二次喷油对点燃式可变滚流进气发动机稀燃影响的研究

利用二次喷油稀燃实验系统研究了二次喷油对可变滚流进气发动机稀燃特性的影响情况。首先，采用纯滚流可变滚流进气系统时，采用较大比例的二次喷油量可以获得更好的稀燃经济性。第二，最低油耗点所对应的喷油正时按照T1、T2和T3顺序依次提前；负荷较大时，对应的最低油耗点喷油正时也相应提前。第三，在可变滚流结构中，二次喷油可能造成局部混合气过浓．导致CO排放增加：同时．在稀燃情况下．增大滚流比可以降低发动机HC和NOχ排放。第四，增大滚流比可以改善发动机低速工况条件下的性能，但应避免机构对燃油喷注的阻隔作用。     

可变滚流与二次喷油对火花点燃式发动机稀燃特性影响的研究

本文研究了可变滚流与二次喷油技术对发动机稀燃特性的影响。研究发现:1)在三种滚流比情况下,发动机比油耗随二次喷油比例的增加,呈下降趋势,说明在缸内只存在滚流运动的情况下,采用较大比例的二次喷油量可以获得更好的燃油经济性。2)喷油正时明显影响发动机燃油耗,在三种滚流比情况下,最低油耗点所对应的喷油正时按照T1、T2和T3顺序依次提前;负荷较大时,对应的最低油耗点喷油正时也相应有所提前。3)增强进气滚流运动可以改善发动机低速工况条件下的燃油经济性和排放特性,但应避免可变滚流机构对燃油喷注的阻隔作用。     

燃烧系统参数对增压中冷柴油-天然气双燃料发动机排放特性和经济性影响的实验研究

将一台6缸、增压中冷柴油机改装为混合器进气方式的柴油—天然气双燃料发动机，对其燃烧系统参数对双燃料发动机排放和经济性的影响进行了实验研究，包括引燃柴油喷油时刻、天然气替代率、中冷后进气温度的影响。双燃料发动机的排放与空燃比及燃烧系统参数密切相关。替代率增加时，排气烟度降低，HC排放升高，当量燃油消耗率升高，CO排放在替代率较小时随替代率增加而升高，但在替代率较高时随替代率增加而略有降低。替代率对NOx排放的影响则与发动机工况有关，在最大转矩和低速大负荷工况，空燃比值较小，NOx排放随替代率的升高而增大；在标定功率工况，空燃比较大，NOx排放随替代率的升高而减小。提前角减小，NOx排放降低。中冷后温度升高，碳烟排放和NOx排放升高，HC和CO排放降低，当量燃油消耗率降低。研究结果表明，采用增压中冷技术、提高CNG替代率、减小引燃柴油喷油提前角，能够有效地降低双燃料发动机的有害排放物。     

稀燃汽油机运转工况对吸附还原法降低NOx排放的影响

应用传统的三效催化器和稀燃NOx吸附还原催化器组成的新型复合尾气催化系统对稀燃发动机不同转速和负荷工况下的排放特性和燃油经济性的影响进行了实验研究．结果表明：稀燃发动机转速对其有害气体排放和燃油经济性的影响与稀燃吸附还原催化转化器稀燃运行时间与浓燃还原运行时间比值大小和绝对时间大小有关．稀燃发动机负荷大小是影响稀燃发动机排放特性和燃油经济性的主要因素，负荷越大，NOx有害气体排放浓度越高，NOx催化转化率越小，燃油经济性越好．     

DME／CNG双燃料均质压燃发动机性能试验研究

研究了二甲基醚和天然气双燃料均质压燃发动机性能和排放特性.结果表明,采用高十六烷值燃料二甲基醚和高辛烷值燃料天然气,可以拓宽均质压燃的运行工况范围.均质压燃发动机在中等负荷工况,热效率比传统压燃式发动机高.小负荷工况,采用二甲醚和大比例EGR方案可以提高热效率.和传统压燃式或点燃式发动机不同,均质压燃发动机的着火始点对经济性影响不大.均质压燃发动机的NOx排放极低,比原机降低95%以上.随着二甲基醚浓度增加,NOx排放增加,HC和CO排放降低;接近爆震燃烧区域,NOx排放急剧升高,而接近稀燃极限区域,HC和CO排放急剧升高,发动机热效率降低.     

电控五气门汽油机稀燃与废气再循环性能对比研究

在一电控喷射稀薄燃烧五气门汽油机上，以稀薄燃烧汽油机电控开发系统及相应的废气再循环系统为试验平台，对五气门汽油机在各种进气模式下实施稀混合气燃烧及废气再循环时的燃油消耗率和排放性能进行了详细的试验研究，进而对本发动机的稀燃性能与废气再循环性能进行了比较，分析实施不同方法对发动机性能的不同影响效果，实验结果表明，采用分层EGR技术以后，EGR比率可达32％，稀燃和分层废气再循环都有效地降低了NOx排放，分层废气再循环对NOx降低的效果更为明显，而且降低速度更快，尤其在中、低负荷，可以使排气中的NOx降低85％～95％．对于油耗，稀燃的效果显然要好于废气再循环，在较高负荷尤为明显，稀燃可显著降低HC、CO，分层EGR对HC、CO排放降低幅度不大。     

葡萄糖水溶液乳化柴油在发动机上的试验研究

使用复配乳化剂通过适当的乳化工艺制备了不同配方的葡萄糖水溶液乳化柴油,并与纯柴油在135柴油机上做了一系列对比试验,研究了发动机燃用不同燃料的燃油经济性和排放特性.试验结果表明:在柴油机参数不作改变的情况下,燃用葡萄糖水溶液乳化柴油可降低发动机的当量燃油消耗率和碳烟排放,在中低负荷时NOx排放量也显著降低,大负荷时CO排放量略有减少,但HC排放在所有负荷工况下都增加;添加助燃剂二茂铁后可进一步改善发动机的燃油经济性和排放特性.     

电控汽油喷射4气门发动机稀燃的试验研究

介绍了利用电控燃油喷射技术、多气门技术和涡流控制阀技术在汽油机上组织稀薄燃烧的方法,对两种稀燃方案——涡流轴向分层稀燃和滚流分区分层稀燃进行了试验研究,结果表明：两种方案分别能在空燃比大于２３、２７时稳定工作,并且能显著提高燃料经济性。在高负荷时采用均质混合气滚流快速燃烧方案,以弥补一般稀燃发动机最大功率有损失的不足     

重型柴油机部分预混压燃模式的燃烧与排放特性

在一台6缸涡轮增压重型柴油机上,基于单次喷射方式,通过调节喷油正时,结合EGR技术,实现了柴油机的部分预混压燃,分析了其燃烧放热特性随喷油正时、EGR、喷射压力和负荷的变化,研究了影响控制混合期与滞燃期的因素及其影响规律.结果表明:部分预混压燃(PPCI)燃烧模式兼具预混燃烧和低温燃烧的特征,是碳烟和NOx同时降低的重要因素,但低温燃烧和稀薄的混合气易于导致燃烧不完全,喷油推迟较晚时引起HC和CO排放显著增加,并引起燃油消耗率增大.这种PPCI模式下,提高喷射压力对NOx和碳烟排放的影响作用不明显,单纯增大喷油压力并不能改善PPCI模式的燃油经济性.当负荷提高至50%以上时,对于早喷预混模式已呈现扩散燃烧阶段,导致NOx和碳烟排放均增大.     

可变滚流对GDI发动机低速工况喷雾和燃烧影响的试验

在可视化缸内直喷(GDI)汽油机台架上,通过进气道入口处翻板和进气道内挡板改变缸内滚流比,使用粒子图像测速技术(PIV)研究了可变滚流对低速条件下喷雾过程的影响,得到喷雾油束的速度场及其对应的剪切应变率和涡量场;进一步通过台架试验,研究可变滚流对燃烧和排放特性的影响.结果表明:翻板和挡板的组合可使缸内较早地形成高强度滚流,滚流比相对于原始状态提高近2倍;高滚流使剪切应变率最大值提高到2,400,s-1,增强了油束内部的剪切作用,涡量最大值也增加到6,000,s-1左右,油束卷吸作用增强,油滴与空气接触面积增大,动量交换加剧,使得喷雾角加大、贯穿距缩短,燃油液滴破碎加剧、蒸发加快,增强缸内油气混合,燃烧放热率增加,燃油消耗率得到改善;高滚流下的CO排放降低,相比低滚流下最大降低32.5%,;但HC和NOx排放增加,相对于低滚流比最大增加54%,和91%,.     

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.     

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.     

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.     

Constrained Optimization of Heat Transfer from an Extended Surface

Two different zero‐order optimization techniques are used to maximize the rates of heat transfer from a fin assembly of a specified cost and in the shape of several annular fins that are mounted on a central stem. The problem is formulated to account for two‐dimensional steady‐state heat transfer that is limited by several inequality constraints. The dimensionless governing equations are used to identify the relevant decision variables. The number of fins making up the assembly is treated as an input parameter. A digital computer is used to determine the required temperature distributions and to implement the optimization search algorithms. Three different fin materials are assessed—aluminum, copper and carbon steel. Design optimizations of the extended surface assembly were made over a range of operating conditions, encompassing several different convection heat transfer coefficients that are representative of free and forced convection in air, and several different overall temperature differences between the substrate surface and air. A few recommendations based on trends in the predicted results are given. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(6): 504–521, 2014; Published online 3 October 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21093