Optical Diagnostic Techniques Research Articles

Thermally-excited fluorescence of strontium products for in-cylinder temperature diagnostics in internal combustion engines

A new optical diagnostic technique for burned gas temperature measurements was introduced using visible thermally-excited fluorescence of strontium monohydroxide (SrOH). The technique is a significant improvement over previously developed alkali metal-based techniques in that it requires only one tracer substance, strontium acetylacetonate in ethanol, compared to two or three alkali metal precursors. Combustion of the precursor forms 1.5 to 12 ppm SrOH, depending on equivalence ratio, and thermal excitation leads to visible light emission. For the purpose of temperature measurements, multiple emission bands were spectrally resolved and recorded with an intensified camera coupled to a spectrometer during experiments in an optical spark-ignited direct-injected engine. A hybrid experimental and computational approach was taken to validate the feasibility of SrOH based temperature measurements as well as to determine missing spectroscopic information. To that end, emission spectra were recorded for equivalence ratios ranging from lean to rich, and GT Power simulations provided a calibration base for burned gas temperatures. The optical engine was operated with early injection leading to near-homogenous mixing prior to ignition. It was confirmed that the measured data follow relationships consistent with a Boltzmann distribution of excited states populations. Furthermore, the experimentally determined energy difference between the excited [Formula: see text] and [Formula: see text] states of SrOH that form the basis of the temperature evaluation was found to be in good agreement with literature data. The calibrated analysis model then allowed to process spectra from over 400 single engine cycles from 10 runs with four different operating conditions to determine instantaneous burned gas temperatures. Average temperatures ranged from 1759 to 2490 K with standard deviations of 46–122 K. Variations were higher for more marginal fuel conditions. Self-absorption of the emission signals was characterized and would lead to a temperature error of no more than 0.5%.

Soot maturity studies in methane-air diffusion flames at elevated pressures using laser-induced incandescence

Two-dimensional laser-induced incandescence (LII) measurements were used for quantitative soot volume fraction (fv) measurements in methane-air diffusion flames at pressures ranging from 0.1 to 0.5 MPa. Additionally, laser-induced fluorescence (LIF) was used for visualization of polycyclic aromatic hydrocarbons (PAHs) considered as important soot precursors. A heat and mass transfer-based LII model was used for the analysis of experimental LII fluence curves to evaluate soot absorption functions, E(m), at various spatial positions in the flames. Based on previous work, variations in the evaluated E(m) was assumed to be related to soot maturity. Generally, the most mature soot was found at the spatial position of maximum fv along the central axis and at the flame edges. Also, the soot maturity at the position of maximum fv at each pressure was found to increase from the flame at 0.1 MPa to 0.5 MPa. A critical examination of the assumptions and uncertainties in the E(m) analysis was made. The present study emphasizes the limitation of assigning soot a constant E(m) in the overall flame for temperature and soot concentration evaluation using the optical methods spectral soot emission (SSE) and line-of-sight attenuation (LOSA), which are commonly used non-intrusive optical diagnostic techniques in sooting high-pressure flames. The study also demonstrates the critical choice of fluence in quantitative imaging LII measurements of fv when the E(m) of soot spans over large range of values.

A REVIEW ON CURRENT SCENARIO OF ORAL CANCER IN INDIA WITH SPECIAL EMPHASIS ON MODERN DETECTION SYSTEMS AND BIOMARKERS

Oral squamous cell carcinoma is a major public health concern worldwide and a growing threat for rapidly developing economies such as India, where it ranks among the top three cancers. This review aims to discuss the national status of oral cancer in terms of incidences and mortality. We have added the emphasis on clinical characteristics of oral potentially malignant disorders and emerging optical diagnostic techniques to detect oral lesions which would otherwise go undetected by a conventional oral examination. Modern detection systems such as autofluorescence, chemiluminiscence, Narrowband imaging and Raman spectroscopy will definitely aid Conventional oral examination for diagnosis. Definitive diagnosis of oral cancer by using saliva and serum-based noninvasive biomarkers can minimize the need of tissue biopsies and patient discomfort. Urgent research efforts are required to find new ways to identify and examine high-risk population for the early diagnosis and prevention of Oral squamous cell carcinoma.

An optical diagnostic technique based on ultraviolet absorption and schlieren for components stratification in a binary-component fuel–air mixture

The evaporation characteristics of multi-component fuel have significant effects on the fuel–air mixing process and subsequent processes, such as ignition, combustion, and harmful pollutants emission formation. When a multi-component fuel is directly injected into the combustion chamber, spatial and temporal equivalence ratio stratification may happen due to the preferential evaporation of components with different volatilities. However, there is a lack of effective optical diagnostics of the spatial stratification in a multi-component fuel spray. In this study, new optical technique based on ultraviolet absorption and visible light schlieren (UAVS) is for the first time proposed to measure the stratification of vapor distributions stratification in a binary-component fuel spray. UAVS technique was applied to investigate the effects of mixing ratios in a binary-component fuel spray (p-xylene and n-hexane) and ambient temperature on the stratification of components with different volatilities. The results denote the UAVS technique as the effective method for the observation of stratification of a multi-component fuel spray. In this study, the stratification phenomenon was the most evident at the ratio of 1:1. At the same time, when the ambient temperature is much higher than the dew point temperature of mixture, the stratification rarely occurs, because of the rapid evaporation thus providing time not enough for preferential evaporation. Graphic abstract

Numerical study on turbulent dispersion of diesel sprays under ultrahigh injection pressure using large eddy simulation

ABSTRACT The modern diesel engines equipped with an advanced fuel injection system up to ultrahigh injection pressure of 300 MPa are under development at present. The impact of injection pressure on fuel spray characteristics such as spray penetration and spray cone angle has been widely concerned in previous studies. However, it is still lack of the detailed investigation on the turbulent dispersion of small droplets produced by a high-pressure injector due to the limited capability of optical diagnostic techniques to simultaneously measure the two phases. Droplet dispersion due to turbulence plays a major role in high-velocity fuel spray mixing and combustion processes involving group evaporation of droplets. Thus, the effect of different injection pressures on droplet dispersion in nonevaporating diesel sprays was investigated using the Euler-Lagrange framework with large eddy simulation (LES) implemented in an open-source code OpenFOAM. Size-dependent instantaneous radial motion and dispersion characteristics of droplets dominated by large-scale turbulent structures within a polydisperse downstream spray were analyzed in detail. Results show that increasing injection pressure can modestly promote the radial dispersion of most droplets with diameter of 2 ~ 12 µm further downstream at the late stage of injection. This could be the result of the increasing interaction time of droplets with larger turbulent structures due to the increase of spray penetration with increasing injection pressure. However, increasing injection pressure has no significant impact on the strength of droplet-turbulence interaction in terms of slip velocity between droplet and gas phases and this could be quantitatively explained by the droplet Stokes number (St) estimated in this study. The most droplets with 0.1 < St < 10 tend to move and concentrate further radially outward, leading to droplet clustering. Thus, the effect of injection pressure on droplet-turbulence interaction is much less than its influence on droplet size for high-velocity fuel sprays, indicating that the ultrahigh injection pressure has much less important impact on the spatial inhomogeneity of droplet distribution than its influence on the evaporation rate of individual droplets.

Experimental investigation into flow blurring atomization

The twin-fluid atomizer employing the cross-stream mixing arrangement for air and liquid prior to the orifice exit is investigated with a scaled-up size transparent injector. Simplistic optical flow diagnostics techniques (Mie scatter and high-speed LED-backlit imaging) were employed to characterize the effect of operating parameters on internal two-phase flow development and the external spray characteristics of a transparent flow blurring (FB) injector of 6 mm exit orifice diameter. Two successive Mie scattering images of the spray are utilized for the PIV analysis along with mathematical manipulation of Mie scatter intensity profile at any axial location to contrast the spray quality for two different operating conditions. Derived droplet velocity field from the PIV algorithm is used to show the spray development confines to the near field region of five diameters downstream of the nozzle exit. The experiments were carried out for different values of air to liquid ratio (ALR) ranging from 1 to 2.5 with an increment of 0.25 for 5 different Liquid flow rates (LFR). Results indicate that the internal two-phase flow mixing characteristics of FB injector dictates the spray formation and its quality. This internal two-phase flow mixing is responsible for the jet break up in liquid tube itself leading to finely atomized spray. Laplace number defined as a product of Euler and Weber number is proposed as an injector performance number as it uniquely links to the spray quality. The impact of operating parameters such as ALR on relative atomization efficiency and spray quality in the near field is characterized.

Oscillation characterization of volatile combustion of single coal particles with multi-species optical diagnostic techniques

This paper investigated the oscillation characterization of volatile combustion of single coal particles using high-speed OH-PLIF and CH* chemiluminescence, meanwhile advanced data-driven algorithm as post-processing. The measurement region of in-situ 500 Hz OH-PLIF system was set to 53mm × 35 mm with a spatial resolution of ~23 µm per pixel, which was used to capture the continuous and whole volatile combustion process of single particle in a group of pulverized coal particles (SPGCP). A high-volatiles bituminous coal (30 wt%) burned at a gas temperature of 1700 K with oxygen mole fractions in the range of 10%–30%. The morphology of volatile flame and dynamic evolution was obtained. Dynamic mode decomposition (DMD) method can provide a new insight into combustion oscillation of pulverized coal. The oscillation frequency characteristics of pulverized coal flame were captured, and the red-shift phenomenon of dominant frequency with the increase of oxygen concentration was found. The particle aggregation might lead the low-frequency oscillation of pulverized coal combustion. On the contrary, individual or separated particle combustion could generate larger oscillation frequency.

Constrained-temperature solutions of coflow laminar diffusion flames

We investigate the use of an experimental 2-D temperature profile to constrain detailed numerical solutions of a sooting coflow laminar diffusion flame. Experimentally, four optical diagnostic techniques are used to measure the two-dimensional temperature field in an ethylene-air coflow flame. This experimental temperature field is then used to impose the temperature in the solution process, thus obviating the need to solve the energy equation and, in particular, to incorporate costly models of radiative losses in the flame. Results are presented for a 40% ethylene-air flame on the Yale Coflow Burner. In the unconstrained solution of the complete set of governing equations, the location of maximum temperature is found along the flame wings, whereas the experimental temperature field has its maximum along the centerline. Similarly, the location of peak soot volume fraction migrates from along the flame wings in the unconstrained calculation, where soot surface growth processes dominate, to the centerline in the constrained case, where soot inception is the dominant condensed-phase formation mechanism. The distribution of soot in the constrained solution is much more consistent with experimental observations, and this fact illustrates how the validation of a soot sub-model may be complicated by the necessity of modeling distributed heat losses in the flame.

Combined Optic-Acoustic Monitoring of Combustion in a Gas Turbine

The need for better combustion monitoring in gas turbines has become more acute with the latest technical requirements, standards, and policies in terms of safety, environment, efficiency, operation flexibility, and operation costs. Combustion Bay One e.U. and FH JOANNEUM GmbH initiated in 2015 an experimental research program about the feasibility and first assessments of placing optical systems near the combustor. The project’s acronym “emootion” stands for “Engine health MOnitOring and refined combusTION control based on optical diagnostic techniques embedded in the combustor”. The motivation of the project is twofold. On one side, one wants to exploit the radiative feature of the flame and to transform it into a piece of reliable information about the combustion status. On the other side, this information can be useful in terms of data interpretation or data reconciliation with other information coming from other sensors such as temperature probes, fast pressure probes, or accelerometers. The focus is put on several aspects of combustor operations: on detection of the flame, on monitoring of the ignition process, on a quality assessment of combustion based on its spectral contents (including soot formation), and on the detection of possible combustion instabilities. Promising results were obtained using photodiodes that offer an adequate trade-off between narrow-band sensitivity and signal time response. It is shown that it is convenient to combine a fast-pressure sensor with an optical sensor in a compact form; this combination has led to the so-called Rayleigh Criterion Probe (RCP). The split in red, green, and blue (RGB) light components and their further analysis allows for mapping the different types of operation. Regarding the probe packaging aspect, it is discussed that the level of light collection needed to keep an acceptable signal-to-noise ratio has been so far a restraint for the use of optical fibres. Solutions are proposed to bring the optical sensor as close as possible to the optical interface and to make it operational and reliable in prevailing heat. This contribution closes with a description of the pressure tests in a new combustion facility built for this purpose. A compact and portable combustion monitoring system including at least 3 RCPs can become an instrumentation standard within the next decade.

Gastric cancer diagnosis using hyperspectral imaging with principal component analysis and spectral angle mapper.

.Significance: Hyperspectral imaging (HSI) is an emerging optical technique that has a double function of spectroscopy and imaging.Aim: Near-infrared hyperspectral imaging (NIR-HSI) (900 to 1700 nm) with the help of chemometrics was investigated for gastric cancer diagnosis.Approach: Mean spectra and standard deviation of normal and cancerous pixels were extracted. Principal component analysis (PCA) was used to compress the dimension of hypercube data and select the optimal wavelengths. Moreover, spectral angle mapper (SAM) was utilized as chemometrics to discriminate gastric cancer from normal.Results: Major spectral difference of cancerous and normal gastric tissue was observed around 975, 1215, and 1450 nm by comparison. A total of six wavelengths (i.e., 975, 1075, 1215, 1275, 1390, and 1450 nm) were then selected as optimal wavelengths by PCA. The accuracy using SAM is up to 90% according to hematoxylin–eosin results.Conclusions: These results suggest that NIR-HSI has the potential as a cutting-edge optical diagnostic technique for gastric cancer diagnosis with suitable chemometrics.

Single-Shot Temperature Measurements in a Scramjet Combustor Using Thermally Assisted Laser-Induced Fluorescence

The knowledge of the temperature in the flowfield of the scramjet is critical to the understanding of its performance. This study represents the application of an optical diagnostic technique, thermally assisted laser-induced fluorescence, to the temperature measurements in the combustor of a supersonic combustion engine. The experiments were conducted in the T4 shock tunnel using a scramjet model. Experimental data were obtained by focusing a laser beam into the combustor and exciting the OH radical. A detailed numerical model that simulates all radiative and collisional processes of relevance with the appropriate system of differential equations was developed for the analysis of the influence of energy transfer processes on the fluorescence signal. The population distributions achieved with numerical modeling of the LIF process validated the approach proposed to deduce temperatures. By evaluating the scramjet LIF spectra with a full spectral fit, a temperature distribution across the combustor width was obtained. The experimental results were compared with the computational fluid dynamics simulations of the combustion process.

Experiments on macroscopic spray characteristics of diesel-ethanol with dispersed cerium nanoparticles

In this study, an experiment of macroscopic spray performance of stabilized nanofuels under high injection and ambient pressure is conducted on a Common rail direct fuel injection. The tested nanofuels have been prepared by DE20 (20% ethanol, 80% diesel by volume) blends with nano-CeO2 at 25 ppm(DE20Ce25), 50 ppm(DE20Ce50),100 ppm(DE20Ce100) respectively. Furthermore, appropriate amount of CTAB whose weight is equal to CeO2 and 2%vol 1-decanol were added as surfactant additive. All tested fuels were ultrasonically oscillated at a frequency of 40 khz for 45min in order to enhance their stability. The macroscopic spray characteristics of diesel-ethanol with dispersed cerium nanoparticles have been measured using the optical diagnostic techniques of shadowgraph. Comparing with those the pure diesel(D100), the spray penetration of DE20, DE20Ce25, DE20Ce50, DE20Ce100 increased by −3%, −1.8%, −0.3% and 9.5%, while the spray cone angle increased by −3%,4%,2.8% and 12.5% as well as spray area increased by −3%,-1.3%,0.6% and 31% respectively. The addition of nanoparticles also enhances the instability of fuel and shortens the crucial breakup time. In addition, the influence caused by increasing viscosity and surface tension are balanced by the disturbance. Furthermore, the macroscopic spray characteristics of DE20Ce50 show little difference with the pure diesel which means it can be a promising alternative fuel for CI engine with no required modification.

Combustion behavior of pulverized sponge iron as a recyclable electrofuel

In this work, the combustion behavior of pulverized sponge iron (PSI), a practical-grade iron product that was proposed as a potential candidate in the metal fuel cycle, was observed directly using high-magnification shadowgraphy and other optical diagnostics techniques. The PSI was combusted in a laboratory-scale, McKenna flat-flame burner. Results suggest that, in agreement with theoretical models, PSI combusted heterogeneously, with most of the particle mass converting to an intact, solid oxide. However, in contrast with previous hypotheses, the formation of a microflame of combusting aerosol that was attached to the particle surface was observed. Results from quantitative shadowgraphy indicated near-instantaneous melting and complex behavior—we attempted to explain these based on the FeO phase diagram. The analysis of micron- and nano-sized combustion products confirmed that the PSI combusted heterogeneously and a gaseous sub-oxide was formed. Combustion under high excess oxygen was hypothesized to reduce the formation of these oxides.

Line-of-Sight optical diagnostic for measuring combustion products using species’ natural emissions

A new line-of-sight optical diagnostic technique was developed for measuring species’ concentrations using broadband (band-pass) filtered natural emission of species (FNES). The unresolved problem in measuring a species’ concentration via FNES is the overlap of different species at certain emission wavelengths, which makes the measurement of a single species problematic. A solution is proposed in this work and applied to measure the time-resolved concentrations of water, carbon monoxide and carbon dioxide during autoignition of an n-heptane mixture. The experiments were performed in a rapid compression machine (RCM) at a gas pressure, gas temperature and equivalence ratio of 23.6 bar, 693 K and 0.455, respectively. A high-speed infrared camera with three filters at wavelength ranges of 4.069 to 4.445 μm, 4.545 to 4.785 μm, and 5.2 to 5.4 μm were used to measure the filtered species’ emissions.

Spray penetration, combustion, and soot formation characteristics of the ECN Spray C and Spray D injectors in multiple combustion facilities

In a collaborative effort to identify key aspects of heavy-duty diesel injector behavior, the Engine Combustion Network (ECN) Spray C and Spray D injectors were characterized in three independent research laboratories using constant volume pre-burn vessels and a heated constant-pressure vessel. This work reports on experiments with nominally identical injectors used in different optically accessible combustion chambers, where one of the injectors was designed intentionally to promote cavitation. Optical diagnostic techniques specifically targeted liquid- and vapor-phase penetration, combustion indicators, and sooting behavior over a large range of ambient temperatures—from 850 K to 1100 K. Because the large-orifice injectors employed in this work result in flame lengths that extend well beyond the optical diagnostics’ field-of-view, a novel method using a characteristic volume is proposed for quantitative comparison of soot under such conditions. Further, the viability of extrapolating these measurements downstream is considered. The results reported in this publication explain trends and unique characteristics of the two different injectors over a range of conditions and serve as calibration targets for numerical efforts within the ECN consortium and beyond. Building on agreement for experimental results from different institutions under inert conditions, apparent differences found in combustion indicators and sooting behavior are addressed and explained. Ignition delay and soot onset are correlated and the results demonstrate the sensitivity of soot formation to the major species of the ambient gas (i.e., carbon dioxide, water, and nitrogen in the pre-burn ambient versus nitrogen only in the constant pressure vessel) when holding ambient oxygen volume percent constant.

Laser fluorescence spectroscopy in predicting the formation of a keloid scar: preliminary results and the role of lipopigments.

Keloid scars, in contrast to other scar types, significantly reduce the patient's quality of life. To develop a nondestructive optical diagnostic technique predicting the keloid scars formation in vivo, laser-induced fluorescence spectroscopy (LFS) was used to study the autofluorescence in skin of patients with various types of head and neck cicatricial deformities. The unexpected results were obtained for the endogenous fluorescence of lipofuscin. Significantly reduced autofluorescence of lipofuscin was registered both in the intact and in the keloid scar tissues in comparison with the intact and scar tissues in patients with hypertrophic and normotrophic scars. Sensitivity and specificity achieved by LFS in keloid diagnosis are 81.8% and 93.9% respectively. It could take place due to the changes in the reductive-oxidative balance in cells, as well as due to the proteolysis processes violation. Therefore, we suppose that the evaluation of the lipofuscin autofluorescence in skin before any surgical intervention could predict the probability of the subsequent keloid scars formation.

Laminar Burning Velocity Measurement Using the Filtered Broadband Natural Emissions of Species

Laminar flame speed plays a fundamental role in understanding hydrocarbon chemistry and is the basis of turbulent flame modeling. The main objective of this research is to visualize a flame and measure its speed using a new optical diagnostic technique, which is based on the natural radiative emissions of various species, mainly hydrocarbons, water and carbon dioxide. This new technique has two main advantages over the Schlieren method. First only one optical access is needed, and second, the preheat zone and the flame front can be observed, and their radiative emission can be quantified. In addition, the condition of the unburned gas in front of the flame can be studied using the new technique to evaluate some of the hypotheses behind unstretched flame speed measurement, such as the trivial change of the unburned gas state. To evaluate and validate the new optical diagnostic technique, the flame propagation of methane, oxygen and nitrogen mixtures was studied using species infrared radiative emissions at...

Super-Resolution Imaging in Fluid Mechanics Using New Illumination Approaches

Quantifying submillimeter flows using optical diagnostic techniques is often limited by a lack of spatial resolution and optical access. This review discusses two super-resolution imaging techniques, structured illumination microscopy and total internal reflection fluorescence or microscopy, which can visualize bulk and interfacial flows, respectively, at spatial resolutions below the classic diffraction limits. First, we discuss the theory and applications of structured illumination for optical sectioning, i.e., imaging a thin slice of a flow illuminated over its entire volume. Structured illumination can be used to visualize the interior of multiphase flows such as sprays by greatly reducing secondary scattering. Second, the theory underlying evanescent waves is introduced, followed by a review of how total internal reflection microscopy has been used to visualize interfacial flows over the last 15 years. Both techniques, which are starting to be used in fluid mechanics, could significantly improve quantitative imaging of microscale and macroscale flows.

Intralipid-Based Phantoms for the Development of New Optical Diagnostic Techniques

Intralipid is a material widely employed for the preparation of phantoms for optical imaging and biophotonics applications in medical field. The development of new optical diagnostic equipment in these fields requires the use of well-designed phantoms with optical properties (including scattering and absorption) mimicking those of biological tissues in all the pre-clinical stages of investigations. For this reason, great research effort has been devoted to optically characterize Intralipid and at preparing optimal phantoms. In this short review, we summarize the principal physico-chemical characteristics of Intralipid and the main contributions in the assessment of its scattering and absorption properties. In addition, the most largely used Intralipid-based homogeneous and non-homogeneous phantoms are discussed. Even though other materials are available for the preparation of phantoms, the use of Intralipid still offers an inexpensive and easy-to-use method for preparing phantoms with finely tuned optical properties.

THERMAL BEHAVIOR OF PYROLYSIS OIL - DIESEL OIL EMULSION IN EVAPORATING MICRONIC DROPLETS

ABSTRACT Transformations inside emulsion droplets of 82 µm have been studied by using laser diagnostics. Arrays of calibrated droplets of emulsion 70/30 w/w diesel oil/pyrolysis oil were injected in pre-heated air flow inside a tubular reactor. Four thermal regimes have been studied: room temperature, 150°C, 250°C, and 350°C. For comparison, droplets of the diesel oil used to form the emulsion were studied in the same experimental conditions. The investigation has been performed by applying the Generalized Scattering Imaging laser technique that allows the simultaneous determination of size and optical properties of droplets. This optical diagnostic technique permitted to infer the chemical-physical changes inside the emulsion droplet by measuring the imaginary part of their refractive index. At 150°C and 250°C, the emulsion droplets suffered progressive depletion of the diesel oil phase. The pyrolysis oil, dispersed in the diesel oil matrix in the form of microdroplets 2 µm sized, underwent partial evaporation, liquid phase pyrolysis, and polymerization. At 350°C almost all the diesel oil had evaporated and the pyrolysis oil microdroplets dispersed in the emulsion droplet had merged to form a single droplet. These residual droplets showed a very narrow size distribution and an absorption coefficient greater than that of the original PO in agreement with the assessment that they represent the combined outcome of evaporation, liquid phase pyrolysis and polymerization of the pyrolysis oil. Samples of residual droplets were captured at the exit of the reactor and analyzed by means of optical microscopy. The microscope analysis was consistent with the laser diagnostics results.