scholarly journals Propagation of CH4-N2O-N2 Flames in a Closed Spherical Vessel

Processes ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 851
Author(s):  
Maria Mitu ◽  
Venera Giurcan ◽  
Codina Movileanu ◽  
Domnina Razus ◽  
Dumitru Oancea
Keyword(s):  
Flame Propagation ◽  
Internal Combustion Engines ◽  
Early Stage ◽  
Initial Pressure ◽  
Spherical Vessel ◽  
Industry Research ◽  
Closed Cell ◽  
Safety Parameters ◽  
Protection Devices ◽  
Expansion Coefficients

Flammable fuel-N2O mixtures raise safety and environmental protection issues in areas where these mixtures are used (such as: industry, research, internal combustion engines). Therefore, it is important to know their laminar combustion velocities and propagation speeds—important safety parameters for design of active protection devices against gas explosions and corresponding safety recommendations. In this paper, the laminar combustion velocities of N2-diluted CH4-N2O flames, obtained in experiments on outwardly propagating flames, at various initial pressures (within 0.5–2.0 bar) and room temperature, are reported. The experiments were made in a 0.5 L spherical cell with central ignition. The laminar combustion velocities were calculated from the constants of cubic law of flame propagation during the early stage of closed cell explosions and the expansion coefficients of unburned flammable mixtures, using the adiabatic model of the flame propagation. The expansion coefficients were determined from equilibrium calculations on flames propagating under isobaric conditions. The laminar combustion velocities were compared with data reported in the literature. Using the laminar combustion velocities and the expansion coefficients, the propagation speeds of N2-diluted CH4-N2O flames were calculated. Both laminar combustion velocities and propagation speeds decrease with the initial pressure increase.

Inert Gas Influence on Propagation Velocity of Methane-air Laminar Flames

2018 ◽  
Vol 69 (1) ◽  
pp. 196-200 ◽  
Author(s):  
Maria Mitu ◽  
Venera Giurcan ◽  
Domnina Razus ◽  
Dumitru Oancea
Keyword(s):  
Experimental Data ◽  
Kinetic Modeling ◽  
Early Stage ◽  
Pressure Rise ◽  
Laminar Flames ◽  
Inert Gas ◽  
Spherical Vessel ◽  
Pressure Time ◽  
Expansion Coefficients ◽  
Propagation Velocities

The flame propagation in methane-air mixtures diluted by inert additives (He, Ar, N2, CO2) was studied by means of pressure-time records of laminar deflagrations occurring in a spherical vessel with central ignition. Experiments were made using mixtures with various equivalence ratios between 0.610 and 1.310 and various inert concentrations between 5 and 25 vol%, at various initial pressures between 50 and 200 kPa. Examination of pressure-time records in the early stage of explosions delivered the normal burning velocities Su via the coefficients of the cubic law of pressure rise, using a previously described procedure. The propagation velocities (or the flame speed) were calculated from the normal burning velocities using the expansion coefficients of the unburnt gas during the isobaric combustion. The propagation velocities of examined systems obtained from experimental data were examined against the propagation velocities obtained from kinetic modeling of methane-air-inert combustion by means of 1D COSILAB package using the GRI 3.0 mechanism.

Application of Advanced Technologies in Natural Product Research: A Review with Special Emphasis on ADMET Profiling

2020 ◽  
Vol 21 (10) ◽  
pp. 751-767
Author(s):  
Pobitra Borah ◽  
Sangeeta Hazarika ◽  
Satyendra Deka ◽  
Katharigatta N. Venugopala ◽  
Anroop B. Nair ◽  
...  
Keyword(s):  
Drug Discovery ◽  
Natural Product ◽  
Dynamic Range ◽  
Early Stage ◽  
Attrition Rate ◽  
Drug Candidates ◽  
Advanced Technologies ◽  
Natural Product Research ◽  
The Status ◽  
Safety Parameters

The successful conversion of natural products (NPs) into lead compounds and novel pharmacophores has emboldened the researchers to harness the drug discovery process with a lot more enthusiasm. However, forfeit of bioactive NPs resulting from an overabundance of metabolites and their wide dynamic range have created the bottleneck in NP researches. Similarly, the existence of multidimensional challenges, including the evaluation of pharmacokinetics, pharmacodynamics, and safety parameters, has been a concerning issue. Advancement of technology has brought the evolution of traditional natural product researches into the computer-based assessment exhibiting pretentious remarks about their efficiency in drug discovery. The early attention to the quality of the NPs may reduce the attrition rate of drug candidates by parallel assessment of ADMET profiling. This article reviews the status, challenges, opportunities, and integration of advanced technologies in natural product research. Indeed, emphasis will be laid on the current and futuristic direction towards the application of newer technologies in early-stage ADMET profiling of bioactive moieties from the natural sources. It can be expected that combinatorial approaches in ADMET profiling will fortify the natural product-based drug discovery in the near future.

scholarly journals Effect of Temperature Conditions on Flame Evolutions of Turbulent Jet Ignition

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2226
Author(s):  
Jiaying Pan ◽  
Yu He ◽  
Tao Li ◽  
Haiqiao Wei ◽  
Lei Wang ◽  
...  
Keyword(s):  
Flame Propagation ◽  
Early Stage ◽  
Turbulent Jet ◽  
Combustion Stability ◽  
Effect Of Temperature ◽  
Main Chamber ◽  
Detailed Chemical Kinetics ◽  
Jet Flame ◽  
Spherical Flame ◽  
Temperature Conditions

Turbulent jet ignition technology can significantly improve lean combustion stability and suppress engine knocking. However, the narrow jet channel between the pre-chamber and the main chamber leads to some difficulties in heat exchange, which significantly affects combustion performance and mechanical component lifetime. To clarify the effect of temperature conditions on combustion evolutions of turbulent jet ignition, direct numerical simulations with detailed chemical kinetics were employed under engine-relevant conditions. The flame propagation in the pre-chamber and the early-stage turbulent jet ignition in the main chamber were investigated. The results show that depending on temperature conditions, two types of flame configuration can be identified in the main chamber, i.e., the normal turbulent jet flame propagation and the spherical flame propagation, and the latter is closely associated with pressure wave disturbance. Under low-temperature conditions, the cold jet stoichiometric mixtures and the vortexes induced by the jet flow determine the early-stage flame development in the main chamber. Under intermediate temperature conditions, pre-flame heat release and leading pressure waves are induced in the jet channel, which can be regarded as a transition of different combustion modes. Whereas under high-temperature conditions, irregular auto-ignition events start to occur, and spherical flame fronts are induced in the main chamber, behaving faster flame propagation.

scholarly journals Laminar Burning Velocities of Hydrogen-Blended Methane–Air and Natural Gas–Air Mixtures, Calculated from the Early Stage of p(t) Records in a Spherical Vessel

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7556
Author(s):  
Maria Mitu ◽  
Domnina Razus ◽  
Volkmar Schroeder
Keyword(s):  
Natural Gas ◽  
Initial Conditions ◽  
Numerical Study ◽  
Early Stage ◽  
Linear Trend ◽  
Burning Velocity ◽  
Pressure Rise ◽  
Spherical Vessel ◽  
Practical Applications ◽  
Hydrogen Addition

The flammable hydrogen-blended methane–air and natural gas–air mixtures raise specific safety and environmental issues in the industry and transportation; therefore, their explosion characteristics such as the explosion limits, explosion pressures, and rates of pressure rise have significant importance from a safety point of view. At the same time, the laminar burning velocities are the most useful parameters for practical applications and in basic studies for the validation of reaction mechanisms and modeling turbulent combustion. In the present study, an experimental and numerical study of the effect of hydrogen addition on the laminar burning velocity (LBV) of methane–air and natural gas–air mixtures was conducted, using mixtures with equivalence ratios within 0.90 and 1.30 and various hydrogen fractions rH within 0.0 and 0.5. The experiments were performed in a 14 L spherical vessel with central ignition at ambient initial conditions. The LBVs were calculated from p(t) data, determined in accordance with EN 15967, by using only the early stage of flame propagation. The results show that hydrogen addition determines an increase in LBV for all examined binary flammable mixtures. The LBV variation versus the fraction of added hydrogen, rH, follows a linear trend only at moderate hydrogen fractions. The further increase in rH results in a stronger variation in LBV, as shown by both experimental and computed LBVs. Hydrogen addition significantly changes the thermal diffusivity of flammable CH4–air or NG–air mixtures, the rate of heat release, and the concentration of active radical species in the flame front and contribute, thus, to LBV variation.

Dimensional Changes of Graphite Flakes and Fracture in Tensile Tests of Gray Cast Iron

2018 ◽  
Author(s):  
Naoya Tada ◽  
Takeshi Uemori
Keyword(s):  
Cast Iron ◽  
Tensile Test ◽  
Internal Combustion Engines ◽  
Gray Cast Iron ◽  
Early Stage ◽  
Dimensional Change ◽  
Tensile Tests ◽  
High Ratio ◽  
Gray Cast ◽  
Dimensional Changes

Gray cast iron has been used as a component in various mechanical parts, such as the blocks and heads of automobile and marine engines, cylinder liners for internal combustion engines, and machine tool bases. It is desirable because of its good castability and machinability, damping characteristics, and high ratio of performance to cost. On the other hand, the weak graphite flakes present in gray cast iron act as stress concentrators and negatively affect the strength of this material. It is therefore important to know the relationship between the distribution of graphite flakes and the strength or fracture of gray cast iron. In this study, a tensile test of gray cast iron was carried out using a plate specimen in a scanning electron microscope, and the microscopic deformation was observed on the surface of specimen. Particularly, the change in the size of graphite flakes during the tensile test was examined, and the observed trend was discussed. We found from the experimental results that the dimensional changes in the graphite flakes varied in the observed area, and that the final fracture occurred in an area where a relatively large dimensional change was observed. This suggests that the fracture location or the critical parts of gray cast iron, can be predictable from the dimensional changes of the graphite flakes at an early stage of deformation.

scholarly journals Evaluation of Carotid Artery Stenting with Distal Filter Protection Device

2018 ◽  
Vol 4 (02) ◽  
pp. 057-064
Author(s):  
Pankaj Banode ◽  
Ashutosh Kharche
Keyword(s):  
Predictive Value ◽  
Carotid Stenting ◽  
Minor Stroke ◽  
Technical Success ◽  
Embolic Protection ◽  
Closed Cell ◽  
First Choice ◽  
Proximal Protection ◽  
Protection Devices ◽  
Distal Filter

Abstract Objectives To assess the use of proximal protection devices in consecutive patients as the preferred means of cerebral embolic protection for primary carotid stenting. Methods and Results This was a prospective single-center study to evaluate the technical and clinical success of proximal protection devices as the first choice for embolic protection in symptomatic (≥ 50%) and asymptomatic (≥ 70%) carotid stenosis. Proximal protection devices were used for embolic protection in 115 consecutive patients. No patients were excluded for anatomical reasons. The filter used was of diameters 6 mm in all cases (Emboshield NAV filter device, Abbotts Healthcare Pvt. Ltd. [Lake Bluff, Il]). In all cases, self-expanding closed-cell designed stent was used (X-act closed-cell self-expanding nitinol carotid-tapered stent, Abbotts Healthcare Pvt. Ltd.). Plaque characterization was done by using real-time high-resolution ultrasound (HR USG) equipment (Aloka Prosound Alpha 7 [Chiyoda, Tokyo, Japan]) using high-frequency linear transducers (> 7 MHz). Follow-up duration was 30 days. Mean age was 61.9 ± 8.27 years. There was male predominance observed in study accounting for 73 out of total 115 studied population. Fifty-six of 115 (48.89%) treated stenoses were symptomatic. Technical success was achieved in 115 of 115 (100%) cases. In both the cases, additional distal filter devices were used. Carotid stenting was successful in 115 (100%) lesions. This study observed higher number of debris in symptomatic and high-risk plaques. This study also observed higher sensitivity, specificity, and accuracy of updated classification for assessing risk of microembolism (captured debris) (sensitivity 73.91%, specificity 95.65%, positive predictive value [PPV] 91.89%, negative predictive value [NPV] 84.62%, accuracy 86.95%). In our study, minor stroke was seen in three (2.61%) patients within 48 hours, and no adverse events were seen within 48 hours to 1 month. Conclusion Proximal protection is a safe method as the first choice for embolic protection. It can be used with a high rate of technical success.

Damköhler Number Analysis on the Effect of Ozone on Auto-Ignition and Flame Propagation in Internal Combustion Engines

2018 ◽  
Author(s):  
Seunghwan Keum ◽  
Tang-Wei Kuo
Keyword(s):  
Flame Propagation ◽  
Ozone Concentration ◽  
Internal Combustion Engines ◽  
Internal Combustion ◽  
Combustion Engines ◽  
Damkohler Number ◽  
Damköhler Number ◽  
Ozone Sensitivity ◽  
Auto Ignition ◽  
Ozone Addition

Ozone assisted combustion has shown promise in stabilizing combustion and extending operating range of internal combustion engines. However, it has been reported that sensitivity of ozone quantity on combustion varies significantly dependent on combustion modes. For example, auto-ignition driv3en combustion in homogeneous charge compression ignition (HCCI) engine was found to be highly sensitive to the ozone concentration, and up to 100 PPM was found to be sufficient to promote combustion. On the other hand, flame propagation in spark-ignited (SI) engine has been reported to be much less sensitive to the ozone amount, requiring ozone concentration about 3000∼6000 PPM to realize any benefit in the flame speed. A better understanding on the ozone sensitivity is required for combustion device design with ozone addition. In this study, a Damköhler number analysis was performed to analyze the vast difference in the ozone sensitivity between auto-ignition and flame propagation. The analysis showed that, for ozone to be effective in flame propagation, the contribution of ozone on chemistry should be large enough to overcome the diffused radical from the oxidation layer. It is expected that similar analysis will be applicable to any additives to provide an understanding of their effect.

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