Delaunay Surfaces

We derive parametrizations of the Delaunay constant mean curvature surfaces of revolution that follow directly from parametrizations of the conics that generate these surfaces via the corresponding roulette. This uniform treatment exploits the natural geometry of the conic (parabolic, elliptic or hyperbolic) and leads to simple expressions for the mean and Gaussian curvatures of the surfaces as well as the construction of new surfaces.Comment: 16 pages, 11 figure

Chemical kinetic mechanism study on premixed combustion of ammonia/hydrogen fuels for gas turbine use

To explore the potential of ammonia-based fuel as an alternative fuel for future power generation, studies involving robust mathematical, chemical, thermofluidic analyses are required to progress towards industrial implementation. Thus, the aim of this study is to identify reaction mechanisms that accurately represents ammonia kinetics over a large range of conditions, particularly at industrial conditions. To comprehensively evaluate the performance of the chemical mechanisms, 12 mechanisms are tested in terms of flame speed, NOx emissions and ignition delay against experimental data. Freely propagating flame calculations indicate that Mathieu mechanism yields the best agreement within experimental data range of different ammonia concentrations, equivalence ratios and pressures. Ignition delay times calculations show that Mathieu mechanism and Tian mechanism yield the best agreement with data from shock tube experiments at pressures up to 30 atm. Sensitivity analyses were performed in to identify reactions and ranges of conditions that require optimization in future mechanism development. The present study suggests that the Mathieu mechanism and Tian mechanism are the best suited for the further study on ammonia/hydrogen combustion chemistry under practical industrial conditions. The results obtained in this study also allow gas turbine designers and modelers to choose the most suitable mechanism for combustion studies

Study on premixed combustion characteristics of co-firing ammonia/methane fuels

Ammonia is believed eventually play an important role in substituting conventional fossil fuels for future energy systems. In this study, to gain a deep insight into the combustion properties of co-firing ammonia/methane fuel blends for the power and steel industry, a detailed chemical-kinetics mechanism model was developed for comprehensively modelling ammonia/methane fuels combustion. Characteristics of ignition delay time, unstretched laminar burning velocity and NO, CO2 and CO emissions in the exhaust gas were obtained over a wide range of equivalence ratios and ammonia fractions. High NO emissions will be a main problem as CO and CO2 emissions tend to drop when adding ammonia into methane. To gain a further understanding of the effect of ammonia substituting methane for combustion use, analyses of laminar premixed flame structures were performed. The impact of ammonia substitution was illustrated by analysing relevant specific radicals. Furthermore, to study the combustion characteristics of ammonia/methane under more practical conditions, effects of engine relevant conditions (elevated pressure and initial temperature) were also studied. Results indicate that pressure has a more prominent effect than initial temperature and there is a good potential that unwanted emissions can be reduced significantly under industrial conditions

Strategies toward experimental assessments of new aviation renewable fuels and blends: The BIOREFLY Project

The reduction of greenhouse gases emissions from the aviation sector is focused on better engine efficiency or optimized flight pathways. However, the most relevant is probably the use of sustainable biofuels. In order to meet the strict jet fuelspecifications for commercial flights, these biofuels(drop-in fuels) must contain only paraffinic hydrocarbons, without heteroatoms. Several renewable aviation fuels have already been certified by ASTM, others are under examination. Anew promising route consists in the thermochemical conversion of lignin, the main co-product from 2nd generation ethanol. The EU FP7 BIOREFLY project will develop a first industrial pre-commercial lignin-to-jet fuel 2000 ty-1demonstration plant. The present work describes strategies, equipment and R&D lines of BIOREFLY, which aims at evaluating the properties of this bio-jet fuel and its blends in view of future ASTM certification. Injection features and the combustion properties of aviation engines will be investigated in an optical combustor rig. Combustion parameters, emissions and chemiluminescence provide fundamental data to understand the combustion behavior for different hydrocarbons species. Tests in micro-gas-turbines (i.e. power generation and APU-derivative units) will assess the effect of fuels in terms of emissions and evaluating their performances

3D simulation of ammonia combustion in a lean premixed swirl burner

To date, a number of mechanical, electrical, thermal, and chemical approaches have been developed for storing electrical energy for utility-scale services. The only sufficiently flexible mechanism allowing large quantities of energy to be stored over long time periods is chemical energy storage in the form of carbon or hydrogen. One chemical considered for hydrogen carriage that can potentially be employed for storage is ammonia. Ammonia can substitute pure hydrogen for storage and be employed for power generation at large industrial scale if the molecule is efficiently burned through mature equipment such as gas turbines, thus providing not only a carbon free fuel, but also a chemical capable of being stored at low energy requirements. Thus, progress on the use of ammonia in gas turbines is a main priority for groups working on the area. Studies need to be conducted in experimental rigs with strong CFD analyses for further industrial implementation. In this paper, modelling of ammonia combustion in a generic gas turbine combustor is explored in order to provide an effective tool for future application. Large Eddy Simulation approach was used to develop a model for ammonia/hydrogen combustion in gas turbine combustors. To capture more details of the turbulent reacting flow, a detailed chemical mechanism was selected for a deep insight. A Partially Stirred Reactor framework was utilized to deal with the turbulence/chemistry interaction. The developed model was then applied to the simulation of lean premixed ammonia/hydrogen flames in a generic swirl burner. A preliminary validation for the model is performed by correlation of NOx emission with experimental data. Results show the model can provide detailed information of flow field, flame structure, emissions, etc. It can be used to optimize the procedure of utilizing ammonia as a fuel in future equipment design

Combustion and emission performance of CO2/CH4/biodiesel and CO2/CH4/diesel blends in a Swirl Burner Generator

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

Visualisation of turbulent flows in a swirl burner under the effects of axial air jets

Meeting emission regulations represents a real challenge in the power generation sector. Swirl combustors and their operation under lean premixed (LP) conditions are a step towards attaining low emissions, especially NOx formation, while ensuring high efficiency. However, performing modifications on combustors and reaching the requirements of efficient combustion systems is difficult due to many combustion problems such as extinction, low reaction rates, mild heat release, instabilities, and mixing issues. Thus, giving careful attention to the hydrodynamics design of the swirl burners with extensive testing methods in both experimental and numerical approaches is crucial to stabilise the combustion phenomena in gas turbines. As a result, this study employed the implementation of CFD simulations in the design of a 150 kW tangential swirl burner and considered the consequences of 50 LPM diffusive air injection at different positions on three-dimensional isothermal flow field characterizations, especially the turbulence, downstream the burner nozzle. Various mass flow rates from 600 to 1000 l/min were used at atmospheric conditions with a geometrical swirl number of 0.913. Experimental work was conducted with good correlation. It was found that using the air injection system could increase the flashback resistance by affecting the velocity defect downstream the burner nozzle. Moreover, the axial air jet reduces the flow field turbulence at the central recirculation zone (CRZ) tip and hence minimises the flow fluctuations and affect its size and position. CFD results show a very good agreement with Laser Doppler Anemometry (LDA) data acquired from the experimental work