FUEL AND COMBUSTION
Year:2020 | Volume:12 | Issue:4 |Papers Count:9

In the present work, the effect of using modular structure on combustion characteristics of the premixed lean hydrogen-air mixture is investigated by utilizing the three-dimensional CFD model, detailed chemistry and transport taking into account heat transfer through the wall combustor. Combustion characteristics are studied for different parameters, namely inlet velocity, wall thermal conductivity and tube curvature for modular structure and are compared with results of simple structure. The results show that using modular structure can significantly move flame front toward inlet section. In modular structure, the role of heat transfer due to secondary fluid increases in comparison with heat transfer in combustor walls. It improves thermal stability in the micro combustor and therefore, the role of wall thermal conductivity and heat transfer in wall combustor will be decreased for modular structure. Using modular structure for lower tube curvature is more effective which it has been shown for tube curvatures of one and two.

In this paper, the effects of intake temperature and methane energy ratio on emission and combustion phasing in reactivity controlled compression ignition (RCCI) engine have been numerically investigated. In this way, AVL-FIRE CFD code employing a detailed chemical kinetics mechanism is used for 3D simulation of combustion process and emissions prediction. Natural gas (NG) with higher octane number (ON) is mixed with air through intake port, while normal heptane with lower ON is directly injected into the combustion chamber during compression stroke. For validation, the results of RCCI engine have been compared to experimental data. For this purpose the effects of the premixed ratio (PR) of NG, normal heptane fraction, and intake temperature on several parameters such as in-cylinder temperature and pressure, rate of heat release, RI, ISFC, soot, and NOx are investigated. The results indicate that these parameters have significant effects on the heavy-duty RCCI engine performance and emissions. By increasing intake temperature the maximum of in-cylinder pressure, rate of heat release, and NOx emission increase significantly while soot emission decreases, also ringing intensity increases up to 10 %. On the other hand, increasing intake temperature reduces volumetric efficiency, as a result IMEP is reduced by 11%. Also by increasing methane energy ratio from 65% up to 85% in the constant intake temperature and pressure, the mixture ON will be risen, which would lead to an increases in ignition delay up to 5 crank angle. Consequently, IMEP as an important factor will be enhanced and also NOx emission decreases because of lower combustion temperature. Consideration of intake temperature and methane energy ratio show that these parameters can play an important role on controlling combustion phasing.

This paper focuses on a numerical simulation and experimental investigation of premixed cylindrical burner with gas mixing system. These burners are used in a condensing boiler. Performance assessment of the burner and mixer at a power of 11 kW is the main purpose of this paper; also, the two-stage methane-air mechanism have been employed for combustion kinetic. Moreover, short length of flame, high radiation and low emissions are among the most important and notable characteristics of these types of burners. To measure flame and burner surface temperature experimental tests have been conducted. Moreover, simulation results have been validated by experimental findings. Obtained results are in a good agreement with experimental findings. In addition, maximum 14% difference have been found between experimental and numerical results. Results indicated that by increasing the equivalence to the stoichiometric ratio, maximum flame temperature and NOx emissions has been increased. Moreover, in this type of burners radiation is the dominant heat transfer mechanism at below 2. 5 cm around the burner. The equivalence ratio at the range of 0. 75 to 0. 85 has been selected as the operating condition of the burner according to the temperature limitation and pollutant production in burner.

In this study a 2D flamelet method is presented based on premixed regime. This method can be considered as a combination of two existing reduced chemistry approaches; the flamelet and manifold approach. This method shares the idea with the flamelet approach that a multi-dimensional flame may be considered as a set of one-dimensional flames (flamelet method) and the flame structure is considered by some control variables. By this method, the data base of chemical variables is constructed in terms of progress and controlling variables. During flame simulation, conservation equations have to be solved for the controlling variables only and the properties are interpolated from the data base. In this research, 2D flamelet generated manifold (FGM) is applied for laminar counterflow flames with two parameters (progress variable and mixture fraction). Test results of premixed counterflow flame shows that detailed chemistry computations are reproduced very well by using 1DFGM with only progress variable. Predictions of temperature and major species mass fractions using 2DFGM have shown very good agreement with detailed chemistry computations especially at high strain rates. Using the FGM method, the computation time has been reduced several times in simulating flames, demonstrating the enormous potential of the method.

In the present article, the effect of injection angle of Methane jet into the air stream for an air/fuel premixer has been investigated by numerical simulations. The simulations have been done for injection angles from 90° (cross flow) to 180° (counter flow) by the use of ANSYS Fluent software. Mixture uniformity was determined in terms of uniformity index of CH4 mass fraction at different outlet cross sections. Results have shown that firstly, mixture uniformity was increased with increase in the injection angle (approaching counter flow situation); after 165° this trend was inverted but in counter flow situation the uniformity increased again. Moreover, it was shown that the injection angle effectiveness depends on airflow Reynolds number and increases with an increase in Reynolds number. In addition, dependence of the premixer performance on Reynolds number at first decreases with increase in injection angle but rises again after the angle of 165° .

Syngas, mainly composed of hydrogen and carbon monoxide, is a suitable candidate for RCCI engines. In the present effort, the impact of syngas with different compositions, on the performance and emissions of a RCCI engine, at constant input energy, has been numerically investigated. For this purpose, three different types of syngas are selected to compare with the simulated one which contains solely H2 and CO. Using these kinds of syngas compared with simulated one, results in less NOx in expense of more other emissions and less GIE. The ratio of hydrogen mass to the mass of other combustible species has a direct relation with maximum pressure and temperature, gross indicated efficiency (GIE) and NOx and a reverse relation with other pollutants. Syngas type I with a 78% reduction in NOx and a 11. 7% reduction in GIE compared to conventional diesel and a 3. 6% increase in exergy destruction compared to simulated syngas is the best alternative syngas in all cases.

In this paper, natural zeolite (clinoptilolite) was desilicated to remove water from diesel fuel. Optimization of desilication conditions was done using Design-Expert 7. 0. 0 software and using response surface methodology. The considered parameters are the concentration of sodium hydroxide solution and the temperature and time of the desilication process. After optimization of desilication process condition, the water sorption percentage was 95. 32% under the optimized condition, the concentration of sodium hydroxide solution 0. 47 molar, temperature 84. 05 ° C and time of 2. 42 hours. To carry out the process of water sorption from fuel, amount of 0. 5% w/v of the desilicated zeolite (5g zeolite/1000mL of the fuel) was mixed with diesel fuel for 2h and the water content was measured by the volumetric Karl Fischer technique. The natural zeolite and the desilicated zeolite at the optimum condition were characterized by XRD, XRF, FTIR and SEM analyses which indicate well desilication process. The results of water sorption before and after the sorption process indicate the acceptable performance of desilicated zeolite.