柴油喷雾燃烧发光机理分析

为探讨柴油机燃烧光的性质,在容弹上采用光强传感器,并应用双色法在不同温度、压力、氧浓度与二氧化碳浓度的条件下,对柴油喷雾的燃烧光强波进行了测量分析。结果表明：在柴油机燃烧过程中,同时存在碳粒的氧化与还原两种反应,其中以氧化反应占优势,碳粒与其附面层温度基本一致。碳粒的附面层反应与柴油中其它气体成分的氧化反应形成火焰,所以可认为碳粒与火焰处于热平衡状态,碳粒的表面反应热以热辐射的方式向外界传递。表面反应热与辐射传热的平衡确定了碳粒的体积与密度。因此柴油喷雾的燃烧光强反映的是碳粒的辐射热强度,燃烧光强波反映的是碳粒的氧化过程。燃烧光强与火焰内的总碳量、氧的分压力、碳粒温度有关,同时还受二氧化碳等还原性气体浓度的影响     

柴油机混合气形成条件对瞬态火焰温度和碳烟质量浓度影响的研究

进气涡流强度、喷嘴的喷孔直径与个数、喷油压力等直接影响直喷式柴油机燃烧室内混合气形成与燃烧过程的进行，从而影响柴油机的动力性、燃油经济性和碳烟排放。作者用同步光导纤维四色法测量系统，研究了进气涡流、喷孔直径和个数对燃烧过程中火焰温度和碳烟浓度的影响。本文介绍的是所进行的研究工作和得到的结果。     

双色法在内燃机燃烧诊断中的应用

系统介绍了双色法的测量原理,阐述国内外双色法在内燃机燃烧火焰分析方面的具体应用。经过多年研究,双色法已成功应用于柴油机燃烧诊断,利用燃烧火焰中实际存在的碳粒,可测量柴油机火焰的温度分布和碳烟浓度分布。汽油机属于无焰燃烧,燃烧过程只产生少量的碳烟,直接应用双色法具有较大难度,国内外可见文献较少,本文介绍了关于双色法汽油机测温的实例。     

火焰参数对辐射图像法不同测温模型的影响

对火焰温度分布的实时测量能够了解燃烧过程、验证燃烧机理、预防工业事故、优化燃烧设备。图像法测温在工业现场的火焰三维温度测量上有明显的优势,但通常均考虑火焰为均匀折射率介质,给测温结果带来了不可避免的误差。本文建立了梯度折射率介质下火焰的辐射成像模型和图像法测温模型,验证了方法的正确性,分析了火焰尺寸对成像的影响及炭黑颗粒浓度对温度场重建的影响。得出随着火焰尺寸的增大,图像强度随火焰尺寸出现先增大后减小的趋势,梯度介质模型与均匀介质模型的差异逐渐增大,随着炭黑颗粒浓度的增加,两种模型的重建精度逐渐下降。     

柴油机气缸内局部瞬态碳粒浓度、火焰温度改进双色法测量系统

介绍了一套新的改进双色法柴油机气缸内局部瞬态火焰温度和碳粒浓度测试系统,其测试原理利用了颗粒的衍射理论,细致地考虑了柴油机缸内碳粒云的光学参数。测试系统中采用了分叉光纤从而省去了一套复杂的光学分光系统。新型的探头设计较好地解决了蓝宝石窗面的积炭问题,对测试系统进行了标定。在缸盖火力面上布置两个具有代表性的测点来测量火焰温度和碳粒浓度,测试结果表明：活塞凹坑部位火焰温度和碳粒浓度均较高;在活塞挤流区,循环变动很大。在活塞凹坑部位和活塞挤流区所测火焰温度和碳粒浓度均有一定相位差。     

电场作用下正癸烷液滴在常温常压下的燃烧特性

通过利用高速摄像机对液滴燃烧时火焰和粒径的实时测量,以及激光诱导白炽光(LII)对碳烟体积分数的测量方法,研究了垂直电场作用下正癸烷液滴在重力场中的燃烧特性,结果表明:当V>0时,随着电压的增加,液滴上半部分的火焰高度不断缩短,下半部分不断被拉长,在电压为5,kV左右时,火焰呈上下对称结构,燃烧速率常数随着电压的增加先减小后增大,碳烟体积分数随着电压的增加先减小后增大再减小;当V<0时,燃烧速率常数随着电压的增加而增大,碳烟体积分数随着电压的增加逐渐减小;燃烧速率常数随电压的变化是由于碳烟颗粒与外加电场的相互作用而造成的,碳烟颗粒向周围环境的辐射换热量的减少是造成燃烧速率常数增大的主要原因.     

用双色法研究进气道喷射乙醇柴油引燃时的燃烧过程

利用高速彩色CCD摄像机的3个单色通道信息进行了双色法计算温度和KL因子的可行性研究，并用乙炔火焰对计算结果进行了验证，讨论了不同双色组合对测试精度的影响。在一台可视化发动机上对进气道喷射乙醇柴油引燃时的燃烧过程进行了分析，结果表明：随着乙醇喷入量的增加，燃烧火焰面积减小，温度及代表碳烟浓度的KL因子也相应下降，说明乙醇对柴油燃烧过程中碳烟的生成有抑制作用。     

使用放热率计算总体辐射热流量的研究

本文发展了一个预测直喷式柴油机缸内总体辐射热流量的模型。该模型利用单区放热率所得资料，配合适当的碳粒形成和氧化的子模型，以计算辐射温度，燃烧区温度，碳粒浓度，碳粒发射率和总体辐射热流量等，计算结果与已发表的实验数据吻合。     

火行为对森林地表可燃物燃烧碳转化的影响

为了从理论上探索森林地表可燃物燃烧过程中碳转化率与宏观展现的火行为间内在联系,依据燃烧现象中能量平衡和元素质量守恒方程,建立起森林地表可燃物燃烧碳转化参数与其火行为参数相关联的数学模型.针对广东林区典型地表可燃物计算结果表明,随着火焰长度或火焰温度的增加,燃烧效率提高,消耗碳向CO_2的转化率η_(CO_2)增大;当火焰温度介于1,000~1,200,K之间时,碳转化率η_(CO_2)以及CO对CO_2排放比的变化范围分别为0.44~0.95和0.02~0.40.进一步分析表明,火焰长度或火焰温度的提高意味着火焰区的燃烧反应更完全,消耗的碳向CO和碳烟颗粒的转化率相对减小,导致碳转化率η_(CO_2)增加.从本质上来说,森林地表可燃物火蔓延过程中的碳转化率实际是火行为的一种表现,由此可以解释野外试验观察到的碳排放效率的变化规律.本项工作中建立的计算模型为可靠估算实际火灾现场碳排放量奠定了基础.     

用光纤燃烧传感器测量汽油机的燃烧时间参数的研究

本文介绍了一个光纤燃烧传感器及ＯＭＡ４光多通道分析仪组成的测量系统，用以测量汽油机燃烧火焰光谱。光谱分析结果再次证实了燃烧火焰中ＣＨ（４３１．５ｎｍ），Ｃ２（５１６．５ｎｍ），Ｈ２Ｏ（５８９ｎｍ）等自由基的特征光谱同Ｃ粒子的热辐射连续光谱叠加在一起，构成了火焰光谱。根据光谱曲线中Ｈ２Ｏ光强峰值变化，可以确定汽油机燃烧过程中重要的时间参数：着火延迟期和燃烧持续期。由于汽油机燃烧循环变动大，与单色仪和ＢＯＸＣＡＲ积分平均器组成的测量系统相比，光纤燃烧传感器＋ＯＭＡ４用光多通道分析仪系统测量汽油机燃烧火焰光谱，测量精度高，工作效率高。     

Study of the characteristic of diesel spray combustion and soot formation using laser-induced incandescence (LII)

In this paper, the planar images of diesel spray combustion flame and soot formation were measured and analyzed by using LII, in a constant volume combustion vessel. The effects of combustion flame and fuel–air mixing characteristics on soot formation and distribution of soot concentration were studied at different conditions. The result indicates that, with increase in ambient temperature and pressure, the ignition delay of diesel fuel is shorter. The increase of ambient temperature and pressure and the reduction of injection pressure shorten the diesel flame lift-off length. The lower the ambient temperature and pressure, the weaker LII signal intensity. At the same ambient temperature and pressure condition, the higher the diesel injection pressure, the smaller the soot production in diesel jet spray, and soot particles are primarily produced in the relative fuel-rich region, which is encompassed by the flame surface front at the downstream of the diesel jet.     

柴油温度对燃烧火焰温度和碳烟生成的影响

通过定容燃烧弹,采用双色法研究不同柴油温度对冷起动过程中燃烧火焰温度和碳烟生成特性的影响,获取缸内燃烧火焰温度分布和表征碳烟分布的KL因子.结果表明:在喷油后3.5 ～ 6.0 ms的燃烧稳定时期,柴油温度为40℃的火焰中大于2 200 K的区域约占60％,柴油温度为20℃的火焰中大于2 200 K的区域约占55％,柴...     

生物柴油碳烟特性的可视化研究

在1台光学可视化发动机上,采用高速摄影法,对不同掺混比例的柴油/生物柴油混合燃料进行研究,获取缸内燃烧火焰图像,通过双色法得到表征缸内碳烟总体分布的KL因子,分析了生物柴油对缸内燃烧过程和碳烟生成特性的影响.研究结果表明,随着生物柴油掺入比例的增加,最高燃烧压力逐渐降低,滞燃期相对延长,燃烧持续期缩短,火焰的亮度和分布面积都随之下降.KL因子的最高浓度降低,碳烟较浓的分布区域减小,碳烟的氧化进程加快.     

Effects of variable O2 concentrations and injection pressures on the combustion and emissions characteristics of the petro-diesel and hydrotreated vegetable oil-based fuels under the simulated diesel engine condition

This experimental research investigates the effects of variable O₂ concentrations and injection pressures on the combustion and emissions characteristics of the diesel (B7) and the hydrotreated vegetable oil (HVO)-based fuels. The O₂ concentrations included 21%, 15% and 10% O₂, while the injection pressures were 80 and 120 MPa. The experimental fuels were the diesel fuel (B7), the neat HVO, the 20%, 50% and 80% HVO (by mass fraction) blended with the diesel. The experiments were carried out in a rapid compression-expansion machine (RCEM) under the direct injection (DI) diesel combustion condition. The analysis was undertaken using the two-color method. The experimental results indicated that the ignition delay, the heat release rate, the flame temperature, the soot density-KL factor, the NO_x and soot-out emissions were inversely correlated to the HVO fraction in the blend. In addition, the findings revealed the similar flame profiles in which the higher flame temperature region and the darker KL density were concentrated around the spray flame upstream, regardless of the HVO mixing ratio. Besides, the decrease in the O₂ concentration resulted in the lower heat release rate, integral heat release, flame temperature, KL factor and NO_x emissions but the longer ignition delay and higher soot concentration, with the highest soot concentration observed under the 15% O₂ environment. Nevertheless, the higher pressure differential (i.e. between the injection pressure and the ambient pressure) contributed to the shorter ignition delay, higher heat release rate, early peak of the flame temperature, wider combustion area, faster soot oxidation rate and higher NO_x production.     

Studies of soot oxidative reactivity using a diffusion flame burner

Oxygen addition to a laminar diffusion flame burner was carried out by intake oxygen enrichment and by fuel oxygenation in order to study the relation between soot oxidative reactivity and the combustion process. For this work, oxidative reactivity of n-heptane-derived soot was analyzed with respect to adiabatic flame temperature at various oxygen concentrations of the oxidizer stream, and compared to those of ethylene-derived soot and soot derived from an oxygenated fuel (a mixture of 70 vol.% n-heptane and 30 vol.% monoglyme (C₄H₁₀O₂), monoglyme mixture). There is a clear inverse relation observed between adiabatic flame temperature and soot oxidative reactivity. However, detailed experiments suggest that the primary factors impacting soot oxidative reactivity are the soot inception limit, which is closely related to soot formation rate, and the soot oxidation process: the earlier soot is formed, the less reactive it becomes. Consequently, ethylene-derived soot is shown to be less reactive than n-heptane-derived soot under the same carbon flow rate and the same adiabatic flame temperature, because soot is formed at an earlier stage with ethylene than with n-heptane. In addition, increasing oxygen concentration in the oxidizer stream made soot less reactive, because not only is the soot inception limit increased by the increase in the flame temperature, but also the soot oxidation process is enhanced by increased abundance of oxidizing gases during the combustion process. From these results, it is concluded that the reason why soot derived from the monoglyme mixture is more reactive than soot from n-heptane is related to the longer time for soot to be incepted, due to the reduced concentration of soot precursors with the oxygenated fuel.     

柴油机双燃料复合燃烧的最佳运行范围研究

通过在进气过程中加入容易汽化的燃料与空气形成一定浓度的预混合气进入燃烧室，利用压燃喷入的柴油形成着火源向整个燃烧室传播，以完成燃烧过程的部分预混双燃料燃烧模式可能是减少柴油机碳烟排放的有效措施。而在该燃烧方案中过低的预混浓度可因火焰无法传播到整个燃烧室而增加HC排放，在保持柴油机压缩比的条件下，过高的预混合气浓度可能使燃烧最高温度上升而对NOx排放不利，甚至在柴油喷入前压燃预混合气而发生爆震。燃烧模式的改变对CO排放水平的影响也可能不利；因此，确定双燃料的最佳运行范围是建立双燃料过程控制的基础，介绍了以液化气和柴油形成双燃料系统时的最佳运行范围的初步研究结果。     

Modeling study of soot formation and oxidation in DI diesel engine using an improved soot model

Particulate emission is one of the most deleterious pollutants generated by Diesel fuel combustion. The ability to predict soot formation is one of the key elements needed to optimize the engine performance and minimize soot emissions. This paper reports work on developing, a phenomenological soot model to better model the physical and chemical processes of soot formation in Diesel fuel combustion. This hybrid model features that the effect of turbulence on the chemical reaction rate was considered in soot oxidation. Soot formation and oxidation processes were modeled with the application of a hybrid method involving particle turbulent transport controlled rate and soot oxidation rate. Compared with the original soot model, the in-cylinder pressures, heat release rate and soot emissions predicted by this hybrid model agreed better with the experimental results. The verified hybrid model was used to investigate the effect of injection timing on engine performance. The results show that the new soot model predicted reasonable soot spatial profiles within the combustion chamber. The high temperature gas zone in cylinder for hybrid model case is distributed broadly soot and NOx emission dependence on the start-of-injection (SOI) timing. Retarded SOI timing increased the portion of diffusion combustion and the soot concentration increased significantly with retarding of the fuel injection timing. The predicted distributions of soot concentration and particle mass provide some new insights on the soot formation and oxidation processes in direct injection (DI) engines. The hybrid phenomenological soot model shows greater potential for enhancing understanding of combustion and soot formation processes in DI diesel engines.     

低压低氧环境下油盆火的燃烧特性和烟气特性

为了研究高原地区低压低氧环境下的燃烧特性和烟气特性,在拉萨和合肥两地区分别进行了正庚烷油盆火实验.实验测量了油盆上方温度、热辐射通量、燃料失重速率、烟气热辐射发射率、烟气组分浓度和火焰高度等燃烧和烟气参数.结果表明:随着海拔高度的升高,油盆火单位面积燃烧速率降低,火焰及热烟气温度降低,对周围环境的热辐射通量和单位面积辐...