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。     

铜分子筛涂覆颗粒捕集催化剂的实验研究

针对柴油催化氧化系统（diesel oxidation catalyst，DOC）、颗粒捕集器（diesel particulate filter，DPF）、选择性催化还原（selective catalytic reduction，SCR）系统应用于轻型车时面临的催化剂布置困难和SCR催化剂温度低等问题，将SCR催化剂涂覆到DPF载体（简称SDPF），实现NO_x减排和PM捕集功能，同时可显著减小后处理催化剂的体积。分别考察SDPF在200、300和400 ℃时不同碳烟加载量下的台架测试背压，测试结果表明SDPF催化剂加载碳烟在0~4.0 g/L范围内背压增长显著，在4.0~6.0 g/L范围内背压增长不明显。选取体积类似的SDPF和SCR催化剂进行新鲜态NO_x转化性能对比测试，测试结果表明：SDPF催化剂仅需相同体积SCR催化剂约2/3的涂覆量即可达到相当的NO_x转化能力，碳烟加载主要影响230 ℃以下的低温段NO_x转化。SDPF载体积炭量达到6.0 g/L后进行快速升温，以测试催化剂的积炭再生性能。测试结果表明：SDPF积炭再生时高温区域集中在出气端中心区域，可探测最高温度低于650 ℃，较充分的碳烟再生时间应大于15 min。     

工作环境对自然吸气柴油机性能影响仿真

基于CY4102BG四冲程自然吸气柴油机,利用GT-POWER一维仿真计算软件建立柴油机工作过程仿真模型,研究高原和水下工作环境对柴油机性能的影响。仿真结果表明：随着海拔的增高,柴油机有效功率有所下降,NO_x排放上升,排气温度增加;随着水下排气背压的增高,柴油机有效功率下降,NO_x排放显著上升。针对柴油机在非标况环境下NO_x排放性能的恶化,通过调节喷油参数来优化柴油机综合性能。经优化,在不同工作环境下柴油机NO_x排放降低7.3%~21.4%,优化效果较为明显。     

基于废气再循环的防爆柴油机清洁燃烧技术

针对某型煤矿用防爆柴油机NO_x排放物污染严重、危害大的问题,分析防爆柴油机的燃烧过程,建立燃烧数学模型。通过流体仿真分析软件对基于废气再循环系统的防爆柴油机的清洁燃烧过程模拟仿真并进行台架试验。试验结果表明：在8种工况下加装废气再循环的系统在优化后的废气再循环开度下防爆柴油机CO排放加权平均值为0.004 5%,与未加装废气再循环的系统相比体积分数增加0.004 5%;加装废气再循环的系统在优化后的废气再循环开度下防爆柴油机NO_x排放加权平均值为93.35×10^-6,与未加装废气再循环的系统相比降低56.17%,采用废气再循环的系统对降低防爆柴油机的NO_x排放效果明显。     

国六柴油机轨压和喷油正时对柴油机性能的影响

为优化柴油机性能,基于一台配备了完整国Ⅵ后处理系统的高压共轨直列4缸柴油机,开展了柴油机负荷特性研究,在此基础上研究轨压和喷油正时对柴油机性能的影响。研究结果表明：以适当较小的轨压配合较为提前的喷油正时可以达到较为理想的柴油机油耗及排放;轨压和喷油正时对HC排放的影响较小;轨压对柴油机油耗、排温、NO_x排放、CO排放的影响较大,且在中等偏高负荷时更为敏感,随着轨压增加了57 MPa,柴油机油耗、排温分别下降了16.1 g/（kW·h）、63 ℃,NO_x排放上升了663×10^-6,CO排放下降了785×10^-6;喷油正时对烟度及柴油机氧化催化器前端温度T₄、柴油机颗粒捕集器前端温度T₅、选择性催化还原系统前端温度T₆的影响较大,且在低负荷时更为敏感。随着喷油正时提前6.0°,烟度下降了0.43%,T₄、T₅、T₆峰值出现在轨压为76 MPa且喷油正时为上止点前7.5°时,温度分别为315.3、338.4、329.3 ℃。     

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。     

离心风机叶型安装角βb(r)径向分布的气动作用研究

基于计算流体力学计算了3种叶型安装角β_b(r)径向分布的离心风机流场,研究了β_b(r)径向分布的变化对叶轮流道内气流角、惯性力及风机性能等参数的影响,为离心风机叶片造型阶段实现叶轮流道内流动的精细控制提供了依据。研究结果表明,β_b(r)分布会显著影响叶轮流道内物理参数的变化趋势,对叶轮出口参数周向分布影响较小。进、出口参数相同时,风机外特性因β_b(r)分布的不同存在明显差异。惯性力流线法向分量对叶轮出口附近吸力面边界层的发展趋势会产生影响,其大小与流线曲率有关。     

低负荷工况下城市类重型柴油车的实际道路排放特性研究

应用便携式排放测试系统（portable emission measurement system, PEMS）,对3辆不同类型的城市类重型柴油车分别进行实际道路行驶排放测试。试验车辆包括：邮政车、垃圾自卸车、小学专用校车。对于处在不同负荷段的数据进行分类整理,分析车辆在低负荷工况下不同负荷段的CO、NO_x、颗粒物数量（particulate number, PN）的排放占比和比排放结果,并结合功基窗口法分析NO_x的排放特性。试验结果表明：在低负荷工况时,尤其是负荷率处于0~20%的阶段,CO、NO_x、PN的排放量占比分别达到72%~86%、60%~87%、52%~88%,且CO、NO_x、PN在低负荷阶段的比排放高于或接近国六排放限值。     

不同硅铝比对Cu-SAPO-34的NH3-SCR性能及低温水热老化稳定性的影响

采用新型一锅法合成一系列硅铝比不同的Cu-SAPO-34催化剂。合成过程中，硅铝比分别设为0.3、0.4、0.5、0.6、0.7、0.8，通入70 ℃含水10%的空气16 h进行低温水热老化。对新鲜和老化后的催化剂的NO_x去除活性、N₂选择性进行了实验测定；并进行了BET、XRD、H₂-TPR以及NH₃-TPD表征实验。结果发现:硅铝比为0.4的Cu-SAPO-34，其NO_x去除效率和低温水热老化稳定性都达到最佳。从XRD、H₂-TPR、NH₃-TPD的表征结果也可以发现:硅铝比为0.4的Cu-SAPO-34催化剂在结构、铜离子特性及分布、表面酸性位点等特征都达到了一个相对优化的状态。由此得出结论:提高Cu-SAPO-34的NH₃-SCR性能以及低温水热稳定性的关键是，合成过程中保证硅铝比维持在一个比较小的值。     

g-C3N4/TiO2可见光催化降解磺胺甲恶唑的研究

以TiO₂颗粒和三聚氰胺为原料,采用高温煅烧法制备g-C₃N₄/TiO₂复合光催化材料,研究其对仿生生态系统中磺胺类抗生素的去除效果。利用扫描电子显微镜（SEM）、X射线衍射仪(XRD)、傅里叶变换红外光谱仪（FTIR）、紫外可见分光光度计（UV-vis DRS）对g-C₃N₄/TiO₂进行表征,并研究在可见光条件下g-C₃N₄/TiO₂对溶液中磺胺甲恶唑（SMX）的光催化降解效果。结果表明,g-C₃N₄/TiO₂具有良好的光催化活性,在可见光照射下,当g-C₃N₄/TiO₂投加量为0.2 g·L^-1时,对初始质量浓度为200 μg·L^-1的SMX的去除率可达84.3%。在相同条件下,而g-C₃N₄和TiO₂只能分别去除21.0%和16.0%的SMX,同时在仿生系统中12.37 g·m^-2 g-C₃N₄/TiO₂可以去除95.35%的SMX。通过质谱分析推测,SMX可能的降解路径分别为S—N键断裂、C—N键断裂、S—C键断裂、SMX的羟基化和SMX上氨基的硝化反应,两种可能的中间产物分别为对氨基苯磺酰胺和3-氨基-5-甲基异恶唑。     

Photocatalytic oxidation on nanostructured chalcogenide modified titanium dioxide

Surface mesoscopic titanium dioxide (P25) films deposited onto conducting glass plates (SnO₂:F) were modified by colloidal Ru_xSe_y nanoparticles (2 nm diameter). A decrease of the photocurrent was found upon modification of TiO₂ films. However, interfacial electron transfer kinetics to oxygen was favored. The increase of the catalyst surface concentration onto TiO₂, shifts the onset of the photocurrent under UV-illumination, to 0.6 V/RHE in presence of oxygen dissolved in the electrolyte. Concomitant to this, the cathodic current becomes important and shifts to more positive potentials. This phenomenon allows the system to work catalytically under open circuit conditions. On non-modified TiO₂, the application of a 0.3 V/RHE potential leads to an enhancement of the photooxidation of formic acid. Photocurrent images revealed a non-homogeneous distribution of the catalyst on the titanium dioxide films.     

Study on the NOx release rule along the boiler during pulverized coal combustion

Numerical simulation and experimental study on NO _x release along the boiler during pulverized coal combustion have been conducted. With the increase of temperature the NO _x emission increased and the peak value of NO _x release moved forward. But when the temperature increased to a certain degree, NO _x emission began to reduce. NO _x emission increased with the increase of nitrogen content of coal. The peak value of NO _x release moved backwards with the increase of coal rank. NO _x emission increased obviously with the increase of stoichiometric ratio. There existed a critical average diameter of the pulverized coal (d _c ). If d ⩽ d _c , NO _x emission reduced with the decrease of pulverized coal size. If d > d _c , NO _x emission reduced with the increase of the pulverized coal size. The results showed that the simulation results are in agreement with the experimental results for concentration distribution of NO _x along the axis of the furnace. Translated from Proceeding of the CSEE, 2006, 26(1): 35–39 [译自: 中国电机工程学报]     

Study on combustion characteristics of blended coals

Power plants in China have to burn blended coal instead of one specific coal for a variety of reasons. So it is of great necessity to investigate the combustion of blended coals. Using a test rig with a capacity of 640 MJ/h with an absolute milling system and flue gas online analysis system, characteristics such as burnout, slag, and pollution of some blended coals were investigated. The ratio of coke and slag as a method of distinguishing coal slagging characteristic was introduced. The results show that the blending of coal has some effect on NO _x but there is no obvious rule. SO _x emission can be reduced by blending low sulfur coal. Translated from Proceedings of the CSEE, 2005, 25(18): 97–103 [译自: 中国电机工程学报]     

Experimental studies on cofiring of coal and biomass blends in India

Concerns regarding the potential global environmental impacts of fossil fuels used in power generation and other energy supplies are increasing worldwide. One of the methods of mitigating these environmental impacts is increasing the fraction of renewable and sustainable energy in the national energy usage. A number of techniques and methods have been proposed for reducing gaseous emissions of NO_x,SO₂ and CO₂ from fossil fuel combustion and for reducing costs associated with these mitigation techniques. Some of the control methods are expensive and therefore increase production costs. Among the less expensive alternatives, cofiring has gained popularity with the electric utility producers. This paper discusses the ‘gaseous emission characteristics namely NO_x,SO₂, suspended particulate matter and other characteristics like specific fuel consumption, total fuel required, actual and equivalent evaporation, total cost of fuel, etc. from a 18.68 MW power plant with a travelling grate boiler, when biomass was cofired with bituminous coal in three proportions of 20%, 40% and 60% by mass. Bagasse, wood chips (Julia flora), sugarcane trash and coconut shell are the biomass fuels cofired with coal in this study.     

Improved electrochromic films of NiOx and WOxPy obtained by spray pyrolysis

Electrochromic films of NiO_x and WO_xP_y were produced by the spray pyrolysis technique. The nickel-oxide-based coatings were obtained from both an alcoholic solution of nickel nitrate and aqueous solution of the mixture nickel nitrate/cobalt nitrate. Coatings obtained from alcoholic solutions showed a noticeable contrast of optical transmittance from fully bleached to colored state. X-ray diffraction analysis showed a slight crystallization in NiO_x after electrochemical treatment: one diffraction peak for as-deposited films turned to three diffraction peaks for electrochemical treated samples. Coatings obtained from aqueous solution of mixture nickel nitrate/cobalt nitrate showed an optimized electrochromic behavior at a Ni:Co proportion of 90:10. At this condition an optical contrast of 50% is found. X-ray diffraction showed that these samples comprised a phase mixture of Co₃O₄ and NiO.WO_xP_y samples were obtained from polytungsten gel in which H₃PO₄ was added. We found that for 8.3 at% of P:W, the electrochromism was optimized. Pyrolytic coatings of WO_xP_y show superior behavior than those of WO_x obtained by spray pyrolysis, both in optical contrast and durability.     

New trends to grow the n-CdZn (S1−xSex)2/p-CuIn(S1−xSex)2 heterojunction thin films for solar cell applications

The n-CdZn(S_1−xSe_x) and p-CuIn(S_1−xSe_x)₂ thin films have been grown by the solution growth technique (SGT) on glass substrates. Also the heterojunction (p–n) based on n-CdZn (S_1−xSe_x)₂ and p-CuIn (S_1−xSe_x)₂ thin films fabricated by same technique. The n-CdZn(S_1−xSe_x)₂ thin film has been used as a window material which reduced the lattice mismatch problem at the junction with CuIn (S_1−xSe_x)₂ thin film as an absorber layer for stable solar cell preparation. Elemental analysis of the n-CdZn (S_1−xSe_x)₂ and p-CuIn(S_1−xSe_x)₂ thin films was confirmed by energy-dispersive analysis of X-ray (EDAX). The structural and optical properties were changed with respect to composition ‘x’ values. The best results of these parameters were obtained at x=0.5 composition. The uniform morphology of each film as well as the continuous smooth thickness deposition onto the glass substrates was confirmed by SEM study. The optical band gaps were determined from transmittance spectra in the range of 350–1000 nm. These values are 1.22 and 2.39 eV for CuIn(S_0.5Se_0.5)₂ and CdZn(S_0.5Se_0.5)₂ thin films, respectively. J–V characteristic was measured for the n-CdZn(S_1−xSe_x)₂/p-CuIn(S_1−xSe_x)₂ heterojunction thin films under light illumination. The device parameters V_oc=474.4 mV, J_sc=13.21 mA/cm², FF=47.8% and η=3.5% under an illumination of 85 mW/cm² on a cell active area of 1 cm² have been calculated for solar cell fabrication. The J–V characteristic of the device under dark condition was also studied and the ideality factor was calculated which is equal to 1.9 for n-CdZn(S_0.5Se_0.5)₂/p-CuIn(S_0.5Se_0.5)₂ heterojunction thin films.     

An ab initio study of the electronic structure and optical properties of CdS1−xTex alloys

The structural, electronic and optical properties of cubic CdS_1−xTe_x alloys, with Te-concentrations varying from 0% up to 100% are investigated. The calculations are based on the total-energy calculations using the full potential-linearized augmented plane wave (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA) for the total-energy calculations, while for electronic properties in addition to that the Engel–Vosko (EV-GGA) formalism was also applied. The ground state properties for all Te-concentrations are presented. The optical dielectric constant is also determined for both the binary and their related ternary alloys.     

Synthesis and assessment of La0.8Sr0.2ScyMn1−yO3−δ as cathodes for solid-oxide fuel cells on scandium-stabilized zirconia electrolyte

Perovskite-type La_0.8Sr_0.2Sc_yMn_1−yO_3−δ oxides (LSSMy, y = 0.0–0.2) were synthesized and investigated as cathodes for solid-oxide fuel cells (SOFCs) containing a stabilized zirconia electrolyte. The introduction of Sc³⁺ into the B-site of La_0.8Sr_0.2MnO_3−δ (LSM) led to a decrease in the oxides’ thermal expansion coefficients and electrical conductivities. Among the various LSSMy oxides tested, LSSM0.05 possessed the smallest area-specific cathodic polarization resistance, as a result of the suppressive effect of Sc³⁺ on surface SrO segregation and the optimization of the concentration of surface oxygen vacancies. At 850 °C, it was only 0.094 Ω cm² after a current passage of 400 mA cm⁻² for 30 min, significantly lower than that of LSM (0.25 Ω cm²). An anode-supported cell with a LSSM0.05 cathode demonstrated a peak power density of 1300 mW cm⁻² at 850 °C. The corresponding value for the cell with LSM cathode was 450 mW cm⁻² under the same conditions. The LSSM0.05 oxide may potentially be a good cathode material for IT-SOFCs containing doped zirconia electrolytes.     

Sputtered Cd1−xZnxTe films for top junctions in tandem solar cells

Cd_1−xZn_xTe alloy films with 1.6 and 1.7 eV band gaps were deposited by RF magnetron sputtering from targets made either of mixed powders or alloys of CdTe and ZnTe (25% and 40%). High-quality polycrystalline films with the (1 1 1) preferred orientation were obtained. The films were characterized using X-ray diffraction (XRD), scanning electron microscopy, resistivity, optical absorption, Raman, and photoluminescence. The EDS, XRD, and optical absorption analysis indicated that the x-value of the as-grown films were typically 0.20 and 0.30 for films sputtered from 25% and 40% ZnTe containing targets, respectively. The as-deposited alloy films exhibit quite low photovoltaic performance when used to make cells with CdS as the hetero-junction partner. Therefore, we have studied various post-deposition treatments with vapors of chlorine-containing materials, CdCl₂ and ZnCl₂, in dry air or H₂/Ar ambient at 390 °C. The best performance of a Cd_1−xZn_xTe cell (, ) was found for treatment with vapors of the mixed CdCl₂+0.5%ZnCl₂ in an H₂/Ar ambient after pre-annealing at 520 °C in pure H₂/Ar.