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The centrepiece of this research of is the Induction Heating Single Particle Burner (IHSPB), a newly developed experimental platform created to answer a fundamental question: what makes a single iron particle ignite? The IHSPB produces a hot, oxygen-rich coflow that suspends, heats, and exposes single particles to a controlled environment. It relies on electrostatic dispersion to isolate individual particles, uses induction heating to generate the thermal coflow, and employs high-speed cameras and hyperspectral pyrometry to observe ignition events and measure temperatures. This integrated approach makes it possible to directly connect ignition behaviour with particle properties and surrounding conditions, something that was previously very difficult to achieve in metal combustion research.

What controls iron ignition? Size, speed, temperature, and oxygen

Through an extensive series of experiments, the research reveals the factors that determine how and when iron particles ignite. Smaller particles ignite more easily because they heat up more quickly and reach ignition temperature faster due to their low thermal inertia. Particle motion is equally important, since slowly moving particles remain longer within the hot environment. This increased residence time gives them a greater chance of absorbing enough heat to ignite. Oxygen concentration also influences ignition probability, although not always in intuitive ways. A richer oxygen environment does improve the likelihood of ignition, but it does not significantly increase the maximum temperature reached by the burning particles. Likewise, raising the temperature of the surrounding coflow does not necessarily produce hotter particles; in fact, a slight decrease in maximum particle temperature is observed as the coflow temperature rises.

Porous iron from hydrogen reduction: a boost for ignition

Another important finding concerns the behaviour of iron produced via hydrogen-based reduction. This process creates porous particles whose internal voids allow hot oxidiser to reach deep into the material. As a result, heat transfer and oxygen accessibility improve, leading to better ignitability. Experiments carried out in a full-scale burner show that these reduced, porous particles perform just as well as untreated virgin iron powders. They provide similar thermal output, show comparable levels of NOx emissions, and burn with similar stability. After combustion, the dominant oxidation product is magnetite regardless of the initial particle type, which supports the idea of iron as a fully recyclable fuel within a circular energy system.

Modelling the fire: predicting ignition with thermal analysis

In addition to experimental observations, the research includes a detailed thermal model that predicts how particle temperature evolves during ignition. The model identifies a critical ignition temperature window between roughly 825 and 850掳C. Within this temperature range, iron particles can reach very high ignition probabilities, which depend on their size, porosity, and the surrounding oxygen concentration. The model provides a powerful tool for scaling up metal-fuel technologies and designing safe and reliable ignition systems for future applications.

Key contributions and their impact

This research makes three major contributions to the field. It introduces a new experimental platform that allows unprecedented control and visibility in single-particle combustion. It defines clear and quantitative ignition criteria for iron particles under controlled temperature and oxygen conditions. Finally, it demonstrates that recycled iron fuel performs just as effectively as virgin material, reinforcing the concept of iron as a sustainable and recyclable energy carrier. Together, these findings advance the scientific understanding of metal fuel combustion and strengthen the foundation needed to integrate iron into future clean energy systems.

Title of PhD thesis: . Supervisors: Prof. Philip de Goey, Dr. Yuri Shoshyn, and Dr. Giulia Finotello.