时间分辨平面激光诱导荧光测量系统

采用当前世界上唯一商品化的德国LaVision公司的时间分辨高速激光诱导荧光测试系统和时间分辨粒子成像测速系统，对旋流燃烧器中旋进涡核(PVC)的形成和火焰诱导抑制进行了实验和线性稳定性的研究分析。

利用德国LaVision公司的层析粒子成像测速(Tomo-PIV)和时间分辨粒子成像测速(TR-PIV)系统，测量汽车活塞发动机内部瞬态湍流场并和理论分析预测结果进行比对。

This study presents planar laser induced fluorescence data recorded within an optically accessible spray-guided direct-injection spark-ignition internal combustion engine at a repetition rate of 6 kHz. The data is calibrated to estimate the local distribution of the equivalence ratio within the combustion chamber from 50-10. BTDC. A standard reference fuel was used as a tracer. Cyclic fluctuations of the transient and spatial fuel distributions are presented.

Energy supply is one of the primary building blocks of our society. Worldwide, and especially in rapidly developing countries, e.g. China and India, the demands of energy for housing, industry, transportation and communication are constantly increasing [83]. The global energy supply is currently dominated by combustion of fossil fuels. In 2008, 85.1% of the global primary energy supply was produced from the combustion of oil (34.6%), coal (28.4%) and natural gas (22.1%). From the 12.4% of renewable energy sources, 82% (in total 10.2%) was bioenergy based on burning renewable rescources [45]. Recent reports confirm that a dramatic shift towards CO2 neutral energy supply is required to stop the current trend of global warming [135]. Nevertheless, the slow developement of renewable energies over the last decades as well as the absence of large technological advancements in nuclear fusion technology indicate that this structure will not substantially change in the coming decades. Besides emissions of CO2, further pollutants are formed during the combustion of fossil or biofuels. From these emissions, nitric oxides (NOx) have been identified as a major problem of practical combustion processes [214]. In the recent decades nitric oxides became a significant contributor to photochemical smog and ozone in urban air [180]. It further participates in the chain reaction removing ozone form the stratosphere with the consequence of increased ultraviolet radiation reaching earth’s surface [90]. NOx is generally formed during the oxidation process of nitrogen containing fuels such as coal and oil. However, the gross NOx emissions are created at high combustion temperatures from nitrogen in the air. These are typical for hard coal plants, internal combustion engines and gas turbines. Hence, it is essential to understand the physico-chemical processes of NOx formation and concepts to reduce or even eliminate NOx emissions.

A burner for investigating lean stratified premixed flames propagating in intense isotropic turbulence has been developed. Lean pre-mixtures of methane at different equivalence ratios are divided between two concentric co-flows to obtain annular stratification. Turbulence generators are used to control the level of turbulence intensity in the oncoming flow. A third annular weakly swirling air flow provides the flame stabilization mechanism. A fundamental characteristic is that flame stabilization does not rely on flow recirculation. The flames are maintained at a position where the local mass flux balances the burning rate, the result is a freely propagating turbulent flame front. The absence of physical surfaces in the vicinity of the flame provides free access for laser diagnostics. Stereoscopic Planar Image Velocimetry (SPIV) has been applied to obtain the three components of the instantaneous velocity vectors on a vertical plane above the burner outlet where the flames propagate. The instantaneous temperature fields have been determined through Laser Induced Rayleigh (LIRay) scattering. Planar Laser Induced Fluorescence (PLIF) on acetone has been used to calculate the average equivalence ratio distributions. Instantaneous turbulent burning velocities have been extracted from SPIV results, while flame curvature and flame thermal thickness values have been calculated using the instantaneous temperature fields. The probability distributions of these quantities have been compared considering the separate influence of equivalence ratio stratification and turbulence.

Active control of a lifted flame is investigated using a coaxial nozzle with magnetic flap actuators arranged on the inner periphery of the annular nozzle. Near-field vortical structures of the methane/air coaxial jet are manipulated by introducing disturbances directly to the initial shear layer. Through the manipulation, we can improve flame stability and flexibly control the liftoff height. It is found that the large-scale vortical structures play a dominant role in the flame stabilization, and its spatio-temporal evolution is examined with the aid of PIV and LIF to elucidate the control mechanism. By introducing flap motion driven with a saw-wave signal, we can force the outer shear layer to roll up into strong vortices in synchronization with the flaps. When the flapping Strouhal number is unity, the lifted flame is anchored at x/Do ~ 1.5. The strong vortices induced by the flaps produce a blob of flammable mixture, which has velocity smaller than the flame speed. The possible stabilization mechanism is that the time period of the premixture supply is balanced with the consumption time of the premixture at the flame base. On the other hand, when the jet is manipulated by a square-wave signal, the lifted flame is located stably at x/Do ~ 4, which is downstream of the inner potential core. It is found that vortical structures in the shear layers break into turbulence close to the nozzle exit. The possible mechanism of the flame stabilization is that the flame propagating upstream is undisturbed due to the absence of intermittent passage of large-scale vortices.

Practical diagnostic strategies for detection of temperature and nitric oxide (NO) in high pressure (p<60bar) combustion systems using Laser-Induced-Fluorescence (LIF) of nitric oxide are investigated. NO-LIF, when applied to elevated pressures, suffers from a decrease of signal due to pressure broadening and attenuation of the propagating laser beam/fluorescence signals. In addition, overlapping of neighboring excitation lines and interference from LIF of other species (mainly O2 and CO2) can significantly influence the overall signal. The main purpose of this study is to investigate NO-LIF strategies which minimize the impact of these complications or allow for correction of their effects. A comprehensive study of NO-LIF in a laboratory high-pressure flame was carried out for various flame stoichiometries, pressures and excitation wavelengths to develop optimized excitation and detection strategies for high-pressure applications. Four main issues are addressed in this study. First, optimized excitation strategies are investigated for high-pressure applications in the A2Σ+−X2Π (0,0), (0,1) and (0,2) bands of NO. Second, CO2-LIF is identified as a major source of interference in the detection of NO-LIF in high-pressure combustion systems involving hydrocarbon chemistry. Third, an accurate multi-line thermometry technique for steady, high-pressure flames is proposed by fitting wavelength-scanned NO-LIF with computational simulations. Finally, measurements optimizing the detection strategies of 2-D NO-LIF imaging in high-pressure flames are reported. The discussion and demonstrations reported in this study provide a practical guideline for application of instantaneous 1-D or 2-D NO-LIF imaging in high-pressure combustion systems.

Detection and imaging of multi-reaction zones is an essential tool for understanding the detailed structure of complicated flames. In this work a combined 4-camera technique is presented for multi-reaction zones imaging. The technique combines highly advanced laser-based diagnostics tools, namely Rayleigh scattering, laser-induced predissociation fluorescence (LIPF) of OH, LIF of PAH, and LIF of formaldehyde (CH2O). The application of this combined technique in turbulent non-homogeneous hydrocarbon flames is quite new. The technique shows its ability to detect simultaneously rich, lean and diffusion reaction zones. The 3 reaction zones can be spatially resolved, providing essential information about their interaction and overall flame stability. Therefore, the detection and study of triple flame structures in non-homogeneous turbulent flames becomes possible. An example of a triple flame structure in a turbulent lifted non-premixed methane flame is presented. The present work proves that the developed technique is a powerful tool for multi-reaction zone measurements in turbulent and laminar flames.

Nitric oxide laser-induced-fluorescence (NO-LIF) 2-D imaging measurements using a new multi-spectral detection strategy are reported for high-pressure flames (1–60 bar). This work builds on previous research that identified interference LIF from O2 and CO2 in high-pressure flames and optimized the choice of excitation strategies as a function of application conditions. In this study, design rules are presented to optimize the LIF detection wavelengths for quantitative 2-D NO-LIF measurements over a wide range of pressures (1–60 bar) and temperatures. Simultaneous detection of LIF in multiple wavelength regions enables correction of the NO signal for interference from O2 and CO2 and allows simultaneous imaging of all three species. New experiments of wavelength-resolved 1-D LIF in slightly lean (/ = 0.9) and slightly rich (/ = 1.1) methane/air flames are used to evaluate the design rules and estimate the NO detection limits for a wide range of flame conditions. The quantitative 2-D measurements of NO in the burnt gas are compared with model calculations (using GRI-Mech 3.0) versus pressure for slightly lean and slightly rich flames. The discussions and demonstrations reported in this study provide a practical guideline for application of instantaneous 1-D or 2-D NO-LIF imaging strategies in high-pressure combustion systems.