FUEL AND COMBUSTION
Year:2013 | Volume:5 | Issue:2|Papers Count:7

The aim of the present paper is to investigate the effects of obstacles with different blockage ratio and geometry on flame acceleration and overpressure of premixed flame propagation using large eddy simulation. The subgrid-scale reaction rate is represented by the Flame-wrinkling combustion model developed by Weller. For the purposes of this paper, three different obstacles with circular, triangular and square cross-sections are studied here covering blockage ratios ranging from 10% to 72%. It is found that square and circular obstacles, result the fastest and the slowest flame acceleration, respectively. Velocity of jet-like flow around the obstacles and the level of turbulence generated by obstacles are increased with increasing blockage ratio and caused an increase in flame speed. The amount of unburned mixture trapped behind the obstacles, which plays a significant role in the overpressure, is found to be the highest for triangular obstacles. The maximum overpressure increases with increasing blockage ratio, but the rate of increase depends on the obstacle geometry. The square obstacles lead to highest overpressures while the circular ones produce the lowest overpressure. The time needed to reach the maximum overpressure decreases with increasing blockage ratio and depends on the obstacle geometry.

Mono Fatty Acid Esters (MFAE) in biodiesel fuel (Palmitic, Stearic, Oleic, Linoleic and Linolenic), imposes unique properties that directly affect the combustion process and engine performance. In this study, the effects of each MFAE in biodiesel fuel on diesel engine brake power were studied. Biodiesel fuel, fatty acid ethyl esters from sunflower oil, soybean oil, corn oil, rapeseed oil, waste oil and their blemdings were used in this research. The biodiesel fuels were tested on MT4-244 diesel engine under full load and 2000 rpm. Then, engine brake power was modeled as a non-linear regression function based on percentage of mono fatty acid ethyl ester (MFAEE). Modeling results showed that the saturated fatty acids with short chain hydrocarbons Stearic (C16=0) and Palmitic (C18=0) have the greatest effect on engine power. Unsaturated fatty acids Oleic (C18=1), Linoleic (C18=2) and Linolenic (C18=3) have the least effect on engine power output. Also, Engine power is reduced by increasing the percentage of unsaturated fatty acids in biodiesel fuel. Ethyl ester of Linolenic, which has three unsaturated carbon bond, reduced engine power. Thus, the biodiesel fuel produced from saturated oils, has ability to increase engine brake power.

In recent years many researchers have done studies about biodiesel as alternative fuel and renewable diesel fuel and its impact on the performance of compression ignition engines and their pollutions. The application of biodiesel has been limited due to its higher cost compared with petroleum-based diesel. Biodiesel is produced from biological sources such as vegetable oil and animal fat. Nowadays, researchers attempt to find low cost and non-edible resources for biodiesel production. In the current investigation, spent bleaching earth oil biodiesel (SBE) is obtained from spent bleaching earth oil that is which is a by-product of corn oil refining process. The obtained biodiesel (SBE) sample and waste cooking oil biodiesel (WCO) were evaluated and compared with diesel fuel. The results for engine performance in maximum torque and engine speed of 1600 rpm, both biodiesel fuels decreased the soot emission with %12.5 and increased the NOx with %6.4 compared with diesel fuel. In the maximum engine speed (i.e. 2800 rpm), SBE biodiesel had positive effect on specific fuel consumption comparing to diesel and shows lower specific fuel consumption comparing to diesel at full load. On the other hand, brake thermal efficiency was approximately %3.6 improved relative to diesel fuel.

In this research, NiMo/F-Al2O3 Nano catalysts were synthesized using impregnation method and modified with different fluorine contents. The synthesized Nano catalysts were examined toward hydrodesulphurization of thiophene. The physicochemical properties of Nano catalysts were assessed by XRD, FESEM, BET and FTIR analyses. Structural and surface properties of Nano catalyst with optimum fluorine contents (1 wt. %) were more favorable than of fluorine-free Nano catalyst. Results show that the surface area of the samples was increased with addition of fluorine, while the catalyst particle size was reduced. Activity of Nano catalysts in the conversion of thiophene showed that the amount of sulphur in final solution was reduced down to 100 ppm. The increasing in activity could be addressed by increasing surface area and excellent structural properties of these Nano catalysts.

Low swirl combustion is an innovative method for stabilizing lean premixed flames. Understanding the stability characteristics and NOx emissions of low swirl flames as well as influence of interaction of several low swirl flames on stability characteristic and NOx emissions are necessary to make low swirl burners applicable to various combustion chambers. The primary objectives of this study are to assess flame stability characteristics and NOx emissions of vane swirl burners. Since in an annular combustor several burners are mounted next to each other, the influence of flames interactions on the stability and NOx emissions of low swirl flames are examined. The data show that the stability of low swirl flames is highly dependent on the fuel-air mixture velocity at the burner exit, the mixture equivalence ratio, and the fuel-air feeding startegy to achieve the desired flame. NOx emissions of a low swirl flame are insensitive to the the fuel-air mixture velocity at the burner exit at a given equivalence ratio, but they are directly proportional to the equivalence ratio. Individual burner stablility is maintained when they are arranged in any annular formation. Although flames interactions have no influence on the overall flame stability characteristics but they increase NOx emissions.

Premixed combustion in a Combined Porous-Free Flame Burner (CPFFB) and a porous burner (PB) is numerically studied at a cylindrical axisymmetric combustion chamber. The cylindrical porous medium is perforated in the center line that a combination of porous burner and free flame is made. Governing equations of mass, momentum, energy and species mass fraction are solved using finite volume method. In this numerical simulation, a reduced multi-step combustion mechanism and realizable k-e turbulence model are used. To validate the numerical results, an experimental prototype of the burner was made and has been tested. The numerical results have a good agreement with the experimental data. The results are compared for both types of the burners. The results show that the flame in CPFFB is stable in a range greater than that of PB. The results show that the CPFFB has a higher thermal power about 50% and lower NO pollutant formation about 20% rather than an equivalent PB.