三维直接数值模拟部分预混发动机内的燃烧过程

采用三维直接数值模拟方法研究了一个类似于部分预混燃烧(PPC)发动机条件下高辛烷值燃料PRF70的着火过程。文章采用了简化的PRF化学动力学机理,包含33个组分和38步基元反应。计算中根据发动机的几何尺寸和真实运行工况加入了气缸内压缩/膨胀的效果,并考虑了燃料的两次喷射,其中第一次喷射形成了较均匀的混合气,第二次燃料喷射增加了混合物分层。研究发现,PPC的燃烧过程非常复杂,是均质压燃、预混燃烧和扩散燃烧三种主要燃烧模式的结合。在两次燃料喷射之间的区域为近化学计量比燃烧,是氮氧化物的生成区;而在化学计量比(φ)大于2的区域,混合不充分聚集了大量未燃碳氢和CO。文章使用Marching cube算法捕捉了三维火焰锋面随时间的变化。最后,使用反应锋面上高斯曲率(k_g)与平均曲率(k_m)的联合概率密度函数(PDF)以及平均曲率随时间变化的概率密度函数,揭示了球形火焰锋面和马鞍形火焰锋面的存在,前者占主要地位,并且随着燃烧的进行,负曲率增加,主要是因为中心的燃料浓区在逐渐消耗。     

高性能甲烷催化燃烧催化剂的制备及其在天然气催化燃烧热水器上的应用

 以镧改性的Ce-Zr-O固溶体储氧材料和钇、锆改性的氧化铝(YSZ-Al2O3)的混合物为载体,浸渍活性组分Co3O4+Fe2O3+MnO2,以蜂窝状堇青石陶瓷材料为基体,制备了甲烷催化燃烧催化剂,考察了该催化剂老化前后的活性,并将其用于强鼓式家用天然气催化燃烧热水器. 结果表明,该催化剂具有很高的活性和稳定性. 使用此催化剂的天然气催化燃烧热水器的热效率达到101.1%, 同时烟气中CO和NOx污染物的排放浓度分别为0.014%和0.003%, 该热水器具有高效节能和环境友好双重优点.     

界面膜引发的乳化燃油燃烧中的振荡反应

有关小分子醇、H。和CO等易燃气体在铂催化下的高温燃烧的温度振荡及以表面活性剂为关键组分的液膜扩散振荡已有报道"－'－．但由界面膜作用而产生的乳化燃油燃烧中的振荡反应尚无其它可操作的原始研究文献,只是在前文［'j中提及过出现该现象．为了解乳化燃油燃烧过程中界面变化及其对燃烧的作用,通过静态燃烧实验配方的调节及变换以改变燃烧界面的情况．实验发现,在乳化燃油中加入一般的食用豆油,并使之水解出长链竣酸盐,则富集在燃烧界面上的长链竣酸盐所形成的界面膜对燃烧的自阻抑作用便会产生明显的振荡反应,形成火焰温度与高…     

The effect of Lewis number variation on combustion waves in a model with chain-branching reaction

In this paper we investigate the linear stability and properties of the travelling premixed combustion waves in a model with two-step chain-branching reaction mechanism in the adiabatic limit in one spatial dimension. It is shown that the Lewis number for fuel has a significant effect on the properties and stability of premixed flames, whereas the Lewis number for the radicals has only quantitative (but not qualitative) effect on the combustion waves. We demonstrate that when the Lewis number for fuel is less than unity the flame speed is unique and is a monotonically decreasing function of the dimensionless activation energy. The combustion wave is stable and exhibits extinction for finite values of activation energy as the flame speed decreases to zero. For fuel Lewis number greater than unity the flame speed is a double-valued function. The slow solution branch is shown to be unstable whereas the fast solution branch is either stable or exhibits the onset of pulsating instabilities via the Hopf bifurcation. The evolution of these instabilities leads to flame extinction.     

Experimental study of laminar lean premixed methylmethacrylate/oxygen/argon flame at low pressure

A fuel-lean laminar premixed methylmethacrylate/oxygen/argon flame at 2.67 kPa with an equivalence ratio (phi) of 0.75 has been investigated with the tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular beam sampling mass spectrometry techniques. Isomers of most observed species in the flame have been identified by measurements of photoionization mass spectra and the near-threshold photoionization efficiency spectra. Mole fraction profiles for about 42 flame species are displayed. Free radicals such as CH3, C2H3, C2H5, C3H3, C3H5, C2H3O, C4H7, C3H5O, C3H7O, C4H3O, C4H9O, C4H5O2, C4H7O2, and C5H7O2, which should be of importance in understanding the formation mechanism of some toxic substances, were detected in the flame. Moreover, no isomers of any PAHs have been detected in the lean flame. Combined with the mole fraction profiles, the formation mechanisms of the free radicals, oxygenated compounds, and other molecular intermediates are proposed and will provide important information on modeling the combustion kinetics of methylmethacrylate (MMA).     

Nonlinear theory of combustion stability in liquid rocket engine based on chemistry dynamics

Detailed models of combustion instability based on chemistry dynamics are developed. The results show that large activation energy goes against the combustion stability. The heat transfer coefficient between the wall and the combust gas is an important bifurcation parameter for the combustion instability. The acoustics modes of the chamber are in competition and cooperation with each other for limited vibration energy. Thermodynamics criterion of combustion stability can be deduced from the nonlinear thermodynamics. Correlations of the theoretical results and historical experiments indicate that chemical kinetics play a critical role in the combustion instability.     

航空煤油替代燃料模型构建方法及HEF航空煤油替代燃料模型

本文在完善燃烧化学特性参数,发展更准确的混合物特性参数计算方法的基础上,提出一套完整的、精确的航煤替代燃料模型构建方法。并采用定容燃烧弹实验系统首次测量了初始温度420和460 K、压力0.1 MPa,实际HEF航煤以及代表性组分十氢萘的层流火焰传播速度,为本文发展和验证替代燃料模型提供充分的实验数据。依据该方法提出了摩尔分数为65%正十二烷、10%正十四烷、25%十氢萘三组分HEF航煤替代燃料模型。充分的的实验和计算结果验证表明,替代燃料模型与实际HEF航煤在物理特性和燃烧化学特性方面有很高的相似性。本文提出的HEF航煤替代燃料模型和实验测量的层流火焰传播速度,为后续化学反应机理的发展与验证奠定了基础。     

The effect of ambient temperature on the propagation of nonadiabatic combustion waves

In this paper, we undertake an analytical and numerical investigation of the linear stability and properties of travelling nonadiabatic combustion wave for the case of nonzero ambient temperature. Here we consider premixed fuel with one-step exothermic reaction described by Arrhenius law. The speed of the front is estimated analytically by employing the matched asymptotic expansion approach and numerically using the shooting and relaxation methods. It is shown that increasing the ambient temperature results in the growth of both the flame speed and the region of existence of the travelling wave solutions in the parameter space. The linear stability of the travelling wave solution is investigated analytically by using the matched asymptotic expansion method and numerically by employing the Evans function approach. We demonstrate that by increasing the ambient temperature the stability of the propagating wave can also be increased.AMS subject classification: cation: 35K57, 80A25     

负载型CeO2-ZrO2固溶体的性能及其在甲烷燃烧Pd催化剂中的应用

以硅改性的氧化铝为载体,用反相微乳液法合成了负载型的CeO2-ZrO2固溶体(Ce-Zr-O/Si-Al2O3),用低温氮吸附、X射线衍射、程序升温还原、拉曼光谱和x射线光电子能谱等方法对Ce-Zr-O/Si-Al2O3的织构性能、热稳定性和储放氧性能等进行了表征.结果表明,负载后的CeO2-ZrO2晶相与负载前相比没有变化,但热稳定性和在低温下的放氧能力及总储氧量明显提高.作为甲烷燃烧Pd催化剂的载体,Ce-Zr-O/Si-Al2O3的性能明显优于CeO2-ZrO2,Si-Al2O3和机械混合物CeO2-ZrO2 Si-Al2O3.使用0.2%Pd/10?-Zr-O/Si-Al2O3为催化剂时,甲烷90%转化率时的温度仅为345℃,比负载在其它载体上的Pd催化剂低175℃.     

F-T柴油在直喷式柴油机中燃烧与排放特性的研究

煤通过Fischer-Tropsch (F-T)合成可得到十六烷值高、硫和芳香烃质量分数极低的F-T柴油。研究分析了未作改动的单缸直喷式柴油机燃用F-T柴油时的燃烧和排放特性。结果表明,与燃用0号柴油相比,燃用F-T柴油时的滞燃期平均缩短18.7%,预混燃烧放热峰值降低26.8%,扩散燃烧放热峰值较高,燃烧持续期相当。燃用F-T柴油时的最高燃烧压力略低,最大压力升高率显著下降,机械损失和燃烧噪音较小,燃油消耗率和热效率都得到显著改善。燃用F-T柴油可同时降低CO、HC、NOx和炭烟排放,其中NOx和炭烟分别平均降低16.7%和40.3%。研究表明,F-T柴油是柴油机良好的清洁代用燃料。     

木醋调质石灰石用于O2/CO2燃煤同时脱硫脱硝性能

采用管式炉和沉降炉分别研究了O₂/CO₂气氛下燃煤预混和烟气喷入木醋调质石灰石的同时脱硫脱硝性能。结果表明,在温度1 173~1 323 K、钙硫比为2.0的条件下,木醋调质石灰石混煤燃烧脱硫效率91.0%~94.9%、脱硝效率23.5%~30.8%。随着钙硫比的增加,木醋调质石灰石混煤燃烧脱硫脱硝效率增大,适宜的钙硫比为1.5~2.0。相同的燃烧温度和钙硫比,含硫量高的煤预混木醋调质石灰石燃烧获得较高的脱硫、脱硝效率。木醋调质石灰石用于O₂/CO₂燃煤脱硫脱硝性能优于醋酸钙。O₂/CO₂燃煤烟气中喷入木醋调质石灰石、钙硫比为2.0、停留时间为0.8 s、在1 223和1 323 K时获得最大脱硫效率和最大脱硝效率为75.8%和86.6%。在上述条件下将氨气喷入反应区,氨氮比为0.75、温度为1 223和1 323 K时,脱硫效率分别为73.2%和63.9%,脱硝效率分别为93.2%和94.8%。     

CSP分析方法在简化燃烧化学反应系统中的应用

基于计算奇异摄动(CSP)思想, 对甲烷/空气预混燃烧系统进行分析. CSP将反应空间分裂, 消除刚性; 将单点分析和全局分析相结合, 合理选择主要组分和稳态物质, 使用CSP的特征指数简化方程. 构建了针对甲烷/空气预混燃烧系统的总包15步反应机理, 并利用Sandia实验室的PREMIX软件包对该系统进行分析, 验证了简化机理的准确性, 证实了CSP分析方法在燃烧系统中应用的可靠性和优越性, 并为研究简化燃烧系统的分析提供了一种新的思路.     

激光诱导荧光法测量内燃机双燃料燃烧过程中的甲醛和羟基

双燃料燃烧是一种实现内燃机高效清洁燃烧的新型燃烧方式,国内外对燃用双燃料的内燃机性能和排放开展了较为广泛的研究,但对双燃料缸内燃烧过程的认识有待深入.本文搭建了一套光学发动机缸内燃烧中间产物激光测试系统,该系统可以实现甲醛和羟基(OH)的二维同时定性测量.为了验证该激光诊断系统的可行性,首先在甲烷层流预混火焰上对甲醛和羟基的激光诱导荧光(LIF)光谱和图像进行采集,确定甲醛和OH激发波长分别为355和282.95 nm.随后在光学发动机上对双燃料缸内燃烧过程中甲醛和羟基进行了非同时测量,分析了双燃料燃烧双阶段放热过程中甲醛和OH分布区域.光学发动机转速为1200 r·min^-1,循环当量总油量为30 mg正庚烷.进气冲程初期气道喷射异辛烷,上止点前10°曲轴转角在缸内直喷9 mg正庚烷.激光诱导荧光成像表明,甲醛生成于低温放热阶段,主要分布在缸内直喷燃油油束附近区域,之后甲醛充满整个燃烧室空间;高温放热过程中燃烧室壁面附近区域的甲醛首先消耗,伴随甲醛消耗OH首先出现于燃烧室边缘,高温放热阶段过后,甲醛基本消失, OH逐渐充满整个燃烧室.最后对双燃料缸内燃烧过程甲醛和OH同时测量发现,甲醛消耗伴随OH的产生,甲醛和OH分布区域总体而言在空间上是分开存在的,但在局部区域甲醛和OH可能并存.     

On the Structure of the Spectra for a Class of Combustion Waves

The stability of a premixed laminar flame supported by a general combustion reaction system is considered using the Evans function method. The spectrum of the linearised second-order differential operator is investigated in detail. The special structure of the differential equations due to an Arrhenius temperature dependence is exploited. It is shown that, for certain combustion systems, the limit of the Jacobian of the reaction terms as the travelling wave coordinate approaches the front and rear of the flame is a lower triangular matrix. For this type of system a simple geometrical method is shown for the study of the essential spectrum of the linearised operator, and for determining the domain of the Evans function. The results are applied to some representative combustion reactions.     

Pd/NiAl_2O_4催化剂上甲烷燃烧反应的红外光谱研究

采用原位红外光谱研究了Pd/NiAl2O4催化剂上甲烷燃烧反应机理,考察了Pd在载体上的氧化-还原状态对催化剂性能的影响.结果表明,甲酸盐向碳酸盐的转化是反应的控制步骤.经预还原处理的催化剂在贫燃富氧条件下反应一段时间后,活性组分仍为Pd-PdO混合形态;Pd单质的存在使O2在其上吸附形成活性O2-物种,从而促进了甲酸盐向碳酸盐的转化.     

铌改性的Pd/Al2O3催化剂催化苯燃烧反应简

采用浸渍法制备了Nb改性的Pd/Al2O3催化剂,考察了该催化剂催化苯燃烧反应性能,并研究了催化剂的稳定性. 结果表明,Nb的添加明显提高了Pd/Al2O3催化剂性能,在195 ℃时苯转化率达到90%,苯的完全燃烧温度降低了40 ℃. 采用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、H2 程序升温还原(H2-TPR)、NH3程序升温脱附(NH3-TPD)和氮气吸附等手段对催化剂进行了表征,结果表明,Nb的加入不仅提高了Pd物种的分散度,同时改变了部分Pd的价态,形成适宜反应的PdO-Pd物种,并促进了催化剂表面氧浓度的增加,使氧物种氧化能力增强,从而提高了催化性能. 1%Pd-5%Nb/Al2O3催化剂的催化活性高于2.0%Pd/Al2O3催化剂.     

Solution combustion synthesis of Co oxide-based catalysts for phenol degradation in aqueous solution

Solution combustion using urea as a fuel was employed to synthesise Co oxide and Al(2)O(3)-, SiO(2)- and TiO(2)-supported Co oxide catalysts. The catalysts were characterised using several techniques such as N(2) adsorption/desorption, XRD, FTIR, UV-vis diffuse reflectance and SEM-EDX, and their catalytic activity was evaluated in phenol degradation in aqueous solution with sulphate radicals. Solution combustion is a simple and effective method in preparation of supported Co catalysts. Co(3)O(4) was the major Co crystal phase in the samples prepared via the combustion synthesis. Bulk Co(3)O(4) particles were not effective in reaction, but supported Co oxides showed higher activity than unsupported Co oxide. The supports influenced Co dispersion and catalytic activity. Co/TiO(2) exhibited the highest activity, but it deactivated much faster than other two supported catalysts. Co/SiO(2) showed a comparable activity to Co/Al(2)O(3) and the best stability among the three Al(2)O(3)-, SiO(2)- and TiO(2)-supported Co catalysts.     

La取代Ba对Ba1-xLaxMn3Al9O19-α催化剂结构及甲烷催化燃烧性能的影响

采用以尿素水解为基础的水热合成法制备了La和Mn取代的六铝酸盐催化剂(Ba1-xLaxMn3Al9O19-α).在Mn含量达到阈值时,研究了不同量的La取代Ba对Ba1-xLaxMn3Al9O19-α的相组成、结构、热稳定性及甲烷催化燃烧活性的影响.当x≥0.4时,水热合成过程中生成的La2(CO3)3在530-580℃分解,800-900℃时与-γAl2O3反应生成LaAlO3钙钛矿相,可抑制由BaCO3分解而生成的Ba2+的固相扩散,从而阻止了BaAl2O4尖晶石相的生成,使Ba2+在固相中保持较高的分散性,促进了六铝酸盐(-βAl2O3)相的形成.当x<0.4时,BaAl2O4尖晶石相的存在引起催化剂比表面积和催化燃烧活性的降低.La3+取代Ba2+后,六铝酸盐结构发生一定程度的扭变.这种扭变越大,所形成的六铝酸盐催化剂的热稳定性越差.Ba1-xLaxMn3Al9O19-α催化剂的甲烷催化燃烧活性随x的增大而增加,x=0.8时催化剂的活性最佳.     

Ni的引入对Pd/Al2O3催化甲烷燃烧性能的影响

采用浸渍法制备了Ni掺杂的Pd/Al2O3催化剂,考察了其低浓度甲烷催化燃烧活性和水热稳定性.结果表明,随着Ni的引入及其含量的增加,Pd/Al2O3催化剂性能明显提高,Ni含量至20%时,在0.4%CH4,4%H2O和空气平衡的原料气组成,80000h-1空速和600oC条件下反应150h后,CH4转化率仍能保持在97.5%以上.X射线衍射、H2程序升温还原、NH3程序升温脱附和透射电镜等结果表明,NiAl2O4晶相的形成改善了载体酸性和活性组分的分散度,从而提高了催化剂性能.     

Ce0.45Zr0.45Y0.07La0.03O1.95/La-Ba-Al2O3质量比对整体式铁基催化剂上稀薄甲烷燃烧的影响

采用共沉淀法和胶溶法分别制备了高性能的储氧材料Ce0.45Zr0.45Y0.07La0.03O1.95(OSM)和耐高温高比表面的La-Ba-Al2O3,并以它们为载体,制备了一系列整体式铁基催化剂.考察了该系列催化剂对甲烷稀薄燃烧的催化性能.并用低温N2吸附-脱附,储氧量(OSC)测试,X射线衍射(XRD)和H2程序升温还原(H2-TPR)等测试手段考察了不同Ce0.45Zr0.45Y0.07La0.03O1.95/La-Ba-Al2O3质量比对催化剂特性的影响.活性测试结果表明,当Ce0.45Zr0.45Y0.07La0.03O1.95/La-Ba-Al2O3质量比为1:1时新鲜和老化催化剂的活性均最好,新鲜催化剂可在50000h-1的高空速条件下使含量为1%(体积分数)的甲烷在446℃起燃,553℃完全转化;低温氮气吸附-脱附测试结果和H2-TPR表明,不同的Ce0.45Zr0.45Y0.07La0.03O1.95/La-Ba-Al2O3质量比使催化剂表现出不同的织构性能和还原性能;XRD测试结果表明,OSM以均一固溶体存在,Fe高度分散在载体上.综合以上表征手段得出:合适的Ce0.45Zr0.45Y0.07La0.03O1.95/La-Ba-Al2O3质量比导致催化剂具有优异的稀薄甲烷催化燃烧活性和热稳定性.