No abstract is provided for this article.
The Coanda effect is the tendency of a fluid to stay attached to a nearby surface. Since its discovery, several applications have been developed in aerodynamics, heat transfer and medical fields using this concept. A potential, and currently unexplored, application of the Coanda effect is its use in heating equipment. However, few research has been conducted on the behavior of flames under a Coanda flow pattern regime. Thus, the present study uses a generic swirl burner to analyze influence of the flow rate and fuel mixture on the flame stability. The objective is to identify differences in the behavior of a flame under an Open jet flow pattern and Coanda jet flow pattern that will lead to further development of novel flat burners. Changes in the burner configuration were made to induce one of the two flow patterns. Methane was used as a fuel and air as an oxidizer. Both gases were supplied to the burner at ~20°C and almost atmospheric pressure. Flow rates were regulated using variable area flowmeter. Gas flow was increased from 3 L/min to a maximum of 12 L/min with incremental steps of 1 L/min. For each gas flow rate, the oxidizer flow rate was increased, and the flame behavior recorded. It was found that a stable Coanda flame could only be induced when an Open jet flame existed. It is theorized that this behavior is due to a coherent structure that breaks down when a stable Open jet flame changes to Coanda flame. The concept is now presented as a novel option for development of novel, large industrial devices capable of stabilizing the flame while reducing size for their use in high temperature processes.
Following on from successful experimental trials employing ammonia/hydrogen blends in a model gas turbine combustor, with favorable NOx and unburned fuel emissions, a detailed numerical study has been undertaken to assess the viability of using steelworks by-product ammonia in gas turbines. Every metric ton (tonne) of steel manufactured using a blast furnace results in approximately 1.5 kg of by-product ammonia, usually present in a vapor form, from the cleansing of coke oven gas (COG). This study numerically investigates the potential to utilize this by-product for power generation. Ammonia combustion presents some major challenges, including poor reactivity and a propensity for excessive NOx emissions. Ammonia combustion has been shown to be greatly enhanced through the addition of support fuels, hydrogen and methane (both major components of COG). CHEMKIN-PRO is employed to demonstrate the optimal ratio of ammonia vapor, and alternatively anhydrous ammonia recovered from the vapor, to COG or methane at equivalence ratios between 1.0 and 1.4 under an elevated inlet temperature of 550K. Aspen Plus was used to design a Brayton-Rankine cycle with integrated recuperation, and overall cycle efficiencies were calculated for a range of favorable equivalence ratios, identified from the combustion models. The results have been used to specify a series of emissions experiments in a model gas turbine combustor.
Renewable biomass derived fuels are of increasing attention for industrial and aerospace applications due to worldwide depletion of fossil fuels and stricter environmental legislations. These facts have prompted continuous development for clean, sustainable and alternative fuels that produce low emissions. Even more, fuel flexibility is a required feature to meet all the former characteristics while reducing operating cost in gas turbines. Thus, some alternative fuels such as syngas or biodiesel can be used for gas turbines as these can comply with these requirements while being obtained from various processes, making them potential candidates for sustainable power generation. On the other hand in many combustion applications, the fuel is originally present as either liquid or solid. To assist mixing and the overall burning rate, the fuel is frequently first atomised and then sprayed into the combustion chamber. Most of the existing approaches dealing with combustion flows are limited to single-phase injection. To remove this limit, a new model for multiphase combustion has been developed. Therefore, this experimental work investigated the performance of a swirl burner using various mixtures of CO2/CH4 blends with either diesel or biodiesel derived from cooking oil. A 20 kW swirl burner was employed to analyse gas turbine combustion features under atmospheric conditions to quantify flame stability and emissions by using these fuels. A TESTO 350XL gas analyser was used to determine NOx and CO emission trends. Comparison between the blends was carried out at different equivalence ratios. CH* chemiluminescence diagnostics was also used and linked with the levels of emissions created through the trials. The results revealed that the use of biodiesel and CO2/CH4 blends mixtures resulted in lower CO production, i.e. 87% lower for the case at 10% CO2. Results showed that a notable reduction of ~50% in NOx was obtained at all conditions for the biodiesel /CO2/CH4 blends. Diesel based flames showed high CH* intensity at the axial profile compared to the biodiesel blends due to their high sooting tendency.
No abstract is provided for this article.
Renewably generated ammonia offers a form of carbon-free chemical energy storage to meet the differences between uncertain renewable supply and fluctuating demand, and has the potential to support future energy requirements as a power-to-X concept. The storage and transportation characteristics of NH3 are favorable compared with H2, however there are significant combustion research challenges to enhance fuel reactivity whilst reducing harmful emissions production. The purpose of the presented work was to evaluate different fuel delivery concepts for a representative GT combustor. An experimental and numerical comparison was made between swirl-stabilized premixed and diffusion NH3-air flames at elevated inlet temperature (473 K). The exhaust NOx and unburned NH3 emissions generated from each concept were quantified to optimize operational combustor performance. High-speed OH* and NH2* chemiluminescence was employed to characterize the change in flame topology with variation in fuel-air equivalence ratio, and the resultant influence on measured emission concentrations. Chemiluminescence intensities were shown to elucidate changes in sampled exhaust emissions, enabling detailed analysis of intermediate chemistry. A comparison was made between experimental data and chemical kinetic simulations with a reactor network model, demonstrating the sensitivity of NOx emissions to premixed fuel-air equivalence ratio. A comparison was also made between exclusive primary airflow, and the staged introduction of secondary air, to quantify the change in NOx production between each configuration and improve fuel burnout. Secondary air loadings were incrementally increased through the combustor, and the change in exhaust emissions mapped. In addition, reactant humidification was employed as a secondary process for NOx reduction, having shown favorable performance with NH3/H2 mixtures to limit thermochemical NO production. The efficacy of humidification was compared for both premixed and diffusion configurations.
Multiphase fuel combustion was carried out in a swirl-stabilised combustor with the aim of expanding the fuel flexibility of the gas turbine for, at least, land-based applications. Improved capability of the gas turbine in this regard will not only augur well for energy security but also could be useful in tackling harmful emissions. In the study, varying amounts of syngas was premixed with air and swirled into a burning diesel spray, the flowrate of which was altered to maintain the same overall heat output at all times. Across the several heat outputs tested, the range of stable flame operation was found to reduce as gas content of fuel mix increased. Moreover, for a combined heat output of 15 kW and a global equivalence ratio of 0.7, a steady increase in flame stability was noted and NOX emissions were found to decrease while CO emissions increased as syngas content in fuel mix increased from 10% to 30%. The increase in flame stability, achieved at the cost of lower heat release rate, was attributed to the changes in reacting flow dynamics evinced by the C2* and CH* species chemiluminescence intensity variation as well as chemical kinetics analysis. The NOX and CO emissions trend was ascribed to decreasing combustion efficiency due to poorer spray quality obtained from the pressure atomiser as liquid flow rate reduces and further worsened by the lower heat release rate and decreasing adiabatic flame temperature as gas ratio of combusted fuel increases.
Lean flame conditions have been used in Combustion Processes and Gas Turbines during the last few years for the reduction of emissions and for their high stability. However, there are problems related to flashback towards the premixing chambers when highly hydrogen enriched blends are used, a problem that occurs when syngas and/or biofuels are used. For this reason, this paper describes an experimental process for data acquisition under different geometries of a swirl burner in order tocharacterize the phenomenon, which was visualized using High Speed Photography. The study was based on the external and internal analysis of the burner. The use of a central combustible injector demonstrated to be beneficial for flashback reduction due to the suppression of some coherent structures. Nevertheless, the presence of the former can cause damaging explosions in the system if the flashback point is reached.
