汽油机的高能点火及其在我国的应用

采用高能点火技术能够提高汽油机动力性和经济性,降低排放。文中介绍了高能点火技术及 其在汽油机上的应用现状。     

压缩天然气发动机点火驱动的设计与研究

介绍了基于电控调压器技术的压缩天然气发动机电控系统.为了实现点火正时和点火能量的精确控制,设计了单缸高能点火驱动系统.基于电路仿真的方法,采用智能IGBT元件简化了点火驱动硬件电路设计.基于32位微控制器的TPU时间处理单元,可以精确实现点火正时的控制、点火提前角的控制及点火能量的控制,软件设计了点火正时和能量的修正方法.另外设计了用点火提前角进行调速的方法.开发的CNG发动机ECU及相应的点火驱动模块,已经成功应用于CNG发动机台架试验.试验结果表明:点火驱动硬件工作正常可靠,可以精确控制点火正时和点火能量,通过调整点火提前角可以实现怠速中调速的效果.     

中国电站锅炉节能点火技术的应用与发展

由于全球能源供应的紧张,原油价格不断上涨及电厂竞价上网政策的出台,降低电厂锅炉运行成本特别是锅炉点火成本是提高火电厂发电效益的重要措施,因此开发和利用无油或少油煤粉直接点火技术,降低点火助燃用油,是当今电力行业普遍关注的课题。本文综述了当前国内火力发电厂较常用的锅炉节能点火技术,阐述了不同锅炉节能点火技术的原理、优缺点及相应的技术改造。     

1 000 MW二次再热机组建设无油电厂的技术经济性分析

锅炉点火方案的选择对燃煤机组的运行费用及点火稳燃的可靠性至关重要,以1 000 MW二次再热机组为例从技术角度对可行的节能点火方案(微油点火、等离子点火、天然气点火)进行了对比,并以具体工程为例进行了经济性计算,1 000 MW二次再热机组建设无油电厂综合技术经济性最优。由于1 000 MW二次再热机组建设无油电厂尚无实际运行经验,也对该配置方案的风险及对策进行了进一步分析,以供工程实施参考。综合性技术经济性评价方法也适用于其他容量等级工程的点火系统设计方案优选。     

煤粉直接点火燃烧器技术及其进展

煤粉直接点火燃烧器应是我国电站煤粉锅炉燃烧器改进的主要方向,提出把直接点火技术与稳燃技术结合设计直接点火燃烧器的思路,对该类燃烧器做了较合理的分类。指出了少油煤粉直接点火燃烧器及无油煤粉直接点火燃烧器两大系列燃烧器发展状况及存在的问题,并指出目前应大力开发无油煤粉直接点火系列燃烧器,对电站锅炉煤粉直接点火燃烧器的研究有指导意义。     

汽油内燃机激光点火技术进展

综述了汽油内燃机激光点火技术进展和国内近期的工作。围绕激光诱导火花的方式,阐述了点火源的形成机理及特点;针对激光器的输出功率、热稳定性、激光传导及耦合的问题,比较了各类诱导火花点火激光器的优缺点,总结了增强激光点火功率的技术手段,指出了汽油内燃机激光点火技术发展方向。     

等离子煤粉点火和微油点火技术在1000MW机组超超临界直流锅炉上的应用

通过对安装了等离子煤粉点火燃烧器的超超临界反向双切圆燃烧方式П型直流锅炉和安装了微油点火燃烧器的超超临界四角切圆燃烧方式塔式直流锅炉的启动调试,系统介绍了等离子煤粉点火技术和微油点火技术的基本原理,探索和总结等了离子煤粉点火和微油点火技术在新建1 000 MW机组两种典型超超临界直流锅炉上的应用,即在锅炉启动调试过程中如何在保证锅炉绝对安全的情况下通过对设备和运行方式的调整进行无油点火和纯微油点火,从而提高电厂机组运行的经济性和安全性。     

循环流化床锅炉油枪动态点火的技术要点

讨论了循环流化床锅炉油枪动态点火过程的影响因素及技术要点，可供循环流化床锅炉点火启动参考。     

电站锅炉等离子点火技术应用研究

本文介绍了等离子无油点火系统的工作原理和系统构成，利用实例对该技术进行了应用性试验研究，考察了煤粉浓度、一次风速、二次风量、拉弧功率等因素对其点火性能的影响。通过测定机组冷、热态启动锅炉的燃烧效率说明等离子点火技术是减少电站锅炉启动及低负荷助燃用油的有效途径。     

燃气喷嘴电火花点火性能及点火位置的试验研究

电火花点火是工程中最广泛使用的燃烧器点火方式,点火成功是燃烧器最基本的技术要求.点火枪与燃气喷嘴的相对位置对点火能否成功具有决定意义,目前还未见相关研究报道.从理论上定性分析了合理的点火的位置,通过试验得出了不同结构形式的燃气喷嘴电火花点火性能,给出了不同结构形式燃气喷嘴电火花点火位置的推荐值,为燃烧器的设计提供了依据.     

A review of spray ignition phenomena: Present status and future research

Theoretical and experimental studies dealing with the spray ignition phenomena are reviewed. Two major topics covered are external-source ignition of liquid fuel sprays and spontaneous spray ignition. Experimental and theoretical investigations of external-source ignition of sprays employing different configurations are discussed first. Three major topics included here are: (i) ignition of quiescent and flowing fuel sprays; (ii) ignition of monodisperse and polydisperse sprays; and (iii) ignition of single-component and multicomponent fuel sprays. Then, experimental studies of autoignition of sprays employing constant-volume enclosures, injection in a uniform air flow, and shock tube techniques, are discussed. Theoretical investigations dealing with spray autoignition phenomena range from phenomenological models to one-dimensional numerical models using global one-step as well as detailed multistep chemistry, and to multidimensional simulations with reduced mechanisms. These models are also discussed in the review. Finally, some advanced topics which are common to both external-source ignition and spontaneous ignition are identified and discussed. An attempt is made to provide a common link between the three dominant ignition modes in sprays, namely individual droplet ignition, droplet cluster ignition, and spray ignition. In a similar manner, common features of external-source ignition and spontaneous ignition of sprays are identified. A general spray ignition model along with important numerical and physical issues are presented. The effect of pressure on spray ignition processes is also discussed. Potential topics for further research are suggested.     

无油直接点火燃烧器在煤粉锅炉上应用的若干问题

无油直接点火燃烧器在常规煤粉锅炉中的应用 ,是一个重要的科技改进。同时 ,这一技术在不断的完善。点火燃烧器的功能 ,在开始的若干工程实践中 ,使其仅具有点火与稳燃功能 ,应该是比较客观的 ,待该技术日益成熟之后 ,使其具有主燃烧器的功能。需从点火器本身功能的加强与合理的点火器布置、形成一个良好的空气动力场两个方面强化点火燃烧器的点火能力。无油直接点火燃烧器在锅炉启动过程中 ,与以前的油枪点火有很大的不同 ,需要对启动程序以及相应的设备进行调整     

Effects of turbulence on nonpremixed ignition of hydrogen in heated counterflow

Experiments were conducted to determine the effects of turbulence on the temperature of a heated air jet required to ignite a counterflowing cold hydrogen/nitrogen jet. In contrast to pseudo-turbulent flows, where turbulence was generated by only a perforated plate on the fuel side, resulting in little effect on ignition in a hydrogen system, fully turbulent flows with perforated plates on both sides of the flow were found to produce noticeable effects. The difference was attributed to the fact that in fully turbulent flows, a significantly larger range of turbulent eddies extend to smaller scales than in pseudo-turbulent flows. At atmospheric pressure, the lowest turbulence intensity studied had ignition temperatures notably lower than laminar ones, while further increases in turbulence intensity resulted in rising ignition temperatures. As a result, optimal conditions for nonpremixed hydrogen ignition exist in weakly turbulent flows where the ignition temperature is lower than can be obtained in other laminar or turbulent flows at the same pressure. Similar trends were seen for all fuel concentrations and at all pressures in the second ignition limit (below 3-4 atm). At higher pressures, turbulent flows caused the ignition temperatures to continue to follow the second limit resulting in ignition temperatures higher than the laminar values. The extension of the second limit ends at the highest pressures (7 to 8 atm) where evidence of third limit behavior appears. Three mechanisms were noted to explain the experimental results. First, turbulent eddies similar in size to the ignition kernel can promote discrete mixing of otherwise isolated pockets of gas. Second, this mixing can promote HO₂ chain branching pathways, which can account for the enhanced ignition noted in the second limit where reaction is governed by crossover temperature chemistry. Third, turbulence limits the excursion times available for reaction, inordinately affecting the slower HO₂ reactions. This is responsible for the increasing ignition temperature with turbulence intensity and pressure.     

Single droplet ignition: Theoretical analyses and experimental findings

Spray ignition represents a critical process in numerous propulsion and energy conversion devices. Compared to a gaseous mixture, ignition in a spray is significantly more complex, as the state of ignition in the latter case can be defined by three distinct ignition modes namely, droplet ignition, droplet cluster ignition, and spray ignition. Ignition for an individual droplet represents the appearance of a flame surrounding the droplet or in the wake region, with a dimension on the order of droplet diameter. The cluster or group ignition refers to the ignition around or inside a droplet cloud, while the spray ignition implies the appearance of a global flame with a characteristic dimension few orders of magnitude larger than a droplet. In all three modes, ignition is preceded by the evaporation of fuel droplets, formation of a combustible gaseous fuel–air mixture, and initiation of chemical reactions producing sufficient radical species. The identification of the dominant ignition mode for given two-phase properties represents a problem of significant fundamental and practical importance. Research dealing with laminar and turbulent spray ignition has been reviewed by Aggarwal [1] and Mastorakos [2], respectively, while Annamalai and Ryan [3] have provided a review of droplet group combustion/ignition. In the present review, we discuss experimental, theoretical, and computational research dealing with individual droplet ignition. Topics include the quasi-steady and unsteady models for the ignition of a fuel droplet in a stagnant environment, the droplet ignition in a high-pressure environment, the convective effects on droplet ignition, and multicomponent fuel droplet ignition. Studies dealing with the two-stage and NTC ignition behavior for a droplet are also discussed. Finally, relationship between the droplet ignition mode to droplet cluster and spray ignition modes is briefly described. Potential topics for further research are outlined.     

火花点火式发动机点火过程数值模拟

本文以着火的热理论为基础,提出了一个火花点火式发动机点火过程的一维数学模型。应用这个数学模型对点火过程进行数值计算,可以得到临界着火半径、最小点火能量和各工况时的着火延迟期,并可研究发动机转速、点火提前角和当量燃空此等参数对着火延迟期的影响。文中对两台汽油机的点火过程进行了实例计算。     

煤粉气流强迫点火特性试验研究

在一座小型煤粉燃烧试验台上,对不同条件下,两种煤粉气流的强迫点火特性进行了试验研究。结果表明,用火炬引燃煤粉气流,存在一个对应于最低煤粉浓度的最佳点燃速度;煤粉气流的着火界限主要受初始温度、点火源温度、煤种和煤粉细度的影响;提高煤粉气流的初始温度、点火源温度和煤粉细度均可使着火范围变宽,挥发份含量高的煤种点火容易。在相同条件下,直流煤粉气流比旋转煤粉气流容易点燃。     

Pulverized coal particle ignition in a combustion environment with a reducing-to-oxidizing transition

A reducing-to-oxidizing (RO) environment is characteristic of what a coal particle experiences in the near-burner region of pulverized coal (pc) furnaces. The RO environment can influence early-stage coal combustion processes such as ignition, aerosol formation, and char burnout. However, fundamental studies have focused on either oxidizing conditions (mimicking the post-flame region) or reducing conditions (mimicking the devolatilization region). The effect of this RO environment on early-stage coal combustion has, until now, not been considered. Here, the role of this reducing-to-oxidizing environment on single-particle ignition is evaluated. Powder River Basin (PRB) sub-bituminous coal was used, with a particle size of 125–149 μm and two nominal gas temperatures of 1300 K and 1800 K. The experimental findings for purely-oxidizing conditions with 20 vol% oxygen are compared with those of reducing-to-oxidizing environment. Single particles were tracked using high speed, high resolution videography. Emission intensities of the particles were used to evaluate the prevailing ignition modes, and to determine the characteristic ignition and induction times in both oxidizing and reducing-to-oxidizing environments. Experimental findings show that homogeneous-to-heterogeneous mode of ignition is prevalent for purely oxidizing conditions for both nominal gas temperatures of 1300 K and 1800 K. However, hetero-homogeneous ignition is favored in reducing-to-oxidizing environment at 1800 K and heterogeneous ignition at 1300 K gas flame temperature. The reducing-to-oxidizing environment leads to longer ignition delay times of about 20% and 40% on average for 1300 K and 1800 K nominal gas temperatures respectively but shorter induction times than those of oxidizing condition. The results show that ignition behavior in a reducing-to-oxidizing post-flame environments can be quite different from those in oxidizing environments.     

火花点火对缸内直喷汽油机HCCI燃烧的影响

实现汽油机均质混合气压燃(HCCI)的难点是着火控制。在缸内直喷汽油机上实现了HCCI燃烧,研究了火花点火对HCCI燃烧特性的影响。结果表明,HCCI燃烧方式较火花点火(SI)火焰传播燃烧方式放热速率快,热效率高,NOx大幅度降低。在HCCI临界状态时,火花点火有助于提高燃烧稳定性,抑制失火和爆燃,降低循环波动;当火花点火时缸内温度远超过临界着火温度时,火花点火对HCCI燃烧影响不大。火花点火在SI／HCCI燃烧模式切换工况时,能提高瞬态过渡平顺性。     

循环流化床锅炉燃煤着火特性

在电加热的小型流化床燃烧系统上,采用热烟气炉下点火方式研究了7个煤种的着火点,并分析了粒径、床温、挥发分、水分等因素对着火特性的影响．提出了煤颗粒在流化床内着火点测定的实验规范,并在TGA上测量着火点,与实际电厂锅炉投煤温度进行了比较．结果表明,在流化床实验台上测得的着火温度可以通过修正来表示实际锅炉上的投煤温度．     

An approach of droplet ignition delay time

When a droplet is suddenly injected into a high‐temperature environment, the droplet self‐ignition phenomenon occurs. A simple model, based on the temperature history of target gas mixture of which the equivalent ratio is equal to 1, was proposed to predict the droplet ignition delay time in this paper. This approach clearly divides the droplet self‐ignition delay into two parts, the physical delay and the chemical delay. The predicted droplet ignition times agree well with the experimental data and numerical simulation results. In addition, the influence of droplet diameter on the droplet ignition delay was discussed in detail using this approach. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20240