Двухканальная система визуализации высокотемпературного горения на основе скоростных камер EVERCAM F 1000-16-C

The possibility of the visualization of remote objects using active optical systems with a copper vapor brightness amplifier has been investigated. Theoretical and experimental dependences for the field of view of the active optical system on the distance between the object and the brightness amplifier (laser monitor, laser projection microscope) have been studied. The visualization results suggest that as the object is moved farther from the brightness amplifier the field of view decreases and the quality of the obtained images gets worse. The maximum distance between the object and the brightness amplifier which is determined based on the superradiance pulse duration does not coincide with the visualization results. The field of view decreases as the distance between the object and the brightness amplifier increases. The feasibility of using a bistatic system for distant objects visualization has been shown.

The paper presents the results of application of optical system with brightness amplification, a laser monitor, to study the surface of aluminum nanopowder at the time of laser ignition and during combustion. Using a laser monitor, we visualized the presence of a liquid phase in the process of laser ignition of aluminum nanopowder combustion for the first time. For quantitative analysis of the combustion process, we propose using the correlation coefficient of the images of laser monitor. The results of calculating the correlation coefficient demonstrated compliance with the change in the intensity of the images of the laser monitor during combustion and visual observation of the combustion process. For the conventional scheme of a laser monitor with a focal length of 8 cm, the distortions introduced by the instability of the brightness amplifier into the measurement results are estimated. When observing a static test object, the correlation coefficient of the images varied from 0.995 to 0.996, while the fluctuation in the correlation coefficient during combustion is in the range from 0.685 to 0.996, which indicates the possibility of this parameter usage for quantitative analysis of combustion processes in the study using a laser monitor.

Countercurrent flame propagation inside vertical PMMA cylinders against pure oxygen flow

A single-cylinder full-metal engine with a real combustion chamber geometry was used to investigate particulate number emissions resulting from transient engine operation. The formation of particulate number emissions depends on mixture formation influenced by the in-cylinder flow and injection, and the formation of fuel films on the in-cylinder walls. For the investigation of this multi-parameter process, simultaneous endoscopic PIV and combustion visualization were applied. Hence, the measurement techniques allowed the investigation of in-cylinder flow, flame propagation, and soot formation. The test rig was modified to apply a generic load step and a realistic tip-in with Miller cycle. The reproducibility of the engine parameters during the transient allowed statistical analysis and the comparison between steady-state operating points. Cause-and-effect chains concerning the formation of soot are concluded by correlation analysis of parameters extracted from the flow field, the flame propagation and the soot luminosity.

Phenomenology of methane flame propagation into compositionally stratified, gradually richer mixtures

A multipass optical system for phase object image brightness amplification is proposed. The image contrast in such systems is demonstrated to reach 70% and more. By amplification on strontium vapor the images have been obtained of dynamic objects with control signals from telemonitors with a video recorder.

Operating features of a copper bromide brightness amplifier in the monostatic laser monitor

Experimental measurements and multi-cycle large eddy simulation (LES) are performed in an optically accessible four-stroke spark-ignition engine to investigate cycle-to-cycle variations (CCV). High-speed combustion imaging is used to measure the early flame propagation and obtain the flame radius and centroids. Large Eddy Simulation generates data-bases for the flame propagation as well as the kinetic energy in the cylinder and confirms the observations from the two-dimensional fields by three-dimensional simulation results. Experiment and simulation are compared with respect to the strength and distribution of CCV. Both approaches reveal CCV causing similar statistics of maximum pressures and combustion speeds. The cycles are categorized as slow and fast cycles using the crank angle of ten percent burnt fuel-mixture. Analysis of the flame centroids shows that slow cycles move further towards the intake-side of the engine compared to fast cycles. The kinetic energy during combustion is averaged for the slow and fast cycles based on the samples being in unburnt and burnt mixture. Studying the kinetic energy level in the unburnt and burnt mixture reveals higher turbulent kinetic energy for the fast cycles as well as larger separation between the global kinetic and the turbulent kinetic energy for the slow cycles, providing evidence for a source of the CCV variations observed in this engine.

Traditional visual biosensing platforms rely on color to display detection results, which can be influenced by individual visual abilities, equipment, parameters, and lighting conditions during photo capture. This limitation significantly impedes the advancement of next-generation portable electrochemical biosensors. Therefore, we propose a visual biosensing device that utilizes distance as an indicator, enabling the facile determination of the length of discoloration, which is inversely proportional to the concentration of the target analyte. The separation of the Signal Generation (SG) and Signal Output (SO) regions effectively mitigates potential interference from the sample color. Additionally, the SG region can be disassembled to facilitate electrochemical impedance spectroscopy (EIS) detection in laboratory settings, enabling dual-mode detection. Meanwhile, the utilization of piezoelectric nanogenerators (PENG) empowers the entire point-of-care testing (POCT) sensing device, effectively addressing the issue of a limited battery life. The biosensing device exhibited a satisfactory linear range (EIS mode, 5 pg/L to 5 mg/L; visual mode, 0.5 ng/L to 5 mg/L) and a low limit of detection (EIS mode, 2.3 pg/L; visual mode, 0.14 ng/L) with S/N = 3 for ochratoxin A (OTA) under optimized conditions. The self-powered and cost-effective dual-mode biosensing platform developed for OTA detection offers clear and easily interpretable results, demonstrating a high accuracy in laboratory settings.

In the territory of the facilities where combustible gases are handled or stored, the combustible gas-air mixture may be formed as a result of the equipment depressurization. Mixture ignition leads to fires, explosions and destruction of buildings and structures. Most often, the combustion of such mixtures occurs in the deflagration mode. Main factor affecting the values of explosion parameters is the speed of flame front propagation. The methodologies presented in the normative documents and in various sources of literature are considered, which are related to the determination of the speed of flame front propagation. The analysis showed that for the same emergency the considered methodology gives significantly different values of the speed of flame front propagation, this causes discussion among the design engineers. The considered methodology is developed based on the experimental data. Thus, the definition of the speed of flame front propagation in the methodology presented in the normative documents is based on the mixture of energy potential. Proprietary methodology considers the physical and chemical properties of gas-air mixtures, but there is no mentioning about the boundaries of their application. The methodology proposed in the article is related to determining the speed of flame front propagation. It is developed based on the theories of hydrodynamics and flame propagation. It is assumed that flame propagation in a gas mixture is similar to a fluid flow in the smooth round pipes. The movement of gas follows the laws of hydrodynamics,  the coefficient of thermal conductivity of the gas mixture is proportional to the coefficient of hydraulic friction, since the physical meaning of the kinematic viscosity coefficient, the diffusion coefficient, and the thermal conductivity coefficient of gases is the same. Among others, they have the same dimension. Verification of the developed methodology for predicting the speed of flame front propagation during gas-air mixture combustion was carried out based on the comparative analysis of the calculation results with the consequences of real emergency explosions. The analysis of the considered accidents led to the conclusion that the proposed methodology realistically describes the process of flame front propagation during gas-air cloud explosion.

The relative enhancements of volume-integrated burning rate and flame surface area under turbulence and heat release rate contributions due to different combustion and flame propagation modes have been compared between conventional and Moderate or Intense Low Oxygen Dilution (MILD) combustion of stratified mixtures (for a global mean equivalence ratio of 0.8) for the first time using three-dimensional Direct Numerical Simulation (DNS) data. The burning rate enhancement under turbulence is found to be comparable to the enhancement of flame surface area for the conventional stratified flames considered here, whereas the burning rate enhancement is found to be considerably greater than flame area augmentation in the MILD cases analyzed here. It has been found that almost all the heat release rate arises due to the lean-premixed mode of combustion for the conventional stratified flame cases considered here. In contrast, the lean premixed mode of combustion accounts for about 50% of the total heat release rate for the MILD cases where rich-premixed and non-premixed modes of combustion contribute significantly to the overall heat release rate. Under the conditions analyzed here, more than 75% of heat release rate arises from the propagation-dominated regions for both MILD combustion and stratified flame cases, but the trend is stronger in the conventional stratified mixture combustion. More than 80% of heat release rate in the globally lean conventional stratified flame cases considered here originates from back-supported flame propagation, whereas both front and back-supported flame propagation modes have comparable contributions to heat release in the MILD combustion cases. The non-premixed mode of combustion has been found to play a more important role in the MILD combustion cases than in the case of conventional stratified flames. This implies that the closures, which work reasonably well for MILD combustion of homogeneous mixtures, may not be sufficient for modeling of MILD combustion of stratified/inhomogeneous mixtures.

<div class="section abstract"><div class="htmlview paragraph">Advanced combustion concepts that rely on the lean-burn approach are a proven solution for increasing the efficiency and reducing the harmful emissions of SI engines. The pre-chamber spark ignited (PCSI) engines utilize high ignition energy of the multiple jets penetrating from the pre-chamber, to enable fast and stable combustion of lean mixture in the main chamber. The combustion is still governed by the flame propagation, so the dilution level and efficiency benefits are highly restricted by strong decrease of laminar flame speeds. Homogeneous charge compression ignition (HCCI) combustion allows a higher dilution level due to rapid chemically driven combustion, however the inability to directly control the ignition timing has proven to be a major setback in HCCI deployment. The addition of the spark plug, to improve the controllability and widen the operating range, resulted in a combustion concept known as spark-assisted compression ignition (SACI), however spark ignition of lean mixtures is very difficult even at close to HCCI conditions. Since one of the features of active pre-chamber is the ability to control mixture dilution at the spark plug location, a combustion concept called pre-chamber induced HCCI combustion (PC-HCCI) that combines pre-chamber ignition and HCCI combustion is proposed. In this concept a near stoichiometric mixture in the pre-chamber is spark ignited and the combustion in pre-chamber triggers kinetically controlled combustion of lean main combustion chamber mixture. As a first step of the research, numerical modelling of the proposed combustion concept is made by employing 3D-CFD and 1D/0D simulation models. The main purpose of the modelling is to define main geometrical and operating parameters required for achieving a pre-chamber induced HCCI combustion and to predict possible benefits of employing such combustion concept.</div></div>

An imaging laser projection system, a laser monitor, is applied for real-time monitoring of the surface of nanopowders during high-temperature combustion. The mirror-based scheme of the laser monitor is used in the experiments to increase the range of observation. For the analysis of surface changes during combustion, the correlation coefficient together with average brightness of the images of laser monitor obtained by digital processing are proposed to use. The results of calculating the correlation coefficient demonstrate compliance with the change in the intensity of the images of the laser monitor during the combustion and visual observation of the combustion process. The distortions introduced by the instability of the brightness amplifier into the measurement results are estimated. When observing a static test object, the variation of correlation coefficient is three orders of magnitude less than fluctuation in the correlation coefficient during combustion, the variation of average image brightness is less than 5%. The obtained results indicate the possibility of the usage of the correlation coefficient and average brightness of the images as informative parameters in the analysis of surface changes of burning nanopowders in studies using laser monitors with both conventional and mirror-based schemes.

At present, natural gas of the Urengoyskoye field is burned in boilers of thermal power plants (TPP) to generate electricity. At the same time, refineries and petrochemical plants deepen the processing of fossil liquid hydrocarbons. The final product of processing is not only motor fuels, ethylene glycols, plastics, accompanying inert gases such as argon, but also a large amount of combustible secondary gaseous mixtures of the methane series. These mixtures contain a wide array of combustible components. Among them there is the methane-hydrogen fraction, which is characterized by a fairly high hydrogen content. A distinctive feature of the use of hydrogen as a fuel is the high rate of flame propagation and the relatively low heat of combustion [1, p.6-8]. The methane-hydrogen fraction due to the volatility of the composition and a wide range of changes in the heat of combustion was recently used in refineries for their own needs as an insignificant additive to combusted natural gas in process furnaces [2-5]. If the methane-hydrogen fraction was not utilized as a fuel in these furnaces, it was burned in flares. Due to the increase in oil refining volumes and the increase in the amount of methane-hydrogen fraction produced, it became realistic to use this gaseous fraction as the main fuel for power boilers of thermal power plants located near petrochemical plants. In the near future, it is planned to use the methane-hydrogen fraction as an additive to the natural gas for 20 power steam boilers of the Nizhnekamsk CHP-1 with a total thermal capacity of 6000 MW. The supplier of the methane-hydrogen fraction is the TAIF NK oil refineries. Depending on the technology of oil refining, the hydrogen content in the methane-hydrogen fraction ranges from 10 to 27% (by weight). The concentration limits of hydrogen ignition in a mixture with air have been experimentally studied by many researchers [6–8] mainly during bench testing or inside laboratories. A feature of the oxidation of hydrogen by air oxygen is the fact that there is a difference between the spread of the flame in limited volumes and in large volumes of the furnace space of energy boilers [9]. In small volumes, when the flame front collides with the wall, oxidation reactions are interrupted, and this does not occur in large volumes. Therefore, the study of flame propagation speed and concentration limits of ignition of methanehydrogen fractions mixed with air in relation to the conditions of furnace volumes of power boilers is relevant. In this work using the in-house software [2-5] calculations were made to determine the burning rate for various compositions of mixtures of methane-hydrogen fractions (MHF) with Urengoi natural gas. It was found that the flame propagation rate of the MHF, compared with hydrogen (see Table 2), decreases 1.76 times. For a mixture of the MHF with Urengoi gas with thermal fractions of the MHF of 12% and 25%, the flame propagation rate increases, respectively, 1.4 times and 1.78 times compared with burning pure Urengoi gas.

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