نشریه سوخت و احتراق
سال دهم شماره 1 (پیاپی 19، بهار و تابستان 1396)

In the present study, we aimed to investigate the optimum amount of surfactants to be used in emulsion and nano-emulsion fuels. This would ideally overcome the probable setbacks rooted in surfactant over use and dramatically decrease fuel production expanses, while preserving the fuel stability. In this regard, tween80 and span80 were exploited to produce emulsion and nano-emulsion fuels. The biodiesel-diesel-water emulsion and nano-emulsion fuels were produced in different quantities and HLBs of surfactant. All evaluations were carried out using the B5 as the base fuel and water volume percentage of 5. The produced emulsions had milky and turbid appearance. Being stable for 8 days, the emulsion with HLB of 6 indicates the highest stability. The volume percentage of 1 at HLB of 6 was determined to be the minimum amount of the surfactants required to produce biodiesel-diesel-water emulsions. Moreover, the volume percentage of 5 with HLB of 8 is reported to be the minimum amount of surfactants required to produce nano-emulsion.

In the current research, a double-layer porous burner has been studied, in which SiC ceramics and alumina silicate (Al2SiO5) balls have been used in the first and second layers, respectively. A very important issue in relation to porous burners is to stabilize the flame on the surface of the porous media. Therefore, it is essential to evaluate the conditions that lead to instability (flashback phenomenon) in order to prevent sudden flashback of the flame in the porous burner. In this paper, the flame temperature, flame stability limit, flashback phenomenon and pollutants formation have been evaluated by changing operating parameters such as diameter of the balls, equivalence ratio and firing rate. Results show that a stable flame prevails in the range of equivalence ratio of 0.35-0.45. The flame moves downstream by reducing the equivalence ratio. Moreover, the maximum flame temperature and the surface temperature decrease by increasing the diameter of the balls. The flame flashback time decreases by increasing the equivalence ratio. In addition, increasing porosity downstream of the burner decreases flashback time. The amount of the excess air has a significant effect on the amount of CO, such that the concentration of CO reduces by reducing the equivalence ratio. The NOx concentration is negligible in all of the experiments (below 5 ppm) due to low temperature of the burner.

The purpose of this study is to investigate the impacts of swirl number and exhaust gas recirculation (EGR) to access better combustion, in a power plant burner. For this purpose, the dual fuel power plant burner DDZG12 in a wall fired boiler, has been chosen as case study. In order to validate the results, two benchmark problems were solved using two developed solvers. The numerical results were compared with experiments and the reliable models to simulate turbulent flow and non-premixed combustion were selected. Firstly, the role of primary air swirl number was evaluated considering that high temperature is one of the main challenges of these types of burners. The results show that reducing the swirl number from 0.8 to 0.48, causes the temperature to reduce 423K at the burner tip as well as 34.88 percent reduction in NOx emissions. The results of EGR show that recirculating 30 percent of the exhaust gas leads to 360K reduction in the temperature on the burner tip and 69.43 percent reduction in NOx emission. The results of EGR also show that recirculating the exhaust gases leads to widening of the flame. This leads to a more uniform temperature, but on the other hand increases the probability of flame impingement on the walls.

The aim of this study was to determine the amount of carbon dioxide uptake and biomass production in a photo bioreactor containing Spirulina microalgae as growth medium by injecting the products of natural gas combustion. A photo bioreactor was fabricated and combustion products of natural gas as well as air were injected by separate diffusers. The photo bioreactor was filled by growth medium without carbon source. In the control and test reactors, carbon dioxide was supplied by air and flue gas, respectively. Light source was natural and artificial. Artificial light source was four fluorescent lamps having 10 Klux intensity, which were operated in continuous and intermittent modes. The concentration of carbon dioxide entering in the test reactor was chosen in the range of 580 to 5000 ppm. The concentration of carbon dioxide in the inlet and outlet gas of the reactor was measured by a carbon dioxide detector equipped with NDIR. The algal biomass production and also changes in pH were measured. The flue gas was used as such without any scrubbing or desulfurization. The maximum production of algae using air and combustion products of natural gas having 4100 and 3300 ppm carbon dioxide using artificial intermittent light was 0.07 and 0.2 gL-1 d-1, respectively. Moreover, the maximum concentration of biomass was 0.25 and 1.04 gL-1, respectively. Carbon dioxide biofixation rate was 2.5 and 3.3% in the 3300 and 4100 ppm carbon dioxide runs. Natural gas combustion products can be injected in the photo bioreactor directly and without prior treatment, and it is possible to remove carbon dioxide and produce algae. Biomass productivity with intermittent light was 35% less than continuous light. With the increasing concentration of carbon dioxide in the combustion gas, algal biomass production increased.

Heat release rate process in SI Engines is directly related to the flame propagation in the combustion chamber. In this study, by simulating natural gas combustion in SI Engines using CFD software, flame behavior is investigated near the wall. Experimental tests were performed for various engine speeds and spark timings. The engine simulation was done and the results were validated with experimental data at various engine operating conditions. The results were in good agreement with the corresponding experimental data. Results show that by keeping the spark plug out of the geometric center of the cylinder, the concentric spherical propagation assumption of flame is not true. The walls near the flame prevent its propagation and its shape deviates from the spherical shape. Finally, it can be concluded that, natural gas turbulent flame propagation occurred in three stages: 1- The initial propagation of flame with high acceleration, in which 15% of the fuel is burned with a high rate of H.R.R. 2- Colliding of the flame with the floor of the piston, H.R.R continues with almost constant rate, in which 30% and 50% of the fuel is burned for the off-centered and centered spark plug location, respectively. 3- Deceleration of flame propagation after colliding with the side walls, in which 55% and 35% of the fuel is burned for off-centered and centered spark plug location, respectively.

In this paper, equilibrium thermodynamics of thermal cracking of heavy hydrocarbons for gasoline production has been investigated. Equilibrium calculations have been performed using the Gibbs free energy minimization method. The dependence of products yield on the operating conditions including temperature (300-1200K), pressure (1-30atm) and the steam to feed ratio (0-0.5) has been studied. Results showed that increasing temperature has a positive impact on the production of gasoline. For instance, in a constant pressure of 1atm, increasing temperature from 500 to 800K led to increasing gasoline yields from 5.41% to 8.92%. This is due to the endothermic nature of thermal cracking of heavy hydrocarbons. However, with increasing pressure at constant temperature, the amount of gasoline production decreased. This circumstance represents the adverse effect of pressure on gasoline yield. Results depicted that with increasing steam ratio from zero to 0.5, gasoline yield declined 45%. It can be concluded that the optimum operating conditions for gasoline production through thermal cracking of heavy hydrocarbons is within a temperature range of 8001200K, the pressure range of 1-5atm and in the absence of steam.

In this paper, the design and construction of a gas turbine combustor test rig and the experimental results of a sample combustor sector at atmospheric conditions are described. This test rig can be used to evaluate the effects of geometric variations on the performance of the combustion chamber. Flammability, stability and ignition maps, exhaust gas composition and temperature profile, and liner wall temperature can be studied. This rig has the potentiality of performing combustion tests with maximum air flow rate of 800m3/h and preheated air up to 1000K, as well as different types of liquid or gas fuels. A single swirler sector of an annular combustor is tested at different air and fuel mass flow rates. The results show that the exhaust gas temperature has a non-linear corelation with the fuel to air ratio. Using a one-dimensional model, the exhaust temperature of the combustion chamber is predicted and compared with the experimental results. The model results show good agreement with the experimental results.