Chemical Investigation of an Oxy-steam MILD Combustion Process Utilizing Hydrogen Peroxide

Adaptation of hydrogen fuel for heating applications presents several challenges, particularly thermal NO _x production and reduced radiative heat transfer. Oxy-steam combustion in the MILD (moderate or intense low-oxygen dilution) regime addresses both challenges by removing the nitrogen from the oxidizer and introducing steam as a diluent that can increase thermal radiation. However, both steam and pure oxygen are required to achieve these conditions. This study investigates the feasibility of using hydrogen peroxide (H₂O₂) as an oxygen and steam carrier for hydrogen-fuelled heating applications, as when heated, H₂O₂ decomposes into water and oxygen. Batch reactor, perfectly stirred reactor, and opposed flow laminar flamelet simulations are conducted over a range of representative conditions to investigate the combustion characteristics of this system. Reactor ignition is found to be enhanced with an increase in H₂O₂ mass fraction within the oxidizer mixture. However, even at a high H₂O₂ content, preheating does not allow significant decomposition of the H₂O₂ into an appropriate radical pool to promote ignition within furnace-relevant residence times, suggesting that external preheating or cracking may be required for practical applications. Fundamentally, H₂O₂-steam flames without precracking show unique flame structures when compared to the equilibrium/cracked mixtures in MILD conditions, similar to those observed in conventional combustion of H₂O₂. A double-peak structure of heat release is observed in the H₂O₂-steam cases, where one peak correlates with the exothermic decomposition of H₂O₂, and the second peak corresponds to the primary combustion process with the fuel. That finding suggests that there is a significant heat addition into the flow that comes from the decomposition process that cannot be neglected in the reactor analysis, and can contribute to low temperature ignition in these conditions.