燃烧系统参数对商用车发动机燃烧和排放特性的影响研究

为改善商用车发动机性能,采用计算流体力学（computational fluid dynamics, CFD）模拟、正交设计等方法,针对某商用车的燃烧室结构参数设计了4种新方案,并选取油束夹角、喷雾锥角、主喷正时等3个喷油参数开展多因素影响研究。结果表明：燃烧室形状曲线向内收缩且最大半径增大的方案1燃烧室可提升缸内湍流特性,改善燃油浓度分布,使燃烧速度加快,油气混合更好,为最优方案。在喷油参数研究方案中,以碳烟（soot）排放为优化指标时,油束夹角对排放特性影响最大,最优匹配方案是油束夹角147°、喷雾锥角15°、主喷正时-1°,其缸内碳烟排放较原机下降13.91%,且NO_x排放减少13.98%;以氮氧化物（nitrogen oxides, NO_x）排放为优化指标时,主喷正时对排放特性影响最大,最优匹配方案是油束夹角160°、喷雾锥角25°、主喷正时-1°,其缸内NO_x排放较原机降低37.79%。     

船用重油多元模型燃料的构建与验证

为了复现实际船用重油燃料燃烧特性,基于化学解构法原理,提出了重油多元模型燃料。选择了正十四烷、2,6,10-三甲基十二烷、四氢化萘和正癸基苯作为基础燃料,表征实际重油的正构烷烃、异构烷烃、环烷烃和芳烃成分。模型燃料的比例依据带权欧几里得距离算法进行最优化求解。针对发展的多元模型燃料,基于流动反应器试验平台对模型燃料的中低温氧化特性进行点对点比较,多组分模型燃料成功复现了典型反应物、中间产物和生成物浓度随温度变化的趋势。基于“解耦法”的机理简化方法,发展了重油多组分模型燃料骨架机理。该机理成功预测了重油馏分的中低温氧化特性。基于该骨架机理进行敏感性分析,得到出烷烃类自由基主导的基元反应对重油碳烟生成密切相关。此外,基于定容燃烧装置数值仿真结果,证明了重油多组分模型燃料对近发动机条件下的喷雾燃烧过程具有较高的预测能力。     

HRD-76柴油生物燃料的模型燃料构建

HRD-76作为典型的第二代柴油生物燃料得到广泛关注.本文通过匹配核磁共振光谱分析的官能团信息,选用2,6,10-三甲基十二烷和正十六烷作为HRD-76燃料的模型燃料.构建了模型燃料的化学反应机理,并对该机理的可靠性进行了验证.最后,利用该模型燃料对HRD-76燃料在不同条件下的着火延迟时间进行了模拟.该模型燃料与实验值和其他经典模型燃料进行了对比,结果表明,本文模型燃料具有简单、高效和精确的特点.模型燃料的构建为深刻认识HRD-76燃烧过程,实现燃烧反应流模拟研究奠定了基础.     

褶皱式玻璃纤维基底的钒基催化剂性能研究

基于NH₃选择性催化还原（selective catalytic reduction, SCR）反应机理,对采用褶皱式玻璃纤维基底的钒基催化剂在重型柴油机中的应用性能进行模拟研究,并与传统堇青石基底钒基催化剂进行对比。利用国六发动机台架测试结果对模拟程序进行了验证,然后研究了氨氮比、NO₂/NO_x比及空速对褶皱式玻璃纤维基底的钒基催化剂在低温下NO_x转化及NH₃泄漏特性的影响。结果表明：低温下褶皱式玻璃纤维基底钒基催化剂的NO_x转化性能明显优于相同条件下的堇青石基底钒基催化剂。氨氮比的增加对褶皱式玻璃纤维基底的钒基催化剂的NO_x转化性能无明显影响;当氨氮比从0.8增加到1.2时,在200 ℃~500 ℃的区间内NH₃的泄漏量由1×10^-6提高到100×10^-6。NO₂/NO_x比增加可有效提高钒基催化剂的低温性能。当温度为150 ℃时,NO₂/NO_x比由0提高为0.5,钒基催化剂的NO_x的转化效率从14.0%上升到76.0%,而NH₃泄漏量由428×10^-6下降为9×10^-6。当温度为200 ℃时,30 000 h^-1空速下钒基催化剂的NO_x转化效率为98.5%,比90 000 h^-1下提升近30.0%;NH₃泄漏量为7×10^-6,比90 000 h^-1下降低150×10^-6。     

氢发动机SCR催化器的NOx转化效率模拟

建立一维选择性催化还原（selective catalytic reduction，SCR）催化器模型，采用稳态、瞬态小样试验标定SCR化学反应动力学机理，并分析SCR催化器对氢发动机排气中NO_x的催化还原过程。结果表明：入口O₂体积分数对NO_x催化还原有抑制作用，但入口H₂O体积分数对NO_x转化效率没有明显影响；当温度为250~400 ℃时，线性温升工况NO_x转化效率高于稳态工况且超过98%；氢发动机排气温度和原排NO_x体积分数随功率增大而增大，当功率大于60 kW且氨氮比等于1时，SCR催化器转化效率小于95%；增加氨氮比对NO_x转化效率的提高作用较小，这是由于在高温条件下增加的NH₃倾向与O₂反应。     

EGR废气组分比例对柴油引燃天然气发动机燃烧与排放特性的影响

为了改善柴油引燃天然气发动机的排放性能，开展废气再循环（EGR）废气组分比例对柴油引燃天然气发动机燃烧过程的影响研究。针对一款直列六缸四冲程柴油引燃天然气发动机进行台架试验，基于试验数据搭建并标定CFD仿真模型，在此基础上研究不同质量比的EGR废气组分（CO₂和水蒸气）对柴油引燃天然气发动机燃烧与排放特性的影响。结果表明，引入CO₂和水蒸气后缸内压力和温度均出现明显下降， EGR废气组分中水蒸气质量分数越高，缸内压力和温度越低。总体来说，CO₂和水蒸气对发动机排放特性的影响明显大于对燃烧特性的影响。当引入EGR废气组分全部为水蒸气时，缸内氮氧化物（NO_x）排放最低（920×10^-6）。当CO₂和水蒸气质量分数相同时，CO排放相较于初始状态下降11%。     

2,6,10-三甲基十二烷的详细化学反应机理构建

2,6,10-三甲基十二烷作为极具潜力的可再生燃料而得到广泛的关注.为了深刻认识该燃料的燃烧过程,本文采用反应类的机理构建方法,为2,6,10-三甲基十二烷构建了详细化学反应机理.该详细反应机理对着火延迟时间的验证结果表明,新反应路径的加入能够提高低温区域的预测精度.同时,对该机理的流动反应器重要组分浓度和层流火焰传播速度也进行了验证.模拟值与实验值吻合良好,证明了该化学反应机理的有效性,也为实现燃料反应流模拟研究创造了条件.     

引燃策略对天然气直喷发动机射流燃烧及排放的影响

基于计算流体力学（computational fluid dynamics, CFD）软件CONVERGE研究了天然气直喷发动机的高压天然气射流混合、引燃燃烧及排放物生成等基础过程,详细分析了引燃方式和引燃距离对这些基础过程的影响。结果表明：高压直喷天然气射流能够明显促进引燃柴油喷雾发展与混合,但引燃柴油喷射对天然气射流发展影响不明显。高压直喷天然气射流火焰中心存在温度较低而天然气浓度较高的火焰内陷区,该内陷区是碳烟的主要生成区域,碳烟高浓度区位于火焰内陷区中后部。与引燃方式相比,引燃距离对火焰浮起长度、火焰内陷长度及NO_x和碳烟排放有更明显影响。随引燃距离增加,火焰浮起长度和NO_x排放增加,火焰内陷长度和碳烟排放减小。柴油喷入天然气中引燃在3种引燃方式中具有最高的放热率峰值和最短的燃烧持续期,其NO_x和碳烟排放最低,但甲烷逃逸量最高。     

正丁醚/柴油混合燃料在单缸柴油机中的燃烧与排放特性研究

基于一台单缸压燃式发动机,研究了正丁醚（di-n-butyl ether, DnBE）/柴油混合燃料的燃烧与排放特性,并与纯柴油的试验结果进行了对比。分别采用平均指示有效压力（indicated mean effective pressure, IMEP）即发动机负荷0.55 MPa、0.65 MPa、0.75 MPa,废气再循环（exhaust gas recirculation, EGR）率0%、15%、30%,喷油正时上止点后-15°、-10°、-5°、0°及正丁醚掺混体积比20%、40%,综合评估了正丁醚/柴油混合燃料在不同发动机运行工况下的特性。台架试验结果表明：相比于纯柴油,正丁醚的添加使得缸内压力上升相位及放热开始时刻提前,并且在30% EGR率工况下更加明显。在所有测试工况下,正丁醚/柴油混合燃料的预混燃烧比例均小于纯柴油,且第一阶段放热率峰值更低。由于十六烷值的差异,40%正丁醚/柴油混合燃料的着火延迟时间与燃烧持续期更短且燃烧重心更早,表明其具有更快的燃烧速率。试验发现大比例正丁醚/柴油混合燃料的燃烧等容度更高,指示热效率高于纯柴油。此外,添加正丁醚后尾气中的NO_x与碳烟排放都会降低,而提高EGR率或推迟喷油均能有效减少NO_x的生成。综合而言,添加正丁醚可以有效缓解柴油机中NO_x排放、碳烟排放与指示热效率之间的权衡关系。     

氢气直喷对发动机燃烧及排放性能的影响

基于一台高压直喷汽油机,将汽油直喷喷射器替换为氢气直喷喷射器,试验研究了发动机燃用氢气与汽油时的燃烧和排放特性差异。采用空气稀释,进一步分析了氢气发动机稀薄燃烧模式下热效率提升潜力及氮氧化物排放特性,明确了氢气燃料对发动机燃烧及污染物排放的影响规律。结果表明,当量燃烧模式下,相比汽油发动机,氢气发动机的燃烧持续期明显缩短,有效热效率降低,NO_x排放升高,CO及总碳氢（total hydrocarbon, THC）排放显著降低。提高氢气发动机的过量空气系数有助于改善有效热效率。在中等负荷工况下,过量空气系数为2.7时有效热效率可达43.5%。增大过量空气系数,氢气发动机能够在保持较高燃烧稳定性的情况下显著降低NO_x排放。在低负荷工况下,当过量空气系数大于2.3时NO_x排放最低可降低至44×10^-6。     

褐煤干燥及热解机理研究现状

单个大颗粒褐煤干燥、热解机理的研究对于褐煤提质技术的开发具有重要的理论与实际意义,可用于该过程的数值计算与优化研究.对于单个大颗粒褐煤而言,在干燥、热结过程中内部存在较大的温度、水含量及挥发分含量的梯度,所涉及到的科学问题为多孔介质传热与传质问题.文中主要针对褐煤的干燥机理、热解机理及堆积态干燥过程机理进行了详细的文献调研.     

Comparing photocatalytic activity consisting of Sb2S3 and Ag2S on the TiO2–SiO2/TiO2 nanotube arrays-support for improved visible-light-induced photocatalytic degradation of a binary mixture of basic blue 41 and basic red 46 dyes

In the present study, a TiO₂ nanotube (TNAs) supported Sb₂S₃–TiO₂–SiO₂ (STS/TNAs), and Ag₂S–TiO₂–SiO₂ (ATS/TNAs) hybrid novel photocatalysts were prepared and characterized by XRD, FT-IR, SEM-EDX, X-ray mapping and, DRS. EIS was employed, and an equivalent circuit model is proposed. Flat-band potential and free carrier concentration were determined by Mott–Schottky plots. The obtained catalysts were used in the photodegradation of a binary mixture of Basic Blue 41 (BB41) and Basic Red 46 (BR46) dyes. Compared with ATS/TNAs, STS/TNAs photocatalyst showed the highest apparent rate constant for BB41 dye, about two times higher, and BR41 dye more than 1.5 times. EIS results agreed with the photodegradation results, so the STS/TNAs system with higher charge transfer ability than the ATS/TNAs system showed the best photodegradation activity. The optimization effect of the amount of Sb₂S₃, TiO₂, and SiO₂ doped on the TNAs on the photocatalytic activity of the STS/TNAs was done using a central composite rotatable design (CCRD) based response surface methodology (RSM). Results have shown catalyst containing 12.2% Sb₂S₃ and 27.1% SiO₂/TNAs (S₃TS₃/TNAs) the best photodegradation activity was obtained. The GC-Mass analysis was done to detect the degradation intermediates formed during the photodegradation process.     

Role of S-S interlayer spacing on the hydrogen storage mechanism of MoS2

Hydrogen storage mechanism and hydrogen storage capacity are the great challenges for the development of hydrogen energy technology. Besides the better catalytic properties, it is crucial to search for suitable material that provides enough space to store H₂ molecule. Similar to graphene, MoS₂ with S-S layered structure opens up a new way to improve the hydrogen storage capacity. By using the first-principles calculations, in this work, we investigate the hydrogen diffusion mechanism, hydrogenation process and hydrogen storage capacity of MoS₂ with S-S interlayer. We find that hydrogen prefers to diffuse into S-S interlayer along the interstitial site (path: IT-IT). H₂ molecule is a stable in S-S interlayer because the charge interaction of H-H atoms is stronger than that of H-S atoms. Finally, we predict that MoS₂ with S-S layered-by-layered stacking can effectively improve the hydrogen storage capacity.     

论温室气体减排法律机制

气候变化是当前人类面临的严重的全球性环境问题,温室气体排放是引起全球气候变化的一个重要原因。介绍了《京都议定书》为发达国家实现温室气体减排目标提供的低成本的替代性法律机制,指出了这些机制存在的不足之处．为在2012年之后的后京都时代进一步完善温室气体减排法律机制提出了建议。     

Heat transfer in solar-bioclimatic houses

A study is presented on the ventilation mechanism of patio dwellings. The combined heat transfer by natural and forced convections, conduction is studied by solving the governing equations for mixed convection and conduction. The flow is assumed to be laminar and two dimensional. The density variation is taken into account by the Boussinesq approximation. The control-volume approach is used for solving the governing equations of conjugate heat transfer involving conduction in the walls. The study covers the Rayleigh number from 10³ to 10⁶, the Reynolds number from 10 to 10³ and k_r = k_mat/k_air from 0 to 100 for Pr = 0.72 (air) and cavity aspect ratio B from 0.8 to 1.3. produced and the results are presented in terms of the Nusselt number as function of other parameters. The mechanism of ventilation in patio systems is discussed.     

Visible light-induced degradation of indigo carmine over ZnFe2O4/Tannin/ZnO: Role of tannin as a modifier and its degradation mechanism

Design and usage of efficient visible light photocatalytic systems for wastewater treatment and degradation of organic dyes are of remarkable interest in the fields of environmental protection. In this study, magnetic ZnFe₂O₄, ZnFe₂O₄/ZnO, Tannin/ZnFe₂O₄ and Tannin/ZnFe₂O₄/ZnO nanocomposites with interfacial contact have been synthesized. The photocatalytic efficiencies of as-obtained samples are analyzed by the degradation of indigo carmine in aqueous solution under UV and visible-light. The degradation ratios of IC are 82% and 99% of IC over the Tannin/ZnFe₂O₄/ZnO under the both of UV light and visible light for 90 min, respectively. And after five times recycling, the photocatalytic performance of IC presence the Tannin/ZnFe₂O₄/ZnO can even reach nearly 89.79%. The results demonstrate that the Tannin/ZnFe₂O₄/ZnO exhibits great photocatalytic efficiency for indigo carmine (IC) compared to their constituent photocatalysts and easy separation from dye solution by magnet. The synergistic interactions between ZnFe₂O₄, tannin and ZnO prolonged lifetime of photoexcited carriers leading to greater absorption in both UV and visible light. This nanocomposite was beneficial for separating the photogenerated charge carriers and facilitating electron transfer. Tannin has a decisive role for increasing the photocatalytic performance of ZnFe₂O₄ due to the abundant units of phenolic groups in tannin molecules. ZnFe₂O₄ makes the Tannin/ZnFe₂O₄/ZnO magnetically separable in a system. This work presents new insights that tannin molecules function as great modifier to improve very impactful tannin-modified magnetic photocatalysts in removing environmental contamination.     

高炉煤气蓄热式燃烧化学动力学机理研究

探讨了低热值煤气蓄热式燃烧的化学动力学特性。针对目前开展蓄热式燃烧数值模拟工作常用的总包化学机理进行优选,并利用PSR反应器对蓄热燃烧典型气氛进行不同时间尺度的演化,分析其主要组分的变化特性。同时将优选出来的总包机理应用到3 MW低热值煤气燃烧炉进行数值模拟预测。结果表明,采用JL机理模拟所得的CO浓度分布与详细化学机理和实验结果接近,而不考虑CO逆反应过程时, LA机理模拟结果显示CO燃烧过快。 JL机理对炉膛全场的温度分布与实验值也更相近,同时炉膛出口处的温度误差为全场误差最大值,约为50 K。 JL机理可以被很好的应用至低热值煤气高温空气燃烧预测。     

正庚烷均质压燃燃烧简化动力学模型

在详细化学反应动力学研究的基础上,通过对正庚烷均质压燃燃烧各阶段反应途径分析和敏感性分析,构建了一个新的包括35种物质和41个基元反应的正庚烷均质压燃简化动力学模型．在发动机模拟方面,对此模型进行有效性分析,结果表明,在一定的边界条件范围内,简化动力学模型在着火时刻、缸内温度和压力方面都与详细动力学模型吻合较好,简化动力学模型适用于模拟HCCI部分燃烧边界条件．     

Graphene-anchored Ni6MnO8 nanoparticles with steady catalytic action to accelerate the hydrogen storage kinetics of MgH2

Transition metal-based oxides have been proven to have a substantial catalytic influence on boosting the hydrogen sorption performance of MgH₂. Herein, the catalytic action of Ni₆MnO₈@rGO nanocomposite in accelerating the hydrogen sorption properties of MgH₂ was investigated. The MgH₂ + 5 wt% Ni₆MnO₈@rGO composites began delivering H₂ at 218 °C, with about 2.7 wt%, 5.4 wt%, and 6.6 wt% H₂ released within 10 min at 265 °C, 275 °C, and 300 °C, respectively. For isothermal hydrogenation at 75 °C and 100 °C, the dehydrogenated MgH₂ + 5 wt% Ni₆MnO₈@rGO sample could absorb 1.0 wt% and 3.3 wt% H₂ in 30 min, respectively. Moreover, as compared to addition-free MgH₂, the de/rehydrogenation activation energies for doped MgH₂ composites were lowered to 115 ± 11 kJ/mol and 38 ± 7 kJ/mol, and remarkable cyclic stability was reported after 20 cycles. Microstructure analysis revealed that the in-situ formed Mg₂Ni/Mg₂NiH₄, Mn, MnO₂, and reduced graphene oxide synergically enhanced the hydrogen de/absorption properties of the Mg/MgH₂ system.     

Synthesis and hydrogen storage property tuning of Zr(BH4)4·8NH3 via physical vapour deposition and composite formation

Zr(BH₄)₄·8NH₃ is considered to be a promising solid state hydrogen-storage material, due to its high hydrogen capacity and low dehydrogenation temperature. However, the possible applications of Zr(BH₄)₄·8NH₃ have been greatly hampered by the complicated and less applicable synthesis process, which must be operated at relatively low temperature (<20 °C). Herein, we reported a simple and facile “heating-(ball milling) BM vial” method via physical vapour deposition to tackle this issue. By this technique, Zr(BH₄)₄·8NH₃ was successfully synthesized. Furthermore, composite formation by adding 10 wt% NaBH₄ to the as-prepared Zr(BH₄)₄·8NH₃ was found to be able to lower down the dehydrogenation peak of Zr(BH₄)₄·8NH₃ from 130 to 75 °C and more excitingly, the possible emission of B₂H₆ and NH₃ from dehydrogenation of only Zr(BH₄)₄·8NH₃ was completely suppressed after addition of NaBH₄. This research presents a new hydrogen-storage system based on Zr(BH₄)₄·8NH₃+NaBH4 composite and it also implies a new development methodology of future hydrogen storage materials.