Axisymmetric Turbulent Methane Jet Propagation in a Co-Current Air Flow Under Combustion at a Finite Velocity

The paper introduces a numerical method for solving the problem of the axisymmetric methane jet propagation in an infinite co-current air flow. For modeling, we used the dimensionless equations of the turbulent boundary layer of reacting gases in the Mises coordinates. To close the Reynolds equation, a modified k - ε turbulence model was used. The k - ε model is considered a low Rhine turbulence model. Assuming that the intensities of convective and turbulent transfers of components are the same and using the stoichiometric ratios of the concentrations of components during combustion, we reduced five equations for the transfer and conservation of the mass of components to two equations for the relative excess concentration of the combustible gas. The concentrations of the components were determined from the solutions of these equations. By using relatively excessive velocities and total enthalpy, we reduced the boundary conditions for the three equations to a general form. To solve the problem in the Mises coordinates, we used a two-layer, six-point implicit finite-difference scheme, which provides the second order of accuracy of approximation in coordinates. The equations for the conservation and transfer of substances being non-linear, an iterative process was implemented. The influence of the radius of the fuel nozzle on the indices of the turbulent jet and flame was investigated. Findings of research show that in an endless co-current flow of fuel with a decrease in the radius of the nozzle, the rate of the chemical reaction and the maximum temperature in the calculation area decrease, and the amount of unburned part of the combustible gas increases

Optimization of Fuel Nozzle Diameter in a Novel Cross Flow Lean Direct Injection Burner

Lean Direct Injection (LDI) concept proves to be an ultra-low NOx combustion scheme for future gas turbine combustors because of its ability to operate at very lean conditions. For LDI burners, the Fuel Nozzle Diameters (FND) play a vital role in deciding a balance between the various performance criteria demanded by the gas turbine industry like efficient usage of fuel, a wide range of flame stability, uniform exit temperature distribution and very low overall emissions. This paper attempts to find the optimum FND in terms of some key combustion parameters, for a novel multi-swirl LDI burner having a cross-flow mixing between fuel jets and swirling air. At first, lean blow out limits were detected from experiments with different FND using two different fuels, methane and liquefied petroleum gas, within a range of air flow rates. It was observed that with the decrease in FND the flame extinguished at a higher equivalence-ratio. Then their performances were compared through CFD simulations with two different combustion models, namely, Eddy Dissipation and PDF Flamelet. The combined results of cold and hot flow simulations showed that with the decrease in FND the fuel jet was able to penetrate deeper into the air swirl by overcoming the air momentum, which resulted in enhanced mixing leading to more efficient utilization of fuel and also uniform exit temperature distribution resulting in lower pattern factor. Thus the findings of this research work should be resourceful in the development of modern cross-flow LDI combustors.

Development of a Technique for Calculating the Temperature of the Multi-Fuel Nozzle Inner Wall in order to Prevent Sedimentation and Overheating

The article presents the results of a theoretical study on obtaining the formula for calculating the temperature of the inner wall of the multi-fuel nozzle cooling jacket. The problem of overheating these nozzles, as well as the formation of carbon-containing deposits in liquid hydrocarbon fuels and coolants, is discussed. The different ways of dealing with sediment formation, including cooling the fuel channel wall to 373 K are considered. In the case of multi-fuel nozzles, several fuels and coolers can be effectively used at once. The properties of some coolants, including TS-1 kerosene and natural gas, have been investigated. Based on the obtained formula for determining the temperature of the multi-fuel nozzle cooling jacket, a theoretical calculation of the internal temperatures of nozzles of the same mass with several coolants was carried out. An analysis of the results of a theoretical study showed that multi-fuel nozzles are cooled better than single-fuel nozzles and allow predicting fuel consumption in order to achieve the required wall temperature, prevent overheating and sediment formation.

Numerical simulation on heating performance and emission characteristics of a new multi-stage dispersed burner for gas-fired radiant tubes

To enhance the temperature uniformity and NOx reduction performance of the gas-fired radiant tubes, we proposed a new multi-stage dispersed burner based on fuel-staging combustion technology in this study. The effect of fuel nozzle structural parameters, including secondary fuel nozzle distance D (30, 50, 70 mm), secondary fuel nozzle diameter ds (2, 3, 4, 5, 6 mm) and tertiary fuel nozzle diameter dt (2.5, 5, 7.5, 10 mm) on the flow field, temperature distribution, NOx generation and thermal efficiency were analyzed by numerical simulations. The results show that the multi-stage dispersed fuel nozzle could slow down the combustion rate and form a low-oxygen dilution zone in the reaction process, reducing the maximum combustion temperature and NOx emission. With the increase of the secondary fuel nozzle distance, the NOx concentration at the outlet decreased from 69.0 ppm to 54.6 ppm, and a decrease of 20.9%. When the secondary fuel nozzle diameter increased from 2 mm to 6 mm, the maximum wall temperature difference gradually increased 72.8 K to 76.3 K. NOx emission at the outlet first decreased, then increased, and was as low as 45.6 ppm at a 5 mm diameter. Furthermore, increasing the tertiary fuel nozzle diameter could reduce the maximum wall temperature difference and NOx emission, and improve thermal efficiency. When dt = 7.5 mm, the overall performance of the radiant tube was the best, and the outlet NOx concentration, wall temperature difference and thermal efficiency were 46.1 ppm, 73.0 K, 63.7%, respectively.

Experimental and Numerical Comparison of Non-Reacting Flow Formation From a 7-Point Lean Direct Injector Array

An experimental and numerical comparison of cold-flow structures from two configurations of a 7-point lean direct injector array was completed for this study. The comparison seeks to have the computational model aid in understanding of the experimental flow fields and expand on the underlying physics involved. Qualitative data of mean axial velocity contours as well as quantitative data of mean axial profiles facilitated the comparison between experiment and numerical solutions. Experimental data was collected using particle image velocimetry (PIV) with water seeding through the center fuel nozzle. The numerical computation was carried out with NASA’s OpenNCC (Open National Combustion Code) using steady state Reynolds Averaged Navier-Stokes (RANS) simulation to calculate gas phase velocities. There were notable quantitative differences in the average axial velocity profiles, especially at locations closest to the dump plane. However, good qualitative agreement was consistent for each 7-point configuration.

Effect of different syngas compositions on the combustion characteristics and emission of a model combustor

There is a growing need to design fuel flexible combustors. This require understanding of the combustion and emission characteristics of the combustors under varying fuel compositions. In the present study, the combustion characteristics and emission of methane and syngas flames were investigated numerically in a swirl stabilized combustor. The numerical model was developed using ANSYS-fluent software and validated using experimental values of temperature, CO2 and NOx emissions. A two-step chemical mechanism was used to model methane-air combustion. Results of the numerical validation showed similar trend between the experimental and predicted temperature along the combustor axis with about 5 % over prediction of the temperature. Syngas-air combustion was thereafter modeled using a 21 step chemical mechanism. Syngas compositions studied were: syngas A (67% CO: 33% H2), syngas B (50% CO: 50% H2) and syngas C (33% CO: 67% H2). Results showed that for pure methane, a V-shaped flame was observed with the flame attached to the fuel nozzle, while a lifted flame was observed for case of syngas A composition. CO gas with higher ignition temperature and flammability as compared to H2 gas is the dominant gas in syngas A fuel composition. Jet flames were observed for syngas B and syngas C. Carbon monoxide is a slow burning gas. Therefore syngas with low CO content has a low tendency of emission of CO from the combustor. This suggests that syngas with high CO content such syngas A may require more residence time to completely combust the CO gas. The NOx emission was observed to have the same trend as that of the combustor maximum temperature. Syngas C flame had the highest NOx emission, while, syngas A flame had no NOx emission. This is due to low combustor temperature observed in the case of syngas A flame. Keywords: Syngas, ANSYS-FLUENT, Swirl-stabilized combustor, NOx emission, Chemical Mechanism