Scientists from the Kutateladze Institute of Thermophysics of the Siberian Branch of the Russian Academy of Sciences, have discovered a way to control the combustion of mixtures of methane, ammonia and hydrogen with the use of weak electric fields. Their discovery could become an important step towards creating innovative combustion chambers in which flame stability and purity will be regulated by a special electric control panel.
The researchers from Novosibirsk turned their attention to hydrogen-based fuel mixtures while studying new options for decarbonizing the energy sector. They found that methane combined with hydrogen can serve as a transition fuel, while ammonia, which does not emit CO₂ upon combustion, can become as a convenient hydrogen carrier. However, these fuels have drawbacks: low combustion rates, ignition difficulties and the risk of emitting nitrogen oxide. This is why the scientists proposed overcoming these drawbacks by using the flame’s ability to conduct electric current. This is made possible by the presence of ions in the combustion zone. Experiments showed that even a relatively low voltage can alter the shape and stability of the flame, as well as temperature distribution. Plus, it requires only a few watts of energy, which is negligible compared to the power released during fuel combustion.
In order to test this hypothesis, the researchers conducted a series of experiments with diffusion flames. The mixtures were fed through a miniature burner, with electrodes positioned either transversely or along the stream. In the first case, the flame bent and deformed while maintaining a laminar, stable and orderly combustion regime. This made it possible to expand the reaction zone and reduce the flame length. In the second case, a more interesting effect was observed: upon reaching a certain voltage, the flame which had previously been hovering above the burner would settle back down. This was accompanied by a hundredfold increase in the current through the flame. The scientists also observed an intermediate regime, in which part of the torch was pressed against the burner and some of it continued to hover.
To examine the internal structure of the flame, the researchers used Gilbert optics, which produces clear images of temperature and density fluctuations. Using this method, they were able to reconstruct the heat distribution and gas composition in the combustion zone. They found that most of the nitrogen oxide emissions are formed in the lean portion of the mixture, where the reaction reaches completion. When exposed to an electric field, the flame shifted toward the jet axis and expanded, indicating a change in the position and size of the oxidation region.
The researchers were particularly interested in ammonia-hydrogen mixtures. Ammonia itself ignites poorly and produces a flame with very low conductivity. However, experiments showed that adding 30% hydrogen leads to drastic changes: the flame begins to exhibit pronounced electrical properties and becomes field-controlled. Although the current strength remains significantly lower compared to methane-hydrogen mixtures, this level is sufficient to use the effect to control the combustion process.
This way, the researchers demonstrated that an electric field can become an effective tool for controlling the combustion of carbon-free fuel mixtures. This is particularly important in the energy sector: electric control could make it possible to operate future gas turbines and boilers without harmful emissions while maintaining high efficiency.
