【作者】 李威；

【导师】 蒋勇；

【作者基本信息】 中国科学技术大学 ， 安全科学与工程， 2019， 博士

【摘要】 火灾事故给人们的财产、生活和生命造成严重危害,灭火剂的应用,能在很大程度上降低火灾发生率和减少火灾造成的危害。出于对生态环境的保护,高效的哈龙类灭火剂将被逐步淘汰,寻找新型替代灭火剂迫在眉睫。含磷类化合物被认为具有高效灭火性能。本文以甲基膦酸二甲酯(DMMP)作为研究对象,以甲烷火焰作为载体,针对无卤素含磷类化合物的灭火性能及其作用机理开展了系统的实验和模拟研究。本文首先基于小尺度同轴扩散火焰进行了灭火实验。由于在DMMP添加浓度低于其蒸气饱和浓度时,单独使用DMMP不能将火焰熄灭,故使用在特定DMMP体积浓度添加条件下,熄灭火焰所需要的最低CO2体积浓度添加量,即最低灭火浓度,表征DMMP的灭火效率。同时在氧化剂侧添加DMMP和C02,通过观察火焰稳定性,测量CO2最低熄灭浓度与DMMP添加量的变化关系。实验发现,当DMMP添加浓度小于0.2%时,CO2的最低灭火浓度随DMMP添加量增大迅速降低,但是当DMMP添加量大于0.6%后,进一步增大DMMP添加量,CO2最低灭火浓度基本保持不变。因此可以认为当添加量大于0.6%时,DMMP的灭火效率达到饱和。有两种机理可以解释DMMP灭火效率的饱和现象,即:火焰中含磷组分集聚成细微颗粒和火焰“反应核”中活性自由基(H、O和OH等)的峰值浓度降低到化学平衡浓度。为了研究DMMP灭火效率出现饱和现象的内在机理,本文应用羟基激光诱导荧光(OH-PLIF)技术对火焰中OH浓度分布进行测量。研究发现,当固定DMMP添加量时,随着CO2添加浓度逐渐增大,火焰“反应核”的强度和规模逐渐减小。而当单独添加DMMP时,“反应核”强度随添加量增大先迅速降低,然后缓慢降低,特别当灭火效率饱和后,“反应核”强度基本保持不变。根据临近熄灭极限时火焰中OH浓度分布发现,当DMMP添加浓度大于0.09%时(灭火效率未饱和),“反应核”的强度基本保持不变。得益于含磷颗粒物对激发激光的反射/荧光,OH-PLIF测量系统可以捕捉到火焰中含磷颗粒物的生成情况。结果显示,当DMMP添加浓度大于0.6%时(DMMP灭火效率饱和),火焰周围有大量含磷颗粒物生成,并且随着DMMP添加量增大颗粒物生成量明显增多。颗粒物的生成导致火焰中参与反应的有效含磷物质的含量随着DMMP添加量增大而达到饱和,进而导致其灭火效率达到饱和。为了研究在不涉及含磷颗粒物生成时(DMMP添加浓度很小),DMMP的火焰抑制效率,本文随后开展了基于本生灯预混火焰的实验研究,测量了 DMMP作用下甲烷/空气预混火焰的层流传播速度,并以火焰传播速度下降幅度作为抑制效率的评价指标。研究发现随着DMMP添加量逐渐增大,其火焰抑制效率也存在饱和效应。本文组建四套含磷火焰抑制机理对实验结果进行预测,然后基于匹配最好的机理展开详细的数值模拟研究。分析了火焰温度、火焰厚度和火焰传播速度敏感性随DMMP添加量的变化,发现基元反应PO2+H+M=HOPO+M(R812)对火焰传播速度影响最大。分别对R812和整体含磷反应的热释放量和H消耗量进行统计,发现随着DMMP添加量增大,两者的热释放贡献率逐渐增大,并且两者对H消耗贡献率逐渐减小。一方面热量释放促进燃烧,另一方面H消耗抑制燃烧,两方面共同作用导致DMMP火焰抑制效率出现饱和效应。本文最后针对基元反应的热效应和化学效应解耦展开数值研究。不同于以往修改反应机理实现物理效应和化学效应解耦,本文通过修改开源程序Chemkin-Ⅱ中组分生成速率方程、能量方程和组分方程实现了实时热效应和化学效应解耦。研究发现R812和DMMP对层流火焰传播速度的化学效应均大于其热效应。更多还原

【Abstract】 The occurrence of fires has serious consequences for people’s property,life and lives.The application of fire extinguishing agents can reduce the incidence of fires and reduce the damage caused by fires to a certain extent.Due to the protection of the ecological environment,the efficient halon fire extinguishing agents will be phased out,and it is extremely urgent to find new alternative fire extinguishing agents.Phosphorus containing compounds are of high efficiency on fire inhibition.In this paper,dimethyl methylphosphonate(DMMP)was used as a representative of halogen-free phosphorus-containing compounds(PCCs).Systematic experiments and simulation studies were carried out to study the fire extinguishing performance and mechanism of DMMP on methane flames.The fire-extinguishing experiments were first carried out based on a small-scale co-flow diffusion flame.Since using DMMP alone cannot extinguish the flame when the partial pressure of DMMP is lower than its saturated vapor pressure,the minimum CO2 volume concentration required to extinguish the flame on base of specific DMMP volume concentration,that is,the minimum extinguishing concentration(MEC),is used to characterize the inhibition efficiency of DMMP.The flame stability was observed with DMMP and CO2 addition to the air.It was found that when the concentration of DMMP was less than 0.2%,MECCO2 decreased rapidly with the increase of DMMP concentration.However,when the concentration of DMMP was more than 0.6%,further addition of DMMP brought about negligible decrease of MECCO2.It is defined that when the addition of DMMP is more than 0.6%,the fire extinguishing efficiency of DMMP is saturated.There are two mechanisms to explain the saturation of DMMP extinguishing efficiency:the effective phosphorus species in the flame are concentrated into fine particles and the peak concentration of active radicals(H,O and OH,etc.)in the "reaction kernel" is reduced to chemical equilibrium level.In order to study the intrinsic mechanism of the saturation of DMMP’s flame inhibition efficiency,OH-PLIF measurement technique was used to measure the OH concentration distribution in flames.It was found that when the amount of DMMP was fixed,as the concentration of CO2 increased,the intensity and scale of the flame"reaction kernel"gradually decreased.When DMMP was added alone,with the increase of DMMP concentration,the intensity of the "reaction kernel" decreased rapidly,and then decreased slowly.Especially when the inhibition efficiency was saturated,the intensity of the "reaction kernel" remained basically unchanged.According to the distributions of OH concentration in the flames near the extinction limit,when the concentration of DMMP was more than 0.09%(the inhibition efficiency was not saturated),the intensity of the "reaction kernel" remained basically unchanged.Thanks to the reflection/fluorescence of the phosphorous particles on the pump laser,the OH-PLIF system can capture the formation of phosphorus-containing particles in the flame.The results showed that when the inhibition efficiency of DMMP was saturated,a large amount of phosphorus-containing particles were formed around the flames,and the amount of particles increased significantly with the increasing of DMMP addition.The formation of particles results in the concentration of the effective PCCs participating in the reactions in the flame to be saturated as the addition of DMMP keeps increasing,thereby causing the inhibition efficiency to be saturated.In order to investigate the flame inhibition efficiency of DMMP without considering the formation of phosphorus-containing particles,this paper experimentally measured the laminar burning velocities of DMMP inhibited methane/air premixed flames based on Bunsen method.The decrease of the laminar burning velocity is used as an indicator of inhibition efficiency.It was found that as the addition of DMMP increased,the flame inhibition efficiency also had a saturation effect.Four sets of phosphorus-containing flame suppression mechanisms were established to predict the experimental results,and then detailed numerical simulation studies were carried out based on the best matching mechanism.The flame temperature,flame thickness and the sensitivity of flame propagation speed to the reaction rate of phosphorus-containing elements were analyzed with the addition of DMMP.It was found that the elemental reaction PO2+H+M=HOPO+M(R812)had the greatest influence on the flame propagation speed.The heat release and H consumption of R812 and the whole phosphorus-containing reactions were statistically analyzed,respectively.It was found that with the increase of DMMP addition,the contributions to the heat release of both objects increased gradually,and the contributions to H consumption of both objects decreased gradually.On the one hand,heat release promotes combustion,on the one hand,H consumption suppresses combustion;and the combined action of both effects leads to saturation effect of DMMP flame suppression efficiency.Finally,numerical studies on the thermal and chemical effects decoupling for the elementary reaction were carried out.Different from the previous physical and chemical effects decoupling by changing the reaction mechanism,this paper realized the real-time thermal effect and chemical effect decoupling by modifying the energy equations and the composition equations in the open source program Chemkin-II.It is found that the chemical effects of R812 and DMMP on laminar burning velocity are greater than their thermal effects.更多还原