نشریه سوخت و احتراق
سال پانزدهم شماره 4 (پیاپی 41، زمستان 1401)

When the fire is placed in the compartment, problems such as lack of access to the fire and lack of settling of spray particles lead to a delay in extinguishing the flame. Therefore, in this research, the growth and spread of the fire and its extinguishing with the water mist system with the effectiveness of the position of the nozzle in the shielded fire have been done using numerical study. The location of the effect of the water mist fire extinguishing system nozzle has been investigated under five case of four sides, central and one side, central and four sides, one side and central. The geometry of the research is a compartment without a roof and there is no door or window in the walls. The fuel source is located in the center of the compartment and there is a plate in the center of the room as a fire shield (protected fire plate) with a height of 50 cm from the floor of the room (on the fire). According to the results, it was found that the three cases of four sides, central mode and one side, and central mode and four sides respectively are the best modes for extinguishing the shielded fire, which extinguishes the fire after 22 seconds. In general, it can be said that the central and one-sided case with less number of nozzles can have the best performance.

A numerical study has been conducted to identify the cryogenic injection and mixing characteristics of a coaxial swirl injector under supercritical pressure. An improved formulation of the Reynolds-averaged Navier-Stokes turbulence models (to close the governing equations), Soave-Redlich-Kwong equation of state (to estimate thermodynamic properties), NIST database (to estimate transport properties) and PISO algorithm (for velocity-pressure coupling) are employed in the flow solver. The present study –distinguished from many other studies by considering real injectors’ geometrical complexities and propellants’ thermodynamic nonlinearities–characterizes supercritical mixing dynamics of the coaxial swirl jets through vorticity budget analysis. Results highlight the tilting/stretching term as the only mechanism of vorticity generation within the injector vortex chamber. At the injector nozzle, the baroclinic torque and volume dilatation terms control the mixing dynamics, too. Numerical observations indicate that the effects of recirculating bubbles (in front of the injector exit plane) are significant and improve the contribution of vortex stretching/tilting in terms of vorticity generation. In addition, the Kelvin-Helmholtz hydrodynamic instabilities also play an important role in the mixing process in the injector nearfield.

By adding nanomaterials to various diesel engine base fuels, one gets nanomaterials enriched fuels, or nanofuels in short. This addition may influence significantly the properties and behavior of the fuel due to unique properties of nanomaterials. The main purpose of this research is to study the physico-chemical properties of diesel fuel containing NPs of Manganese Oxide (MnOx) synthesized with a concentration of 100 ppm and Graphene Oxide (GO) with concentrations of 10 and 20 ppm and also by their hybrids. In this regard, the partial changes in the physical properties of density and viscosity in nanofuels by the concentrations of 0.2% and 0.6%, respectively have been observed.  The study also is based on the effect of nanometal oxide additives like Manganese Oxide and Graphene Oxide to diesel fuel. Metal oxide additive are doped with diesel fuel. The changes in diesel fuel properties (viscosity, flash point and fire point) due to introduction of nanometal oxide additive were observed. The diesel fuel with nanometal oxide additive presented a marginal increase in performance. Exhaust emissions for the diesel fuel with nanometal oxide additive showed significant decrease in levels of pollutants emission.

In the present study, the influence of the oxidizer preheating temperature and oxygen mass fraction as the effective parameters on the flameless combustion under oxy-syngas, air-syngas, and oxygen-enriched conditions have been investigated. The simulations have been carried out with applying the counter-flow diffusion flame solver using GRI3.0 chemical kinetics. In order to separate the physical and chemical impacts of substituting CO2 with N2, a virtual species (VCO2) has been used with physical properties similar to CO2 without being present in the reactions chain. According to the obtained results, physical and chemical impacts are dominant for lower preheating temperatures and higher preheating temperatures, respectively. The investigation of ignition delay time shows that under oxy-syngas conditions, increasing the H2/CO ratio from 0.25 to 1 and from 1 to 4 leads to a decrease in the axial distance of ignition from 0.4 cm to 0.39 cm and it changes from 0.39 cm to 0.375 cm, respectively. The comparison between the oxygen mole fraction and the inlet preheating temperature indicates that the preheating temperature has a greater effect on the reactive flow structure parameters such as ignition delay and released heat.
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Diesel engines are considered the main sources of energy production and diesel fuel consumption. The use of biodiesel fuel as a part of diesel engines can have a positive effect on reducing the use of fossil resources and the emission of pollutants. Using biodiesel fuel, along with its advantages, has disadvantages such as increasing the emission of nitrogen oxides, which is considered a toxic gas. Many researchers have proposed different additives to cover some of the disadvantages of biodiesel fuel. In this article, two types of oxygen additives, including dimethyl carbonate and n-butanol, were combined with small amounts in B2 (2% biodiesel and 98% diesel) and B5 (5% biodiesel and 95% diesel) fuels. Using small amounts of these additives can reduce the cost of fuel production. Based on the obtained results, B2D10N10 and B2D10N0 fuel samples were able to increase the braking power of the diesel engine by about 12 and 10%, respectively, compared to B2 fuel. On the other hand, the use of fuel samples containing dimethyl carbonate and n-butanol additives in B2 fuel reduced the special brake fuel consumption by about 18% compared to diesel fuel and about 32% Diesel engines are considered the main sources of energy production and diesel fuel consumption. The use of biodiesel fuel as a part of diesel engines can have a positive effect on reducing the use of fossil resources and the emission of pollutants. Using biodiesel fuel, along with its advantages, has disadvantages such as increasing the emission of nitrogen oxides, which is considered a toxic gas. Many researchers have proposed different additives to cover some of the disadvantages of biodiesel fuel. In this article, two types of oxygen additives, including dimethyl carbonate and n-butanol, were combined with small amounts in B2 (2% biodiesel and 98% diesel) and B5 (5% biodiesel and 95% diesel) fuels. Using small amounts of these additives can reduce the cost of fuel production. Based on the obtained results, B2D10N10 and B2D10N0 fuel samples were able to increase the braking power of the diesel engine by about 12 and 10%, respectively, compared to B2 fuel. On the other hand, the use of fuel samples containing dimethyl carbonate and n-butanol additives in B2 fuel reduced the special brake fuel consumption by about 18% compared to diesel fuel and about 32% compared to B2 fuel. Using the combined additives of dimethyl carbonate and n-butanol increased the thermal efficiency by an average of 15-30% compared to diesel, B2, and B5 fuels. The addition of dimethyl carbonate and n-butanol in combination in small amounts significantly reduced carbon monoxide emissions. The highest amount of carbon dioxide emission occurs in fuels containing the combined compounds of dimethyl carbonate, n-butanol, and B5, which was about 10-15% higher than the control sample. During the optimization process, the B2D3N2 fuel sample was selected as the optimal formulation in combining diesel fuel, biodiesel, dimethyl carbonate, and n-butanol.

Undesirable effects of entropy wave, such as higher levels of NOx emission, combustion instability and generated noise, have been well known. However, the thermal and hydrodynamic conditions of the combustor can largely modify the extent of unfavorable influences by subsiding the strength of the generated hot spots. In this study, therefore, hot spot annihilation in a lean-premixed Ethylene combustor is numerically studied using the flamelet model and large eddy simulation. The effects of various thermal and hydrodynamic conditions, such as inlet inlet velocity on entropy waves in both thermally convective and adiabatic combustor, are investigated. The resultant acoustic noise, potentially generated by the entropy waves, is also compared among studied cases, which demonstrates the necessity of embedding the thermo-hydrodynamic effects on the entropy waves in low-order models of combustion instability prediction. The results show that increase in inlet velocity improves combustion efficiency, it aids entropy waves survival and may cause subsequent instability or higher emission production. The results of this study can be beneficial to operate a lean-premixed combustor precisely in conditions far from generation of noise, emission or instability

In this article, the influences of swirl intensity on the mixing pattern, successful ignition probability, and flame propagation manner in a non-premixed gas burner with natural gas fuel have been examined by using numerical simulation and high-speed digital imaging. The ignition success probability maps were scrutinized under changing spark location in axial and radial directions. The flow field and mixing pattern were further inspected with the aid of numerical simulation. High-speed digital imaging was employed to study the initial flame kernel propagation. The ignition success probability diagrams defined three areas. The first, dubbed the ineffective zone, holds less than a 20% ignition success chance. The second, known as the transitional zone, has an ignition success probability between 20% and 80%. Ignition success here significantly depends on the spark location. The third area—the high-probability zone—has over an 80% ignition success chance. Findings from the study demonstrate an increased swirl number promotes a higher mixing rate, but it doesn't enhance the distribution of successful ignition probability. Higher swirl numbers actually reduce the high-probability zone, whereas lower swirl numbers allow a broader distribution in the burner outlet and better ignition characteristics.