Experimental study on lean-burn characteristics of an SI engine with hydrogen/gasoline combined injection and EGR

Hydrogen has shown potential for improving the combustion and emission characteristics of the spark ignition (SI) dual-fuel engine. To reduce the additional NO_x emissions caused by hydrogen direct injection, in this research, the cooperative control of the addition of hydrogen with exhaust gas recirculation (EGR) in the hydrogen/gasoline combined injection engine was investigated. The results indicate that both the addition of hydrogen and the use of EGR can increase the brake mean effective pressure (BMEP). As the α_H2 value increases from 0% to 25%, the maximum BMEP increases by 9%, 12.70%, 16.50%, 11.30%, and 8.20%, respectively, compared with the value without EGR at λ = 1.2. The CA0-10 tends to increase with increases in the EGR rate. However, the effect of EGR in increasing the CA0-10 can be offset by the addition of 15% hydrogen at λ = 1.2. Measurements of the coefficient of variation of the indicated mean effective pressure (COV_IMEP) indicate that the addition of hydrogen can effectively extend the EGR limit. Regarding gaseous emissions, NO_x emissions, after the introduction of EGR and the addition of hydrogen, are lower than those of pure gasoline without EGR. An 18% EGR rate yields a significant reduction in NO_x, reaching maximum decreases of about 82.7%, 77.8%, and 60% compared to values without EGR at λ = 1.0, 1.2, and 1.4, respectively. As the EGR rate increases, the hydrocarbon (HC) emissions continuously increase, whereas a blend of 5% hydrogen can significantly reduce the HC emissions at high EGR rates at λ = 1.4. Finally, according to combustion and emissions, the coupling of a 25% addition of hydrogen with 30% EGR at λ = 1.2, and the coupling of a 20% addition of hydrogen with an 18% EGR rate at λ = 1.4 yield the best results.     

Effect of the turbulence intensity on knocking tendency in a SI engine with high compression ratio using biogas and blends with natural gas,propane and hydrogen

This research presents the test results carried out in a diesel engine converted to spark ignition (SI) using gaseous fuels, applying a geometry change of the pistons combustion chamber (GCPCC) to increase the turbulence intensity during the combustion process; with similar compression ratio (CR) of the original diesel engine; the increase in turbulence intensity was planned to rise turbulent flame speed of biogas, to compensate its low laminar flame speed. The research present the test to evaluate the effect of increase turbulence intensity on knocking tendency; using fuel blends of biogas with natural gas, propane and hydrogen; for each fuel blend the maximum output power was measured just into the knocking threshold before and after GCPCC; spark timing (ST) was adjusted for optimum generating efficiency at the knocking threshold. Turbulence intensity with GCPCC was estimated using Fluent 13, with 3D Combustion Fluid Dynamics (CFD) numerical simulations; 12 combustion chamber geometries were simulated in motoring conditions; the selected geometry had the greatest simulated turbulent kinetic energy (TKE) and Reynolds number (Re) during combustion. The increased turbulence intensity was measured indirectly through the periods of combustion duration to mass fraction burn 0–5%, 0–50% and 0–90%; for almost all the fuel blends the increased turbulence intensity of the engine, increased the knocking tendency requiring to reduce the maximum output power to keep engine operation just into the knocking threshold. Biogas was the only fuel without power derating by the conditions of higher pressure and higher turbulence during combustion by GCPCC and improve its generating efficiency. Peak pressure, heat release rate, mean effective pressure and exhaust temperature were lower after GCPCC. Tests results indicated that knocking tendency was increased because of the higher turbulent flame speed; fuel blends with high laminar flame speed and low methane number (MN) had higher knocking tendency and lower output power.     

Experimental based comparative exergy analysis of a multi-cylinder spark ignition engine fuelled with different gaseous (CNG,HCNG, and hydrogen) fuels

The experimental investigation was carried out on a multi-cylinder spark ignition (SI) engine fuelled with compressed natural gas (CNG), hydrogen blended CNG (HCNG) and hydrogen with varying load at 1500 rpm in order to perform comparative exergy analysis. The exergy analysis indicates that work exergy, heat transfer exergy and exhaust exergy were the highest with hydrogen at all loads due to its high flame temperature, low quenching distance, and high flame speed. The engine's exergy efficiency was the highest with hydrogen (34.23%), and it was about 24.23% and 24.08% with CNG and HCNG respectively at high load (20.25 kW). This indicates a higher potential of hydrogen to convert chemical energy input of fuel into heat and then power output. The exergy destruction was observed minimum with hydrogen at all loads, and it was drastically reduced at high loads. The combustion irreversibility which was calculated using species present during combustion, was the main contributor to exergy destruction, and it decreased with hydrogen. The minimum combustion irreversibility was 11.75% with hydrogen, followed by HCNG and CNG with 16.46% and 18.88% respectively at high load. The high quality of heat due to high in-cylinder temperature and low entropy generation during combustion caused by less number of chemical species in hydrogen combustion are the main reasons for lower combustion irreversibility with hydrogen.     

中国先进加工制造工艺与装备技术中的关键科学问题

根据中国国家自然科学基金委员会安排，研讨先进加工制造工艺与装备科学与技术的发展趋势。针对中国先进加工制造和装备学科存在的基础研究不系统、不深入的共性状况，以国家需求为目标，以加强先进制造工艺与装备的理论基础研究和应用基础研究为突破口，提出国家自然科学基金“十一五”(2006～2010)期间先进加工制造工艺和装备领域需要研究的科学问题、研究方向、工程目标，以及应该优先发展的重点方向。 先进加工制造是实现高效率、高精度和低成本制造的技术支撑。先进加工制造的目标是高效化、精密化、智能化、集成化、数字化和洁净化，关键技术包括高速/高效切削加工技术、高速/超高速磨削技术、精密/超精密加工技术、非传统加工及其复合加工技术，以及相关的先进加工制造装备的制造技术。 摘要根据中国国家自然科学基金委员会安排，研讨先进加工制造工艺与装备科学与技术的发展趋势。针对中国先进加工制造和装备学科存在的基础研究不系统、不深入的共性状况，以国家需求为目标，以加强先进制造工艺与装备的理论基础研究和应用基础研究为突破口，提出国家自然科学基金“十一五”(2006～2010)期间先进加工制造工艺和装备领域需要研究的科学问题、研究方向、工程目标，以及应该优先发展的重点方向。 先进加工制造是实现高效率、高精度和低成本制造的技术支撑。先进加工制造的目标是高效化、精密化、智能化、集成化、数字化和洁净化，关键技术包括高速/高效切削加工技术、高速/超高速磨削技术、精密/超精密加工技术、非传统加工及其复合加工技术，以及相关的先进加工制造装备的制造技术。 高速/高效切削加工技术的科学问题包括切削加工时刀具和工件材料相互作用过程刀具摩擦、磨损和破坏机理，工件材料高速切削变形理论与工件表面成形机理，高速切削刀具与机床的动力学分析，高速切削过程的智能监控理论与技术。研究方向包括高速/高效切削机床与刀具，难加工材料的高速/高效切削加工，高速/高效切削表面质量，高速/高效切削加工的动力学与稳定性。工程目标包括超高速切削，机床主轴转速达到1×106r·min-1，铣削铝及其合金的切削速度达到1×104m·min-1；高性能切削，机床主轴功率达到100kW，进给速度达到50m·min-1；采用多坐标驱动，提高机床的柔性和效率。     

加权网络中考虑边权和度的熟人免疫策略

在加权网络中,节点之间的边权值代表节点之间联系的紧密程度,节点的度表示该节点的邻居个数。为了有效抑制加权网络中的病毒传播,提出一种考虑边权和度的熟人免疫策略（AI-CWD）。该策略考虑免疫边权值与度乘积最大的节点,并分别在人工网络和真实网络中对该策略进行了实验分析。同时,进一步研究了边权值和度在乘积中的占比对该策略免疫效果的影响。研究结果表明,在相同的免疫节点密度下,对边权值与度乘积最大的节点进行免疫后网络中感染节点的密度比最大权值免疫、改进的熟人免疫和基于ClusterRank算法免疫的方法要低,亦即AI-CWD免疫效果要优于以上三种免疫策略。并且在相同免疫节点密度下,通过对边权值和度的占比与感染节点密度关系的研究,可以得出：存在一个最优的[α]值,使得最终的感染节点密度最低。     

阿伏加德罗常数测量与千克重新定义

当千克用固定普朗克常数h的方法定义时,X射线晶体密度法(XRCD)即被用来定义和复现千克,它采用对浓缩²⁸Si原子计数的方法来测量阿伏加德罗常数N_A,已将N_A和h的测量不确定度达到2×10^-8,并反过来确定硅球的质量实现对千克的量值复现。阐述了晶格常数、同位素、浓缩硅、硅球直径及表面氧化层等阿伏加德罗常数测量的关键技术的研究进展。介绍了原子计数法千克定义及其量值复现方法,该方法将为国际单位制改制之后我国质量量值复现提供参考。     

Compressive Measurement Identification of Linear Time-Invariant System Application in DC Motor

In traditional system identification (SI), actual values of system parameters are concealed in the input and output data; hence, it is necessary to apply estimation methods to determine the parameters. In signal processing, a signal with N elements must be sampled at least N times. Thus, most SI methods use N or more sample data to identify a model with N parameters; however, this can be improved by a new sampling theory called compressive sensing (CS). Based on CS, an SI method called compressive measurement identification (CMI) is proposed for reducing the data needed for estimation, by measuring the parameters using a series of linear measurements, rather than the measurements in sequence. In addition, the accuracy of the measurement process is guaranteed by a criterion called the restrict isometric principle. Simulations demonstrate the accuracy and robustness of CMI in an underdetermined case. Further, the dynamic process of a DC motor is identified experimentally, establishing that CMI can shorten the identification process and increase the prediction accuracy.     

TH—38水稳剂及其在柴油机发电机组上的应用

使用ASTM-D1384-87标准和极化曲线法对TH-38水稳剂的缓蚀性能进行研究,并与进口同类药剂Nalco-2000、Qc-2 进行比较,结果表明:TH-38的缓蚀、分散性能达到进口药剂Nalco-2000、Qc-2的水平,可以替代进口药剂在柴油机发电机组上的密闭高温循环水系统使用。     

非饱和土等效时间流变模型

为了理论分析流变速率效应力学特性,需要建立非饱和土流变模型.首先把非饱和土屈服面分为LC和SI屈服面。其次根据LC屈服面的压缩蠕变公式,利用等效时间法建立相应的黏塑性体应变速率公式,结合巴塞罗那屈服方程和相关联流动法则,获得LC屈服面的三维流变速率方程,揭示了本文与Gennaro-Pereira提出的LC后继屈服面方程的异同。再次,根据SI屈服面的吸力压缩蠕变公式,利用等效时间法建立相应的黏塑性体应变速率方程.最后,把LC和SI屈服面的流变速率方程与弹性方程相结合,建立非饱和土等效时间三维弹黏塑性模型.当不考虑流变速率效应时,LC和SI流变屈服方程可以退化到巴塞罗那模型的塑性屈服方程.理论分析了非饱和土一维流变特性,并与土工试验数据进行对比,两者较为吻合。三轴加载条件下的流变特性数值分析结果表明,按不同方式施加到同一恒载时,随着恒载维持时间的增长,不同加载方式引起的体积流变趋向一致,但剪切流变有较明显的差别.     

Efficiency and emissions in a vehicle spark ignition engine fueled with hydrogen and methane blends

This paper shows the results of the tests carried out in a naturally aspirated vehicle spark ignition engine fueled with different hydrogen and methane blends. The percentage of hydrogen tested was up to 50% by volume in methane. The tests were carried out in a wide range of speeds with the original ignition timing of the engine. Also, lean equivalence ratios were proved. Just the fuel injection map was modified for each fuel blend and equivalence ratio tested. In this paper, the results of thermal efficiency and pollutant emissions achieved at full load have been compared with the corresponding gasoline test results. The best balance between thermal efficiency and pollutant emissions was observed with the 30% hydrogen and 70% methane fuel blend.