汽油机双火花塞轻度均质稀燃特性的测试分析

在单火花塞均质预混燃烧室结构的基础上增设双火花塞点火系统,通过改造电控燃油喷射系统实现了双火花塞轻度均质稀燃模式的稳定运行。通过设置双火花塞化学当量比(过量空气系数λ为1)、双火花塞轻度均质稀燃(λ为1.1)和单火花塞化学当量比(λ为1)的状态,测试了双火花塞对轻度均质稀燃过程及其燃烧特性的影响。研究表明:双火花塞在加速缸内稀燃的总体效应主要体现在10%~50%累积燃烧放热的前期燃烧期;轻度均质稀燃(λ为1.1)状态的双火花塞燃烧放热和循环变动特性仍明显优于单火花塞化学当量比状态;在低负荷非稳定燃烧工况,双火花塞在加速缸内燃烧过程、减小循环变动率和提高燃烧稳定性的效果上更加突出。台架测试表明:在稀燃运行区域,双火花塞轻度均质稀燃模式的燃油经济性较单火花塞化学当量比燃烧模式提升了3%~6%,并有助于降低有害物的排放。     

基于AVL-BOOST的米勒循环发动机性能分析研究

传统奥托循环发动机的燃油消耗率较高,经济性较差,不能满足日益严格的油耗法规和混合动力汽车的要求,因此改善发动机燃油经济性变得日益迫切。在混合动力发动机上采用米勒循环、EGR(废气再循环)以及高压缩比等技术均有利于降低燃油消耗率。在新设计的进气凸轮工作转角下,研究了EGR率、气门正时、压缩比等主要因素对发动机进气过程、泵气损失、燃烧过程以及发动机性能的影响规律。结果表明:推迟进气门关闭时刻,有利于降低缸内燃烧压力和温度,进气门迟闭角每增大10°CA,缸内最大温度约降低120 K,但过大的气门晚关时刻会使缸内燃烧恶化,一定程度上削弱了由于泵气损失的降低对燃油经济型的改善。在2 000 r/min,外特性工况,270°CA进气凸轮工作转角下,压缩比为13时,发动机燃油消耗率达最低为253.1 g/(kW·h)。在2 000 r/min, 1.2 MPa工况,EGR率为5%时,燃油消耗率降到了235 g/(kW·h),相比原机,采用米勒循环技术后发动机经济性有较大改善。     

废气再循环温度对小排量增压汽油机燃烧及性能的影响

为研究不同废气再循环(EGR)温度对汽油机燃烧特性的影响,基于一台1.3T涡轮增压汽油机改造了低压EGR系统,通过开关EGR冷却水使EGR达到不同的温度.结果表明:在1 500r·min-1,10%EGR率,小、中、大3个负荷工况下,随着EGR温度升高,燃油消耗率有升高趋势,但是其升高幅度不超过0.3%.EGR温度升高后,最佳点火提前角提前,中、小负荷燃烧持续期增长,大负荷燃烧持续期基本不变.在大负荷工况下,当关闭EGR冷却后,EGR温度急剧升高,会对进气过程产生不利影响,发动机最大仅能达到的平均有效制动压力为1.166 MPa,相比于该转速下10%EGR率低温EGR能达到的1.202 MPa,下降了3%.     

二次喷射对火花辅助压燃燃烧及爆震特性影响的试验研究

火花辅助压燃(SACI)是一种由火焰传播诱导未燃混合气自燃的新型燃烧方式.但SACI爆震现象限制了热效率的进一步提升.针对这一问题,基于一台高压缩比缸内直喷汽油机,首先对SACI燃烧及爆震界定进行了分析;然后开展了二次喷射策略对SACI燃烧及爆震特性影响的试验研究.结果表明:火花点火是SACI燃烧的一个重要环节,点火过于提前会导致SACI爆震的产生.SACI爆震的压力振荡幅值(MAPO)要高于SI爆震且分布更加离散.二次喷射在燃烧室内可以形成不同的燃油浓度分层,对SACI有良好的爆震抑制效果.当采用喷射比例4∶1、一次喷射时刻300°,CABTDC、二次喷射时刻140°,CABTDC时,通过对爆震的抑制获得最优燃烧特性,循环变动系数降低了1.18%,,有效燃油消耗率降低了约3.11%,有效热效率提高了1.05%.     

低压EGR对增压直喷汽油机燃烧和油耗的影响

基于一台增压直喷米勒循环发动机,加装低压废气再循环系统(LP-EGR),通过改变EGR率,研究LP-EGR对汽油机燃烧和油耗的影响。研究结果表明:在中小负荷工况下,EGR通过降低泵气损失来减小发动机油耗,油耗最高能减小8.41%;在大负荷工况下,EGR通过抑制爆震,修正点火时刻来降低油耗,油耗最高能减小5.67%;在近全负荷工况下,EGR通过降低排气温度,减少"过喷油"来降低油耗,油耗可减小20.4%。在燃烧方面,EGR会导致燃烧放缓,燃烧循环变动增大。随着EGR率的增大,着火时刻推迟,燃烧持续期增大,最大放热率降低,缸内最高温度降低;由于优化了点火提前角,缸内最高压力增大。     

可变截面涡轮增压器与废气再循环

以一台重型柴油机为试验对象,研究可变截面涡轮增压器(VGT)和废气再循环(EGR)阀门开度对柴油机增压比、空燃比、燃油消耗率及NO_x,CO,HC,CO2和烟度等排放特性的影响.研究结果表明,随着EGR阀门开度的增大,增压比、空燃比降低,经济性变差.EGR阀门开度和VGT阀门开度对NO_x排放影响很大,随EGR阀门开度和VGT阀门开度增大,NO_x排放的体积分数显著降低,但HC,CO,CO2的体积分数和烟度升高.为实现降低NO_x排放的同时控制燃油消耗率和烟度的升高,可在中等负荷时选择EGR阀门开度50%、VGT阀门开度45%的控制策略;在高负荷时选择EGR阀门开度75%、VGT阀门开度55%的控制策略.     

缸内直喷汽油机复合燃烧技术

针对缸内直喷汽油机(GDI)存在的主要排放未燃HC和NOx问题,提出了燃烧理论空燃比的复合喷射燃烧技术,运用了废气再循环(EGR)分层技术.复合喷射通过稳压腔辅助喷射燃油和缸内直接喷射燃油,使缸内形成准均质混合气,以满足各种工况下GDI对混合气的要求.在负荷由小到大直至满负荷的范围内都可避免出现过稀区、过浓区,这利于燃烧并减少HC排放;利用在进气管上设计的独特的废气通道,通过滚流分层充气方法,将进气冲程再循环的废气和油气分层,以形成废气-油气-废气馅饼状分层,从而提高了废气再循环率,降低了NOx排放.两种技术的结合,可以解决GDI发动机存在的主要排放问题.实验证明:复合燃烧系统与EGR分层充气技术的有效结合,可以在各种工况下降低NOx排放,降低量为61%;可以降低冷启动时的HC排放,降低量至少为50%.     

Atkinson循环发动机燃油经济性与排放性试验

在外特性及汽油机常用工况点下,研究了高压缩比Atkinson循环发动机的燃油经济性与排放特性.研究表明:Atkinson循环发动机在外特性工况下,扭矩降低5%,有效燃油消耗率降低5%~8%左右;在2 000 r/min,0.2 MPa与3 000 r/min,0.3 MPa常用工况点下,扭矩损失较小,泵气损失分别降低34%与24%,有效燃油消耗率分别降低9.0%与7.5%;负荷越低,泵气损失减少越明显;在排放特性上,NO_x排放分别降低了65.0%与31.5%,HC排放增加23.7%与26.0%.      

EGR和冷EGR对柴油机燃烧和排放的影响

设计了一种带冷却系统的柴油机废气再循环(EGR)装置,并进行了EGR及冷EGR对柴油机燃烧和排放性能影响的试验研究.结果表明,在各种工况下,EGR都可以显著降低NOx排放,当EGR率为15%时,中高负荷下NOx排放可以降低50%左右,当EGR率为30%时,高负荷下NOx排放可以降低75%左右.但是,EGR率的增加会给柴油机的动力性、燃油消耗率、烟度、CO和HC排放带来不同程度的负面影响,使柴油机的最大爆发压力及放热率峰值下降且出现的位置略微后移.使用冷EGR、中高负荷下,NOx排放可以减少15%左右,烟度排放略有降低.     

不同压缩比对湍流射流点火发动机性能和爆震影响的试验研究

本文基于一台四冲程单缸发动机开展了不同压缩比对湍流射流点火(TJI)汽油发动机性能和爆震特性的影响研究,试验所采用的压缩比为9、11、13和15,在每个压缩比工况下对不同过量空气系数λ进行研究．结果表明,高压缩比可以拓展湍流射流点火汽油发动机的稀燃极限,压缩比15工况下,可以实现λ=3稳定燃烧．增大压缩比并配合预燃室喷油可缩短发动机燃烧的滞燃期和燃烧持续期,进而提高射流点火发动机燃烧效率．1.4<λ<1.9时,随着过量空气系数增加,主燃烧室内混合气变稀,滞燃期和燃烧持续期在低压缩比工况(CR=9、11、13)呈上升趋势,此时主燃烧室混合气浓度对燃烧过程的影响占主导作用;但是随着压缩比逐渐升高至15,滞燃期和燃烧持续期的上升趋势不再明显;而当λ>1.9时,主燃烧室混合气过于稀薄,此时预燃室射流火焰对主燃室燃烧的影响增强．试验还发现,射流点火发动机和普通火花塞点火发动机在压力振荡方面存在较大差异,射流点火发动机的压力振荡从燃烧初期阶段开始一直持续到燃烧结束,这主要是由于高温射流对主燃室多点点火造成的压力振荡．在高压缩比和较浓混合气工况下,射流点火发动机可能还会发生早燃,因...     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with     

Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to     

《Chinese Science Bulletin》SUBJECT INDEX TO VOLUME 59(2014)

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An on-line scaling method for improving scalability of a database cluster

The explosive growth of the Internet and database applications has driven database to be more scalable and available, and able to support on-line scaling without interrupting service. To support more client's queries without downtime and degrading the response time, more nodes have to be scaled up while the database is running. This paper presents the overview of scalable and available database that satisfies the above characteristics. And we propose a novel on-line scaling method. Our method improves the existing on-line scaling method for fast response time and higher throughputs. Our proposed method reduces unnecessary network use, i.e. , we decrease the number of data copy by reusing the backup data. Also, our on-line scaling operation can be processed parallel by selecting adequate nodes as new node. Our performance study shows that our method results in significant reduction in data copy time.     

An improved R-tree based on childnode''s probability

R-Tree is a good structure for spatial searching. But in this indexing structure,either the sequence of nodes in the same level or sequence of traveling these nodes when queries are made is random. Since the possibility that the object appears in different MBR which have the same parents node is different, if we make the subnode who has the most possibility be traveled first, the time cost will be decreased in most of the cases. In some case, the possibility of a point belong to a rectangle will shows direct proportion with the size of the rectangle. But this conclusion is based on an assumption that the objects are symmetrically distributing in the area and this assumption is not always coming into existence. Now we found a more direct parameter to scale the possibility and made a little change on the structure of R-tree, to increase the possibility of founding the satisfying answer in the front sub trees. We names this structure probability based arranged R-tree (PBAR-tree).     

Integrating GIS Web services based on mediating architecture

The geographic information service is enabled by the advancements in general Web service technology and the focused efforts of the OGC in defining XML-based Web GIS service. Based on these models, this paper addresses the issue of services chaining,the process of combining or pipelining results from several interoperable GIS Web Services to create a customized solution. This paper presents a mediated chaining architecture in which a specific service takes responsibility for performing the process that describes a service chain. We designed the Spatial Information Process Language (SIPL) for dynamic modeling and describing the service chain, also a prototype of the Spatial Information Process Execution Engine (SIPEE) is implemented for executing processes written in SIPL. Discussion of measures to improve the functionality and performance of such system will be included.     

Tracking data management using topology of moving object database system for moving object constrained trajectory in LBS application

Advances in wireless technologies and positioning technologies and spread of wireless devices, an interest in LBS (Location Based Service) is arising. To provide location based service, tracking data should have been stored in moving object database management system (called MODBMS) with proper policies and managed efficiently. So the methods which acquire the location information at regular time intervals then, store and manage have been studied. In this paper, we suggest tracking data management techniques using topology that is corresponding to the moving path of moving object. In our techniques, we update the MODBMS when moving object arrived at a street intersection or a curved road which is represented as the node in topology and predict the location at past and future with attribute of topology and linear function. In this technique, location data that are corresponding to the node in topology are stored, thus reduce the number of update and amount of data. Also in case predicting the location,because topology are used as well as existing location information, accuracy for prediction is increased than applying linear function or spline function.