Control of homogeneous charge compression ignition combustion in a two-cylinder gasoline direct injection engine with negative valve overlap

Homogeneous charge compression ignition (HCCI) has challenges in ignition timing control, combustion rate control, and operating range extension. In this paper, HCCI combustion was studied in a two-cylinder gasoline direct injection (GDI) engine with negative valve overlap (NVO). A two-stage gasoline direct injection strategy combined with negative valve overlap was used to control mixture formation and combustion. The gasoline engine could be operated in HCCI combustion mode at a speed range of 800–2 200 r/min and load, indicated mean effective pressure (IMEP) range of 0.1–0.53 MPa. The engine fuel consumption is below 240 g/(kW⁻¹·h⁻¹), and the NO _x emission is below 4 × 10⁻⁵ without soot emission. The effect of different injection strategies on HCCI combustion was studied. The experimental results indicated that the coefficient of variation of the engine cycle decreased by using NVO with two-stage direct injection; the ignition timing and combustion rate could be controlled; and the operational range of HCCI combustion could be extended. Translated from J Tsinghua Univ (Sci & Tech), 2006, 46(5): 720–723 [译自: 清华大学学报]     

构件技术在医院信息管理系统重构中的应用研究

基于构件技术的软件开发已经成为软件复用的主要手段。通过分析某两层C/S结构医院信息管理系统(HIS)功能体,引入三层B/S体系结构,并应用CORBA规范建立系统业务逻辑层,以实现医院信息管理系统的重构。最后通过其中医院门诊收费子系统的病人挂号模块的PB构件设计实例,说明该重构方法是可实现的。     

基于构件技术的软件复用在HIS重构中的应用

基于构件技术的软件开发已经成为软件复用的主要手段.通过分析某两层C/S结构医院信息管理系统功能体,引入三层B/S体系结构,并应用CORBA规范建立系统业务逻辑层,以实现医院信息管理系统的重构.最后通过某医院门诊收费子系统的病人挂号模块的PB构件设计实例,说明该重构方法是可实现的.     

An integrated model for negative valve overlap early injection HCCI combustion

Using exhaust top dead center injection (ETCI) mode to realize homogeneous charge compression ignition (HCCI) combustion would cause fuel wall wetting and combustion efficiency reduction, and there is no effective one-dimension simulation model to calculate and analyze the fuel wall wetting and evaporation process. In the research, a new type of integrated model is developed for the new application, HCCI combustion simulation based on ETCI mode. The model includes the following sub-models: fuel injection model, impingement model, film evaporation model, and combustion model. The improved Hiroyasu model and the Bai's model are coupled with homogenous combustion model and film evaporation model to calculate impingement fuel evaporation. The developed model is validated by experiment in a single cylinder diesel engine with ETCI combustion mode. The simulation and experimental results show that, film evaporation is mainly related to cylinder gas temperature and wall temperature, and there is an evident two stage heating process. The cumulate heat release rate is linear with exhaust valve closing (EVC) timing and wall temperature. The burned fuel fraction increases by 6 percent as the EVC timing advances by every 10 °CA, and increases by 4 percent as the wall temperature increases by every 50 K. The cumulate heat release rate decreases with the increase of boosting pressure, and the higher the boosting pressure, the smaller the decrease degree of cumulate heat release rate is.     

Optimization of a heavy-duty compression-ignition engine fueled with diesel and gasoline-like fuels

Optimal injection strategies for a heavy-duty compression-ignition engine fueled with diesel and gasoline-like fuels (#91 gasoline and E10) and operated under mid- and high-load conditions are investigated. A state-of-the-art engine CFD tool with detailed fuel chemistry was used to evaluate the engine performance and pollutant emissions. The CFD tools feature a recently developed efficient chemistry solver that allowed the optimization tasks to be completed in practical computer times. A Non-dominated Sorting Genetic Algorithm II (NSGA II) was coupled with the CFD tool to seek optimal combinations of injection system variables to achieve clean and efficient combustion. The optimization study identified several key parameters that influence engine performance. It was found that the fuel volatility and reactivity both play important roles at the mid-load condition, while the high-load condition is less sensitive to the fuel reactivity. However, high volatility fuels, such as gasoline and E10, were found to be beneficial to fuel economy at high-load. The study indicates that with an optimized injection system gasoline-like fuels are promising for heavy-duty CI engines due to their lower NOx and soot emissions and higher fuel economy compared to conventional diesel fuels. However, the high in-cylinder gas pressure rise rate associated with Partially Premixed Combustion of gasoline-like fuels can become problematic at high-load and the low-load operating limit is also a challenge. Potential solutions are discussed based on the present optimization results.     

负阀重叠早喷模式HCCI燃烧数学模型与计算分析

针对早喷模式中的排气上止点燃油喷射(ETCI)模式,综合广安博之模型、Bai模型的优点加以改进,并将空间均质燃烧与油膜蒸发燃烧相耦合,建立了一种新型的基于喷雾、燃油附壁、油膜蒸发、燃烧等一系列过程适用于缸内早喷模式的数学模型。利用该模型对135单缸柴油机ETCI燃烧模式进行校核计算,并通过试验验证进一步对燃烧过程中的工况参数及调节参数进行了研究。研究结果表明:在ETCI模式下,存在部分油膜附壁,油膜的蒸发主要与缸内的气体温度与壁温有关,且存在明显的两阶段加热过程。累积放热率与排气门关闭时刻和壁温基本呈线性关系,排气门关闭时刻提前10°CA,累积放热率上升约6%;壁温升高50K,累积放热率上升4%。增压压力升高,累积放热率降低,增压压力越大,累积放热率降低的幅度越小。     

Virtualizing Network and Service Functions： Impact on ICT Transformation and Standardization

Virtualization of network/service functions means time sharing network/service（and affiliated）resources in a hyper speed manner.The concept of time sharing was popularized in the 1970s with mainframe computing.The same concept has recently resurfaced under the guise of cloud computing and virtualized computing.Although cloud computing was originally used in IT for server virtualization,the ICT industry is taking a new look at virtualization.This paradigm shift is shaking up the computing,storage,networking,and ser vice industries.The hope is that virtualizing and automating configuration and service management/orchestration will save both capes and opex for network transformation.A complimentary trend is the separation（over an open interface）of control and transmission.This is commonly referred to as software defined networking（SDN）.This paper reviews trends in network/service functions,efforts to standardize these functions,and required management and orchestration.     

Effects of valve events on the engine efficiency in a homogeneous charge compression ignition engine fueled by dimethyl ether

Combustion characteristics of a homogeneous charge compression ignition (HCCI) engine were investigated with regard to the residual gas, i.e. internal exhaust gas recirculation (IEGR), by changing the intake and exhaust maximum opening points (MOP) and the exhaust cam lifts. Three different exhaust camshafts were used and had 2.5 mm, 4.0 mm and 8.4 mm exhaust valve lift. In-cylinder gas was sampled at the intake valve immediately before ignition to measure the IEGR rate. The heat release, fuel conversion efficiency and combustion efficiency were calculated using the in-cylinder pressure and composition of exhaust gases to examine the combustion features of the HCCI engine. The negative valve overlap (NVO) was increased as exhaust valve lift was reduced. Longer NVO made an increased IEGR through exhaust gas trapping. The IEGR rate was increased as the exhaust valve timing advanced while it was affected more by exhaust valve timing than by intake valve timing. Combustion phase was advanced by lower exhaust valve lift and early exhaust and intake MOP. It was because of higher amount of IEGR gas and effective compression ratio. The fuel conversion efficiency with higher exhaust valve lift was higher than that with lower exhaust valve lift. The late exhaust and intake MOP made the fuel conversion efficiency improve.     

三层C/S分布式结构模型的实际应用

三层C/S结构的组成及优点,并结合实际阐述了三层C/S模型方案的设计与实现。