Turbulent Ignition Regimes in 20 L Explosion Vessel: CFD Simulations

The understanding of the ignition process is important for many practical and fundamental applications including safety, chemical conversion, flame stabilization, and internal combustion engines operation. The ignition process can be influenced by many factors, including the pre-ignition turbulence level. Turbulence can generally be generated intentionally by the introduction of gases into the combustion chamber, but it can also occur unintentionally, for example by a sudden release of gases into the atmosphere as a result of an accident. Through the small scale 20 L CFD simulations of the ignition process of a stoichiometric methane-air mixture at different ignition energies and levels of turbulence, the present work aims to create a simple operational map that correlates the ignition energy with the degree of turbulence to understand in which areas flame propagation is successful and in which it is not. Such a tool may be useful both for evaluating the operation of internal combustion engines, where ignition and flame propagation are desired phenomena, and for a preliminary assessment of the risk and probability of ignition. This approach may also be applied in the future to other gaseous (as in the case of hydrogen), liquid, or solid systems

Preliminary Risk Evaluation of Methanol/water Storage in Fuel Cell Integrated Systems for Onboard Applications

In this work, a preliminary risk evaluation of the methanol/water storage in fuel cell integrated systems is performed. The system which couples methanol steam reforming and the fuel cell to generate electricity is considered as a solution in several industrial projects for onboard applications. The challenge of such a system is to control the thermal loads to operate under fully autothermal conditions, recycling the dissipated heat from the fuel cell to preheat and evaporate the reactant mixture. To implement these systems, safety issues must be identified and minimized. Considering the autothermal operating conditions of the methanol steam reforming unit, the water/methanol ratio was set at 3. Under these conditions, the mixture is safer than pure methanol in terms of flammability and toxicity, but not yet inherently safe. Starting from the generation of a hole on the storage tank as initiating event, the consequence analysis as well as some preliminary risk considerations is performed by using empirical models. In this work, the focus was on the effects of a vapour cloud explosion and comparisons were made between a methanol-water solution, pure methanol, and gasoline, used in the conventional internal combustion engine

Oxidative Methanol Reforming for Hydrogen-fed HT-PEMFC: Applications in the Naval Sector

CO2 emissions from marine transport contributes to about 3% of the overall greenhouse gas (GHG) emissions. International regulations and the Paris agreement require to cut them by 50% by 2050. Moreover, the latest International Maritime Organization (IMO) regulations strongly limits SOx emissions. One of the most promising alternatives to conventional fuels is hydrogen, which can meet the environmental targets set by the international community, if coupled with H2-fed PEM fuel cells (PEMFCs) due to their high efficiency. On-board H2 production starting from a suitable liquid source can be competitive compared to compressed/liquid H2. Methanol (MeOH) is a suitable candidate due to: high H2 content, relatively low reforming temperature, absence of sulfur compounds, and the possibility of being obtained from renewable materials. This work investigates the coupling of autothermal oxidative MeOH steam reforming (OSRM) with high temperature PEMFCs (HT-PEMFCs). The latter outperforms low temperature (LT) PEMFCs, concerning resistance to CO poisoning and high operating temperature, allowing an integrated OSMR reactor – HT-PEMFC and energetically self-sustaining system. The integrated system has also been designed considering also MeOH storage tank and the main auxiliary units, and the dimensions appear very interesting for the installation on board of ships, also in terms of emissions

TURBULENT FLAME PROPAGATION OF DUSTS AND DUST MIXTURES

The present work aims at studying the explosive phenomena of dust and dust mixtures to get insights into the driving mechanisms and the explosion features affecting the flame propagation and then the course of explosion. This will be achieved by means of an extensive experimental and simulative study. The major activities that will be carried out during my PhD period are: 1. Modelling of the flame propagation of combustible dust/air and hybrids; 2. Understanding of all the issues of the standard equipment; 3. Investigation of flame propagation features and key parameters (physical, operating, chemical) controlling the flame velocity The activities are strictly related to each other. The formulation and application of a Mallard-Le Chatelier-inspired theoretical flame propagation unveils that the flame laminar burning velocity depends on several parameters that take into account the thermal behavior of the dust subjected to heating starting from the flame front to the colder layers. As a consequence, a thermal analysis of any combustible dust seems to be of crucial importance in order to fully understand the explosive behavior both in terms of intrinsic (laminar) burning velocity but also in terms of flammability/explosibility parameters. Moreover, the analysis of the thermal behavior of combustible dusts can be useful to explain a series of synergistic effects that arise in dust mixtures that can sometimes be more dangerous than pure dusts, as found by Sanchirico et al. (2018). Moreover, starting from a deep study of the fundamentals of the flame propagation of dusts and dust mixtures, the main issues related to standard test vessels will be investigated and evaluated. In particular, CFD simulations of the 20 L vessel with dust mixtures and 1 m3 sphere for the measurements of Pmax/(dP/dt)max/KSt will be developed to understand their ability dispersing a uniform dust cloud and generating a uniform turbulence field. In both the vessel, the effect of the pre-ignition turbulence level on the turbulent combustion regime and on the deflagration index was also investigated. Moreover, the overdriving phenomenon as well as the thermal effects due to the pyrotechnic ignitors explosion were assessed in both the vessel and relative to combustible dusts characterized by homogeneous or heterogeneous flame propagation. Finally, we tried to formulate a procedure to fully understand the flame propagation mechanism of the investigated dust, which standard test vessel is better to use to have conservative and reliable evaluations of explosion parameters and which issues have to be considered during testing

Flash point of biodiesel/glycerol/alcohol mixtures for safe processing and storage

Mixtures of biodiesel, glycerol, and ethanol/methanol are commonly processed and stored in biodiesel production. In this work, non-ideal models are used to calculate the Flash Points (FPs) of binary and ternary mixtures, using data available from different feedstocks. Despite the fact that biodiesel is considered safer than common diesel fuels, results show a synergistic effect of biodiesel/methanol and biodiesel/ethanol mixtures, resulting in a reduction of the flash point of mixtures to values lower than the ones of pure compounds. Most soluble ternary mixtures were found flammable, the only exception being mixtures with a relatively lower alcohol content (45% mol. ethanol or 42% methanol) at temperature lower than 303 K. Accidental increase in temperature can cause domino effect, due to the higher solubility and the formation of new flammable ternary mixtures

Prevention and Control of the Spread of Pathogens in a University of Naples Engineering Classroom through CFD Simulations

The design of ventilation and air conditioning systems in university classrooms is paramount to ensure students’ correct number of air changes per hour and an optimal thermal profile for their comfort. With the spread of the COVID-19 virus, these systems will inevitably need to evolve to cope with the current virus and any new airborne pathogens. The aim of this study is to analyze the quality of the ventilation system and the importance of the use of PPE in Lecture Hall C of the University of Naples Federico II compared to the premises in Piazzale Tecchio. After dimensioning the lecture theatre with the Autodesk software AutoCAD 2021, CFD simulations were carried out with the Computational Fluid Dynamics program Ansys 2021 R2. To study the trajectory of virus droplets released by a potentially infected student in the center of the classroom, the multispecies model was used, with carbon dioxide serving as the tracer gas for the virus cloud. After determining the CO2 contour zones at fifteen-minute intervals for a total duration of two hours, the probability of infection was calculated using the Wells–Riley equation

Humic acids on fire? Physico-chemical, thermal, flammability features and extraction process of different humic acids in support of their possible applications

: Humic acids (HA) consist in a multitude of heterogeneous organic molecules surviving the biological and chemical degradation of both vegetal and animal biomasses. The great abundance and chemical richness of these residues make their valorisation one of the most promising approaches to move towards a circular economy. However, the heterogeneity of the biomass from which HA are extracted, as well as the production process, significantly affects the nature and the relative content of functional groups (i.e. quinones, phenols and carboxylic and hydroxyl moieties), eventually changing HA reactivity and ultimately determining their application field. Indeed, depending on their properties, these substances can be used as flame retardants in the case of pronounced resilience degree (i.e., absent or low reactivity), or as antioxidant or antimicrobial agents in the case of pronounced reactivity, thanks to their redox behaviour. In this work we investigated the flammable, the thermal and the physico-chemical features of HA extracted from different composted biomasses to identify the reactivity or the resiliency of these moieties. Several techniques, including flammability characterization (LIT and MIE), laser diffraction granulometry, TG, XRD analyses, FTIR spectroscopy on both solid and gaseous phases, and Raman spectroscopy were integrated to investigate the correlation among the safety parameters, the distributions of particle sizes, as well as the thermal, the chemical properties of HA powders and the influence of post-extraction processes on HA final properties

Hydrogen Safety Challenges: A Comprehensive Review on Production, Storage, Transport, Utilization, and CFD-Based Consequence and Risk Assessment

This review examines the central role of hydrogen, particularly green hydrogen from renewable sources, in the global search for energy solutions that are sustainable and safe by design. Using the hydrogen square, safety measures across the hydrogen value chain—production, storage, transport, and utilisation—are discussed, thereby highlighting the need for a balanced approach to ensure a sustainable and efficient hydrogen economy. The review also underlines the challenges in safety assessments, points to past incidents, and argues for a comprehensive risk assessment that uses empirical modelling, simulation-based computational fluid dynamics (CFDs) for hydrogen dispersion, and quantitative risk assessments. It also highlights the activities carried out by our research group SaRAH (Safety, Risk Analysis, and Hydrogen) relative to a more rigorous risk assessment of hydrogen-related systems through the use of a combined approach of CFD simulations and the appropriate risk assessment tools. Our research activities are currently focused on underground hydrogen storage and hydrogen transport as hythane

Redox behavior of potassium doped and transition metal co-doped Ce0.75Zr0.25O2 for thermochemical H2O/CO2 splitting

CeO2 slow redox kinetics as well as low oxygen exchange ability limit its application as a catalyst in solar thermochemical two-step cycles. In this study, Ce0.75Zr0.25O2 catalysts doped with potassium or transition metals (Cu, Mn, Fe), as well as co-doped materials were synthesized. Samples were investigated by X-ray diffraction (XRD), N2 sorption (BET), as well as by electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) to gain insight into surface and bulk features, which were connected to redox properties assessed both in a thermogravimetric (TG) balance and in a fixed bed reactor. Obtained results revealed that doping as well as co-doping with non-reducible K cations promoted the increase of both surface and bulk oxygen vacancies. Accordingly, K-doped and Fe-K co-doped materials show the best redox performances evidencing the highest reduction degree, the largest H2 amounts and the fastest kinetics, thus emerging as very interesting materials for solar thermochemical splitting cycles