https://www.jfnc.ir/ Fuel and Combustion en daily 1 Wed, 13 Dec 2017 00:00:00 +0330 Wed, 13 Dec 2017 00:00:00 +0330 https://www.jfnc.ir/article_53995.html Biodiesel due to its environmental benefits and similar properties with gasoil is considered as fossil fuels alternative. Rapeseed oil is used to produce biodiesel in presence of K2CO3/Al2O3. For catalyst preparation K2CO3 was loaded on the Al2O3 as support using impregnation. Taguchi experimental design was used in a completely randomized design with two replications for trans esterification reaction and investigating the effect of reaction time, temperature and catalyst amount on the biodiesel production efficiency and optimize the number of experiments. Also Molar ratio (alcohol: oil) 15 to 1, catalyst amount 0.5, 1, 1.5, 2, 3 and 5 wt.%, reaction temperature of 55, 65 and 75 °C, reaction time of 0.5, 1, 1.5, 2, 2.5 and 3 hr. and stirring rate of 600 rpm was used for trans esterification reaction. Biodiesel yield (99%) was obtained by trans esterification process at 65 °C using 2 wt. % of K2CO3/Al2O3 in 2 hr. Other researcher’s results comparison shows that the loading ratio of K2CO3 compared to KNO3 and Ca(NO3)2 can increase the biodiesel production efficiency in alumina base catalysts. Analysis of variance analysis with regard to catalyst, reaction time and temperature variables indicates that temperature changes have no significant effect on the efficiency of methyl ester, but the effect of time and amount of catalyst variations used on the conversion rate of the reaction is quite significant. https://www.jfnc.ir/article_250532.html Various LNG mixtures primarily consist of methane and smaller amounts of other alkanes, which, despite their similarities, can exhibit different combustion phenomena. This study investigates the effect of LNG composition on ignition delay time and the likelihood of knocking. To this end, a C0-C4 kinetic model was developed based on a recently published methanol model, with the addition of C2-C4 sub-models. Eleven standard LNG mixtures were then simulated and studied under various experimental conditions at equivalence ratios of ϕ = 0.4 and 1.2. The results show good agreement with experimental data for high and intermediate temperatures (T ≥ 1000 K). The model outputs were also compared with the performance of two other well-established detailed models; the model developed in this study provides more successful predictions. Finally, the formation pathway of combustion products was investigated using rate of production analysis. As demonstrated, two distinct regimes—high-temperature and low-temperature—are identified for the combustion of each fuel component. At high temperatures, all fuel components undergo direct decomposition into small species and radicals, followed by combination with oxygen. At low temperatures, for methane, the formation of C2H6 from the methyl radical (CH3) is very significant, and the cascade hydrogen abstraction process is an effective mechanism in the continuation of the combustion pathway. This also applies to larger fuel components, rather than direct combination with oxygen. https://www.jfnc.ir/article_251439.html The aim of the present study is to investigate the effect of inlet geometry on thermal conditions, flame structure, and the stable flame formation limit in ammonia-methane combustion in a furnace with a non-premixed burner. Variations in fuel inlet diameter, air inlet diameter, and the distance between the air and fuel inlets are considered as the parameters related to inlet geometry. For this purpose, a numerical study has been conducted using the Reynolds stress turbulence model, the eddy dissipation concept combustion model, and KAUST ammonia-methane chemical kinetics, while also considering the discrete ordinate radiation model. The results show that increasing the mass fraction of ammonia in the fuel leads to a decrease in the maximum flame temperature, fundamental changes in flame structure and volume, as well as alterations in the stable flame formation limit. Among the geometric parameters investigated, decreasing the distance between the fuel and air inlets, decreasing the fuel inlet diameter, and finally decreasing the air inlet diameter led to improved stable combustion conditions for the burner and also create thermal conditions similar to those of pure methane combustion within the combustion chamber, respectively. The main effect of changing the inlet diameters is on the recirculation rate of combustion products into the unburned mixture and the inlet shear layer flow, whereas the greatest effect of ammonia is on altering the reaction pathways of the combustion process. https://www.jfnc.ir/article_250470.html Given the significant contribution of building heating systems to combustion-related pollutant emissions, the application of advanced post-combustion technologies to improve exhaust gas quality and mitigate environmental impacts has become increasingly important. In this study, the performance of a dielectric barrier discharge (DBD) cold plasma reactor was experimentally investigated in two residential heating systems, including a cast-iron hot-water boiler and a wall-mounted gas water heater. The results demonstrated that the application of cold plasma technology reduced carbon monoxide emissions by 52% and 40% and unburned hydrocarbon emissions by 36% and 50% in the cast-iron boiler and wall-mounted gas water heater, respectively, while also enhancing the oxidation of combustion products. In contrast, nitrogen oxide emissions increased by 44% in the cast-iron boiler and 52% in the wall-mounted gas water heater. Although the findings confirm the high potential of cold plasma technology for reducing major combustion pollutants, they also identify the increase in nitrogen oxides as a critical challenge, highlighting the need to optimize reactor operating parameters to achieve simultaneous control of these pollutants. https://www.jfnc.ir/article_251734.html Impinging gas jets exhibit complex transient structures because of interactions among flow momentum, species mixing, and the impingement plate. This study examines the evolution and mixing of a transient helium jet issuing from a 0.8-mm-diameter single-orifice nozzle at a pressure ratio of 5 and a nozzle-to-plate distance of 20 mm using time-resolved Schlieren imaging and transient numerical simulation. For quantitative assessment, experimental and numerical jet widths were compared at several axial locations, and transverse helium mass-fraction profiles were extracted. Maximum mass fraction, half-width at half-maximum (HWHM), and spatial decay rate of the jet core were analyzed. The maximum helium mass fraction decreased from 0.949 at 5 mm to 0.138 at 19 mm, corresponding to an approximately 85% reduction in core concentration. Over the same interval, HWHM increased from 0.469 to 2.509 mm, indicating more than a fivefold expansion of the mixing-zone width. The spatial decay rate of the core decreased from 0.139 to 0.014 mm⁻¹, showing that core dilution was nonlinear and most intense near the nozzle. Analysis of the velocity field, streamlines, and vorticity indicated shear-layer formation and entrainment of ambient air into the jet. Velocity and pressure profiles revealed reduced axial momentum, enhanced radial motion, and central pressure recovery, indicating stagnation-region formation and momentum redistribution before wall-jet development. Results show that core-concentration decay and transverse mixing-zone growth proceed at different rates; hence, simultaneous assessment of concentration, width, and dynamic metrics provides a more comprehensive description of impinging-jet evolution. https://www.jfnc.ir/article_253390.html In the present study, RGB image processing was applied as a low-cost and non-intrusive approach for quantitative re-analysis of methane–oxygen premixed flame images obtained in a cylindrical meso-scale reactor with a 5 mm inner diameter. The analysis focused on stable asymmetric and repetitive extinction and re-ignition (RERI) regimes at oxygen flow rates of 0.5, 0.75, and 1.0 SLM and nitrogen dilution levels of 0, 37.5, and 50%. For each RERI condition, three consecutive images with adequate flame visibility were processed independently and averaged. Mean red, green, and blue intensities, composite Gray intensity, the blue-to-green ratio (B/G), and pixel-wise color distributions were evaluated. The results showed that the mean B/G ratio was higher in RERI than in the Stable regime under all investigated conditions, although its dependence on equivalence ratio was non-monotonic and partial overlap occurred in some cases. R, G, and Gray consistently decreased from the last Stable condition to the first RERI condition, whereas B showed stronger dependence on operating conditions. Pixel-wise R–G and B–G distributions also changed between the two regimes. Previous optical and spectroscopic studies were used only to interpret qualitative co-trends with visible-light intensity and spectral features associated with 〖CH〗^* and 〖C₂〗^*, since Lux, 〖CH〗^*, and 〖C₂〗^* were not independently and simultaneously measured in the present dataset. Overall, combined RGB descriptors provide a practical framework for monitoring flame-regime changes, while broader validation is required for automatic classification or combustion control. https://www.jfnc.ir/article_254352.html This study presents the design, fabrication, and experimental evaluation of a cost-effective micro gas turbine platform based on an automotive turbocharger for distributed-power and advanced combustion research [3], [4]. The thermodynamic cycle was modeled in GasTurb and optimized through a uniform random-search procedure to minimize specific fuel consumption while maintaining a nominal shaft-power target near 100 kW. The optimized solution yielded a pressure ratio of 5, a corrected air mass flow rate of 0.618 kg/s, a predicted shaft power of 110.93 kW, and a specific fuel consumption of 0.3356 kg/kW·h, providing the basis for selection of a Holset HX55 turbocharger. The experimental system integrated the compressor–turbine assembly with a modular combustion chamber, an independent lubrication unit, a blower-based starting system, and a multi-sensor data-acquisition architecture. Propane-fueled tests were conducted through start-up, transient acceleration, imposed fuel-flow disturbance, and steady-state operation [7]. The rig achieved a maximum measured air mass flow rate of 0.35 kg/s and a peak combustion-chamber thermal power of approximately 225 kW. During steady operation, the compressor isentropic efficiency stabilized at about 70%, while the compressor discharge temperature increased from 332 to 369 K as the system moved to the higher-load condition. The asymptotic convergence of calculated turbine and compressor powers at steady state supported the expected single-shaft power balance. The modular combustor also remained stable through the imposed transient disturbance. The results demonstrate that an appropriately selected and integrated automotive turbocharger can provide a technically robust and economically attractive high-flow test platform, with clear potential for future investigations of biofuels, hydrogen, recuperated cycles, and distributed-generation concepts