Smouldering combustion is an important and complex phenomenon that is central to a wide range of problems (hazards) and solutions (applications). A rich history of research in the context of fire safety has yet to be integrated with the more recent, rapidly growing body of work in engineered smouldering solutions. The variety of disciplines, materials involved, and perspectives on smouldering has resulted in a lack of unity in the expression of key concepts, terminology used, interpretation of results, and conclusions extracted. This review brings together theoretical, experimental, and modelling studies across both fire safety and applied smouldering research to produce a unified conceptual understanding of smouldering combustion. The review includes (i) a synthesis of nomenclature to generate a consistent set of terms for the underlying processes, (ii) an overview of smouldering emissions and emission treatment systems, (iii) a distillation of ignition and extinction research, including the role of heat losses and factors underpinning smouldering robustness, (iv) a review of the temporal and spatial distribution of heat and mass transfer processes as well as their solution using analytical and numerical methods, (v) a summary of smouldering chemical kinetics, and (vi) a summary of key gaps and opportunities for future research. Beyond merely review, a new conceptual model is provided that articulates similarities and critical differences between the two main smouldering systems: porous solid fuels and condensed fuels in inert porous media. A quantitative analysis of this conceptual model reveals that the evolution of a smouldering front, while a local process, is determined by a global energy balance that is cumulative in time and has to be integrated in space. As such, the fate of a smouldering reaction can be predicted before the effects of global heat exchange have affected the reaction. This approach is relevant to all forms of smouldering propagation (including fire safety), but it is particularly important when using smouldering as an engineered process that results in the positive use of the energy released by the smouldering reaction (applied smouldering). In applied smouldering, predicting the fate of a reaction ahead of time allows operators to modify the conditions of the process to maintain self-sustained smouldering propagation and thus fully harness the benefits of the reaction.

Timahdit oil shale was used as a porous medium to characterize the structure of a combustion front propagating with co-current downward air supply. A new 1D experimental device was first calibrated using a model porous medium. With the model porous medium, the front propagates as a plane and horizontal surface while using oil shale the front propagates as an inclined curved surface. The peak temperature was 1100 °C; despite the relatively large diameter of the cell (91 mm) and the good thermal insulation, the heat losses were estimated at 42% of the heat released by the combustion. The thickness of the front was characterized using a new gas micro-sampling system: the char oxidation and the carbonate decarbonation zones are approximately 10 and 15 mm thick, respectively. The oil formed during the pyrolysis is adsorbed in the porous medium in the course of the experiment, and expulsed from the cell by the end.

Co-current combustion front propagation in a bed of crushed oil shale (OS) leads to the production of liquid oil, of a flue gas and of a solid residue. The objective of this paper was to provide a detailed chemical characterization of Timahdit oil shale and of its smoldering combustion products. The amount of fixed carbon (FC) formed during devolatilization is measured at 4.7% of the initial mass of oil shale whatever the heating rate in the range 50-900 K min À1. The combustion of oil shale was operated using a mix of 75/25 wt. of OS/sand with an air supply of 1460 l min À1 m À2. In these conditions, not all the FC is oxidized at the passage of the front, but 88% only, with a partitioning of 56.5% into CO and the rest into CO 2. A calorific gas with a lower calorific value of 54 kJ mol À1 is produced. Approximately 52% of the organic matter from OS is recovered as liquid oil. The front decarbonates 83% of carbonates.

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This study investigated the interactive effects of temperature, residence time, and carrier gas flow rate on the liquid fuel production through the pyrolysis of waste polyethylene (WPE) in a bench-scale semi-batch reactor. To enhance the liquid fuel production, fifteen experiments were conducted based on a central composite design. The adaptive neural fuzzy model was adopted to establish the relationship between liquid fuel production and operating conditions. The R-squared value of the experimental and adaptive neural fuzzy model predicted that liquid fuel production was 0.9934. Four additional experimental results verified the adaptive neural fuzzy model's applicability. Subsequently, the genetic algorithm (GA) was adopted to optimize operating conditions to maximize liquid fuel production. The GA optimized operating conditions (temperature, residence time, and carrier gas flow rate) were: 488 • C, 20 min, and 20 mL/min. The liquid fuel under the optimal operating conditions was analyzed by Fourier-transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS). The liquid fuel had similar main functional groups as diesel. The components of the liquid fuel were mainly 1-alkenes and n-alkanes ranging from C7 to C36. The effects of operating conditions on liquid fuel fractions and mean molecular weight were also investigated.

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Due to the growing energy demands of the world and the rapid depletion of fossil fuels, it is necessary to study new energy sources. The waste have a great potential to be tapped, as besides being a raw material abundant, their use helps in reducing the level of environmental pollution and curbing the volume of waste in cities. However, one should know well the combustion process these waste before using them as fuel. Thus, Ignition behavior of combustible wastes was studied in a built fixed bed reactor. To provide a controlled thermal radiation for the ignition instant, a radiative heat flux is generated by a metal surface called a cone heater calibrated to establish the radiative heat flux density provided by a thermal resistance of 2 kW. The heat flux was 25 to 30 kWm2 over the top surface of the fuels. To validate the process, experiments with charcoal were performed varying the diameter of particles and air flow. After this, the polyethylene and human feces were analyzed. Their effects were investigated on the ignition time.