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Among the liquid fuels supporting the decarbonization of the energy conversion chain, alcohols play a key role. Mainly considered for engine application, their use in stationary systems designed for power generation is receiving considerable attention but requires further investigation. This work aims at demonstrating the feasibility of thermochemical conversion of low-molecular-weight alcohols, methanol, ethanol, and 1-butanol, in a small-scale unit exercised under moderate or intense low-oxygen dilution combustion conditions. The highly recirculated flow field configuration allows for the stabilization of the process over a wide range of reactor temperatures. The experimental campaign is carried out by varying the mixture equivalence ratio and the thermal power. The burner was exercised with different gas feeding configurations, namely, premixed and non-premixed. Experimental results are reported in terms of operational temperatures and pollutant emissions (CO and NO x ). For all of the fuels and thermal power, it was possible to reach NO x levels lower than 20 ppm and CO below 40 ppm for a wider range of the mixture equivalence ratio than hydrocarbon fuels. Despite similarities in the temperature profiles and CO emissions, NO x levels increase with the complexity of the alcohol molecules and their distribution is also a function of the injection strategy. Simulations in a perfectly stirred reactor and in a counterflow diffusion flame were performed to provide insights into the key factors controlling the NO x emission levels and distribution. Numerical results with a perfectly stirred reactor model show the role of NO x chemistry in determining the different emission levels of the three alcohols. On the other hand, simulations with a counterflow diffusion flame suggest that the separate reactant supply to the combustion chamber represents the key parameter in determining the experimental NO x distribution in the non-premixed mode.

Even in the presence of the formidable growth of renewable energy sources, advanced combustion processes have and will continue to have an irreplaceable role as a driving force for energy market. This is indeed motivated by the same huge amount of energy that can be conveniently stored in the form of energy carriers, made available from the renewable sources. The coupling of the appropriate combustion conversion technology with locally available biofuels certainly is among the most effective solutions, now on the table, to face the decarbonization challenge. In this framework, moderate or intense low oxygen dilution (MILD) combustion is among the best candidates to support the transition toward the net zero emission target. Indeed, due to its inherent features, it is highly fuel flexible and efficient, allowing for the utilization of whatever energy carrier can be considered in the decarbonization strategy. It is also characterized by an inherent low or absent pollutant emission. The novelty of this minireview is to highlight the relevance of the kinetics involved in MILD combustion processes with particular focus on biofuels, identifying invariant temperatures, relevant for process stabilization for any energy carrier. A critical evaluation of advantages and drawbacks of the use of raw bioliquids in MILD combustion conditions is reported. Then, challenges, open questions, and future perspectives on the use of biofuel in MILD combustion are discussed.

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