were exposed for five hours to fully developed post-flame exhaust gases, simulating real industrial turbine or burner conditions. The surfaces and subsurface regions of the samples were analysed using scanning electron microscopy (SEM; Zeiss Sigma HD FEG-SEM, Carl Zeiss, Oberkochen, Germany) and energy-dispersive X-ray spectroscopy (EDX; Oxford Instruments X-MaxN detectors, Oxford Instruments, Abingdon, United Kingdom), while mechanical properties were evaluated by tensile testing, and the gas-phase compositions were tracked in detail for each fuel blend. Results show that exposure to methane causes moderate oxidation and some grain boundary carburisation, with localised carbon enrichment detected by high-resolution EDX mapping. In contrast, 99% cracked ammonia resulted in much more aggressive selective oxidation, as evidenced by extensive surface roughening, significant chromium depletion, and higher oxygen incorporation, correlating with increased NOx in the exhaust gas. Tensile testing reveals that methane exposure causes severe embrittlement (yield strength +41%, elongation −53%) through grain boundary carbide precipitation, while cracked ammonia exposure results in moderate degradation (yield strength +4%, elongation −24%) with fully preserved ultimate tensile strength (870 MPa), despite more aggressive surface oxidation. These counterintuitive findings demonstrate that grain boundary integrity is more critical than surface condition for mechanical reliability. These findings underscore the importance of evaluating material compatibility in low-carbon and hydrogen/ammonia-fuelled combustion systems and establish critical microstructural benchmarks for the anticipated mechanical testing in future work. Full article
(This article belongs to the Special Issue Experiments and Diagnostics in Reacting Flows)
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16 pages, 13161 KB  
Article
Experimental Assessment of the Effects of Gas Composition on Volatile Flames of Coal and Biomass Particles in Oxyfuel Combustion Using Multi-Parameter Optical Diagnostics
by Tao Li, Haowen Chen and Benjamin Böhm
Processes 2025, 13(6), 1817; https://doi.org/10.3390/pr13061817 - 8 Jun 2025
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Abstract
This experimental study examines the particle-level combustion behavior of high-volatile bituminous coal and walnut shell particles in oxyfuel environments, with a particular focus on the gas-phase ignition characteristics and the structural development of volatile flames. Particles with similar size and shape distributions (a [...] Read more.
This experimental study examines the particle-level combustion behavior of high-volatile bituminous coal and walnut shell particles in oxyfuel environments, with a particular focus on the gas-phase ignition characteristics and the structural development of volatile flames. Particles with similar size and shape distributions (a median diameter of about 126 µm and an aspect ratio of around 1.5) are combusted in hot flows generated using lean, flat flames, where the oxygen mole fraction is systematically varied in both CO2/O2 and N2/O2 atmospheres while maintaining comparable gas temperatures and particle heating rates. The investigation employs a high-speed multi-camera diagnostic system combining laser-induced fluorescence of OH, diffuse backlight-illumination, and Mie scattering to simultaneously measure the particle size, shape, and velocity; the ignition delay time; and the volatile flame dynamics during early-stage volatile combustion. Advanced detection algorithms enable the extraction of these multiple parameters from spatiotemporally synchronized measurements. The results reveal that the ignition delay time decreases with an increasing oxygen mole fraction up to 30 vol%, beyond which point further oxygen enrichment no longer accelerates the ignition, as the process becomes limited by the volatile release rate. In contrast, the reactivity of volatile flames shows continuous enhancement with an increasing oxygen mole fraction, indicating non-premixed flame behavior governed by the diffusion of oxygen toward the particles. The analysis of the flame stand-off distance demonstrates that volatile flames burn closer to the particles at higher oxygen mole fractions, consistent with the expected scaling of O2 diffusion with its partial pressure. Notably, walnut shell and coal particles exhibit remarkably similar ignition delay times, volatile flame sizes, and OH-LIF intensities. The substitution of N2 with CO2 produces minimal differences, suggesting that for 126 µm particles under high-heating-rate conditions, the relatively small variations in the heat capacity and O2 diffusivity between these diluents have negligible effects on the homogeneous combustion phenomena observed. Full article
(This article belongs to the Special Issue Experiments and Diagnostics in Reacting Flows)
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