基于FGM模型的同轴射流非预混火焰大涡模拟

采用直接数值模拟方法对二甲醚(Dimethyl Ether,DME)射流推举燃烧进行了研究（DNS）,分析了DME射流推举火焰结构、燃烧模式和推举稳定机理。数值模拟工况条件为：燃料由狭缝射出,初始温度500 K,射流速度138 m/s;伴流空气的初始温度1 000 K,流速3 m/s,压力为0506 6 MPa。研究表明：DME射流推举火焰与传统的边火焰有很大不同,在射流核心区内存在1条低温放热分支以及紧随其后的中温着火分支,并且推举稳定点位于贫燃侧;DME湍流射流推举火焰包含冷焰反应区(Cool Flame Zone,CFZ)、中温反应区(Intermediate Temperature Zone,ITZ)、富燃高温区(High Temperature Rich Burn Zone,HTR)以及贫燃高温区(High Temperature Lean Burn Zone,HTL)4种模式;在CFZ与ITZ区内湍流混合占主导,并且湍流混合会抑制低温放热;在HTR与HTL区内放热速率占主导地位,但是湍流会显著增强超贫燃区间内的高温放热速率;大部分热量在HTL和HTR区产生,而CFZ和ITZ区对总体产热的贡献微乎其微,但是所产生的中低温组分加快了高温着火过程;射流推举稳定性由贫燃侧的高温自着火反应机制所控制。     

碳氢燃料预混火焰中苯的生成规律

为了研究碳氢燃料预混火焰中苯的生成规律,首先在定容燃烧弹上进行了实验,对不同工况下,90号汽油和模拟汽油(由异辛烷和正庚烷按9:1的质量比例配制)燃烧产物中的苯进行了采集和定量分析;随后利用高速摄像机对这两种燃料在定容燃烧弹中的燃烧图像进行了拍摄,将定容燃烧弹中的预混燃烧火焰划分热焰区、蓝焰区和冷焰区;最后,利用CHEMKIN软件对不同火焰结构区域中模拟汽油的燃烧过程进行了化学动力学分析.结果表明,苯在预混火焰中的冷焰、蓝焰区域内形成,并在热焰中完全氧化;苯来源于未完全燃烧的碳氢,其排放量取决于未完全燃烧区中苯的质量分数和未完全燃烧区的容积;汽油燃烧过程中形成的碳粒在一定程度上能减少苯的排放量;汽油机冷起动时,燃烧室壁面吸附作用将对苯的排放量有重要影响.     

微管流动反应器中大分子直链烷烃着火特性

利用实验及数值计算研究了当量比为1的正癸烷、正十一烷、正十二烷、正十四烷和正十六烷/空气混合气在具有确定温度边界微管流动反应器内的着火特性.研究分析了几种直链烷烃低流速弱火焰在0.1～0.5 MPa压力下的火焰结构、热释放率及反应特性.计算结果表明几种典型单组分燃料有相似的火焰结构.其弱火焰呈现冷焰、蓝焰和热焰这3个反...     

喷射参数对二甲醚PPCCI发动机燃烧与排放特性的影响

在一台6缸增压电控共轨二甲醚发动机上进行试验,研究了预喷时刻、预喷燃料量、喷射压力、主喷时刻等喷射参数对二甲醚部分预混合充量压缩燃烧(PPCCI)发动机燃烧与排放特性的影响。试验结果表明:随预喷时刻提前,缸内压力峰值降低,二甲醚发动机缸内燃烧由两阶段放热转变为PPCCI三阶段放热,氮氧化物(NOx)排放显著降低,HC和CO排放升高;随预喷射燃料量增加,缸内压力峰值及预混合燃烧的冷焰反应和热焰反应速率明显增大,NOx排放逐渐降低,HC和CO排放显著升高;随喷射压力降低,预混合燃烧热焰反应速率增加,主喷扩散燃烧始点推迟,扩散燃烧放热率峰值和NOx排放明显降低,HC和CO排放升高;随主喷时刻推迟,预喷预混合燃烧几乎没有变化,主喷扩散燃烧延后,缸内压力峰值和放热率峰值降低,NOx排放显著降低,HC和CO排放升高。     

正庚烷预混火焰中PAHs的生成机理

应用CHEMKIN软件对正庚烷预混火焰中碳黑的先驱物PAHs的生成机理进行研究,得到了包含49种组分、94个基元反应的简化模型.该饥理包含正庚烷的燃烧和PAHs的生成两部分,正庚烷的燃烧模型构建在Patel等人模型的基础上,增加了3个低温区关键反应;PAHs生成机理主要根据脱氢加乙炔(HACA)反应机理添加.新模型能够模拟正庚烷预混燃烧的冷焰和热焰反应以及预测PAHs的生成过程,与详细模型计算结果吻合较好.为CFD多维模型与化学反应动力学模型相耦合的燃烧计算提供了可行的途径.     

自由射流预混合微火焰的燃烧特性

对静止空气中自由射流微喷管甲烷/空气预混合火焰的燃烧特性进行了实验研究,考察了火焰高度特征及其相关影响因素,详细探讨了尺度变化对微火焰熄火极限的影响.结果表明:微喷管射流预混合火焰为层流火焰,火焰高度与微喷管出口流速成止比,火焰高度随当量比减小而减小;同一当量比下,无量纲参数H/d(火焰高度/微喷管直径)与出口Re数呈线性关系.微尺度效应导致预混合火焰淬熄速度明显增大,同时可燃极限当量比远大于1,微预混合火焰发生淬熄的主要原凶是微尺度下热量和质量扩散作用明显增强.     

低氧稀释条件下煤粉颗粒燃烧特性实验研究

在平面扩散火焰煤粉燃烧实验系统上采用光纤光谱仪和CMOS相机分别测量了不同燃烧气氛(O_2/N_2、O_2/CO_2)、热协流温度(1 473～1 873 K)和氧气体积分数(5%～20%)下烟煤煤粉燃烧火焰的辐射光谱和火焰图像,获得了不同燃烧条件下煤粉颗粒温度沿程分布和燃烧特性。结果表明:在O_2/N_2或O_2/CO_2气氛下,随着热协流温度和氧气体积分数的降低,火焰颜色由亮黄色逐渐转变为暗红色,煤粉颗粒温度降低;随着热协流氧气体积分数的下降,煤粉颗粒温度波动系数减小了37%,颗粒温度分布更均匀;与O_2/N_2气氛相比,O_2/CO_2气氛下煤粉火焰光强减弱,煤粉着火距离增加,煤粉颗粒的平均温度降低了24～103 K,颗粒温度波动系数最大减小了24%。     

三岔火焰及分层火焰的直接数值模拟分析

采用甲烷-空气详细反应机理对4种部分超出可燃极限的层流火焰状态开展了直接数值模拟,包括"焰后支持"和"焰前支持"两种布局的分层火焰和两种不同当量比分布的三岔火焰,并对火焰结构进行了分析.将计算域内各网格单元的热力学状态投影到二维化学反应-扩散流形(REDIM)表格中,发现N_2和CO_2的散点图分布都位于同一个二维REDIM表格中,表明该二维REDIM表格对这4个燃烧状态均能良好描述.此外,为了检验火焰指数的概念,对这4个燃烧状态的火焰结构进行了分析.结果表明:虽然火焰指数可以部分反映火焰内部的燃烧状态,但对于火焰-三岔点的描述不够合理,有必要对其表达式进行改进和完善.     

不同喷管间距甲烷微火焰阵列温度场和燃尽特性研究

为了优化微阵列火焰燃烧加热系统,在相同的燃料负荷和喷管物理条件下,构建了甲烷预混和微火焰阵列燃烧模型,并研究了不同喷管中心间距对温度场和燃尽率特性的影响规律。研究结果表明,由若干微小喷管火焰优化组成的阵列可形成温度均匀的加热场;随着喷管中心间距减小,火焰间相互影响程度增加,均温加热场的温度提高;喷管中心间距继续减小,微喷管阵列火焰开始聚并、向大火焰转变,燃烧反应区间变长、均温场处的燃尽率下降,微喷管火焰丧失微火焰特性;因此确定微火焰阵列加热场喷管中心间距这一重要参数时,需综合考虑温度均匀性、热负荷、燃尽率和污染物等因素。     

湍流状态下双燃料混合物自燃和火焰传播过程

采用直接数值模拟(DNS)方法,研究了低速机缸内热力学状态下甲烷/正庚烷混合物的着火及燃烧过程,分析了湍流状态下双燃料混合层中的着火特性及火焰发展过程．结果表明：第一阶段着火后,湍流作用下混合气偏浓区域生成冷焰;第二阶段着火后,甲烷/空气预混气侧生成多个高温膨胀核心．混合分数梯度平缓区域更易生成高温核心,而混合分数梯度较大时会增大标量耗散率、加强热量和活性基团的耗散,不利于燃烧反应的稳定发展．湍流作用下火焰前沿形成褶皱向两侧传播,热膨胀核心位置的火焰前沿传播较快．甲烷/空气预混气侧含氧量增加导致火焰前沿传播加快,前沿褶皱程度逐渐降低;正庚烷侧火焰前沿在传播下游存在冷焰反应区域,形成“双火焰”结构,随着反应进行,火焰前沿传播进入更浓的混合物中,双火焰面之间的距离逐渐缩短．     

Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

液压系统常见的故障诊断及处理

任何工程机械式液压设备使用时出现故障是不可避免的。但是怎样确定故障的原因及找到好的解决方法，这是使用者最关心的问题。讲述了液压系统常见的故障及其排除方法。     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Economie d'énergie en trigénération

Trigeneration is defined as the production of three useful forms of energy—heat, cold and power—from a primary source of energy such as natural gas or oil. For instance, trigeneration systems typically produce electrical power via a reciprocating engine or gas turbine and recover a large percentage of the heat energy retained in the lubricating oil, exhaust gas and coolant water systems to maximize the utilization of the primary fuel. The heat produced can be totally or partially used to fuel absorption refrigerators. Therefore, trigeneration systems enjoy an inherently high efficiency and have the potential to significantly reduce the energy-related operation costs of facilities. In this paper, we describe a model of characterization of trigeneration systems trough the condition of primary energy saving and the quality index, compared to the separate production of heat, cold and power. The study highlights the importance of the choice of the separate production reference system on the level of primary energy saving and emissions reduction.     

Mineralogical characterization of the intraseam layers of Lofoi lignite deposits in Florina basin (western Makedonia,northwest Greece)

The mineralogical composition of intraseam layers from Lofoi lignite deposits (northwest Greece) is the subject of the present study. The samples were examined by means of X-ray diffraction (XRD), thermo-gravimetric (TG/DTG) and differential thermal analysis (DTA), and Fourier transform infrared (FT-IR) spectrometry. The clay minerals prevail in most samples, with illite-muscovite being the dominant phase, and kaolinite and chlorite being the other major clay components. No smectite was found. Quartz and feldspars, dominate in two cases. The studied materials are characterized as clays to clayey sands, showing significant similarities with the intraseam layers of the adjacent Achlada lignite deposits.     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

Innovative methodologies in renewable energy: A review

This paper is concerned with innovative approaches to renewable energy sources computation methodologies, which provide more refined results than the classical alternatives. Such refinements provide additional improvements especially for replacement of fossil energy usages that emit greenhouse gas (GHG) into the atmosphere leading to climate change impact. Current knowledge gap among each renewable energy source calculation is rather missing fundamentals of plausible, rational, and logical explanations for the interpretation of results. In the literature, there are rather complicated and mechanically applicable methodologies, which require input and output measurement data match with missing physical explanations. The view taken in this review paper is to concentrate on quite plausible, logical, rational, and effectively applicable innovative energy calculation methodologies with simplistic fundamentals. For this purpose, a set of renewable energy methodological approaches is revisited with their innovative structures concerning solar, wind, hydro, current, and geothermal energy resources. With the increase in the renewable energy utilizations to combat the undesirable impacts of global warming and climate change, there is a need for better models that will include physical environmental conditions and data properties in the probabilistic, statistical, stochastic, logical, and rational senses leading to refined and more reliable estimations with application examples in the text. Finally, new research directions are also recommended for more refined innovative energy system calculations.     

Decomposition of limestone in a solar reactor

The thermal decomposition of limestone has been selected as a model reaction for developing and testing an atmospheric open solar reactor. The reactor consists of a cyclone gas/particle separator which has been modified to let the concentrated solar energy enter through a windowless aperture. The reacting particles are directly exposed to the solar irradiation. Experimentation with a 60 kW reactor prototype was conducted at PSI's 90m² parabolic solar concentrator, in a continuous mode of operation. A counter-current flow heat exchanger was employed to preheat the reactants. Eighty five percent degree of calcination was obtained for cement raw material and 15% of the solar input was converted into chemical energy (enthalpy).The technical feasibility of the solar thermal decomposition of limestone was experimentally demonstrated. The use of solar energy as a source for high-temperature process heat offers the potential of reducing significantly the CO₂ emissions from lime producing plants. Such a solar thermochemical process can find application in sunny rural areas for avoiding deforestation.