Research On Inhibition Mechanism Of Water Fog On Deflagration Accident In Engine Room Of Hydrogen-powered Ship

With low-carbon and environmental protection becoming the mainstream of social development,hydrogen,with its excellent green and eco-friendly characteristics,has gradually been applied in various industries.It is well-known that hydrogen gas has the advantages of wide availability and no pollution.However,its low ignition energy(0.019 m J),high laminar burning speed(S_L=2.8 m/s,Φ=1.5),easy leakage,and difficult storage remain the primary factors constraining its development.Therefore,once a hydrogen gas leak occurs,the risk of explosion leading to significant casualties and property damage is extremely high.Fine water mist,as an excellent suppressant,features no pollution and low cost.However,the suppression mechanism of fine water mist is not yet clear.Therefore,to reduce the risk of accidents in hydrogen-powered ships,it is urgently needed to conduct research on the suppression mechanism of fine water mist on hydrogen-air combustion.In this study,experiments and numerical simulations are conducted based on a small-scale hydrogen-air explosion suppression experimental platform and the FLACS,FLUENT,and CHEMKIN software.The main research contents are as follows:(1)The fine structure of small-scale hydrogen-air flames was studied using a semi-open hydrogen-air deflagration experimental system.By combining the k-epsilon RNG model in the FLUENT software with a detailed hydrogen-air chemical reaction mechanism,the influence of obstacles on the characteristics of hydrogen-air deflagration in ship compartments was investigated.The results showed that the simulation results based on the k-epsilon RNG model with the detailed chemical reaction mechanism were highly consistent with the experimental data,effectively reproducing the experimental results.The accelerated propagation of hydrogen-air flames was primarily attributed to the narrow space formed by obstacles and the pipe walls.The generation of turbulent vortices originated above the obstacles and developed in the downstream region.The main cause of turbulent vortex formation was the interaction between high-speed airflow and obstacles,resulting in low-pressure gradient regions.Turbulent vortices were found to be the primary cause of turbulent flame formation and the main carriers of turbulent kinetic energy diffusion.(2)The mechanism of explosion suppression by water mist was revealed through a semi-open hydrogen-air deflagration experimental platform and the CHEMKIN software.The comprehensive effects of water mist and obstacles on hydrogen-air deflagration were studied.The results showed that the instability of thermal diffusion under lean conditions was the main influencing factor for surface instability of hydrogen-air flames,and the presence of water mist exacerbated the surface instability of hydrogen-air flames.When obstacles were not considered,8μm,15μm,and 30μm water mist significantly reduced the flame speed and explosion overpressure of hydrogen-air mixtures,while the fine water mist of 45μm acted as a flame acceleration agent.When considering the relative positions of the spray location and obstacles,8μm,15μm,and 30μm water mist had little suppression effect when released near obstacles.However,when using 45μm water mist,a significant suppression effect was observed.(3)A three-dimensional hydrogen-fueled ship compartment model was constructed based on FLACS to investigate the large-scale characteristics of hydrogen leakage,diffusion,and deflagration.The influence of water mist diameter and spray location on the suppression effect of hydrogen-air explosions under large-scale conditions was studied using the FLACS spray model,aiming to explore the deflagration suppression mechanism of ultrafine water mist.The results showed that for fine water mist with diameters of 80μm,120μm,160μm,200μm,250μm,300μm,and 400μm,the critical deflagration suppression diameter was 160μm.When the water mist diameter was smaller than 160μm,the flame acceleration effect was stronger.When the water mist diameter was larger than 160μm,the deflagration suppression effect improved with increasing diameter.Additionally,the spray location also had a significant impact on the deflagration suppression effect.When the spray location was at a distance of 0 m from the ignition source,a flame acceleration effect was observed,resulting in a 72.8%increase in peak overpressure.At a spray location distance of 2 m from the ignition source,the peak overpressure was reduced by 32%.At a spray location distance of 4 m from the ignition source,the peak overpressure was reduced by 21.3%.The research results not only provide a theoretical basis for reducing the consequences of hydrogen explosion accidents and determining the optimal diameter range for water mist adoption but also serve as experimental references for numerical simulations of hydrogen-air deflagration suppression in semi-open spaces,promoting the development of hydrogen-air deflagration suppression theory.In terms of engineering applications,this study provides a theoretical basis for the layout of fire-fighting equipment in hydrogen-fueled ship compartments and establishes a theoretical foundation and safety assurance for the safe use of hydrogen in engine compartments.