Analysis of combustion and flame propagation characteristics of LPG and Gasoline fuels by laser deflection method

This work is to investigate the combustion characteristics and flame propagation of the LPG (liquified petroleum gas) and gasoline fuel. In order to characterize the combustion processes of the fuels, the flame propagation and combustion characteristics were investigated by using a constant volume combustion chamber. The flame propagation of both LPG and gasoline fuels was investigated by the laser deflection method and the high-speed Schlieren photography. The result of laser deflection method show that the error of measured flame propagation speed by laser method is less than5% compared with the result of high-speed camera. The flame propagation speed of the fuel is increased with the decrease of initial pressure and the increase of initial temperature in the constant volume chamber. The results also show that the equivalence ratio has a great effect on the flame speed, combustion pressure and the combustion duration of the fuel-air mixture.     

Symptoms of self-excited combustion oscillation and their detection

Monitoring of OH chemiluminescence through an optical fiber was demonstrated to be a useful method in detecting self-excited combustion oscillations. OH chemiluminescence intensity detected by the optical fiber showed mostly excellent agreement with those obtained by high speed CCD camera measurements when combustion oscillations were strong. Symptoms of self-excited combustion oscillation were also studied in order to predict the onset of combustion oscillation before it proceeded to a catastrophic failure. For the purpose, we have found and proposed unique measures to tell the onset of self-excited combustion oscillations based on the careful statistics of fluctuating properties in flames, such as pressure or emission of OH radicals.     

Swirl effect on the flame propagation at idle in a spark ignition engine

The objectives of the study are to investigate the effect of swirl on the flame propagation and to propose a flame propagation model that predicts the behavior of the flame front in the presence of significant swirl flow field by analyzing flame images pictured with a high speed digital video at idle. The velocity distribution of the charge in the cylinder was measured using an LDV measurement system. From the experimental results and analyses, a new flame propagation model is proposed in which flame frontal locations can be traced by superposing the convective flow field and the uniform expansion speed of the burned gas, and the proposed model reveals that the increase of the flame propagation speed in the presence of swirl motion within 1 ms after ignition is mainly due to the flame stretch, and mainly due to increased turbulence intensity later than 1 ms after ignition.     

燃烧室结构对天然气转子发动机燃烧过程的影响

以一台由端面进气汽油转子发动机改装而来的预混天然气转子发动机为研究对象,在FLUENT软件的基础上通过编程实现转子发动机三维网格的偏心运动,并选择合适的湍流模型、燃烧模型以及详细的CHEMKIN化学反应机理,建立基于化学反应动力学的端面进气天然气转子发动机三维动态数值模拟模型。通过与试验数据进行对比和分析,验证模型的可靠性。在此基础上,研究燃烧室结构对端面进气天然气转子发动机的缸内流场、温度场和中间产物浓度场的影响。结果表明,当燃烧室凹坑布置于转子曲面长度方向的前端和转子曲面宽度方向的中心时,燃烧过程同时利用了燃烧室后部的滚流以及燃烧室中部高速流区对火焰的加速作用,缸内整体燃烧速率最大。同时,其缸内压力最大以及中间产物OH的生成量也最大,其压力峰值比中置凹坑燃烧室提高了19.9%,但其NO质量分数仍在0.5%以内。     

利用平面激光诱导荧光技术及CH滤镜测量微喷管射流火焰OH及CH基元

微射流火焰形貌观测及火焰中重要基元的准确测量,对利用微尺度火焰燃烧特性研制开发微型燃烧动力系统具有重要意义。本文建立了微喷管射流火焰实验及光学测量系统,对H_2和CH_4微射流火焰进行了实验研究,测量了两种重要基元(CH,OH)的空间分布。首先,探索了相机曝光时间对H_2微射流火焰成像的影响,得到了不同流速下H_2微射流火焰形貌的变化规律。其次,采用平面激光诱导荧光测量技术得到了不同燃料流速下H_2及CH_4微射流火焰中OH基元分布,同时还利用单反相机加CH滤镜通过长时间曝光(30s)的方法获得了CH_4微射流火焰中CH基元的分布。结果表明,火焰图像清晰度随曝光时间增加提高,曝光时间30s时可获得H_2微射流火焰的清晰照片;采用分辨率2 048×2 048的ICCD相机可获得微尺度火焰OH基元分布的清晰图像。微射流火焰形貌及重要基元的实验结果表明相关数值计算方法准确可靠。     

Chemiluminescence-based sensing of flame stoichiometry: Influence of the measurement method

Lean combustion presents many advantages in terms of low NO_x emissions, but it has the problems of being close to the lean blowout limit and more susceptible to instabilities and therefore, measuring equivalence ratio in real time with high accuracy is an important objective. Previous works have analyzed the chemiluminescence emission from the flame and its relationship with flame properties by using different measurement methods that led to different kind of results. Therefore, this study has been focused on the analysis of the influence of the measurement method on the chemiluminescence vs. equivalence ratio curves and the experimental results confirmed the existence of a significant influence. In addition, theoretical calculations seem to reveal that the change in the trends observed for different equivalence ratio ranges may be associated to the existence of different combustion regimes, what may have consequences regarding the applicability of this sensing method for very lean flames.     

Characteristics of propagating tribrachial flames in counterflow

The effect of fuel concentration gradient on the propagation characteristics of tribrachial (or triple) flames has been investigated experimentally in both two-dimensional and axisymmetric counterflows. The gradient at the stoichiometric location was controlled by the equivalence ratios at the two nozzles; one of which is maintained rich, while the other lean. Results show that the displacement speed of tribrachial flames in the two-dimensional counterflow decreases with fuel concentration gradient and has much larger speed than the maximum speed predicted previously in two-dimensional mixing layers. From an analogy with premixed flame propagation, this excessively large displacement speed can be attributed to the flame propagation with respect to burnt gas. Corresponding maximum speed in the limit of small mixture fraction gradient was estimated and the curvefit of the experimental data substantiates this limiting speed. As mixture fraction gradient approaches zero, a transition occurs, such that the propagation speed of tribrachial flame approaches stoichiometric laminar burning velocity with respect to burnt gas. Similar results have been obtained for tribrachial flames propagating in axisymmetric counterflow.     

Effects of needle response on spray characteristics in high pressure injector driven by piezo actuator for common-rail injection system

The common-rail injection systems, as a new diesel injection system for passenger car, have more degrees of freedom in controlling both the injection timing and injection rate with the high pressure. In this study, a piezo-driven injector was applied to a high pressure common-rail type fuel injection system for the control capability of the high pressure injector’s needle and firstly examined the piezo-electric characteristics of a piezo-driven injector. Also in order to analyze the effect of injector’s needle response driven by different driving method on the injection, we investigated the diesel spray characteristics in a constant volume chamber pressurized by nitrogen gas for two injectors, a solenoid-driven injector and a piezo-driven injector, both equipped with the same injection nozzle with sac type and 5-injection hole. The experimental method for spray visualization was based on back-light photography technique by utilizing a high speed framing camera. The macroscopic spray propagation was geometrically measured and characterized in term of the spray tip penetration, spray cone angle and spray tip speed. For the evaluation of the needle response of the above two injectors, we indirectly estimated the needle’s behavior with an accelerometer and injection rate measurement employing Bosch’s method was conducted. The experimental results show that the spray tip penetrations of piezodriven injector were longer, on the whole, than that of the solenoid-driven injector. Besides we found that the piezo-driven injector have a higher injection flow rate by a fast needle response and it was possible to control the injection rate slope in piezo-driven injector by altering the induced current.     

液化石油气中硫化物的测定方法

对液化石油气中硫化物的分析方法进行了评述。总硫测定多采用氧化微库仑法,灯法等。形态硫分析多采用气相色谱与硫选择性检测器结合的方法,这些检测器有火焰光度检测器（FPD）,原子发射检测器（AED）,硫化学发光检测器（SC）和脉冲火焰光度检测器（PFPD）等。其中硫化学发光检测器能较好地检测液化石油气中的各种形态硫化物。此外,液相色谱法,燃烧－离子色谱法,极谱法和核磁共振法等也可用于硫化物的分析。     

Flow direction characteristics in the vicinity of the spark plug in an S. I. Engine

The flame speed may be decomposed into the burning speed and the flame transport speed. The flame transport speed is affected considerably by the flow direction, variation rate of flow direction, and flow speed in the combustion chamber. Especially, the flow direction and the variation rate of flow direction at the spark plug location during the ignition period have an important effect on the ignition process and the early flame propagation process. We measured the flow direction component and the variation rate of flow direction with a hot wire probe at the spark plug location. It was shown that the representative flow direction of ignition period is the right-vertical direction of crank shaft and it was used to investigate the variation rate of flow direction.     

Large eddy simulation of turbulent premixed flame in turbulent channel flow

Large eddy simulation of turbulent premixed flame in turbulent channel flow is studied by usingG-equation. A flamelet model for the premixed flame is combined with a dynamic subgrid combustion model for the filtered propagation flame speed. The objective of this work is to investigate the validity of the dynamic subgridG-equation model to a complex turbulent premixed flame. The effect of model parameters of the dynamic subgridG-equation on the turbulent flame speed is investigated. In order to consider quenching of laminar flames on the wall, wall-quenching damping function is employed in this calculation. In the present study, a constant density turbulent channel flow is used. The calculation results are evaluated by comparing with the DNS results of Bruneaux et al.     

某型航空发动机压气机叶片干冰清洗试验研究

为研究某型航空发动机压气机叶片干冰清洗效果并获取关键参数值,分析了压气机叶片干冰清洗的原理,测试了干冰清洗对压气机叶片的清洗效果。采用人工涂抹法模拟不同积垢的压气机叶片,进行压气机叶片干冰清洗试验,在不同的参数下系统地研究干冰质量流量、喷射角度和压气机转速等参数对干冰清洗效果的影响,获得干冰清洗压气机叶片的最佳参数范围。试验结果表明,干冰清洗对压气机叶片有较好的清洗效果,人工涂抹法可以较好地模拟实际的压气机叶片积垢情况,获得清洗关键参数干冰质量流量、喷射角度和转速的较优范围。     

Large eddy simulation of turbulent premixed combustion flow around bluff body

Large eddy simulation (LES) of turbulent premixed flame stabilized by the bluff body is developed by using sub-grid scale combustion model based on the G-equation describing the flame front propagation. The basic idea of LES modeling is to evaluate the filtered-front speed, which should be enhanced in the grid scale by the scale fluctuations. The dynamic sub-grid scale models newly introduced into the G-equation are validated by the premixed combustion flow behind the triangle flame holder. The objective of this study is to investigate the validity of the dynamic sub-grid G-equation model to a complex turbulent premixed combustion such as bluff body stabilized turbulent premixed flames for realistic engineering application. A new turbulent flame speed model, introduced by the sub-grid turbulent diffusivity and the flame thickness, is also proposed and is compared with the usual model using sub-grid turbulent intensity and with the experimental data. The calculated results can predict the velocity and temperature of the combustion flow in good agreement with the experiment data.     

Effect of the injection parameters on diesel spray characteristics

The characteristics of the diesel spray have affected certain aspects of engine performance, such as the power, fuel consumption, and emissions. Therefore, this study was performed to investigate the effects of various injection parameters. In order to obtain the effect of injection parameters on diesel spray characteristics, the experiment is performed by using a high temperature and pressure chamber. The behaviors of the spray are visualized by using a high speed video camera, spray angle, penetration, and various other things.     

Analysis of wave propagation in fluid-filled viscoelastic pipes

This paper describes the investigation of the propagation wave speed and wave attenuation in viscoelastic fluid-filled pipes. Relatively predictable for metal pipes, these are largely unknown for plastic pipes, since they depend on the pipe wall properties. Wave number measurements, encompassing both wave speed and wave attenuation, were carried out on different water-filled plastic pipes using three hydrophones. The frequency-dependent wave speed and attenuation were calculated from the transfer function between three pressure measurements. Experimental results for different pipe wall materials, particularly those with applications in water supply installations, are presented. The purpose of this paper is to present a method of analysis in the frequency domain that can be used to determine the acoustical properties of fluid-filled plastic pipes.     

均匀液滴喷射过程仿真与试验研究

针对液滴喷射增材制造试验参数调整困难、实施难度较大的现存问题,基于流体体积(Volume of fluid,VOF)两相流模型,建立均匀液滴喷射过程流场的计算模型。采用数值模拟的方法,对液滴喷射过程中的液滴流形态、压力场和速度场及其影响因素进行了研究,揭示了形成均匀液滴流的内在变化规律,得到了均匀液滴喷射过程的最优频率。在模拟结果的基础上,建立了液滴喷射装置并配置了相应的高速拍照系统,对射流断裂形态、喷射过程、喷射速度进行了试验研究。结果表明,射流速度主要取决于喷射压强,液滴流均匀性主要取决于扰动频率和扰动振幅,射流的压力场则呈周期性变化。模拟结果与试验结果吻合较好,说明所提出的建模方法是可行的,为不同情况下射流内部流场的计算提供了实用的方法,也为液滴喷射增材制造技术的应用奠定了理论基础。     

Ethanol (C(2)H(5)OH) spray of sub-micron droplets for laser driven negative ion source

Liquid ethanol (C(2)H(5)OH) was used to generate a spray of sub-micron droplets. Sprays with different nozzle geometries have been tested and characterised using Mie scattering to find scaling properties and to generate droplets with different diameters within the spray. Nozzles having throat diameters of 470 μm and 560 μm showed generation of ethanol spray with droplet diameters of (180 ± 10) nm and (140 ± 10) nm, respectively. These investigations were motivated by the observation of copious negative ions from these target systems, e.g., negative oxygen and carbon ions measured from water and ethanol sprays irradiated with ultra-intense (5 × 10(19) W∕cm(2)), ultra short (40 fs) laser pulses. It is shown that the droplet diameter and the average atomic density of the spray have a significant effect on the numbers and energies of accelerated ions, both positive and negative. These targets open new possibilities for the creation of efficient and compact sources of different negative ion species.     

基于火焰动态形变特征的转炉炼钢终点判定

炼钢转炉炉口火焰的动态形变特征与吹炼数据有密切的关系,在不同吹炼时期显示出不同的规律性,是吹炼过程中的显著特征。准确地表示和描述火焰边界动态形变对依据火焰图像判定转炉吹炼终点具有重要意义,且能克服静态边界特征存在的振荡剧烈问题。提出一种表述火焰边界动态形变的方法,首先定位了符合人眼感知的火焰区域中心;其次,利用此中心对火焰边界进行极坐标建模;最后,依据边界模型定义了火焰边界动态形变幅度谱的提取方法,对动态形变过程进行描述,并将其应用于转炉终点的判定。为保证火焰边界动态形变描述的有效性,对原火焰图像及提取到的火焰边界进行了处理。实验结果表明,与现有的差分链码曲率、边界不变矩和圆形度等火焰边界静态特征相比,所提算法有较高的识别率,且能满足实时性要求,有较高应用价值。     

Effects of Service Condition on Rolling Contact Fatigue Failure Mechanism and Lifetime of Thermal Spray Coatings——A Review

The service condition determines the Rolling Contact Fatigue(RCF) failure mechanism and lifetime under ascertain material structure integrity parameter of thermal spray coating. The available literature on the RCF testing of thermal spray coatings under various condition services is considerable; it is generally difficult to synthesize all of the result to obtain a comprehensive understanding of the parameters which has a great effect on a thermal spray coating’s resistance of RCF. The effects of service conditions(lubrication states, contact stresses, revolve speed, and slip ratio) on the changing of thermal spray coatings’ contact fatigue lifetime is introduced systematically. The effects of different service condition on RCF failure mechanism of thermal spray coating from the change of material structure integrity are also summarized. Moreover, In order to enhance the RCF performance, the parameter optimal design formula of service condition and material structure integrity is proposed based on the effect of service condition on thermal spray coatings’ contact fatigue lifetime and RCF failure mechanism. The shortage of available literature and the forecast focus in future researches are discussed based on available research. The explicit result of RCF lifetime law and parameter optimal design formula in term of lubrication states, contact stresses, revolve speed, and slip ratio, is significant to improve the RCF performance on the engineering application.     

Evolution of flame shape to a vortex pair

The PSC (Propagation of Surfaces under Curvature) algorithm is adapted to the simulation of a flame propagation in a premixed medium including the effect of volume expansion across the flame front due to exothermicity. The algorithm is further developed to incorporate the flame anchoring scheme. This methodology is successfully applied to numerically simulate the response of an anchored V-flame to two strong free stream vortices, in accord with experimental observations of a passage of Karman vortex street through a flame. The simulation predicts flame cusping when a strong vortex pair interacts with flame front. In other words, this algorithm handles merging and breaking of the flame front and provides an accurate calculation of the flame curvature which is needed for flame propagation computation and estimation of curvature-dependent flame speeds.