甲烷-空气预混气体燃烧特性研究

采用纹影系统、压力传感器和高速相机对甲烷-空气预混气体在定容燃烧弹中的燃烧特性进行研究,分析了当量比对拉伸火焰传播速度、未拉伸火焰传播速度和层流燃烧速度的影响及定容弹中压力的变化规律。结果表明,当量比对预混气体燃烧过程有重要影响,且存在临界当量比1.1,在临界当量比下预混气体燃烧最剧烈,层流燃烧速度达到最大值(0.368 m/s),燃烧压力也达到峰值(0.703 MPa)。当预混气体当量比小于临界值时,拉伸火焰传播速度、未拉伸火焰传播速度、层流燃烧速度和燃烧压力随当量比增加而增加;而当预混气体当量比大于临界值时,速度和压力随当量比增加而减小。     

载流雾化水惰化甲烷空气预混气体特性实验研究

设计了预混气体载流雾化水惰化和抑制燃烧管实验台,对层流火焰的燃烧速度、稳定性及拉伸变形规律进行实验研究,分析了雾化水抑制和熄灭层流预混火焰的过程和机理,获得了雾化水惰化爆炸极限内甲烷和空气预混气体的特性。研究结果表明:浓度为7%的甲烷和空气预混气体,最小惰化雾化水通量为20.8ml/(m2.min);对于浓度为9%的甲烷和空气预混气体,最小惰化雾化水通量为32.9ml/(m2.min);对于浓度为11%的甲烷和空气的预混气体,最小惰化雾化水通量为44.6ml/(m2.min)。研究成果为雾化水熄灭甲烷火焰和抑制甲烷爆炸具有一定的指导意义。     

基于浓度敏感性分析和遗传算法的甲烷燃烧机理简化与优化

采用良搅拌反应器模型和层流预混火焰模型计算甲烷/空气燃烧过程,通过元素流通法和浓度敏感性分析法,对甲烷燃烧详细化学动力学机理GRIMECH 3.0进行简化。利用遗传算法,以甲烷/空气详细机理获得的组分浓度和一维层流火焰速度为目标,对简化机理进行优化。结果表明,相比于优化之前的简化机理,优化后的简化机理在描述甲烷/空气燃烧反应的组分浓度、层流火焰速度以及反应物和产物的时空分布方面,具有更高的精度。     

甲烷对合成气层流预混火焰传播特性的影响

为研究甲烷对合成气层流预混火焰化学动力学特征及合成气层流预混火焰传播特性的影响,选用GRI3.0-机理,模拟研究300 K条件下含0～70%甲烷的合成气层流预混火焰传播速度、火焰温度、反应敏感性及重要自由基浓度等。结果表明:合成气层流预混火焰传播速度、绝热火焰温度随甲烷比例的增加非线性下降,火焰传播速度峰值对应的当量比随甲烷增加显著向贫燃侧发展;富燃条件下,随着甲烷少量加入(≤30%),火焰中自由基H浓度显著下降,火焰传播速度受抑制作用显著;随着甲烷的继续增加,不足的自由基OH抑制自由基CH_3的生成,影响自由基H的消耗,削弱CH_4对层流预混火焰传播速度的抑制作用。     

预混燃烧室的NOx与CO排放性能研究

建立了一套预混燃烧装置,进行了不同过量空气系数a、预混段长径比L/D、燃气平均速度v和旋流器旋流数Sn下的燃烧试验,研究了不同燃料-空气预混条件对燃烧尾气中污染物NOx与CO体积分数的影响。结果表明:当过量空气系数a1.1时,NOx与CO体积分数均呈下降趋势;预混长径比L/D在4~8时,增长预混长度可以减少污染物NOx的排放;减小燃气平均速度可以降低NOx体积分数,但CO体积分数略有增加;强旋流(Sn1.56)可以增强预混,降低NOx体积分数,但强旋流下CO体积分数增加迅速。     

可燃气体爆炸破坏效应的试验研究

借助高速摄像机及ProAnalyst软件,研究可燃气体体积分数和障碍物对可燃气体爆炸破坏力的影响。测定不同体积分数下的甲烷-空气预混气体爆炸冲击波超压,和爆炸火焰波在有无乒乓球方向传播的平均速度。试验结果表明:超压和平均速度均随着甲烷体积分数的增加呈现先增大后减小的变化趋势,其最大值均出现在甲烷体积分数为10%～11%之间;同一体积分数下的甲烷-空气预混气体爆炸火焰波在有乒乓球方向传播的平均速度比没有乒乓球方向传播的平均速度大。根据试验结果,推导出可燃气体爆炸冲击波超压和爆炸火焰波传播平均速度与可燃气体体积分数之间的函数关系,并得出障碍物对爆炸火焰波传播的加速作用随着体积分数的增加呈现先加强后减弱的变化趋势。     

基于PDF模型的镁铝合金粉尘燃烧特性试验及仿真研究

为了深入研究镁铝合金粉尘非预混燃烧特性，在传统哈特曼管基础上进行了针对性的优化改进，采用模拟试验与CFD仿真相结合的研究手段，分别从粒径、质量流量和空气湿度3个方面对镁铝合金粉尘的燃烧特性进行了详细的研究。结果表明，80μm、120μm、150μm及270μm镁铝合金粉尘的平均反应温度分别为2 349.8 K、2 253.7 K、2 167.3 K和2 094.7 K。当粉尘质量流量一定时，单一颗粒粒径越大，颗粒与空气接触的比表面积则越小，燃烧反应温度越低；镁铝合金粉尘燃烧分为富氧和贫氧燃烧，粉尘与空气质量流量比45.54∶100为镁铝合金粉尘富氧与贫氧燃烧的临界点，当空气质量流量大于粉尘质量流量10倍时，氧气与镁铝合金粉尘接触时间短，反应温度低于点火温度，不足以支撑燃烧反应进行；当粉尘质量流量大于空气质量流量10倍时，氧气含量过低，同样不足以支撑燃烧反应进行。空气湿度越大，燃烧反应最高温度越低，燃烧反应平均温度会出现先增后降的现象。研究结果可为工业生产、抛光、打磨等工序中的防燃、防爆问题提供参考依据及基础理论。     

瓦斯爆炸过程中火焰传播的实验与数值模拟研究

为了研究矿井瓦斯爆炸火焰发展过程中结构与参数的动态变化特征,建立小尺寸管道气体爆炸实验平台,结合高速纹影摄影技术,探测了不同浓度的甲烷-空气预混气体火焰在管道内传播的结构变化特性,并得出速度变化特征曲线。同时建立相应的数学模型和物理模型,通过模拟实验研究管道内气体爆炸反应过程中火焰传播速度变化过程,计算图像和实验图像走向趋向一致。     

喷粉压力对KHCO_3冷气溶胶甲烷抑爆效果影响研究

为实现主动式喷粉抑爆系统的最佳抑爆效果,基于5 L管道爆炸试验平台,测试喷粉压力对碳酸氢钾(KHCO_3)冷气溶胶分散状况的影响,并开展KHCO_3冷气溶胶对于9.5%甲烷-空气预混气体爆炸的抑制试验,考察了不同喷粉压力下形成的KHCO_3冷气溶胶对甲烷爆炸压力及火焰传播的抑制效果。结果表明:喷粉压力显著影响KHCO_3冷气溶胶的分散状况,进而影响其甲烷抑爆效果,KHCO_3冷气溶胶在低喷粉压力下难以分散且抑爆效果不佳,仅对前期火焰产生抑制作用;随着喷粉压力增加,KHCO_3冷气溶胶抑爆效果逐渐提升,甲烷爆炸火焰传播减缓,最大爆炸压力降低;但当KHCO_3冷气溶胶得到充分分散时,继续增加喷粉压力对其抑爆效果提升很小。     

氢气对预混甲烷/空气燃爆过程的影响

为研究氢气的加入对不同体积分数甲烷/空气预混爆炸过程影响的规律,在尺寸为150 mm×150 mm×1 000 mm的管道中通入体积分数为8%、9.5%和11.5%的甲烷/空气预混气体,然后加入一定体积分数的氢气。氢气所占体积分数分别为0、0.74%、1.48%、2.95%、4.40%。分别对加入不同体积分数的甲烷爆炸过程中爆炸压力、火焰图像和爆炸温度进行测量、分析。结果表明:只有在8%纯甲烷爆炸时能够形成完整的郁金香火焰。8%和9.5%甲烷体积分数试验中,氢气的加入使火焰面由上下对称变得不对称,火焰阵面上移,火焰速度加快;爆炸中的最大超压增大并且最大超压时刻点提前。在11.5%的甲烷加氢试验中,随加氢量增加,爆炸压力、温度、火焰速度分别略微降低。这表明氢气的加入在体积分数为8%的爆炸反应中较大地促进了反应,而体积分数为11.5%时加氢后爆炸反应减弱。通过理论分析计算了半封闭管道中体积分数为9.5%甲烷爆炸温度和实测温度之间的差异。爆炸压力和温度的变化能很好地反映加入氢气对甲烷爆炸的影响。     

Safety parameters for oxygen-enriched flames

The utilization of low-quality gaseous fuel from biomass gasification and the abundance of oxygen-rich streams obtained as a by-product of nitrogen-air separation by membrane technology has incentivized the development of sustainable oxygen-enriched combustion technologies in the last decades. However, a dearth of experimental and numerical analysis addressing the reactivity and safety aspects of these mixtures at initial low temperatures can be observed in the current literature.In this work, the heat flux burner was adopted for the measurement of the laminar burning velocity of methane in oxygen enriched air at different equivalence ratios. Results were compared with numerical data obtained by means of detailed kinetic mechanisms developed at the University of Bologna and the Gas Research Institute (GriMech3.0). Simplified correlations for the estimation of the laminar burning velocity with respect to the oxygen content at any equivalence ratio were developed, tested and evaluated.An elemental reaction-based function was found appropriate for the estimation of the overall reactivity of the investigated mixtures. Besides, numerical analyses were performed to characterize the flame structures in terms of temperature and product distribution under several initial conditions. These results gave further insights into the reaction mechanisms of gaseous fuels in the case of oxygen-enriched air, highlighting potential bottlenecks for kinetic model refinements. Eventually, relevant safety parameters were estimated, in particular the flammability range of the fuel/oxidant mixture, in terms of lower and upper flammability limits.     

Combined effects of initial pressure and turbulence on explosions of hydrogen-enriched methane/air mixtures

Hydrogen-enrichment has been proposed as a useful method to overcome drawbacks (local flame extinction, combustion instabilities, lower power output, etc.) associated to turbulent premixed combustion of natural gas in both stationary and mobile systems. For the safe use of hydrogen-enriched hydrocarbon fuels, explosion data are needed.In this work, a comparative experimental study of the explosion behavior of stoichiometric hydrogen-enriched methane/air (with 10% of hydrogen molar content in the fuel) and pure methane/air mixtures is presented. Tests were carried out in a 5 l closed cylindrical vessel at different initial pressures (1, 3 and 6 bar), and starting from both quiescent and turbulent conditions.Results allow quantifying the combined effects of hydrogen substitution to methane, pressure and turbulence on maximum pressure, maximum rate of pressure rise, burning velocity and Markstein lengths.     

Explosion behavior of hydrogen–methane/air mixtures

The effects of enriching natural gas with hydrogen on local flame extinction, combustion instabilities and power output have been widely studied for both stationary and mobile systems. On the contrary, the issues of explosion safety for hydrogen–methane mixtures are still under investigation.In this work, experimental tests were performed in a 5 L closed cylindrical vessel for explosions of hydrogen–methane mixtures in stoichiometric air. Different compositions of hydrogen–methane were tested (from pure methane to pure hydrogen) at varying initial pressures (1, 3 and 6 bar).Results have allowed the quantification of the combined effects of both mixture composition (i.e., hydrogen content in the fuel) and initial pressure on maximum pressure, maximum rate of pressure rise and burning velocity. The measured burning velocities were also correlated by means of a Le Chatelier’s Rule-like formula. Good predictions have been obtained (at any initial pressure), except for mixtures with hydrogen molar content in the fuel higher than 50%.     

A new phenomenological model of gas explosion based on characteristics of flame surface

This paper presents a new model of explosion propagation in a closed vessel. The foundation of the formulation is a sub-model of turbulent burning velocity based on the assumption that the burning velocity of a turbulent wrinkled flame can be determined from the flame surface. In addition, model development includes simple sub-models of heat transfer and free convection. In order to verify the physics, the model was utilized to simulate the explosion of a methane–air mixture in two different test vessels. The results obtained by use of this new model were compared with results obtained by use of the classical model. While the simulations showed that both are accurate, the new model presented in this paper (called “flame surface model” for simplicity) is more flexible and can easily accommodate sub-models of different phenomena that can play an important role in fuel–air explosions.     

A numerical modelling of an influence of CH4, N2, CO2 and steam on a laminar burning velocity of hydrogen in air

The influence of additives of various chemical natures (CH₄, N₂, CO₂, and steam) at a laminar burning velocity S_u of hydrogen in air has been studied by numerical modelling of a flat flame propagation in a gaseous mixture. It was found that the additives of methane to hydrogen–air mixtures cause as a rule monotonic reduction in the S_u value with the exception of very lean mixtures (fuel equivalence ratio ? = 0.4), for which a dependence of the laminar burning velocity on the additive's concentration has a maximum. In the case of the chemically inert additives (N₂, CO₂, H₂O) the laminar burning velocity of rich near-limit hydrogen–air flames drops monotonically with an increase in the additive's content, but no more than 1.5 times, and the adiabatic flame temperature changes slowly in this case. In the case of methane as the additive, the laminar burning velocity is diminished approximately 5 times with an increase in the adiabatic flame temperature from 1200 to 2100 K. Deviations from the known empirical rule of the approximate constancy of the laminar burning velocity for near-limit flames are shown.     

非线性拉伸对甲烷-空气预混火焰燃烧特性的影响

使用定容燃烧弹与高速纹影照相系统研究了不同当量比下甲烷-空气预混气体的层流火焰燃烧特性。实验数据同时应用传统线性模型和非线性模型分析了不同当量比对球形扩展火焰的传播速率和马克斯坦长度的影响。结果显示:随着当量比的增加,层流燃烧速率先增大后减小,直到当量比为1.1时,火焰速率达到最大值。马克斯坦长度始终为正值,且随着当量比的增大而增大。在所有当量比条件下,线性和非线性方法计算的火焰速率大致相同,差值小于0.01 m/s;线性方法得到的马克斯坦长度均大于非线性模型计算的结果,并随着当量比的增大,两种方法得到的马克斯坦长度的差值更加显著。     

螺旋隧道火灾特性小尺寸实验研究

为探明螺旋隧道火灾特性,防止人员高温伤害,基于Froude准则,搭建比例1∶67的小尺寸螺旋隧道实验模型,采用模型实验方法研究不同坡度和不同风速下螺旋隧道火灾温度分布规律及烟气蔓延特性。研究结果表明:低坡度条件下,螺旋隧道内高温区以火源为中点呈对称分布状态;随着坡度的增加,隧道内高温区逐渐向下游延伸,火源处拱顶下方温度呈现先增大后降低再升高的变化规律;无论是自然风还是机械纵向通风,新鲜冷空气的吹入对隧道温度的降低起到主导作用,且风速越大,温降幅度越大;随着隧道坡度和自然风速的增加,火羽流由竖直狭长型转变为燃烧不稳定的大截面火焰,同时坡度增加抑制了火灾烟气逆流,促进了烟气向火源下游的蔓延速度,大大提高了排烟的有效性,减少人员伤害。     

Influence of coal particles on methane/air mixture ignition in a heated environment

The temperature at which coal dust glows is normally much lower than the auto-ignition temperature (AIT) of methane/air mixtures, and thus a better understanding is needed regarding methane/air ignition in a heated environment in the presence of coal particles. A horizontal tube apparatus was used to test the effect of brown coal and two kinds of bituminous and anthracite on methane/air combustibility. For the four coal samples tested, the presence of coal particles significantly reduced the minimum temperature for ignition of methane/air mixtures in a heated environment. No. 1 bituminous coal with 12 mm diameter decreased the ignition temperature value from 595 to 500 °C. It is thought that pre-ignition of low-AIT volatiles emitted from the heated coal particles ignited the methane/air mixtures. Volatiles, sulfur content, and large porosity of piled coal particles all enhanced ignition of methane/air mixtures in a hot environment, while water content and small particle size reduced ignition. For anthracite, no ignition occurred when temperatures of the heated environment were lower than the AIT of methane (595 °C), except for the 12-mm-diameter sample. Anthracite did not readily ignite methane/air mixtures and the ignition mechanism was somewhat similar to that of a burning cigarette.     

Laminar burning velocities of hydrogen–air mixtures from closed vessel gas explosions

The laminar burning velocity of hydrogen–air mixtures was determined from pressure variations in a windowless explosion vessel. Initially, quiescent hydrogen–air mixtures of an equivalence ratio of 0.5–3.0 were ignited to deflagration in a 169 ml cylindrical vessel at initial conditions of 1 bar and 293 K. The behavior of the pressure was measured as a function of time and this information was subsequently exploited by fitting an integral balance model to it. The resulting laminar burning velocities are seen to fall within the band of experimental data reported by previous researchers and to be close to values computed with a detailed kinetics model. With mixtures of an equivalence ratio larger than 0.75, it was observed that more advanced methods that take flame stretch effects into account have no significant advantage over the methodology followed in the present work. At an equivalence ratio of less than 0.75, the laminar burning velocity obtained by the latter was found to be higher than that produced by the former, but at the same time close enough to the unstretched laminar burning velocity to be considered as an acceptable conservative estimate for purposes related to fire and explosion safety. It was furthermore observed that the experimental pressure–time curves of deflagrating hydrogen–air mixtures contained pressure oscillations of a magnitude in the order of 0.25 bar. This phenomenon is explained by considering the velocity of the burnt mixture induced by the expansion of combusting fluid layers adjacent to the wall.     

甲烷/空气混合气燃爆特性的实验研究

对不同初始压力和温度条件下的甲烷/空气混合气的爆炸极限进行实验研究,利用最大-最小准则来确定爆炸极限.分析了温度和压力对甲烷/空气混合气燃爆特性的影响.采用氮气作为惰性气体,对其防爆抑爆效果进行了实验研究.