Citation: Raho, B.; Colangelo, G.; Milanese, M.; de Risi, A. A Critical Analysis of the Oxy-Combustion Process: From Mathematical Models to Combustion Product Analysis. Energies 2022, 15, 6514. https:// doi.org/10.3390/en15186514 Academic Editor: Antonio Crespo Received: 19 July 2022 Accepted: 2 September 2022 Published: 6 September 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Review A Critical Analysis of the Oxy-Combustion Process: From Mathematical Models to Combustion Product Analysis Brenda Raho , Gianpiero Colangelo * , Marco Milanese and Arturo de Risi Department of Engineering for Innovation, University of Salento, SP per Monteroni, 73100 Lecce, Italy * Correspondence: gianpiero.colangelo@unisalento.it; Tel.: +39-0832-299440 Abstract: Fossil fuels are the most widely used resource for energy production. Carbon dioxide (CO 2 ) emissions are correlated with climate change, and therefore these emissions must be reduced in the future. It is possible by means of many different technologies, and one of the most promising seems to be oxyfuel combustion. This process, with oxygen and recirculating gas, produces a concentrated stream of CO 2 and water. In recent years, many scientists carried out research and studies on the oxyfuel process, but a sufficient level of knowledge was not yet reached to exploit the great potential of this new technology. Although such areas of research are still highly active, this work provides an overview and summary of the research undertaken, the state of development of the technology, and a comparison of different plants so far. Keywords: oxy-combustion; carbon capture cequestration; mathematical models; heat transfer; ignition; flame propagation; emissions; pilot project 1. Introduction From the industrial revolution to the first half of the 20th century, fossil fuels accounted for a significant fraction of global energy. Coal is regarded as the cheapest and most abundant resource, compared to all other fossil fuels, such as oil and natural gas [1,2]. During its fossilization process, it includes concentrations of hydrogen, oxygen, and other minerals, and its calorific value depends on their degree of concentration. Coal is one of the main resources for the energy industry, and its increasing use worldwide led to problems of emissions of a significant amount of CO 2 into the atmosphere, according to the general reaction: C n H m +(n + m4 )O 2 → nCO 2 + m/2 H 2 (1) CO 2 is then released into the environment in a volume equal to the amount of carbon involved in the reaction. For energy-related CO 2 emissions in 2021, 0.6 Gt of CO 2 emissions from fuel combustion were produced from coal, 0.7 Gt of CO 2 from oil, and 0.2 Gt of CO 2 from gas [3]. Coal, as the most abundant, available, and affordable fuel, is the most reliable and easily accessible energy source, making a crucial contribution to world energy security [4,5] and constituting one of the fundamental pillars for the technological and social devel- opment of populous nations, such as China and India. Renewable energies are being developed, but to date, fossil fuels alone account for about 81% of energy consumption. However, this is not in line with the European Union’s 2030 target of reducing emissions by 55% compared to 1990 and the 2050 target of becoming the first climate-neutral continent. For these reasons, there must be a leap toward near-zero emission technologies. There are different strategies for reducing CO 2 emissions, such as the use of renewable energies with solar or wind energies that directly produce the electricity that can be used, geothermic energies capable of storing hot water under the earth’s surface into ducts to be reused for heating homes or reusing it in generators for the production of electricity Energies 2022, 15, 6514. https://doi.org/10.3390/en15186514 https://www.mdpi.com/journal/energies