Novel Combustion Techniques for Clean Energy

This Special Issue contains successful submissions as an answer to the invitation to bring together research on advances in design, modeling, and performance of novel combustion techniques for clean energy. The following keywords described this Special Issue: combustion energy policy, efficiency, emissions, pollutants, and modeling.

The Special Issue constitutes an answer to current climate and civilization challenges, such as increased energy demand, higher levels of atmospheric pollutants, and global warming. Since the world community currently depends mainly on nonrenewable fossil fuels, which are unfriendly to the environment, developing novel techniques for clean combustion is highly urgent [1,2,3]. That is why growing efficiency requirements and limitations of pollutant emissions lead to the emergence of advanced energy technologies. Some of them are oxyfuel combustion [4], chemical-looping combustion (CLC) [5], and moderate or intense low-oxygen dilution (MILD) flameless combustion [6].

The submitted papers covered several different combustion aspects. The combustion characteristics and kinetics of coal, RDF, and their blends were experimentally investigated in a micro-thermal gravimetric analyzer at four different heating rates by Azam et al. According to the obtained results, as the RDF in blends increases, the reactivity of the blends increases, resulting in lower ignition temperatures and a shift in peak and burnout temperatures to a lower temperature zone [7]. As an optimal thermochemical process for obtaining valuable products, such as char, oil, or gas from waste tires, pyrolysis was investigated by Cepic et al., The analysis of pyrolytic oil and char showed that these products can be used as fuel [8]. Various kinds of pilot burners and fuels to examine the effects of their geometry and their location relative to the main burner of a real size combustor were experimentally investigated by Lee et al. The obtained results revealed that not only pilot burner flame shape but also the vertical location of the pilot burner from the main burner combustor had a significant effect on combustor durability [9].

The paper by Zhao et al. deals with arsenic emission from coal combustion power plants due to its high toxicity [10]. The developed model of arsenic volatilization model based on the ash fusion temperature, coal type, and combustion temperature during coal combustion allows describing the complex mechanisms that occur during combustion. Artificial intelligence (AI) techniques for the optimization of a 660 MWe supercritical power plant performance were applied by Ashraf et al. Several AI techniques and algorithms were presented and incorporated to formulate the step-wise methodology in the spirit of industry 4.0-data analytics [11,12]. A comprehensive simulator of fluidized and moving bed equipment (CeSFaMB) for modeling a fluidized bed CLC combustion process was applied by Zylka et al. Coal and biomass as fuels were considered in the study. On the other hand, ilmenite, i.e., a natural mineral, as an oxygen carrier was selected, which is an important issue considering safety and environmental reasons [13]. The model’s validation showed that the maximum relative errors between simulations and experiment results did not exceed 10% [14]. A study of visualization experiment on the influence of injector nozzle diameter on diesel engine spray ignition and combustion characteristics was presented by Tang et al. [15]. The authors examined three injectors with different nozzle orifice diameters to study the diesel spray, ignition, and flame-wall impingement visualization experiment. The authors obtained several exciting results. Among others, by processing the spray and combustion flame images, indicators like the numerical value well represented the fuel-air mixture quality and the total soot generation level under different experiment conditions [15].

All these activities are concise with the global scientific modeling trend, allowing better description and recognition of complex systems [16,17,18,19].

The concepts shown in this Special Issue do not cover all the possibilities of modern combustion techniques. However, they significantly contribute to developing and disseminating these technologies.