Kinetic modeling and experimental study on the combustion,performance and emission characteristics of a PCCI engine fueled with ethanol-diesel blends

The combustion process in the Premixed Charge Compression Ignition (PCCI) engine is basically restricted by the in cylinder charged mixture components. Also, the homogeneity of the charged mixture is determining the quality and process of the chemical reaction during the first stage of combustion which establish the auto-ignition process. In the present work, the engine experimental setup is equipped with a new suggested modification on the original fuel system device in order to produce a perfect commixture of diesel/ethanol at different blends ratio with the charged air. The obtained laboratory results are used to validate the simulation's data of the PCCI engine ignition. The prediction is performed using a detailed kinetic reaction mechanism. The simulation study has been achieved to predict the auto-ignition timing and the combustion characteristics of the PCCI engine fueled with different blends of ethanol and diesel at different volume percentage. The obtained results show that the premixed ratio of the ethanol in the ethanol/diesel fuel blends can be used to control the auto-ignition timing and the combustion characteristics at different engine air/fuel ratios. Also, the main pathway of this work is to establish the influence of the engine operating parameters which including the premixed ratio, fuel–air equivalence ratio on the engine performance, combustion and emission characteristics of the PCCI engine. These effects are studied and traced through the simulation result data of the in-cylinder pressure, temperature, and gas phase heat release at different a premixed ratio of ethanol-diesel fuels blends of 0, 10, 20, 30,40 and 50% (by volume).     

炭/炭复合材料飞机刹车盘表面加工质量对其磨合性能的影响

在mm-1000试验机上对炭／炭复合材料（CCC）飞机刹车盘3组表面粗糙度不同的试样进行刹车模拟试验。以摩擦表面相对作动向运动时，摩擦表面微凸体发生弹－塑性变形、发生磨损进入磨合状态。采用Talysurf-4仪测定了CCC刹车盘磨合前后的表面形貌及其粗糙度，用SEM对磨损表面和磨粒形貌进行了研究。当刹车盘表面波度较小而表面微观粗糙度在Ra=12.5μm时，有利于在摩擦面上形成摩擦膜，使刹车副很快进入磨合状态。使用恰当的加工方法和加工精度可以缩短磨合时间的磨合刹车次数。     

Finite element analysis of thermoelastic contact problem in functionally graded axisymmetric brake disks

An analysis of thermoelastic contact problem of functionally graded (FG) rotating brake disk with heat source due to contact friction is presented. Finite element method (FEM) is used. The material properties of disk are assumed to be represented by power-law distributions in the radial direction. The inner and outer surfaces considered are metal and ceramic, respectively. Pure material is considered for the brake pad. Coulomb contact friction is assumed as the heat source. It is divided into two equal parts between pad and brake disk which leads to thermal stresses. Mechanical response of FG disks are compared and verified with the known results from the literatures. The results show that the maximum value of radial displacement in mounted FG brake disk is not at outer surface. It is found that the all areas between pad and brake disk is in full-contact status when the ratio of pad thickness to brake disk thickness is 0.66. It is observed that the total strain due to thermomechanical load is negative for some parts of the disks, whereas, the thermal strains are always positive. It can be concluded that gradation index of the metal-ceramic has significant effect in the thermomechanical response of FG disks.     

隔离车盘形制动单元设计计算

介绍了将原用于铁路客车制动系统的盘形制动单元移植到铁路货车的方法和设计理念,重点对移植后的盘形制动的实算摩擦系数、换算闸瓦压力、制动倍率、制动距离等技术参数进行了演算和推演,并对盘形制动移植的可行性进行了分析和论证。     

The study of ignition and emission characteristics of hydrogen-additive hydro-processed renewable diesel

This study was conducted to understand the effects of hydrogen (H₂) addition on the combustion and emission characteristics of hydro-processed renewable diesel. Experiments were performed in a constant volume combustion chamber (CVCC) at varying H₂ concentrations (0%, 5%, and 10% (by vol.)) relative to air (100%, 95%, and 90% (by vol.)), initial temperatures (T_ini) of 600, 650 and 700 K, equivalence ratios (φ) of 0.5, 1.0, and 1.5 and a fixed initial pressure (P_ini) of 10 bar. Overall, HRD has lower ignition delay (ID) and total ID. However, H₂ addition to HRD delayed the fuel's auto-ignition due to excess H₂ oxidation (H₂+OHH₂O + H) reaction taking place, which turns the chain reactions from branching to propagation, resulting from increasing in ID. Moreover, increasing of H₂ concentrations enhanced the maximum pressure rise (P_max) and heat release rate (HRR), whereas carbon dioxide (CO₂) and unburned hydrocarbon (HC) were decreased due to the higher magnitude of the lower heating value of H₂ than that of pure HRD. Since H₂ itself is a carbon-free molecule, the carbon content of the fuel is reduced. H₂ has the characteristics of fast combustion, resulting in a more flammable and complete mixture, which also makes HC emissions to become lower. However, the higher energy density of H₂ significantly raises the combustion temperature, and subsequent nitrogen oxides (NOx) were increased. The kinetic modeling predictions revealed that the IDs for HRD-H₂ were elongated due to the increased hydroperoxyl (HO₂) and hydrogen peroxide (H₂O₂) mole fractions which led to improved stability.     

摩托车刹车制动器夹紧力微机试验台的研制

摩托车盘式刹车制动器的在刹车时行程较短（1～2mm），但作用力大（最大达10kN），这个特点使得传感器的选用和测试方法的选定都较困难。本文介绍一种利用自制弹性变形片及光栅检测技术来解决摩托车刹车制动器夹紧力的测量问题。