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Efficient utilization of low calorific value fuels is challenging due to their limited burning rates and stability. This study explored the use of upward-increasing magnetic fields as a novel approach to enhance flame stability in such conditions, focusing on non-premixed highly diluted methane flames with nitrogen. Employing a vertical burner, magnetic intensities were varied to observe their impact on laminar jet diffusion flames. This research revealed that the gradient magnetic fields significantly modify flame characteristics. At lower magnetic intensities, the influence on flame structure, temperature, and stability was minimal. However, as magnetic intensity increased, notable changes in flame features such as height, shape, and thermal distribution were observed, suggesting a threshold intensity beyond which the magnetic influence becomes pronounced. The research further demonstrated that gradient magnetic fields could enhance the blow-out concentration limit, indicating an effective strategy for managing combustion in diluted fuels. The findings provide valuable insights into magnetic fields' role as a control mechanism, offering potential advancements in combustion technology and contributing to the broader pursuit of energy efficiency and reduced emissions in industrial applications. • Non-premixed methane flames with nitrogen highly diluted under upward-increasing gradient magnetic fields were examined. • Magnetic field intensity, flow rate, and dilution ratio jointly influence the shape and height of the flame. • The magnetic field enhances the heat release rate upstream of the flame and alter temperature distribution. • Increased heat release rate and accelerated preheating expand the flame's stabilization regime. [ABSTRACT FROM AUTHOR]

The more properties of biodiesel one wishes to represent, the more complex the surrogate mixture becomes. Often the aim is to represent the H/C and O/C ratios and molecular weight using a small number of pure components. In this article, a turbulent jet diffusion flame of a biodiesel surrogate, composed of 50% Methyl Decanoate, 40% n-heptane, 9% methyl crotonate and 1% ethanol is modeled and simulated. The strategy used is to apply the Directed Relation Graph technique for a first reduction, and Layerless Neural Network to define the main chain and obtain a skeletal mechanism. The results obtained for temperature and mass fractions of CO 2 , CO and H 2 O agree reasonably with literature data for a mechanism of 147 reactions and 45 species. The small number of species facilitates the simulation of the coupling between turbulence and chemical kinetics, a desirable feature of reduced mechanisms. • A skeletal mechanism is obtained for a biodiesel surrogate. • The cost to resolve reactive flow is reduced by two orders of magnitude. • The skeletal mechanism is defined using Layerless Neural Networks. • AI provides the reactions of the ester group to the biodiesel surrogate. [ABSTRACT FROM AUTHOR]

Abstract: Investigations of structure and reaction zones of unconfined methane–hydrogen laminar jet diffusion flames are presented. In a lab-scale burner, experiments have been conducted using a mixture of pure methane and pure hydrogen in different volumetric proportions. Digital photographs of the flames have been captured and the radial temperature profiles at different axial locations outside the flame zone have been measured. Numerical simulations are carried out with a C2 chemical kinetics mechanism having 25 species and 121 reaction steps and an optically thin radiation sub-model. The numerical results are validated against the experimental data. Parametric studies have been carried out for a range of methane–hydrogen mixtures with volumetric proportion of hydrogen in the mixture varying from 0% to 80%. Variation of flame height, contours of temperature, mass fractions of product species and the net reaction rates of methane and hydrogen for various cases are presented and discussed in detail. Further, analysis of net reaction rates of important reactions involving methane and hydrogen with radicals such as O, H and OH are analyzed. The maximum temperature in the domain is seen to decrease for the fuel mixtures with higher hydrogen content. The overall flame length also decreases. For a fuel mixture having 40% hydrogen by volume, the net molar consumption rates of methane and hydrogen are found to be almost equal. Examination of individual reactions of fuel species with radicals shows that hydrogen is mainly consumed by its reaction with OH, whereas methane consumption is mainly through its reactions involving H as well as OH radicals. [Copyright &y& Elsevier]

Abstract: The formation, dynamics and structure of cellular flames in circular non-premixed jets are examined with three-dimensional numerical simulations incorporating detailed descriptions of chemistry and transport. Similar to past experiments reported in the literature, CO2-diluted hydrogen in diluted or pure oxygen co-flowing streams in the proximity of the extinction limit are considered. As in the experiments, several preferred cellular states are found to co-exist with the particular state realized depending on initial conditions as well as on the jet characteristics. The simulations provide additionally the temporal transitions to different stationary or rotating cellular flames, their detailed structure, and the dependence of the scaling of the realized number of cells with the vorticity thickness. [Copyright &y& Elsevier]

The behavior of laminar jet diffusion flames in the presence of non-uniform magnetic fields has been investigated and the results of this experimental study are presented. It has long been recognized that magnetic fields can influence the behavior of laminar diffusion flames as a result of the paramagnetic and diamagnetic properties of the constituent gases. Using a magnet assembly consisting of neodymium iron boron magnets and gray steel prisms, a non-uniform upward decreasing magnetic field was applied to a laminar jet diffusion flame produced using a slotted burner port. The experimental results show that under certain conditions the application of the magnetic field decreased the flame height, prevented the flame from attaching to the prisms, increased the intensity of the flame, decreased the flow rate for which visible soot inception occurred, and increased the flow rate below which the flame extinguished. It was also observed that the degree to which these phenomena occur is proportional to the product of the magnetic induction times the gradient of the magnetic induction. A discussion as to the reasons for these observations is provided. In addition to traditionally defined dimensionless parameters, the previously defined magnetic Grashof number, the magnetic Froude number, and the ratio of the gravitationally induced buoyancy forces to the magnetically induced body forces are identified as key parameters for determining when a magnetic field will affect diffusion flame behavior. Using these dimensionless parameters, the experimental data was cast in a form that clearly indicated the universal nature of diffusion flame behavior in a non-uniform upward decreasing magnetic field. A power law curve fit to the dimensionless data is presented and discussed. [Copyright &y& Elsevier]

• The flame blow-out limit is the maximum when there is only the front bottom wall. • The jet diffusion flame blow-out behavior due to the bottom wall was revealed. • The flame is easily exhibited the lift-off phenomenon when there is have the rear bottom wall. • The flame tilt angle is divided into two variation regions when there is have the bottom wall. • A generalized correlation on the jet diffusion flame tilt angle is developed. This study investigated the influence of different rear bottom wall lengths on the blow-out limit, flame shape, flame mean length, and flame tilt angle of jet diffusion flames under cross-wind conditions. The experimental results reveal that the bottom wall had a significant effect on the flame blow-out limit. The flame blow-out velocity was maximum only when the front bottom wall existed, and all jet diffusion flames had similar blow-out velocity under the influence of the rear bottom wall. Once the length of the rear bottom exceeded a certain value, the jet diffusion flames were prone to lift-off. Moreover, the jet diffusion flames adhered to the bottom wall, which is attributed to the Coanda effect. The flame length significantly increased under the influence of the bottom wall. Additionally, under the influence of the front bottom wall, the flame length was maximum when the cross-wind velocity was higher. Under the influence of different rear bottom wall lengths, the flame tilt angle was divided into two variation regions. Among them, the flame tilt angle affected only by the front bottom wall was minimum. The flame tilt angle was maximum when the rear bottom wall length was 20 cm. Finally, the empirical formula of the jet diffusion flame tilt angle was obtained by analogy analysis and exhibited good correlation with the experimental data. [ABSTRACT FROM AUTHOR]

• The flame blow-out limit of the triangle nozzle is the maximum. • The flame of rectangular and cross nozzles is easily exhibited the lift-off phenomenon. • The flame blow-out limit and the flame shape variation is explained from the perspective of the moment of inertia. • There are two growth curves of flame length for the circle and triangle nozzles. Four nozzle types were used to investigate the blow-out limit, flame shape, flame mean length, and flame tilt angle of jet diffusion flames under cross-wind conditions. The experimental results revealed that the nozzle geometry had a minor influence on the flame blow-out limit when the fuel jet velocity was low. As the fuel jet velocity increased, the nozzle geometry had a significant influence on the flame blow-out limit, the blow-out velocity of the triangle nozzle was the maximum, and the rectangular nozzle was minimum. The nozzle geometry had a significant influence on the down-wash and lift-off of the flame under cross-wind conditions. The triangle nozzle was prone to the appearance of the down-wash phenomenon, and the rectangular nozzle flame easily exhibited the lift-off phenomenon. Additionally, the effect of the nozzle geometry on the flame blow-out limit and flame shape was explained from a moment of inertia viewpoint. The flame length of the rectangular and cross nozzles monotonously increased with the increase of the momentum flux ratio of the fuel jet to the cross-wind. However, two growth curves occurred as the flame length of the circle and triangle nozzles increased with the momentum flux ratio of the fuel jet to the cross-wind. Additionally, for the jet diffusion flames under cross-wind conditions, the nozzle geometry exerted a smaller effect on the flame tilt angle. [ABSTRACT FROM AUTHOR]