Advances in imaging of chemically reacting flows

This review explores the recent advancements in laser-based medical imaging techniques, highlighting their significant contributions to modern diagnostic practices. Laser technologies, including fluorescence imaging, photoacoustic imaging, and femtosecond lasers, have revolutionized non-invasive medical imaging by offering high-resolution and precise visualization of biological structures and processes. These techniques not only enhance early disease detection, particularly cancers, but also support real-time guidance during surgeries, improving patient outcomes. Furthermore, the integration of artificial intelligence (AI) has further optimized diagnostic accuracy and analysis efficiency. Despite these advancements, challenges such as high equipment costs, the need for specialized training, and a lack of standardized protocols still hinder widespread adoption in clinical settings. This review discusses the ongoing innovations in laser-based imaging, the ethical considerations surrounding AI integration, and the potential for future developments, emphasizing the importance of continued research to maximize the benefits of these technologies for patient care.

Gaining information of species, temperature, and velocity distributions in turbulent combustion and high-speed reactive flows is challenging, particularly for conducting measurements without influencing the experimental object itself. The use of optical and spectroscopic techniques, and in particular laser-based diagnostics, has shown outstanding abilities for performing non-intrusive in situ diagnostics. The development of instrumentation, such as robust lasers with high pulse energy, ultra-short pulse duration, and high repetition rate along with digitized cameras exhibiting high sensitivity, large dynamic range, and frame rates on the order of MHz, has opened up for temporally and spatially resolved volumetric measurements of extreme dynamics and complexities. The aim of this article is to present selected important laser-based techniques for gas-phase diagnostics focusing on their applications in combustion and aerospace engineering. Applicable laser-based techniques for investigations of turbulent flows and combustion such as planar laser-induced fluorescence, Raman and Rayleigh scattering, coherent anti-Stokes Raman scattering, laser-induced grating scattering, particle image velocimetry, laser Doppler anemometry, and tomographic imaging are reviewed and described with some background physics. In addition, demands on instrumentation are further discussed to give insight in the possibilities that are offered by laser flow diagnostics.

A new combustion regime identification methodology using the neural networks as supervised classifiers is proposed and validated. As a first proof of concept, a binary classifier is trained with labelled thermochemical states obtained as solutions of prototypical one-dimensional models representing premixed and nonpremixed regimes. The trained classifier is then used to associate the regime to any given thermochemical state originating from a multi-dimensional reacting flow simulation that shares similar operating conditions with the training problems. The classification requires local information only, i.e. no gradients are required, and operates on reduced-dimension thermochemical states, in order to cope with experimental data as well. The validity of the approach is assessed by employing a two-dimensional laminar edge flame data as a canonical configuration exhibiting multi-regime combustion behaviour. The method is readily extendable to additional classes to identify criticality phenomena, such as local extinction and re-ignition. It is anticipated that the proposed classifier tool will be useful in the development of turbulent multi-regime combustion closure models in large scale simulations.

The spatiotemporal resolution of diagnostic X-ray images is limited by the erosion and rupture of conventional stationary and rotating anodes of X-ray tubes from extreme density of input power and thermal cycling of the anode material. Conversely, detector technology has developed rapidly. Finer detector pixels demand improved output from brilliant keV-type X-ray sources with smaller X-ray focal spots than today and would be available to improve the efficacy of medical imaging. In addition, novel cancer therapy demands for greatly improved output from X-ray sources. However, since its advent in 1929, the technology of high-output compact X-ray tubes has relied upon focused electrons hitting a spinning rigid rotating anode; a technology that, despite of substantial investment in material technology, has become the primary bottleneck of further improvement. In the current study, an alternative target concept employing a stream of fast discrete metallic microparticles that intersect with the electron beam is explored by simulations that cover the most critical uncertainties. The concept is expected to have far-reaching impact in diagnostic imaging, radiation cancer therapy and non-destructive testing. We outline technical implementations that may become the basis of future X-ray source developments based on the suggested paradigm shift.

This article discusses some recent progress and future trends in turbulent combustion. Issues in turbulent combustion modeling (TCM) and some perspectives in active control are specifically considered. Modeling methods are first briefly surveyed to identify future developments. It is anticipated that further progress will be made in physical modeling based on flame surface density concepts and that physical modeling of turbulent flames will rely more heavily on modern computational tools like direct numerical simulation (DNS), large eddy simulations (LES), detailed numerical modeling (DNM) of simple flames. Physical modeling as it is practiced today will continue to evolve into more reliable methods for industrial design applications. As the computational resources progress one may also foresee that LES methods will take over and that research will shift from the Reynolds average approach to the more advanced LES computation of turbulent reactive flows. Because turbulent combustion is so complex, physical modeling and LES calculations will continuously need detailed experiments. These will emphasize field measurements based on imaging methods. It is expected that current progress in optical diagnostics will continue. Imaging diagnostics will become more easily applicable to practical situations. Their spatial and temporal resolution will be enhanced. Images will continue to provide qualitative information on the basic processes of turbulent combustion but improved experimental methods will yield more quantitative data. Another area which holds promises is that of active control. From current progress in this field one may foresee that advanced control schemes will play an increasing role in experimental investigations of instabilities and in practical optimization of turbulent combustors. “Intelligent combustor” concepts combining control loops with a combustion system are now being explored and will probably become of importance in enhancing the stability of combustion, in augmenting the domain of operation and in reducing the pollutant emission levels.

I. Bio-Physilcal Principles of Image Structure and Perception.- Spatial and Spatio-Temporal Analysis of Biological Form and Function.- Signal Detection Theory: Limitations and Applications.- II. Advances in Source & Detector Technology.- Methods of Microwave Imagery for Diagnostic Applications.- Time-of-Flight Method for Positron Tomographic Imaging and State-of-the-Art of Detector Technology for Emission Tomography.- Scanned Projection Radiography.- Photoelectronic Imaging and Optical Recording.- Compton Tomographic Imaging: Design Aspects and Performance.- III. Clinical Imaging: Basic Principles of Acoustical NMR and Transmission Tomographic Imaging.- Acoustical Imaging: Theory Limitations and Relationships to Other Imaging Modalities.- Nuclear Magnetic Resonance (NMR) Imaging: An Overview.- Computerized Transmission Tomography: CT and Digital Volume Scanning.- Some Imaging Characteristics of the Dynamic Spatial Reconstructor X-Ray Scanner System.- IV. Clinical Imaging: Basic Principles of Emission Tomography & Radiopharmaceutical Chemistry.- Positron Emission Tomography (PET).- Current Status and Limitations of Single Photon Emission Imaging.- Biochemical Considerations in the Design of Radiopharmaceuticals.- V: Image Processing & Autoradiography.- Image Processing and Display.- Film Analysis Systems and Applications.- VI: Results of Clinical Evaluation: State-of-the-Art Performance of New Radiographic Transmission Techniques.- Digital Radiography: Developments, Limitations, Clinical Results.- Workshop in Clinical Applications of Transmission Tomography.- VII: The Results of Clinical Evaluation: Studies of the Central Nervous System.- The Interrelationships of Cerebral Blood Flow and Cerebral Metabolism and Its Study with Positron Emission Tomography in Man.- Dynamic Emission Tomography of Regional Cerebral Blood Flow.- Spect Brain Perfusion Studies Using N-Isopropyl I-123 P-Iodoamphetamine (IMP).- VIII: The. Results of Clinical Evaluation: Studied of the Heart and Lungs.- Utility of Imaging Techniques to Predict and Manage Patients with Cardiovascular Abnormalities.- Utility of Radionuclide Studies in Patients with Pulmonary Vascular and Airways Diseases.- IX: The Results of Clinical Evaluation: Studies of the Abdomen and Pelvis.- Clinical Studies of the Abdomen: Scintigraphic and Other Techniques in the Management of Patients with Abdominal Disease.- Real-Time Ultrasound.- Comparison of Different Imaging Techniques for the Prediction and Imaging of Patients with Abdominal, Pelvic, or Thyroid Disease.- Utilization of Special Computerized Tomography and Nuclear Medicine Techniques for Quality Control and for the Optimization of Combined Precision Chemotherapy and Precision Radiation Therapy.- Single Photon Emission Computed Tomography and Albumin Colloid Imaging of the Liver.- Automatic Analysis of Diagnostic Features from Digitized Radiocolloid Liver Images.- Interventional Ultrasound.- X: Cost-Effective and Cost-Benefit Assessment of New High Technology Procedures.- Diagnostic Imaging in Developing Countries.- Technology and the State: The Emergency of Health Care Rationing.- New and Emerging Health Care Technologies: Assessing Efficacy, Safety and Costs.- XI: Meeting Overview and Images of the Future.- Images of the Future.- Author Index.- Speakers/Participants List of Addresses.

Sidewall quenching of atmospheric laminar premixed flames studied by laser-based diagnostics

Combustion instability due to thermo-acoustic interactions in high-speed propulsion devices such as gas turbines and rocket engines result from pressure waves with very large amplitudes propagating back and forth in the combustion chamber. Exposure to the pressure fluctuations over a long period of time can lead to a cataclysmic failure of engines. The underlying physics governing the generation of the thermo-acoustic instability is a complex interaction among heat release, turbulence, and acoustic waves. Currently, it is very difficult to accurately predict the expected level of oscillations in a combustor. Hence development of strategies and engineering solutions to mitigate thermo-acoustic instability is an active area of research in both academia and industry. In this work, we carry out numerical modeling of thermo-acoustic instability in a self-excited, laboratory scale, model rocket combustor developed at Purdue University. Two different turbulent combustion models to account for turbulence-chemistry interactions are considered in this study, the flamelet model and the transported probability density function (PDF) method. <br>In the flamelet modeling approach, detailed chemical kinetics can be easily incorporated at a relatively low cost in comparison to other turbulent combustion models and it also accounts for turbulence-chemistry interactions. The flamelet model study is divided into two parts. In first part, we examine the effect of different numerical approaches for implementing the flamelet model. In advanced modeling and simulations of turbulent combustion, the accuracy of model predictions is affected by physical model errors as well as errors that arise from the numerical implementation of models in simulation codes. Here we are mainly concerned with the effect of numerical implementation on model predictions of turbulent combustion. Particularly, we employ the flamelet/progress variable (FPV) model and examine the effect of various numerical approaches for the flamelet table integration, with presumed shapes of PDF, on the FPV modeling results. Three different presumed-PDF table integration approaches are examined in detail by employing different numerical integration strategies. The effect of the different presumed-PDF table integration approaches is examined on predictions of two real flames, a laboratory-scale turbulent free jet flame, Sandia Flame D and the self-excited resonance model rocket combustor. Significant difference is observed in the predictions both of the flames. The results in this study further support the claims made in previous studies that it is imperative to preserve the laminar flamelet structure during integration while using the flamelet model to achieve better predictions in simulations. In the second part of the flamelet modeling study, computational investigations of the coupling between the transient flame dynamics such as the ignition delay and local extinction and the thermo-acoustic instability developed in a self-excited resonance combustor to gain deep insights into the mechanisms of thermo-acoustic instability. A modeling framework that employs different flamelet models (the steady flamelet model and the flamelet/progress variable approach) is developed to enable the examination of the effect of the transient flame dynamics caused by the strong coupling of the turbulent mixing and finite-rate chemical kinetics on the occurrence of thermo-acoustic instability. The models are validated by using the available experimental data for the pressure signal. Parametric studies are performed to examine the effect of the occurrence of the transient flame dynamics, the effect of artificial amplification of the Damkohler number, and the effect of neglecting mixture fraction fluctuations on the predictions of the thermo-acoustic instability. The parametric studies reveal that the occurrence of transient flame dynamics has a strong influence on the onset of the thermo-acoustic instability. Further analysis is then conducted to localize the effect of a particular flame dynamic event, the ignition delay, on the thermo-acoustic instability. The reverse effect of the occurrence of the thermo-acoustic instability on the transient flame dynamics in the combustor is also investigated by examining the temporal evolution of the local flame events in conjunction with the pressure wave propagation. The above observed two-way coupling between the transient flame dynamics (the ignition delay) and the thermo-acoustic instability provides a plausible mechanism of the self-excited and sustained thermo-acoustic instability observed in the combustor.<br>The second turbulent combustion model considered in this study is the transported PDF method. The transported PDF method is one of the most attractive models because it treats the highly-nonlinear chemical reaction source term without a closure requirement and it is a generalized model for a wide range of turbulent combustion problems.Traditionally, the transported PDF method has been used to model low-Mach number, incompressible flows where the pressure is assumed to be thermodynamically constant. Since there is significant pressure fluctuations in the model rocket combustor, the flow is highly compressible and it is necessary to account for this compressibility in the transported PDF method. In the past there has been very little work to model compressible reactive flows using the transported PDF and no effort has been made to model thermo-acoustic instability using the transported PDF method. There is a pressing need to further examine and develop the transported PDF method for compressible reactive flows to broaden our understanding of physical phenomenon like thermo-acoustic instability, interaction between combustion and strong shock and expansion waves, coupling between acoustic and heat release which are observed in high-speed turbulent combustion problems. To address this, a modeling framework for compressible turbulent reactive flows by the using the transported PDF method is developed. This framework is validated in a series of test cases ranging from pure mixing to a supersonic turbulent jet flame. The framework is then used to study the thermo-acoustic interactions in the self-excited model rocket combustor.

Advanced laser-based imaging diagnostics is an important tool for the development and optimization of modern combustion devices that can fulfil the future requirements in terms of energy efficiency maximization and pollutant minimization. The determination of the conditions prior to combustion in terms of fuel concentration, fuel/air equivalence ratio and temperature is crucial for the control of the subsequent combustion process. At the same time, fresh-gas and burned gas temperatures are important for modelling of combustion, spray evaporation and pollutant formation. These two tasks for diagnostics development have therefore been addressed recently. While laser-induced fluorescence of organic molecules in liquid fuels has frequently been carried out on a qualitative level, a more detailed understanding of individual molecules that are applied as ‘‘fuel tracers’’ in an otherwise non-fluorescing fuel has developed in recent years (C Schulz and V Sick 2005 Tracer-LIF diagnostics: Quantitative measurement of fuel concentration, temperature and air/fuel ratio in practical combustion situations Prog. Energy Combust Sci. 31 75--121). The first applications were based on the pragmatic assumption that absorption cross-sections and fluorescence quantum yields were independent of temperature and pressure and that fluorescence was either independent of or inversely dependent (in the case of aromatic compounds) on oxygen partial pressure. Recent measurements of these interdependencies show that a quantitative interpretation of signals under combustion conditions (especially in internal-combustion-engines) requires a detailed understanding of the underlying photophysics (W Koban, J D Koch, V Sick, N Wermuth, R K Hanson and C Schulz 2005 Predicting LIF signal strength for toluene and 3-pentanone under engine-related temperature and pressure conditions Proc. Combust. Inst. 30 1545--53). The signal dependence on temperature and oxygen concentration, in turn, is strong enough to propose new imaging techniques for temperature and oxygen concentration based on organic tracer molecules (W Koban and C Schulz 2005 Toluene as a tracer for fuel, temperature and oxygen concentrations SAE technical paper series 2005-01-2091). Recent results also show that extreme care must be taken when applying concepts that have been developed under ambient conditions to in-cylinder measurements in internal combustion engines (W Koban and C Schulz 2005 FAR-LIF: Myth and reality European Combustion Meeting (Louvain-la-Neuve, 2005). Laser-based temperature measurements in reactive systems are often affected by the presence of particles, droplets or surface scattering. The recently developed technique of multi-line NOLIF temperature imaging (W G Bessler and C Schulz 2004 Quantitative multi-line NO-LIF temperature imaging 2004 Appl. Phys. B 78 519--33) can be applied to stationary systems and is robust against the above mentioned influences. Examples in sooting flames, high-pressure flames (W G Bessler, C Schulz, T Lee, D I Shin, M Hofmann, J B Jeffries, J Wolfrum, and R K Hanson 2002 Quantitative NO-LIF imaging in high-pressure flames Appl. Phys. B 75 97--102), spray flames and wall-near thermometry are presented.

There is a crucial need to improve energy conversion efficiencies and minimize the environmental impact of turbulent combustion systems for energy production. Lean premixed turbulent combustion operation will significantly reduce efficiency-based thermal losses and combustion emissions. However, the performance of lean turbulent combustion technology is inevitably limited by the effects of flame extinction. Flames operating at lean conditions are susceptible to stabilization dynamics caused by local reaction extinction; this leads to global flame blowout and termination of the combustion energy production process. An improved understanding and prediction of flame extinction and stability will guide strategies to enhance efficiency, reduce emissions and improve performance of turbulent combustion systems. This research is focused on understanding the physical mechanisms of flame extinction using a newly-developed physics-based model. The novelty of this model is that it interactively couples the physics of the turbulent flow through a dynamic Lagrangian vortex method and the strained flame reaction kinetics using a one-dimensional opposed-jet flame. This innovative modeling strategy effectively captures the dynamic flame stability and extinction for turbulent premixed combustion.

Data-based instantaneous conditional progress variable dissipation rate modeling for turbulent premixed combustion

Paraovarian cysts are common, accounting for 10–20% of all adnexal lesions, and most of them are benign. On the other side, paraovarian tumors of borderline malignancy are very rare, only about forty cases were reported all over the world. Here, we present a case of 16 years female with left lower abdominal pain, pelvic sonography showed a cystic mass in Douglas pouch with solid mural nodule. She underwent laparoscopy, we detected and extirpated a paraovarian cyst of about 10x10 cm with solid component 3x3 cm and corpus luteum cyst 5x5 cm. After histopathological analysis, it was proved to be borderline ovarian serous tumor Stage Ic according to the International Federation of Gynecology and Obstetrics (FIGO) staging. As till now, there is no clear guideline regarding the management of this tumor; the treatment strategy was determined on the basis of ovarian tumor guidelines, with preservation of fertility. In conclusion, paraovarian cysts is a common disease and usually benign. It rarely causes clinical problems, but caution is necessary as there is a possibility of a malignant or borderline tumor. As in ovarian tumors, even if the size of the solid component of the tumor detected by diagnostic imaging is very tiny, malignant or borderline malignant tumors should be considered.

Laser-based imaging and characterization of individual nanostructures provides significant advantages over other imaging techniques, such as scanning probe microscopy and electron microscopy, by allowing simultaneous imaging and spectroscopic measurements. Laser-based techniques also involve simpler sample preparation, cause minimal sample damage and provide high-throughput measurements over large sample areas. In this article, we review recent progress in this field focusing on applications in the study of individual carbon nanostructures, mainly carbon nanotubes and graphene. Absorption, Rayleigh, Raman and photoluminescence techniques will be discussed for optical-based detection, and photocurrent and photothermal current techniques will be discussed for electrical detection. Each optical technique relies on a different physical process, allowing spectroscopic investigation of the fundamental optical, thermal and optoelectronic processes for individual nanoscale carbon structures. In addition, we will compare the various advantages of wide-field and focused (confocal) laser excitation/detection geometries and discuss ongoing efforts to overcome the speed and resolution limitations of laser-based imaging.

Investigation of droplet ignition under microgravity conditions using laser-based techniques—an overview

Direct numerical solution of turbulent nonpremixed combustion with multistep hydrogen-oxygen kinetics