Study On The Fire Extinguishing Performance And Mechanism Of Eco-friendly Hydrofluoroalkenes

As halon extinguishing agents,which have high values of ozone depletion potential and global warming potential are banned by a series of bills,however,there's still lack of proper substitutes.Thus,it is urgent to develop new eco-friendly fire suppressants.Recently researchers are focused on an environmentally friendly compounds?hydrofluoroalkenes,which own much shorter atmospheric lifetime than hydrofluorocarbons due to their unsaturated double bonds.Besides,hydrofluoroalkenes have low toxicity and nonflammability.Taking the molecular structure of 2-BTP as the reference,three hydrofluoroolefins,HFO-1234ze?E?,HFO-1234yf and HFO-336mzz?Z?are selected to be the research objects.The fire suppression effectiveness,the thermal decomposition properties and the extinguishing mechanism of these HFOs were investigated experimentally and numerically.On this basis,the potential of the HFOs as the halon alternatives were evaluated.First of all,as fire extinguishing agent the most important property is fire extinguishing performance.In this paper,a cup burner apparatus was used to evaluate the fire suppression effectiveness of selected chemicals,and the flame behavior during the experiment was recorded by a high-speed camera.The minimum extinguishing concentrations of HFOs and HFCs were determined,and the extinguishing effectiveness of each compound was ranked.Based on the results,the effect of molecular composition and structure on the suppression ability was discussed.For HFO-1336mzz?Z?,this paper conducted more in-depth experimental study,such as the relationship between the flame size and the extinguishing concentration,and the increase of the flame temperature with the addition of HFO-1336mzz?Z?Secondly,the extinguishing mechanism of HFOs was discussed in the text.The process of extinguishing agent acting on the flame can be divided into two steps:first,the extinguishing agent is heated and decomposed into many small fragments,and then reacts with·H,·O and·OH free radicals in the flame to slow the chain reactions and thus inhibit the flame.Therefore,this article divides this section into two parts:In the first part,the thermal decomposition properties of HFOs were stuied experimentally.The decomposition ratios under different temperature were measured,and the pyrolysis products were detected by GC-MS.Based on the detection results,the possible decomposition reaction pathways were proposed.In the second part,the premixed CH₄/air/HFO-1234yf flame was studied numerically by gas phase dynamics software chemkin 17.0.The effect of HFO-1234yf on the adiabatic combustion temperature,and the effect on the laminar premixed flame speed were investigated.In addition,the main endothermic/exothermic reactions and generation/consumption of free radicals in the system were analyzed,and the key reactions of promotion/inhibition combustion were found out by sensitivity analysis.Furthermore,similarities and differences of fire extinguishing mechanism between HFO-1234yf and HFC-227ea were discussed.In the end of this paper,the causes of combustion promotion and suppression by HFOs were summarized,and the application potential of HFOs as fire extinguishing agent was evaluated.Then the shortcomings of the present research work are analyzed and the future research of HFOs extinguishing agents is prospected.