激光诱导白炽光烟雾粒子成像分析仪(LII)

采用LaVision公司的时间分辨粒子成像测速系统FlowMaster-TR和时间分辨激光诱导白炽光成像FlameMaster-LII系统，以3千赫重复频率同时测量湍流举升射流火焰的平面碳烟结构和速度场。

采用LaVision的激光诱导荧光和激光诱导白炽光测量方法，对生物柴油碳链长度对小口径光学柴油机缸内碳烟形成过程的影响进行了研究。

采用LaVision公司由增强型CCD相机构成的平面激光诱导荧光（PLIF）测试系统对直喷汽油发动机内混合物形成的不同的激发态复合物和模型燃料的应用有效性进行了分析研究。

采用LaVision公司以增强型CCD相近非核心部件搭建的平面激光诱导荧光系统（PLIF）对发动机气缸内进行激光诱导荧光（LIF）测量时对激光吸收的一种修正方法进行了探索和研究

采用LaVision公司以增强型CCD相机为核心构建的平面激光诱导荧光（PLIF）测试系统，对直喷汽油发动机工作在废气再循环模式下缸内NO激光诱导荧光的定量成像进行了测量和分析。

采用LaVision公司以增强型CCD相机为核心构成的平面激光诱导荧光测试系统（PLIF）对均质混合进气直喷汽油发动机中燃料和空气的混合程进行了测量和研究。

采用由LaVision公司的增强型CCD像机为核心构成的平面激光诱导荧光PLIF测试系统，用激发态复合物Exciplex作为示踪粒子，分析研究汽车发动机燃料混合物的制备过程特别是喷雾气液两相转化过程。

采用LaVision以增强型CCD相机为核心器件构成的PLIF测试系统，根据双线原子激光诱导荧光原理，测量分析发动机内部的准瞬态二维温度场。

Laser-induced incandescence can be applied to raw exhaust at the open tailpipe, or along the exhaust train using either an in situ optical cell or by extractive sam-pling to an external cell. While in situ measurements are preferable to avoid artifacts caused by extractive sam-pling, the experimental setup may be complex and thus more expensive to implement. In this paper we make a direct comparison of time-resolved in situ versus ex-tracted-sample measurements for rapid engine tran-sients of load and speed. In addition, we compare meas-urements for exhaust extracted from three different loca-tions: 1) at the turbocharger output; 2) at the muffler entrance; 3) at the muffler exit. The results show that extractive sampling sufficiently replicates in situ meas-urements obtained at the muffler entrance, and that rapid transients in soot concentration vary to a small but detectable degree with the measurement location.

采用LaVision公司的增强型CCD相机对火焰喷射对象进行了测量。研究了喷嘴直径对火焰举升长度的影响。

The purpose of this experimental work is to study lean premixed n-heptane/air flames in order to identify the factors governing flame structure and flame stabilization. The experimental burner is composed of a cylindrical combustion chamber placed in a pressurized and cooled casing. Downstream, a converging nozzle with variable section allows to rise the pressure up to 8 bar inside the combustion chamber. Combustion air can be preheated up to 600°C. The n-heptane/air injector is a radial swirler injector which induces an estimated value of 1.74 for the swirl number. The premix tube is a 70mm length and 10 mm diameter cylinder. The droplets are detected by laser tomographic imaging and their size is measured by light diffraction. The reacting zone is visualized by CH* chemiluminescence imaging and the structure of inner recirculation zone by P-LIF-OH imaging. The analysis of laser tomographic images points out the pre-heating effect on the vaporization of liquid fuel. At T = 25°C and P = 1 bar, droplets are not totally evaporated in spite of their small initial diameter, (50 μm without combustion). Totally prevaporized regime is achieved for temperature values above 100°C. Measurements of CH* chemiluminescence for a fixed mean flow velocity V = 70 m/s, and for T = 25°C, 100°C and 200°C show that the flame remains weakly anchored at the nozzle exit. The flame stability evolves with the combustion air temperature and is linked with the position of the Inner Recirculation Zone (IRZ). On the other hand the pressure is a stabilizing factor for constant conditions of velocity and equivalence ratio, because the position of the IRZ does not fluctuates. At constant injection velocity, aerodynamic structure is modified by pressure increasing. At a given critical pressure value, the flame becomes unstable until it reaches a stable flash-back state.

An ongoing research ramjet program initiated at ONERA under support of DGA (French ministry of Defence) aims to improve methodology for ramjet combustion chamber design and tuning by using validated CFD codes. A transparent model rig was used for aerodynamic tests with air flows at atmospheric pressure and room temperature. In the case of the simulation of a Solid Ducted Rocket (SDR) combustor, two fuel holes were located at the head end of the combustor in order to simulate the fuel supply from the auxiliary gas generator in the case of a real combustor. Among the various mechanisms that are controlling the development of the combustion processes inside the combustor, the mixing is certainly one of the most crucial as far as stability or efficiency are concerned. The work presented in this paper is addressing the characterization, in absence of combustion, of the turbulent flow velocity and scalar fields associated to the mixing between fuel (simulated by CO2) and air. Particle image velocimetry (PIV) and gas sampling analysis are the two techniques that were used to serve that purpose. Results presented in this paper are very useful to assess the ability of numerical computations, based either on Reynolds-Averaged Navier-Stokes (RANS) or Large-Eddy Simulations (LES) approaches, to reliably predict velocity and fuel concentration fields inside this research combustor.

Laser-Induced Incandescence (LII) occurs when a high-energy pulsed laser beam encounters graphitic particulate matter particles like soot or carbon black. The particles absorb laser energy from the beam and see an increase in their internal energy, resulting in an increase of temperature. At the same time, the particles loose energy through heat transfer mechanisms. If the energy absorption rate is sufficiently high, particle temperature will rise to levels where significant incandescence (blackbody emission) can occur .Typically, Laser-Induced Incandescence produces 50ns to 1μs long light pulses at atmospheric pressure. So far, LII measurements had been restrained to conduction-dominated conditions, whereby signals are short-lived (less than one microsecond) and require sensitive nanosecond resolution instrumentation. This thesis introduces a novel LII – based measurement method performed under high vacuum conditions. The novelty of LII under vacuum resided in the fact that heat conduction away from the soot particle becomes negligible below 10-2 mbar and this constituted a step away from the typical situation, whereby laser absorption is followed by heat conduction from the particles to the surrounding medium. Instead, sublimation and radiative heat transfer would follow laser absorption. The consequence was the obtention of long-lived LII signals (up to 100 microseconds) and a large gain of photons (ranging between 50 to 300) emitted per primary soot particle during LII temperature decays. Furthermore, the refractive index function E(m) value could be determined directly from measured radiative temperature decays, with potentially an uncertainty of circa 7%, which outperformed current soot extinction measurements. In addition, for laser fluences below 0.06 J/cm2, a regime where only laser energy absorption and radiative heat transfer apply would be reached and LII signals became independent of particle size.

An experimental study of the interaction of a planar diffusion flame with a line vortex is presented. A planar diffusion flame is established between two coflowing, equal velocity streams of acetylene diluted with nitrogen and air. A line vortex is generated on demand by momentarily pulsing one of the flow streams by way of electromagnetic actuation of a piston in the flow apparatus. The flame–vortex interactions are diagnosed by planar laser-induced incandescence for soot yield and by particle image velocimetry for vortex flow characterization. The results show that soot formation and distribution are influenced by the reactant streams from which vortices are initiated. The vortices interacting with the flame from the air side produce more soot and soot is distributed in and around the vortex core in diffuse layers. In contrast, topography of soot in vortices interacting from the fuel side is such that soot is confined to thinner layers around the vortex core which does not contain any soot. The flame curvature is found to influence the local soot production with the flame regions convex to the fuel side containing more soot locally. It is also found that the overall soot yield is less sensitive to the vortex strength and is of lower magnitude when vortex is spun from the fuel side. The knowledge of this type of asymmetry in soot yield in flame–vortex interactions is useful for combustion engineering and design of practical devices.

Laser-Induced Incandescence (LII) is investigated in laminar premixed flat ethylene/air flames at pressures up to 5 bar in a recently constructed high-pressure burner. Time-resolved LII signals were compared with a numerical model considering the influence of pressure on the LII signal decay. Peak particle temperatures after laser heatup were measured by the detection of the LII signal at two wavelenghts. Laser-induced emission spectra enabled to check for interfering signals. Gas-phase temperatures were requiered to compare the LII signal decay with the model and were measured using multi-line NO-LIF thermometry.