燃烧模型对多孔介质内预混燃烧的影响

采用二维非稳态数学模型研究燃烧模型多孔介质内预混燃烧影响.燃烧模型分别为单步和多步化学反应动力机理（17种组分,58个反应）,CH4/空气当量比的范围为0.55～1.0.对比分析两种燃烧模型下燃烧器中心处的温度、组分浓度分布曲线.结果表明,多步燃烧模型对燃烧器内温度、组分浓度分布有更准确的预测,并与文献结果比较,证实了二维非稳态数学模型的正确性.此外,将二维的温度场进行比较,结果表明单步化学机理的反应区域小,温度梯度大,而多步化学反应由于各反应步骤存在时间尺度的差异,反应区域大,温度梯度相对较小,与实际燃烧情况能很好的吻合.     

多孔介质微燃烧器预混燃烧的数值研究

开发了带有回热夹层的多孔介质微燃烧嚣,对其预混燃烧性能进行了数值模拟,研究了燃烧功率和过量空气系数对微燃烧器的出口尾气温度、燃烧效率、壁面温度和热损失率的影响.结果表明:在较宽的燃烧范围内,微燃烧器具有较高的燃烧效率和较低的热损失率,而且随着燃烧热功率和过量空气系数的增大,微燃烧器的外壁面温度和热损失率反而减小;多孔介质微燃烧器的最佳燃烧功率为200 w,最佳的过量空气系数范围为2.5相似文献   

掺混氢气对乙醇燃烧的化学作用模拟研究

为了更好地了解掺入氢气对乙醇燃烧时的作用机理,利用CHEMKIN PRO程序,对稀燃工况下的乙醇/氢气预混层流燃烧进行了化学反应动力学分析,采用一种辨识方法,对不同掺氢体积分数下,掺氢对乙醇燃烧的主要产物和中间产物的化学作用及热/稀释作用进行了区分、研究和讨论.结果表明:氢气的化学作用会促进乙醇消耗和中间组分的生成,并使其反应摩尔分数分布曲线向反应上游移动,增加反应速率;而热/稀释作用会抑制组分的生成,使反应摩尔分数分布曲线向下游移动,减缓反应速率;综合作用会使掺氢后的化学反应提前发生,并对有害污染物甲醛的产生起到抑制作用.     

脂肪预处理发酵联产氢气和甲烷的研究

针对脂肪难以产氢、能源转化率低的问题,以肥猪肉作为脂肪代表物,研究了其预处理后发酵联产氢气和甲烷的特性.结果表明,在产氢阶段,碱和脂肪酶预处理促进了脂肪的水解,提高了累积产氢量.驯化菌种能较快的适应底物环境,从而缩短延滞期并提高了产气速率.碱水解时应控制体系的Na+终浓度不超过0.2mol/L,更高的碱用量会因Na+浓度过高而抑制产氢.为了提高能源转化率和原料利用率,提出了利用脂肪发酵产氢后的有机酸废液继续联产甲烷的创新工艺,并利用该工艺得到底物总挥发性固体的单位产氢潜力为32.6mL/g,联产甲烷潜力为24.88mL/g.其中单产氢气的能源转化率为0.85%,联产甲烷以后的能源转化率可提高至2.99%.     

甲烷燃烧NO_x生成的数值研究

采用非预混燃烧模型与组分传输的一步反应模型,模拟了甲烷燃烧及NOx的生成,得出燃烧温度场、NO生成情况。模拟结果表明:采用非预混燃烧模型模拟时结果更接近实测值,模拟更准确;甲烷扩散燃烧时NO产生区域主要集中在高温火焰后侧,在前部低温区基本没有NO生成;燃烧中P-NO生成量比T-NO量小两个数量级,NO产生几乎完全被热力型NO机制支配,在燃烧过程中应特别注意高温区域的影响。     

多孔介质预混燃烧气固温度分布特性试验研究

为研究多孔介质燃烧、传热和生成物特性，采用非接触式红外测温仪对多孔介质预混燃烧室中气、固两相温度分布进行了试验研究.结果表明预混气体在多孔介质中燃烧时，气相和固相的温度是不同的，存在－60～+100 K的温差.试验得到了不同当量比、热流密度和孔径下的燃烧室气、固温度分布.在火焰前缘，固体骨架的温度高于多孔介质内气体的温度，对气体有预热作用；在火焰后缘，气体温度高于固体骨架温度，对固体骨架有蓄热作用.当量比降低，气、固温差波动变小；当量比不变，热流密度增大，气、固温度差值在轴向长度方向变化小.     

水蒸气对甲烷燃烧影响的数值模拟研究

为了研究水蒸气对于甲烷燃烧微观反应进程的影响,利用Chemkin 17.0研究了水蒸气对甲烷燃烧的绝热火焰温度、预混火焰温度和层流预混火焰燃烧速度的作用规律,研究了水蒸气对甲烷燃烧过程中链式反应进程的影响。结果表明,随着水蒸气摩尔分数的增加,甲烷燃烧火焰温度降低,预混火焰传播速度下降,且火焰中的H、O、OH自由基浓度均下降,但是OH自由基所占的比例增加,导致由OH自由基所传递的反应占主导地位。水蒸气的加入强化了CH3➝CH2（s）➝CH2➝CH➝CH2O过程,同时强化了CH3➝CH3O➝CH2O过程,改变了甲烷燃烧的链式反应。     

非预混甲烷湍流扩散火焰中碳烟生成的模拟研究

采用FLUENT软件并基于详细化学反应机理和RANS-PBE-PDF碳烟模型对非预混湍流扩散火焰中碳烟的生成进行数值模拟,研究分形维数取不同数值对碳烟生成的影响.结果表明,随着分形维数增大,碳烟凝结体尺度、碳烟体积分数和碳烟颗粒凝结频率减小;随着克努德森数的增大,碳烟的凝结频率减小;通过与实验数据对比验证了基于RANS-PBE-PDF碳烟模型的模拟数据的准确性,并得出碳烟凝结体的最终分形维数接近于1.8的结论.     

超细水雾抑制瓦斯燃烧火焰的实验研究

通过搭建模拟回采工作面小尺寸实验平台,利用改造后的家用燃气灶作为燃烧器,研究了可燃预混气体火焰在超细水雾作用下火焰的变化过程,并测得了超细水雾作用于火焰过程中火焰的温度.通过改变通风速度和超细水雾的雾化速率,揭示了可燃预混气体在超细水雾氛围中火焰与温度的变化规律.通过建立稳定火焰面的力和速度平衡,找出了火焰形状拉伸扭曲的原因是破坏了火焰外焰和热气层交界面上力和速度的平衡;在其他条件一定的情况下,向模拟工作面上施加超细水雾后,火焰周围流场扰动明显增大,与在单独通风条件下相比,火焰温度跳动变化幅度和频率增大;在保证超细水雾质量浓度不变条件下,通风速度越大,则混合气体扰动越大,温度的跳动就越大,火焰的燃烧就越不稳定.实验结果表明超细水雾能很好地抑制瓦斯火焰的燃烧.     

微燃烧稳定性分析和微细管道燃烧实验研究

为了研究微尺度下的燃烧特性，在考虑散热和熄火距离影响的基础上建立了二维火焰燃烧模型，模型表明在微尺度燃烧中容易发生熄火和吹熄，不容易发生回火.同时在2 mm内径的微细T型管道中通入了氢气和空气的预混气体进行预混燃烧实验，测试了燃烧的火焰温度、流量和燃烧效率的关系.实验结果表明，采用T型管道有利于维持火焰的稳定，不容易被吹熄，但在氢气或空气流量小时容易发生熄火；低流速下，燃烧效率较高，可以完全反应，高流速下，混合气来不及在管道内反应，燃烧效率较低.无论流速的高低，在化学计量比附近燃烧效率较高.     

基于层次分析-熵值法的氢内燃机异常燃烧风险评估

为了综合评估进气道喷射（PFI）氢内燃机异常燃烧风险,基于层次分析法（AHP）构建了异常燃烧风险系数模型,分别探究喷氢参数对指标层（异常燃烧特征参数）及目标层（异常燃烧风险系数）的影响. 结果表明：通过改变喷氢参数,可以使进气道残余氢气量下降33.4%~41.6%,显著降低了回火的可能性. 当喷氢角度为30°~45°、喷氢流量为4.36~4.96 kg/h时,缸内混合气均匀性系数较大,有利于组织燃烧,却不能保证炽热区域温度等参数处于较低水准. 所构建的异常燃烧风险系数模型能够结合多个特征参数对氢内燃机异常燃烧（早燃及回火）风险进行有效评估. 当喷氢角度为45°、喷氢流量为4.96 kg/h时,各项特征参数均处于合理区间,异常燃烧风险系数下降了3.6%~6.8%,降低了异常燃烧的可能性.     

化工工艺残渣燃烧及氯化氢排放实验研究

利用热重分析仪对化工制药工艺过程产生的残渣的燃烧进行了实验研究,结果表明化工残渣有较高的燃烧热值,低位发热量为3 631 kJ.kg-1,且燃烧过程中有氯化氢气体产生.为了使残渣能够更好的燃烧,实验过程中分别加入了木屑和煤,发现木屑及煤的混入具有良好的助燃效果.进一步加入氧化钙固氯剂,通过实验研究了不同钙氯比条件下固氯效果.实验结果表明,加入固氯剂后能够有效地抑制氯化氢的生成.钙氯质量比为4∶1,能够得到最佳的固氯效果,固氯率达到85%,继续添加固氯剂,固氯效果基本保持不变.同时发现,温度在650℃左右氧化钙固氯效果最佳,接近82.6%.700℃后,固氯效果有明显下降.     

纳米TiO2催化燃烧脱除氮氧化物的实验研究

对纳米TiO2催化CaO燃烧脱除氮氧化物进行了实验研究。探讨了纳米TiO2添加量、Ca/N摩尔比、燃烧温度及不同条件下制备的纳米TiO2对分析纯CaO脱除氮氧化物效率的影响。纳米TiO2添加剂,工艺条件变化对NOx脱除效率影响的变化规律:NOx脱除效率随着纳米TiO2含量的增加迅速增加,最佳比例为8%,单独脱除效率在36.5%,加入CaO后,脱除效率提升到40.6%;不同Ca/N,氮氧化物去除率不同,实验数据表明最佳Ca/N为1.22;燃烧温度对纳米TiO2的脱氮效率也有很大的影响,最佳燃烧温度为850℃;对于不同温度下合成的TiO2,750℃下合成的TiO2脱除效率最高。     

Thermal efficiency characteristics of hydrogen internal combustion engine

To study the economic advantages of hydrogen internal combustion engine,an experimental study was carried out using a 2.0Lport fuel-injected(PFI)hydrogen internal combustion engine.Influences of fuel-air equivalence ratioΦ,speed,and ignition advance angle on heat efficiency were determined.Test results showed that indicated thermal efficiency(ITE)firstly increased with fuel-air equivalence ratio,achieved the maximum value of 40.4%(Φ=0.3),and then decreased whenΦ was more than 0.3.ITE increased as speed rises.Mechanical efficiency increased as fuel-air equivalence ratio increased,whereas mechanical efficiency decreased as speed increased,with maximum mechanical efficiency reaching 90%.Brake thermal efficiency(BTE)was influenced by ITE and mechanical efficiency,at the maximum value of 35%(Φ=0.5,2 000r/min).The optimal ignition advance angle of each condition resulting in the maximum BTE was also studied.With increasing fuel-air equivalence ratio,the optimal ignition angle became closer to the top dead center(TDC).The test results and the conclusions exhibited a guiding role on hydrogen internal combustion engine optimization.     

流化床燃烧中煤含灰量对灰渣形成特性的影响

为了研究煤颗粒灰质量分数对煤在流化床燃烧过程中灰渣形成特性的影响,在一台小型流化床反应炉上进行煤的灰质量分数对灰渣形成特性的实验.按煤颗粒的灰质量分数,把义马烟煤分为6个颗粒组,并选用各颗粒组的3个粒径范围的煤颗粒进行燃烧实验,研究煤颗粒的灰质量分数对底渣质量分数、底渣与飞灰中的碳量质量分数和粒径分布的影响.结果表明,随着煤颗粒灰质量分数的增加,燃烧形成的底渣质量分数增加,而煤颗粒的燃尽率和飞灰中的碳质量分数都降低.在粒径和燃烧时间相同的条件下,随着颗粒灰质量分数的增加,底渣中留在本粒径档的颗粒质量分数明显增加,而细颗粒的质量分数明显减少.而颗粒灰质量分数对飞灰的粒径分布没有明显的影响.     

Numerical simulation of excess-enthalpy combustion flame propagation of coal mine methane in ceramic foam

Based on the assumption of a local non-equilibrium of heat transfer between a solid matrix and gas,a mathematic model of coal mine methane combustion in a porous medium was established,as well the solid-gas boundary conditions.We simulated numerically the flame propagation characteristics.The results show that the flame velocity in ceramic foam is higher than that of free laminar flows;the maximum flame velocity depends on the combined effects of a radiation extinction coefficient and convection heat transfer in ceramic foam and rises with an increase in the chemical equivalent ratio.The radiation extinction coefficient cannot be used alone to determine the heat regeneration effects in the design of ceramic foam burners.     

Effect of wall temperature and random distribution of micro organic dust particles on their combustion parameters

The effect of wall temperature on the characteristics of random combustion of micro organic particles with recirculation was investigated. The effect of recirculating in micro-combustors is noticeable, hence it is necessary to present a model to describe the combustion process in these technologies. Recirculation phenomenon is evaluated by entering the exhausted heat from the post flam zone into the preheat zone. In this work, for modeling of random situation at the flame front, the source term in the equation of energy was modeled considering random situation for volatizing of particles in preheat zone. The comparison of obtained results from the proposed model by experimental data regards that the random model has a better agreement with experimental data than non-random model. Also, according to the results obtained by this model, wall temperature affects the amount of heat recirculation directly and higher values of wall temperature will lead to higher amounts of burning velocity and flame temperature.     

Effect of VFe addition on hydrogen storage behavior of TiMn1.5-based alloys

The hydrogen absorption and desorption behavior of TiMn1.25Cr0.25 alloys with VFe substitution for partial Mn was investigated at 273, 293 and 313 K. It is found that VFe substitution increases their hydrogen storage capacity, decreases the plateau pressure and the hysteresis factor of their pressure-composition-temperature (PCT) curves. After annealing treatment at 1223 K for 6 h, TiMn0.95Cr0.25(VFe)0.3 alloy exhibits a lower hydrogen desorption plateau pressure (0.27 MPa at 313 K) and a smaller hysteresis factor (0.13 at 313 K); the maximum and effective hydrogen storage capacities (mass fraction) are 2.03% and 1.12% respectively, which can satisfy the demand of hydrogen storage tanks for proton exchange membrane fuel cells (PEMFC).     

The measurement of internal surface characteristics of fuel nozzle orifices using the synchrotron X-ray micro CT technology

The design of fuel nozzle orifices at micrometer scales is crucial for generating desired fuel spray patterns, and consequently optimizing fuel combustion and emission in internal combustion engines. Although there have been several recent advancements in the characterization of orifice internal geometries, quantitative studies on the orifice internal wall surface characteristics are still challeges due to the lack of effective measuring methods. A new method for quantifying the internal wall surface characteristics of fuel nozzle micro-orifices is presented in this study to achieve a better understanding and prediction of spray characteristics: Firstly, by using the synchrotron X-ray micro CT technology, a three-dimensional digital model of the fuel nozzle tip was constructed. Secondly, a data post-processing technique was then applied to unfold the orifice internal wall surface to a flat base plane. Finally, the conventional surface characteristic quantification techniques can be used to evaluate the wall surface characteristics. Two diesel nozzles with identical orifice geometry design but different hydraulic grinding time were measured using this method. One nozzle was hydro-ground for 2 s while the other was not. The internal wall surfaces of the two orifices were successfully unfolded to base planes and their surface characteristics were respectively analyzed. The surface fluctuation data were perfectly reproduced by a Gaussian distribution function. The standard deviations of the distribution demonstrate the fluctuation range and the distribution of the entire surface fluctuation profiles. As an effective parameter to evaluate the hydraulic grinding process and the spray behaviors, the standard deviation was considered feasible for the analysis of the orifice internal wall surface characteristics.