Low-load hydrogen-diesel dual-fuel engine operation – A combustion efficiency improvement approach

Hydrogen-diesel dual-fuel operation can provide significant benefits to the performance and carbon-based emissions formation of compression-ignition engines. The wide flammability range of hydrogen allows engine operation at extremely low equivalence ratios while its high diffusivity and flame speed promote wide range combustion inside the cylinder. Nonetheless, despite the excellent properties of hydrogen for internal combustion, unburned hydrogen emissions and poor combustion efficiency have been previously observed at low-load conditions of compression ignition engines.The focus of the present study is to assess the effects of different engine operation and diesel injection parameters on the combustion efficiency of a heavy-duty dual-fuel engine while observing their interactions with the brake thermal efficiency (BTE) and emissions formation of the engine. In an attempt to reduce the unburned hydrogen rates at the exhaust of the engine, exhaust gas recirculation (EGR) and different diesel injection strategies were implemented. Statistical methods were applied in this study to reduce the experimental time.The results show a strong connection between unburned hydrogen rates, combustion and brake thermal efficiencies with the EGR rate. Higher EGR rates increase the intake charge temperature and provide improved hydrogen combustion and fuel economy. Operation of the dual-fuel engine at low-load with high EGR rate and slightly advanced main diesel injection can deliver simultaneous benefits to most of the harmful emissions and the BTE of the engine. Despite the efforts to achieve optimal engine operation at low loads, the combustion efficiency for most of the tested cases was in the range of 90%. Thus, increased hydrogen rates should be avoided as the benefits of the dual-fuel operation are weak at low-load conditions.     

Theoretical study on the effect of low-temperature reforming on gasoline compression ignition (GCI) at low-load conditions

In this paper, the influence of reforming conditions on the reforming products of gasoline, as well as the effect of main reforming products on GCI combustion at low-load conditions has been studied by experiment and numerical simulation. The results show CO, H₂ and CH₄ are the major reforming products, and their production is improved by higher reforming temperature, oxygen concentration and reforming time. The production of CO and H₂ is mainly determined by the dehydrogenation reaction between fuel molecules and OH, while the one between iC₈H₁₈ and O₂ is essential for the CH₄ generation. The combustion efficiency rises sharply with more CO addition, but increases first and then decreases with increased H₂, while the peak value of 96.71% is achieved. Besides, higher combustion efficiency is obtained with more internal exhaust gas recirculation (i-EGR) used. The increased OH and H radicals can be attained by adding CH₄, which further improves combustion efficiency.     

低负载量Ru-W-B/NaY催化剂的制备及其加氢性能

通过浸渍-化学还原法制备出了一系列低负载量的钌基催化剂，在Ru-B二元催化体系中加入少量W，催化剂催化性能显著提高，且采用反加法、超声波辅助法及添加分散剂PEG对载体NaY进行涂覆，进一步改良了Ru催化剂的加氢性能。采用XPS、H2-TPD、XRD、SEM、ICP-OES等一系列表征手段对催化剂物相结构、组成、形貌等进行详细表征，发现采用反加法、添加W、超声波辅助、使用PEG对载体NaY进行涂覆制备的催化剂活性金属粒子分散更均匀，活性位数量更多。以对苯二酚加氢制1，4-环己二醇为探针反应对所制备的催化剂进行活性测试，发现Ru-W-B/NaY-IUP（1500）0.6加氢性能最为优越，对苯二酚转化率为99.7 %，1，4-环己二醇选择性为92.3 %，而钌负载量仅为0.45 %。此外，研究了反应液pH值对加氢反应的影响，发现反应液pH值对反应结果的影响巨大，当反应液呈碱性时，其反应速率得到极大提高，说明碱性环境更有利于对苯二酚加氢制1，4-环己二醇。     

The influence of task design on upper limb muscles fatigue during low-load repetitive work: A systematic review

Ergonomic interventions such as increased scheduled breaks or job rotation have been proposed to reduce upper limb muscle fatigue in repetitive low-load work. This review was performed to summarize and analyze the studies investigating the effect of job rotation and work-rest schemes, as well as, work pace, cycle time and duty cycle, on upper limb muscle fatigue. The effects of these work organization factors on subjective fatigue or discomfort were also analyzed. This review was based on relevant articles published in PubMed, Scopus and Web of Science. The studies included in this review were performed in humans and assessed muscle fatigue in upper limbs. 14 articles were included in the systematic review. Few studies were performed in a real work environment and the most common methods used to assess muscle fatigue were surface electromyography (EMG). No consistent results were found related to the effects of job rotation on muscle activity and subjective measurements of fatigue. Rest breaks had some positive effects, particularly in perceived discomfort. The increase in work pace reveals a higher muscular load in specific muscles. The duration of experiments and characteristics of participants appear to be the factors that most have influenced the results. Future research should be focused on the improvement of the experimental protocols and instrumentation, in order to the outcomes represent adequately the actual working conditions.Relevance to industryIntroducing more physical workload variation in low-load repetitive work is considered an effective ergonomic intervention against muscle fatigue and musculoskeletal disorders in industry. Results will be useful to identify the need of future research, which will eventually lead to the adoption of best industrial work practices according to the workers capabilities.     

离心式制冷机组的低负载启动

本文分析了Carrier 19XL型离心式制冷机组低负载启动困难的原因，提出了三种解决方案。同时本着保证单机高负载运行的原则，提出了两种将系统低负载供冷转化为单机设备高负载运行的方案。每种方案均有原理、简述及利弊分析。     

Influence of Organic Friction Modifier on Liquid Slip: A New Mechanism of Organic Friction Modifier Action

Recent work using a number of experimental techniques has shown that simple Newtonian liquids can slip against very smooth, lyophobic surfaces. Most previous work has examined lyophobic surfaces produced by forming self-assembled monolayers on smooth substrates. However it has also been shown that octadecanoic (stearic) acid solution in hydrocarbon can promote slip of the liquid against smooth surfaces. This raises the intriguing possibility that one mechanism of action of organic friction modifier additives may be to promote slip in hydrodynamic contacts and thus reduce friction. To test this conjecture, experiments have been carried using a low-load, hydrodynamic friction tester in which a glass cylinder is loaded against a very smooth sapphire flat which has been previously immersed in stearic acid solution. The contact is supplied with a solution of stearic acid in hexadecane and the glass cylinder is rotated at a speed sufficient to generate a full hydrodynamic film. It is found that this system gives significantly lower friction than when using hexadecane alone or when the sapphire is slightly roughened. The results are consistent with the occurrence of liquid slip at the sapphire surface.     

混流式水轮机低负荷运行水力稳定性的研究

目前已经建成或正在建的大型水电站中混流式机组运用广泛。由于水力因素影响,机组固有特性决定其无法在低负荷稳定运行。因此,本文通过介绍混流式机组在低负荷运行时的稳定性影响因素、尾水管压力脉动的成因、特性、对机组稳定性的影响以及其与运行工况和空化关系,提出运用多元线性回归分析算法建立回归模型的思路。利用该模型定量分析机组稳定性与工况参数、空化系数和时间因子的影响关系,进行稳定运行区的划分和机组稳定运行时的寿命预测。     

四角切圆燃烧过程稳定性动态分析模拟研究：Ⅱ.结果及分析

本文应用控制理论中的稳定性分析理论，在所建立的动态模型的基础上，考察了在不同条件下锅炉稳定燃烧的能力，认为决定锅炉低负荷运行能力的主要因素是，燃烧过程对风煤配比失调的敏感性；采用钝体及其改进型燃烧器后，稳定燃烧过程能够克服的最大燃料扰动量增大，即锅炉低负荷运行能力得到了提高。最后对提高煤粉气流的着火能力以及锅炉燃烧的稳定性进行了分析。