FUEL AND COMBUSTION
Year:2018 | Volume:11 | Issue:2 |Papers Count:8

Prediction of cross ignition is one of the most formidable challenges in annular combustors. In order to study cross ignition, it is necessary to consider at least a sector of a combustor comprising of at least three burners, which makes the study both numerically and experimentally expensive. In this light, developing an analytical method to predict cross ignition probability is of practical interest. The main objective of the present paper is to develop an analytical method to predict cross ignition probability in an annular combustor utilizing 18 second generation EV burners. The present model is developed based on the previously proposed model by Hirsch et al. [7]. Here, the developed model is validated against experimental data. Validations show that the present model can accurately predict cross ignition probability. The validated model is used to improve cross ignition probability in the investigated gas turbines. The present model can be used during the combustor design and optimization processes. Furthermore, the model can be utilized as a fly on tool in the gas turbine logic to improve cross ignition probability.

The dynamics of premixed flame propagating in a channel is inherently unstable. This instability shows itself as a flame inversion and finally tulip flame. The present study is investigated the effect of a 90° bend on the propagation of the tulip flame. The three-dimensional (3-D) large eddy simulation (LES) approach is performed utilizing the artificially thickened flame (ATF) combustion model with a 7-step chemical mechanism. The present results show that the onset of the flame deformation at the horizontal portion of the channel that coincides with the decreasing in the pressure growth and the flame front propagation speed, the flame inversion occurs. At this moment, the formation of a pair of large-scale vortex in the burned gas near the flame causes a change in the flow field around the flame front. In the horizontal section of the channel, the 3-D tulip flame forms with four tongues. After entering the bend, the lower tongues speed up and dominate the flame propagation. Hence, after a while, the upper tongues completely fade and the lower tongues occupy the entire width of the channel. Although the bend has not a significant change on the increasing trend of the chamber pressure, the amplitude of the flame speed oscillation decreases to some extent.

The positive influence of the swirl of reactants on the air- fuel mixing has been widely discussed in previous studies. However, they have been mostly focused on the swirl of air. The present work numerically investigates the influences of the swirl of fuel on the structure and the environmental features of a diffusion flame, while the swirl of air is kept constant. The results show that the increase of fuel swirl is associated with the increase of mixing rate, flame width, and flame peak temperature, and the decrease of CO emission and flame length. However, the trend of the variation of NO with fuel swirl number has a minimum somewhere in the middle. The results also illustrate that the co- swirl injection leads to higher mixing rate, peak temperature, emission of NO, and lower emission of CO, as compared to the counter- swirl injection. In this work, the optimum swirl of fuel is observed to have the same value and to be in the same direction as the swirl of air. In this case, the emissions of NO and CO are decreased by 15.2% and 92.7% as compared to the reference design (in which the fuel has no swirl), respectively.

A gas turbine combustor has been investigated experimentally in this paper. The effect of air and fuel flow rates on the on combustor performance and lean blow out at atmospheric and steady condition is the goal. The combustor is a can type with swirl pressure fed injector. An axial swirler with swirl No. equal to 0.8 has been installed. The kerosene has been used as fuel while the air temperature at combustor inlet is equal to 315 K. The combustor Stability loop has been determined with several tests. Then variation of temperature inside the combustor and at combustor exit with respect to the injector back pressure and air flow rate are measured.4 operating conditions have been selected due to detail investigation of flame temperature contour inside the combustor. The results show that the flame holds near the walls. Also, the pattern factor show that the best condition is when the flame is totally inside the combustor while the air flow rate is minimum. Furthermore, it is cleared that the lean blow out is not uniform. It means that with increasing the air flow rate, upper section of flame has been quenched and then the lower section of flame.

In this study, the production of biogas from vinasse by using three SGBR reactors with the same volume of 5.6 liters for three hydraulic retention times (2, 3 and 4 days) and organic loading rates of 86002, 28667 and 21500 mgCOD/L.d was investigated. The water bath method was used to provide the temperature of mesophyll reactors at 35, and NaOH solution was used for buffer. The biogas volume was measured using the water displacement method. The results showed that the methane production was almost constant with HRT of 4, 3, and 2 days after 11, 13, and 16 days, respectively. Methane gas production with HRT of 2, 3, and 4 days was 6.66, 16.66 and 27.38 LCH4 (STP)/L.day per liter of vinasse, respectively. For three reactors, methanogen and acidogenic bacteria were in the equilibrium state at pH 5.57 after 2 days. The amount of methane gas production per volatile solids with the HRT of 2, 3, and 4 days was 244, 345 and 434 m3CH4/gvs, respectively.

Water electrolysis is the major method for production of high purity oxygen gas. In this process, water decomposes into its elemental constituents, oxygen and hydrogen gases. In this study, various inexpensive substrates such as nickel foam, stainless steel sheet, nickel grid, brass sheet and copper sheet are used as an oxygen electrode. The electrochemical techniques such as cyclic voltammetry and linear sweep voltammetry were used to evaluate the performance of electrodes. The obtained results of this study showed that nickel foam has a lower overpotential in the current density of 50 and especially 150 mA cm-2 than other samples. The overpotential of nickel foam at a current density of 50 and 150 mA cm-2 were 442 and 580 mV, respectively, which are lower than two nickel mesh, 60 mV, and stainless steel sheet, 48 mV. In addition, nickel foam had a good performance in real condition and its cell efficiency at 25, 40 and 60 °C showed 59.24, 61.83 and 67.70 percent, respectively.

The present investigation concerns prediction of NOx emissions in a stationary gas turbine combustor using reactor network modeling approach. Here, the reactor network is constructed based on spatiotemporal distribution of mixture fraction upstream of the flame front and flow residence time in the flame volume. To such aim, large eddy simulation is carried out to evaluate mixture fraction distribution upstream of the flame front, while the residence time is calculated by using RANS simulations. Moreover, the flame front position and flame volume is discerned using both RANS simulations and ENERGICO software. Obtained results are validated against experimental data. Such validations show that present method can accurately predict NOx emissions in the dry low emissions combustor. In an attempt to enrich the present investigation, parametric studies are carried out to evaluate effects of fuel composition, chemical kinetics, flame location, and combustion regime on the NOx production paths. Obtained results reveal that flame position and fuel composition have the most considerable effects on the NOx emissions among the investigated parameters. Based on above investigations, the present combustor is modified to reduce the NOx emissions from 25 ppmvd to 15 ppmvd.