Acetone Fluorescence Research Articles

Droplet Velocity Measurement Of Acetone-Water Spray Using Fluorescence-Based Particle Image Velocimetry

A method for measuring the velocity of liquid droplets emanating from an effervescent injector into ambient air was experimented using a mixture of acetone and water. Conventional methods such as Laser Doppler Velocimetry and Particle Image Velocimetry, which utilise Mie-scattering, have limitations due to multiple scattering and strong surface reflections, respectively. In the current study, we demonstrate fluorescence-based particle image velocimetry, which can overcome the abovementioned difficulty. Unlike previous similar studies that used fluorescent dyes, the inherent fluorescence of acetone is utilised in our strategy. The acetone and water were mixed in different volume ratios, and the effervescent jet was produced with air. The Gas-to-Liquid ratio of 8% was considered in this study. The spray droplets were excited using the fourth harmonic of the Nd-YAG laser. Two acetone Planar Laser laser-induced fluorescence images are acquired with a CCD camera and with a 20 µs time difference. The velocity vectors are obtained based on the cross-correlation between the two images. The results showed that absorption greatly influences the estimated velocity distribution. At a low acetone concentration, the velocity distribution became uniform around the jet centre line. A high-intensity laser could improve the velocity estimate in the core of the aerated jet. The proposed method can be applied directly to ambient and pressurised conditions where wall scattering is dominant. The directional independence of the fluorescence is also an advantage in scenarios where the imaging angle is a constraint.

Negative LIF Development For H2 Jet Characterization: Influence Of Tracers

This study focuses on the development of a new laser diagnostic based on Laser Induced Fluorescence by seeding the gas (N2) in which hydrogen is injected with fluorescent tracer. In this paper, three tracers were characterized, two aromatic compounds (toluene and difluorobenzene) and one ketone (acetone). The first part of this study compared the fluorescence of both aromatic compounds without injecting H2 . More particularly the influence of a temperature variation on the quantum yield and cross section absorption was regarded. It appeared that difluorobenzene was more suitable LIF measurement than toluene as it has a higher quantum yield that is less dependent to temperature variation. Then, Negative LIF was tested using two different tracers (difluorobenzene and acetone) and considering three different post-processing methods to consider the temperature variation inside the hydrogen jet: no temperature correction, temperature calculated based on a CFD RANS simulation, temperature calculated via an isentropic expansion and adiabatic mixture hypothesis. Results evidence that the first and the third methods presents respectively a lower and upper limit for the hydrogen mole fraction when the second method is biased by the presence of shock and expansion structures near the injector nozzle. Finally, it appears that, with the proper temperature correction, difluorobenzene and acetone yield similar results, despite the fact the acetone fluorescence needing more amplification to be captured, the signal to noise ratio is lower than for aromatic compounds.

Quantification of Mixing Quality Effects on Flashback Limits for H2-Rich Fuel Gases in Lean Premixed Combustion Using Laser-Induced Fluorescence of Acetone

Abstract One of the main challenges arising from hydrogen-rich fuel mixtures is to prevent flame flashback. In typical gas turbines, the fuel is commonly injected through holes in the axial swirler vanes to achieve a high mixing quality. However, this injection method is not perfect and can cause nonhomogeneous mixing regions, so that locally rich fuel clusters can significantly increase flashback propensity. This work aims to establish a link between the local mixing quality of fuel and air and flashback limits obtained experimentally under elevated pressure conditions. The nonreacting experiments have been conducted at an atmospheric mockup test rig and acetone-planar laser-induced fluorescence (PLIF) has quantified the local fuel concentration. Zones of high equivalence ratio are evident close to the center body wall. The near-wall equivalence ratio fields reveal that the critical probability of the local equivalence ratio being greater than the one for perfect premixing is between 20% and 35% for all hydrogen concentrations at the flashback limits observed. A probability of 35% is selected as a critical threshold to derive a correlation between the local and the global equivalence ratio in technical premixing. Even though the correlation is specific to the investigated burner configuration, the presented methodology offers valuable insights into the impact of the local mixing quality on flashback propensity, which can improve flashback prediction models formulated for perfect premixing conditions.

Flame development in prechamber assisted engine: High-speed PLIF

Prechamber-assisted combustion reduces emissions and improves engine performance through lean and knock limit enhancement. The spark plug ignition is replaced by multiple, high-temperature, radical-rich jets that entrain and ignite the main chamber charge, enabling the engine to operate at leaner air–fuel mixtures. Current work reports first cycle resolved planar laser-induced fluorescence (PLIF) measurements following the flame development process, starting from the mixture formation inside the prechamber to the post-combustion jets in the main chamber. The mixing and flame development inside the prechamber is visualized at 100 kHz with Acetone PLIF using an inventive engine-mounted optical prechamber (OPC) setup. Following the burning (/burned) prechamber jet interaction with the unburned main chamber, the mixture is imaged using the fuel and flame tracer (FFT) PLIF approach. The innovative 50 kHz FFT-PLIF approach is based on the fluorescence of acetone as fuel (unburned) and combustion-generated SO2 as a flame (burned) tracer with 266 nm laser excitation. The main chamber is fueled with premixed methanol seeded with 6.8 acetone and 2.6% (m/m) di-tert-butyl disulfide (DtBDS) while prechamber is injected with methane at 6 bar using solenoid and check valve assembly. The flow of the main chamber mixture into the prechamber creates a turbulent jet inside the prechamber. The inflow increases as the pressure ratio drops, generating significant recirculation inside the prechamber. Partially oxidized products remain near the top center of the prechamber even as the flame propagates through the throat. Combined flame and fuel images reveal the dynamics of the interaction layer between the prechamber jet and the main chamber fuel–air mixture.

Amino acid and acetone fluorescence sensors based on a stable light-emitting Cd(II) metal-organic framework with derivatives of isonicotinic acid

As one of the most promising category of functional materials, luminescent metal–organic frameworks (LMOFs) have been widely investigated as fluorescence chemical sensors which can offer a reliable diagnostic tools in biomedical research. Herein, a luminescent Cd-MOF [Cd2(L)2(H2O)]n (Cd-MOF) (H2L = 3-(3-carboxylphenyl) isonicotinic acid), was synthesized by and characterized in detail. Single-crystal structure determination reveals that Cd-MOF crystalizes in the monoclinic crystal system with C2/c space group. Experimental results show that Cd-MOF is a highly selective and sensitive luminescent sensor for rapidly detecting acetone, l-Tryptophane (L-Trp) and l- Aspartic acid (L-Asp) in water. It can significantly test acetone in common solvents, selectively identify l-Trp-and l-Asp-in 12 amino acid aqueous solutions, and enhance the fluorescence signal of Tryptophan and quench l-Asp-with the detection limit of 17.6 μM and 68.8 μM respectively. However, upon the interaction with electron rich amino acid (L-Trp), the Cd-MOF shows the selective “Turn-On” behavior, which may also be supported by the DFT studies.

Simultaneous visualization of instantaneous unburnt and preheating zones in turbulent premixed flames under transverse acoustic excitations

Instantaneous unburnt and preheating zones of bluff-body stabilized turbulent premixed flames under transverse acoustic excitations were investigated using simultaneous planar laser-induced fluorescence (PLIF) of acetone and CH2O, as well as multi-point hot-wire measurements. The PLIF images show that the unburnt zone marked by acetone images, the preheating zone marked by CH2O images, and the pixel-by-pixel product of acetone/CH2O have an increasing distribution area when slowly enlarging the sound pressure level (SPL). Wrinkled and bent edges of the unburnt and preheating zone can be seen at conditions away from the flame blow-off in the presence of the transverse acoustic excitations, and their sizes and areas increase as the flame blow-off is approached. At conditions near the flame blow-off with enlarging SPL to 123 dB, the flame turns from side to side over time and a large scale of the acetone/CH2O regions can be observed to deflect inside the center product zone, implying that the cold reactants can enter the product zone from the unburnt/preheating zones. The unburnt/preheating mainstream presents strong wrinkles and partial fractures. Such a phenomenon indicates that the local extinction of the shear layer flame can also be facilitated due to the turbulent fluctuation enhanced by the transverse acoustic wave. For a low flow velocity, increasing variations of the unburnt and preheating zones in the presence of the transverse acoustic wave can be revealed. The curvature of the acetone PLIF shows that the unburnt zones are more likely to be wrinkled with an increasing SPL and flow velocity. The root-mean-squared velocity measurements stress that the transverse acoustic wave mainly affects the turbulent premixed flame by enhancing the turbulent fluctuations.

Aggregation-induced emission-active fluorescent polymer sensors for the detection of water in organic solvents, Cu2+ and hemolysis

The hydrophobic polymer HDDA-EDT-SADA with aggregation-induced emission (AIE) property was synthesized via the thiol-ene click copolymerization of salicylaldehyde azine (SA) derivative diacrylate monomer SADA and commercially available 1,2-ethanedithiol (EDT) and 1,6-hexanediol diacrylate (HDDA). HDDA-EDT-SADA was found to display unexpected intense fluorescence in acetone and DMSO compared to that in other good solvents, which dramatically decreased by adding small amount of water. We demonstrate that HDDA-EDT-SADA can be used as a fluorescent sensor for water detection in acetone and DMSO. To improve the water solubility of the AIE-active polymer, SADA was copolymerized with dithiothreitol (DTT) and poly(ethylene glycol) diacrylate (PEGDA) to give an amphiphilic AIE polymer PEGDA-DTT-SADA. Similar fluorescence phenomenon was also found in DMF, suggesting that PEGDA-DTT-SADA could serve as an indicator for water detection in DMF. Thanks to the PEG segments and DTT units, the PEGDA-DTT-SADA was able to well-disperse in water via the formation of stable micelles. The PEGDA-DTT-SADA selectively complexed with Cu2+ and thus could be used as a fluorescent sensor for Cu2+ detection in aqueous media. Moreover, the PEGDA-DTT-SADA could be utilized as a fluorescent sensor for hemolysis ratio detection of red blood cells (RBCs) due to the inner filter effect.

Mixing and scalar dissipation rate in a decaying jet

The temporal development of the mixing field in a decaying jet (Re = 50,000) was quantified by measuring mole fraction and scalar dissipation rate (SDR) in a decaying, isothermal, turbulent gaseous jet. The 2D scalar field was measured by using planar laser induced fluorescence of acetone and, with appropriate image processing, this allowed estimation of the SDR using the two in-plane components within 16% error. The instantaneous and averaged distributions of the mole fraction are reported for downstream dimensionless distances up to 7 nozzle exit diameters and 35 exit flow timescales after end of injection. With advection of the last uniform exit concentration (UEC) profile core away from the nozzle exit, a region of weak concentration arises at the decaying jet's trailing edge. Estimates made in a Lagrangian frame of reference show that the trailing edge of the jet becomes leaner, after the end of injection (AEI), faster than in the steady state, confirming the existence of an ‘entrainment wave’. The normalised probability density functions of the 2D SDR at various stations and times AEI differ from a lognormal distribution at both low and high SDR values with negative skewness and positive excess kurtosis. A pseudo 3D SDR, made by including an estimate for the out of plane component, showed reduced departure from lognormal. The departure may be attributed to the disappearance of the strong shear layer associated with the absence of nozzle momentum AEI. To the authors’ knowledge, this study provides the first measurements of the SDR in a decaying, isothermal turbulent jet.

Oxygen Concentration Distribution Measurement of the Nozzle Flow Field by Toluene/Acetone Planar Laser-Induced Fluorescence

Planer laser induced fluorescence (PLIF) of toluene and acetone is performed for visualization of spatial distribution of oxygen in gas and oxygen mixing region in the nozzle flow field. The principle of the calibration methods of oxygen concentration distribution are expounded in this paper. As the two tracers had different situations on oxygen quenching effect, the ratio of the fluorescence images of the two tracers could be used to measure the oxygen concentration in the mixed area. In this way, the ratio of fluorescence signal intensity of toluene to acetone was found to be linearly related to oxygen concentration. By using this calibration relationship, we can measure the oxygen concentration distribution of the nozzle flow field with an accuracy of 12.6%. It indicates that this measurement method can be applied in turbulent flow field. The variation trend of oxygen concentration distribution in nozzle flow field can be analyzed by capturing multiple PLIF images in time sequence, which has the important reference value to the development process of nozzle burner flame.

Preparation and luminescence properties of isoquinoline-nucleated polycyclic aromatics

Two isoquinoline-nucleated polycyclic aromatic compounds, 4,5-diphenyl-7H-dibenzo[de,g]quinolin-7-one (A) and 3,4-diphenyl-6H-phenanthro[3,4,5-defg]quinolin-6-one (B), were synthesized in high yields through three-component reaction of phenanthrene diketone or pyrene diketone, ammonium acetate and 1,2-diphenylethyne in one-pot. Their structures, thermal stabilities, photophysical properties and energy levels are investigated systematically. Both compounds emit very weak fluorescence in acetone, but their luminescence intensity increased significantly when the water content reaches 50% for A and 40% for B, exhibiting aggregation-induced emission (AIE) characteristics, and showing that the AIE effect of the compound A is stronger than that of the compound B. The vacuum-processed doped devices based on the compound B showed green emission with a maximum brightness of 2162 cd/m2, a maximum current efficiency of 2.97 cd/A and a maximum external quantum efficiency (EQE) of 2.23%.

Highly Polarized Benzo[k]fluoranthene Imide Derivatives: Large Solvatofluorochromism, Dual Fluorescence and Aggregation Induced Emission Associated with Excited-State Intramolecular Charge Transfer.

The highly conjugated imides, 9-diphenyl-aminobenzo[k]fluoranthene imide and N-phenylcarbazo[2,3-k]fluoranthene imide, were produced by Buchwald-Hartwig reaction of N-octyl-9,10-dibromobenzo[k]fluoranthene imide with diphenylamine. In a similar manner, reaction of the N-ethylhexyl-9,10-dibromo derivative with carbazole leads to formation of 9-(N-carbazoyl)benzo[k]fluoranthene imide. All the benzo[k]fluoranthene imide (BFI) derivatives in solution show remarkable solvatofluorochromism. Diphenylamino and 9-(N-carbazoyl) derivatives, having twisted structures, exhibit fluorescence bands at short wavelengths in highly polar solvents, and they emit dual fluorescence in acetone. Moreover, the 9-(N-carbazoyl) derivative displays aggregation-induced emission in highly aqueous acetone solutions. The results of density functional theory calculations demonstrate that a considerable spatial separation exists between the HOMO and LUMO coefficients of the N-arylamine substituted BFIs. The results indicate that the ground-to-excited state transitions of these compounds have intramolecular charge transfer character.

Acetone photophysics at 282 nm excitation at elevated pressure and temperature. II: Fluorescence modeling

This is the second in a series of two papers that presents an updated fluorescence model and compares with the new experimental data reported in the first paper, as well as the available literature data, to extend the range of acetone photophysics to elevated pressure and temperature conditions. This work elucidates the complete acetone photophysical model in terms of each and every competing radiative and non-radiative rate. The acetone fluorescence model is then thoroughly examined and optimized based on disparity with recently conducted elevated pressure and temperature photophysical calibration experiments. The current work offers insight into the competition between non-radiative and vibrational energy decay rates at elevated temperature and pressure and proposes a global optimization of model parameters from the photophysical model developed by Thurber (Acetone Laser-Induced Fluorescence for Temperature and Multiparameter Imaging in Gaseous Flows. PhD thesis, Stanford University Mechanical Engineering Department, 1999). The collisional constants of proportionality, which govern vibrational relaxation, are shown to be temperature dependent at elevated pressures. A new oxygen quenching rate is proposed which takes into account collisions with oxygen as well as the oxygen-assisted intersystem crossing component. Additionally, global trends in ketone photophysics are presented and discussed.

Acetone photophysics at 282 nm excitation at elevated pressure and temperature. I: absorption and fluorescence experiments

This is the first in a series of two papers that presents new experimental data to extend the range of acetone photophysics to elevated pressure and temperature conditions. In this work, a flexible static and flow system is designed and characterized to study the independent as well as coupled effect of elevated pressure and temperature on acetone photophysics over pressures of 0.05‒4.0 MPa and temperatures of 295‒750 K for 282 nm excitation wavelength in nitrogen and air as bath gases. Experimental results show that at 282 nm excitation, relative fluorescence quantum yield increases with increasing pressure, decreases with increasing temperature, and that the pressure sensitivity varies weakly with elevated temperature. The previously assumed linearity of fluorescence with tracer number density is shown to only be valid over a small range. Additionally, acetone fluorescence is only moderately quenched in the presence of oxygen. The present findings yield insight into the competition between the non-radiative and collisional rates at elevated temperature and pressure, as well as provide validation datasets for an updated fluorescence model developed in the second paper.

Experimental and Numerical Investigation on Spark Ignition of Linearly Arranged Non-Premixed Swirling Burners

ABSTRACTThe ignition characteristics of a non-premixed multiple-burner linear combustion chamber was investigated experimentally and numerically, focusing on the determination of the mechanisms driving flame propagation from burner to burner. For different inter-burner spacings, overall equivalence ratios and bulk velocities, measurements of the velocity field and the mixture fraction distribution have been performed, respectively, with laser doppler anemometry and planar laser-induced fluorescence of acetone in the un-ignited flow. It was shown that in every individual burner, gas mixes with air within a central recirculation zone (CRZ) where the mixture is flammable except in the axial central rich gas jet and the annular air jet. Flammable mixture from the CRZ is extracted by the annular jet and this results in the existence of bridges of positive flammability factor in the inter-burner region. These bridges allow flame fragments to travel from the CRZ of the ignited burner to the CRZ of the adjacent unignited one, leading to burner-to-burner flame propagation. The ignition probability that sparking within a burner results in ignition of the adjacent one was obtained by performing many separate ignition trials with a laser spark. Ignition probability contours were also computed using a previously developed stochastic low-order ignition model and a large eddy simulation (LES) time-averaged solution of the cold flow. The quantification of the probability a flame kernel leads to burner ignition explained the differences existing between experimental results and the model. The results presented in this article extend our understanding of the mechanisms underlying the global ignition behavior of non-premixed annular combustion chambers.

Scalar dissipation rate statistics in turbulent swirling jets

The scalar dissipation rate statistics were measured in an isothermal flow formed by discharging a central jet in an annular stream of swirling air flow. This is a typical geometry used in swirl-stabilised burners, where the central jet is the fuel. The flow Reynolds number was 29 000, based on the area-averaged velocity of 8.46 m/s at the exit and the diameter of 50.8 mm. The scalar dissipation rate and its statistics were computed from two-dimensional imaging of the mixture fraction fields obtained with planar laser induced fluorescence of acetone. Three swirl numbers, S, of 0.3, 0.58, and 1.07 of the annular swirling stream were considered. The influence of the swirl number on scalar mixing, unconditional, and conditional scalar dissipation rate statistics were quantified. A procedure, based on a Wiener filter approach, was used to de-noise the raw mixture fraction images. The filtering errors on the scalar dissipation rate measurements were up to 15%, depending on downstream positions from the burner exit. The maximum of instantaneous scalar dissipation rate was found to be up to 35 s−1, while the mean dissipation rate was 10 times smaller. The probability density functions of the logarithm of the scalar dissipation rate fluctuations were found to be slightly negatively skewed at low swirl numbers and almost symmetrical when the swirl number increased. The assumption of statistical independence between the scalar and its dissipation rate was valid for higher swirl numbers at locations with low scalar fluctuations and less valid for low swirl numbers. The deviations from the assumption of statistical independence were quantified. The conditional mean of the scalar dissipation rate, the standard deviation of the scalar dissipation rate fluctuations, the weighted probability of occurrence of the mean conditional scalar dissipation rate, and the conditional probability are reported.

Fuel–Air Mixing Experiments in a Directly Fueled Supersonic Cavity Flameholder

In the present study, planar laser-induced acetone fluorescence was used to quantify the streamwise concentration distribution of an ethylene fuel surrogate (acetone-seeded nitrogen) injected directly into the recirculation region of a cavity flameholder embedded in a nonreacting supersonic airflow. The effect of injection configuration and fueling rate were studied. Parallel injection from the cavity front wall resulted in an ultra-fuel-rich recirculation region (beyond the upper flammability limit of an ethylene–air mixture) with a mixing efficiency that degraded with increased fueling rate. Downstream angled injection from the cavity floor yielded a substantial improvement in terms of the spatial uniformity and flammability of the local mixture. Its mixing efficiency was observed to be independent of fueling rate. The superior mixing ability of the latter injection configuration has the potential to provide increased cavity flameholder operability through a broader range of ignition and blowout limits and more flexibility in terms of ignitor placement than conventional direct-fueling schemes. Further investigation of its performance over a wider range of reacting conditions is warranted.

2-Pyridone-based fluorophores containing 4-dialkylamino-phenyl group: Synthesis and fluorescence properties in solutions and in solid state

Novel highly emissive 2-pyridone-based compounds 3a,b and 4a–d were synthesized by a convenient one-pot method from 4-(dialkylamino)acetophenones (1a,b) and cyanoketene dithioacetal (2a) or sulfonyl ketene dithioacetals (2b,c), and their fluorescence properties were investigated. A simple structure modification of 2-pyridones significantly affected their optical properties including the emission wavelength and fluorescence intensity. All the 6-(4-dialkylamino)phenyl-2-pyridones showed positive solvatofluorochromism and intense blue-green fluorescence in nonpolar solvents such as chloroform (Ф: 0.80–0.92) and dichloromethane (Ф: 0.83–0.94). A hypsochromic shift of the fluorescence emission maxima and strong fluorescence in a polar solvent were observed by substituting the dimethylamino group with a diethylamino group. Introduction of a sulfonyl group disturbed the molecular planarity of compounds 4a, 4b, and 4d, resulting in a strong fluorescence in acetone (Ф: 0.86–0.95) and acetonitrile (Ф: 0.59–0.88). These results indicate that 2-pyridone-based compounds have great potential as fluorophores for various practical applications.

Turbulent Non-Premixed Flames Stabilized on Double-Slit Curved Wall-Jet Burner with Simultaneous OH-Planar Laser-Induced Fluorescence and Particle Image Velocimetry Measurements

A double-slit curved wall-jet (CWJ) burner utilizing a Coanda effect by supplying fuel and air as annular-inward jets over a curved surface was employed to investigate the stabilization characteristics and structure of propane/air turbulent non-premixed flames with varying global equivalence ratio and Reynolds number. Simultaneous time-resolved measurements of particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of OH radicals were conducted. The burner showed a potential of stable and non-sooting operation for relatively large fuel loading and overall rich conditions. Mixing characteristics in cold flow were first examined using an acetone fluorescence technique, indicating substantial transport between the fuel and air by exhibiting appreciable premixing conditions. PIV measurements revealed that the flow field consisted of a wall-jet region leading to a recirculation zone through flow separation, an interaction jet region resulting from the collision of annular-inward jets, followed by a merged-jet region. The flames were stabilized in the recirculation zone and, in extreme cases, only a small flame seed remained in the recirculation zone. Together with the collision of the slit jets in the interaction jet region, the velocity gradients in the shear layers at the boundaries of the annular jets generate the turbulence. Turbulent mean and rms velocities were influenced by the presence of the flame, particularly in the recirculation zone. Flames with a high equivalence ratio were found to be more resistant to local extinction and exhibited a more corrugated and folded nature, particularly at high Reynolds numbers. For flames with a low equivalence ratio, local quenching and re-ignition processes maintained flames in the merged jet region, revealing a strong intermittency, which was substantiated by the increased principal strain rates for these flames.

Transient effects of fuel–air mixing in a partially-premixed turbulent swirl flame

Unsteady interactions of flow, fuel–air mixing and reaction in a lean partially-premixed turbulent swirl flame are investigated using simultaneous particle image velocimetry and planar laser-induced fluorescence of OH and acetone with a repetition rate of 10kHz. The flame is operated with methane and air in a gas turbine model combustor at ambient temperature and pressure. Transport and mixing of fuel is visualized by fluorescence of acetone, which is added with 9% by volume to the methane. The dominant unsteady flow structures are a precessing vortex core (PVC) in the shear layer of the inner recirculation zone and the lower stagnation point (LSP) at the flame root. The measurements show that fuel and air are largely separated at the inlet of the combustion chamber, but are then strongly mixed by the PVC. A well-mixed zone of unburned fuel and air is formed around the vortex, and then ignited by recirculating burned gas. At the flame root, the PVC induces periodic changes in the composition of the unburned gas, which varies between pure air and well-mixed fuel and air. Reaction is locally quenched at the LSP when fresh air without fuel is present, and re-ignition takes place when mixed fuel and air arrive at the boundary of recirculating burned gas. Generally, the results show that the enhancement of fuel–air mixing induced by the PVC contributes significantly to the stabilization of the flame, and that the flame dynamics can only be properly understood when an analysis of transient mixing mechanisms is included.

A comparison of selected organic tracers for quantitative scalar imaging in the gas phase via laser-induced fluorescence

This paper compares three of the tracers most commonly used for laser-induced fluorescence in gaseous flows, toluene, naphthalene, and acetone. Additionally, anisole (methoxybenzene, CH3OC6H5) is included in the comparison. Each tracer is employed to image the scalar field in the same nonreacting transient impinging turbulent jet. The jet fluid is seeded with tracer vapor in a bubbler, excitation is at 266 nm, and both air and nitrogen are used as bath gases. Measured signals are compared to theoretical predictions based on fluorescence quantum yield, absorption cross-section, and vapor pressure. We find that anisole shows the highest total signal intensity of all investigated species, while naphthalene features the highest signal per molecule. Acetone has the advantage of being insensitive to quenching by oxygen and that its fluorescence is partly at visible wavelengths. In addition to this volatility-limited scenario at room temperature, we also compare the expected relative signals for elevated temperatures and for a hypothetical case in which the amount of admissible tracer seeding is limited.