Frontiers in Fuels

4 papers from the IFRF 2025 have been published recently in special editions of the high- impact journals Measurement: Energy and Frontiers in Fuels. Details of the papers and abstracts are provided below.  As open-access articles, downloadable pdfs of the first 3 papers can be obtained from Measurement: Energy and Frontiers in Fuels, with the fourth paper due to be published soon.

There is still the opportunity for presenters at the conference to convert their material into open-access papers. The Frontiers in Fuels special edition remains open for the moment, and as advised previously, IFRF/Frontiers have a number of Article Publishing Charge awards we can make available to allow free publication. For the Measurement: Energy journal, the special edition is closed, but authors can still make late submissions to the journal as regular papers. In the application cover letter, authors should state the submission is intended for the IFRF 2025 special issue.

Please also note that we will be giving authors the same option to publish their work in high- impact journals for accepted abstracts at next year’s 2027 IFRF Conference.      

Leicher J, Giese A, Wieland C, ‘The role of combustion (and fuels) in a decarbonizing world’, Frontiers Fuels; 4;1748966, Mar 2026

Abstract– Access to energy is essential for the modern world, yet at the same time, anthropogenic greenhouse gas emissions are caused by energy-related activities across all sectors due to the predominance of fossil fuels. Today, most of the primary energy is still being provided by fossil fuels, with combustion being a key technology. In order to combat climate change, energy has to be decoupled from greenhouse gas emissions, with electricity and electrification being important pathways towards a net-zero energy system. However, electricity also has drawbacks as an energy carrier, especially in the context of large-scale energy storage, but also for applications requiring high energy densities. This, in addition to providing dispatchable power generation capacities for grid balancing and covering longer periods of reduced renewable power generation, is expected to result in significant contributions of synthetic and biogenic fuels to the energy landscape. The main purpose of combustion-based technologies will change from providing most of the primary energy to the energy system to complementing variable renewable energies when and where needed. This change of purpose has consequences for the directions of combustion research and development: while traditional topics such as equipment efficiency and pollutant emissions such as NOX will still be important, other topics such as more flexible and dynamic operation modes, hybrid applications and system integration will play a much bigger role in the future, along with the use of new fuels such as hydrogen or ammonia.

Mansouri, Z ‘New insights into iron fuel combustion: integrated in-situ and ex-situ diagnostics of ignition delay, melting–oxidation, disruptive phenomena and nanoparticle sizing’, Measurement: Energy; 8; 100073, Dec 2025

Abstract– Iron powders are attracting growing interest as recyclable energy carriers, offering high-temperature heat release during combustion and the potential for a carbon-free, closed energy cycle. However, key aspects remain insufficiently characterised, including single-particle combustion times over broad size ranges and the formation, size and concentration of nanoparticles during combustion. This study provides the first experimental investigation of irregular iron particles up to 250 μm in size. Combustion experiments were conducted using a controlled gas-supply, a tri-concentric tube burner with a motorised powder injector, and a quartz drop tube leading to a stainless-steel chamber for by-product collection and gas sampling. In-situ diagnostics employed a high-speed camera and a photomultiplier tube (PMT) module, while nanoparticle sizing used an aerodynamic particle sizer (APS). Ex-situ characterisation was performed by scanning electron microscopy (SEM). PMT data combined with particle-size analysis yielded new correlations for ignition delay and liquid-phase oxidation times. Ignition delay follows a second-order polynomial relationship, in contrast to the power-law behaviour reported for spherical particles, while liquid-phase oxidation shows simultaneous melting and oxidation and may be more accurately termed the melting-oxidation phase. Particle growth rates during this phase indicated oxidation rates of approximately 10–20 μm/ms. At later stages, oxide-shell rupture led to the ejection of molten nanoparticles, producing a bright secondary oxidation phase beyond the particle surface. SEM micrographs revealed a variety of disruptive events, including inter-particle collisions, impacts with the surrounding quartz tube, partial oxidation, micro-explosions and the development of surface cavities. Real-time APS measurements of exhaust emissions further demonstrated a unimodal nanoparticle distribution with a peak at 583 nm and evidence suggesting the presence of sub-500 nm particles.

Thekkedath N, Adendorff M, Mabic K, Iplik  E, Eckart S, Krause H, ‘Oxygen enrichment studies in hydrogen-natural gas burner: A pilot-scale study on emissions and thermal performance’, Measurement: Energy; 9; 100085, Mar 2026

Abstract– Decarbonising high-temperature industrial furnaces requires efficient and low-emission combustion strategies. Hydrogen and oxygen enhanced combustion (OEC) are promising alternatives to conventional air-fuel systems, but their combined impact on heat transfer, efficiency, and NOx emissions under practical operating conditions remains underexplored. This study explores the combustion behaviour of a commercial 200 kW burner operating with hydrogen, natural gas, and their blend under varying oxidizer oxygen concentrations, ranging from air-fuel combustion (21 % O2) to pure oxyfuel combustion (100 % O2). Conducted at pilot-scale, the research aims to understand how fuel composition and oxygen enrichment influence NOx emissions, heat transfer, wall temperature distribution, and flue gas energy losses. The results reveal that oxygen enrichment plays a dominant role in shaping combustion performance, while the choice of fuel (whether hydrogen, natural gas, or a blend) has a comparatively minor effect. Oxygen enrichment significantly improved heat transfer and reduced flue gas losses, resulting in thermal efficiency increase from ~45 % in air-fuel to ~80 % in oxyfuel combustion. Burner configuration such as delayed combustion and flameless combustion strongly influenced temperature uniformity and NOx emissions, where flameless configuration resulted in enhanced mixing, reduced thermal stratification and lower NOx compared to simple delayed combustion. Under delayed and flameless oxyfuel conditions, NOx emissions dropped below 2 mg/MJ for both fuels. With this study, a reduction of ~90 % in NOx emission while moving from air-fuel to oxyfuel condition was observed for natural gas and hydrogen. Interestingly, at flameless combustion operation, hydrogen showed lower NOx emission than natural gas. Constant-temperature studies confirmed that nitrogen availability, rather than flame temperature, dominated NOx formation under flameless conditions. These findings highlight the potential of oxyfuel and OEC to deliver cleaner and more energy-efficient operation in industrial furnaces, regardless of fuel composition. The insights gained are particularly relevant for industries transitioning toward hydrogen-based energy systems and seeking to meet decarbonisation, NOx emission and efficiency targets.

Heeley A, Finney K, Szuhánzski J, Gheit, A Hee j L, Pourkashanian M, ‘Decarbonisation of Industrial Heating Processes using Hydrogen Cofiring, Frontiers Fuels; accepted April 2026

Abstract – This paper aims to evaluate whether cofiring hydrogen and natural gas mixtures are suitable as industrial furnace fuels and to identify further characteristics that need more detailed understanding to enable successful implementation of fuel switching. The outcome of this research and further investigations will ensure that the full capability of fuel switching becomes available to energy-intensive process operators. Co-firing natural gas and hydrogen leading to dedicated hydrogen combustion are pathways to decarbonise industrial processes and can enable future hydrogen utilisation and interoperability with fossil fuels. The key observations from pilot-scale industrial furnace trials at the University of Sheffield Energy Innovation Centre included: (1) Radiant heat flux depended primarily upon furnace temperature with no relationship measured with varying fuel composition (2) The chamber geometry, radiant heat flux from solid surfaces and control temperature achieved were more significant to the furnace heat exchange than the fuel mixture (3) Firing with natural gas and hydrogen mixtures did not affect furnace temperature or uniformity beyond variations attributable to other process conditions (4) Gas temperatures and species were distributed uniformly within the fully mixed atmosphere, which represented ⅔ of the chamber volume (5) Gas temperature and species distributions were not affected by fuel composition, therefore measurements from the centre of the chamber were representative of the mean conditions in the fully mixed atmosphere (6) CFD modelling of the gas and temperature distributions within the furnace enabled thermodynamic and fluid dynamic characteristics to be understood and afforded confidence in experimental and model outcomes Co-firing hydrogen with natural gas and dedicated hydrogen firing as an interoperable fuel to substitute for natural gas could be a key means to decarbonise hard to abate foundation industries, whilst making continued use of existing capital assets. This investigation demonstrated that understanding hydrogen firing and co-firing will enable the mitigation of perceived risks arising from decarbonisation of energy-intensive industries with low and zero carbon fuels.