Experimental and advanced numerical characterization of toluene fires

• Implementation of detailed kinetic mechanism in computational fluid dynamics (CFD). • Quantification of mass burning rate, heat release rate, and temperature distribution. • Comparison of experimental (cone calorimeter) and numerical (CFD) data. • Identification of the main areas characterizing the flame structure of toluene. • Production of hybrid approach optimizing accuracy, flexibility, and computation costs. Toluene is employed in a variety of industrial applications worldwide being a largely adopted solvent and an active element in many products used in pharmaceutical, cosmetic, construction, paint, ink, and other industries. More recently, the use of this compound has been also suggested as a hydrogen carrier because of the implementation of the liquid organic hydrogen carrier (LOHC) strategy within the framework of the energy transition. In addition, the determination of the physico-chemical behavior of toluene can provide a positive impulse also for the representation of surrogate mixtures suitable for gasoline and diesel. The direct use of toluene as well as its consideration as a component of surrogate mixtures for fossil- and bio-derived fuels promotes accurate evaluations of its safety properties. In this work, an experimental campaign based on a modified procedure employing a cone calorimeter for the evaluation of mass and thermal properties of liquid toluene exposed to fire conditions is presented and compared with a numerical study employing a computational fluid dynamic (CFD) approach. The impacts of the kinetic sub-models were tested by comparing the estimated temporal and spatial distributions of temperature and exhaust composition assuming a reduced mechanism, a single-step infinitely fast reaction, and a hybrid approach. An excellent agreement among the implemented approaches was found, providing a robust database and model for the characterization of accidental scenarios involving toluene. Further insights on the flame structures and the phenomena ruling the pool fire of toluene were obtained, based on the utilization of the dedicated kinetic mechanism in CFD analysis. The strategies and assumptions posed to combine experimental and detailed numerical analyses can be also intended as a possible procedure for the characterization of the consequence analysis related to accidental releases of liquid substances.