Premixed lean combustion is widely used in Combustion Processes due to the benefi ts of good fl ame stability and blowoff limits coupled with low NOx emissions.However, the use of novel fuels and complex fl ows have increased the concern about fl ashback, especially for the use of syngas and highly hydrogen enriched blends.Thus, this paper describes a combined practical and numerical approach to study the phenomenon in order to reduce the eff ect of fl ashback in a pilot scale 100 kW tangential swirl burner.Natural gas is used to establish the baseline results and eff ects of diff erent parameters changes.The fl ashback phenomenon is studied with the use of high speed photography.The use of a central fuel injector demonstrates substantial benefi ts in terms of fl ashback resistance, eliminating coherent structures that may appear in the fl ow channels.The critical boundary velocity gradient is used for characterization, both via the original Lewis and von Elbe formula and via analysis using CFD and investigation of boundary layer conditions in the fl ame front.
Combustion characteristics of palm biodiesel/methyl esters (PME) and natural gas (NG) blend were examined using a model gas turbine swirl burner at vane angle (θ) 30°, 45° and 60°. A twin fluid air blast atomiser was utilised for atomising liquid fuel at air-to-liquid ratio (ALR) 2.50. Swirling flow was initiated by using an axial swirler as main air passed through it. Combustible mixture was formed as swirling air flow mixed up with liquid fuel spray at burner outlet. Flame colour for PME/NG was mainly bluish, resembling that of neat PME despite subtle liftoff was observed in PME/NG swirl flames. Flame spectroscopic analysis showed that PME/NG swirl flames were more intense than baseline PME. Furthermore, θ = 60° operation led to significantly lower reaction intensity. Meanwhile, PME/NG combustion with 20%-30% NG input power fraction was observed to lower nitric oxide (NO) emission by a factor of 2.7 when compared with diesel and neat PME in θ = 60° combustion. Novel empirical models for emissions were also proposed, enabling the estimation of NO emission from PME/NG combustion at different NG input power proportions and vane angle. This research shows that PME/NG combustion is a promising way of reducing NO emission against neat PME and diesel in gas turbine operation. Moreover, flame instability provoked by liftoff in dual fuel operation is not aggravated, mainly due to nullification by intensified global reaction when NG is added. Such attributes feature PME/NG as a viable alternative fuel for use in land-based power generation gas turbines.
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Ammonia mixed with methane is a potential clean fuel for engine applications toward a low carbon economy. Studies are scarce on ignition phenomenon for ammonia/methane fuels in literature. In the present study, the ignition characteristics for ammonia–methane–air mixtures have been investigated by both experimental measurements and numerical simulations. Ignition processes of a 60%ammonia/40%methane (mol%) fuel blend were investigated with shock-tube experiments. Measurements of the ignition delay times were performed behind reflected shock waves for such fuel/air mixtures with different equivalence ratios of 0.5, 1, and 2, at pressures around 2 and 5 atm within the temperature range of 1369 to 1804 K. Experimental results were then compared with numerical prediction results employing detailed kinetic mechanism, which showed satisfactory agreement within most of the range of the temperatures, equivalence ratios, and pressures investigated. Within the temperature range of 1300 to 1900 K, pressure range of 1 to 10 atm, equivalence ratio range of 0.5 to 2, and methane proportion range of 0% to 50% in fuel blends, the impacts of temperature, pressure, equivalence ratio, and methane additive were simulated on the ignition delay times of the fuel blends based upon the numerical model. It was found that the improvement of ammonia/methane ignition is significant with the increase of temperature, pressure, and methane additive while it is relatively not sensitive to equivalence ratio within the studied conditions. This suggests a promising potential of such fuel blends in real engine application. In addition to the calculations, reaction sensitivity analyses were also performed to have a deep insight into the observed differences between ammonia/methane/air ignition delay times with variation of conditions.
Ammonia-hydrogen fuel blends are an attractive option for the decarbonization of the energy sector with improved combustion characteristics over pure ammonia fuels. However, further research into methods of reducing NOx and NH3 emissions is necessary for combustors operating with these fuel blends. This paper details a novel burner design for partially premixed ammonia-hydrogen fuel injection incorporating considerations for waste heat, unburnt ammonia and improved combustion residence times. Laser Doppler anemometry (LDA) and computational fluid dynamics using a 3D RANS realizable k-epsilon model were employed to characterise the three-dimensional isothermal flow field of the design. The results show a promising flow profile with an anchored flame, a central recirculation zone and increased residence times.
Ammonia is a hydrogen carrier fuel that does not produce CO2 emissions in direct combustion. While ammonia combustion systems have been successfully trialled in a wide range of applications including aircraft engines and gas turbines, ammonia’s low laminar burning velocity and high ignition energy is one of the barriers to its more widespread use. The design and use of ammonia-methane combustors helps overcome these barriers, while also acting as a pathway to a lower-carbon economy. Hence the purpose of this study was to investigate the flame behaviour in terms of stability and emissions production in premixed methane swirl stabilised flames with both diffusion and premixed ammonia injection configurations. Temperature measurements, OH*, and NH2* chemiluminescence measurements were taken. Product gas values were measured for up to 50% (vol.) of ammonia and for 0.8 to 1.4 equivalence ratios at two power ratings (i.e. 6.4 and 10.7 kW). Chemiluminescence results for these conditions show radical concentration’s centre of gravity moving lower with an increase in ammonia concentration. NH2* radicals peaking at 30% ammonia volume fraction. This study also found correlations between radical formation and temperature profiles for numerical validation purposes.
This work presents an approach where biomimetic structures are tested for stabilisation and reduction of the boundary layer to reduce flashback propensity.Micro structures have been designed to have the shape of microriblets similar to those found in shark skin and other vegetable organisms.Various texture geometries were produced by micro Wire Electro Discharge Machining.These geometries were tested in a bespoke flame channel under isothermal conditions to observe the flow boundary profile with the aim of using combustion as a next step to determine the resistance to flashback propagation.CFD analyses were also performed using in-house simulation software Hydro3D utilising LES modelling.Experimental and simulation results were compared and showed an improvement of the boundary layer using the micro-riblets based on their structural patterns.
CO2 emitted from gas turbines in power plants is considered a major contributor to the global environmental damage. Carbon Capture and Storage (CCS) integrated with oxy-fuel (OF) combustion is an advanced and innovative approach that may be used in turbines to reduce these emissions. This method is based on CO2 recycling, however the obstacle to using this recirculation approach in gas turbines is reduction in their performance and reliability. This paper attempts to address the problem in a novel way by investigating theoretically a number of blends that can overcome the performance and reliability issues of pure CO2. These blends, comprising of argon, H2O and CO2, can be used as a working fluid with oxygen and methane as reactants. Additionally, a numerical model for an industrial gas turbine is employed. The aim is to find the optimum blend for complete NOx elimination with a recirculation of products. This study uses 0-D chemical kinetic software (Gaseq), an empirical selection approach with design of experiments and, 1-D chemical kinetic software (CHEMKIN-PRO). Results identify the optimum blend which is numerically assessed in an industrial gas turbine that has been experimentally correlated. The efficiency of this turbine running the selected blend is 1.75–13.93% higher than when running with natural gas/air conditions. This shows the promising use of this blend for a future high efficiency CCS-Oxyfuel approach in gas turbine combustors.
Combustion of biogas in gas turbines is an interesting option for provision of renewable combined heat and power from biomass. Due to an increasing share o
Combustion instabilities in gas turbine has been a major setback in the quest for efficient and clean combustion. Accurate characterisation and prediction of these disturbances is required to suppress them either at the design stage or in a close loop control when the system is in operation. The use of flame transfer functions has been a common approach in different literatures. Flame temperature is critical to the chemical time scale of the combustion system as it affects the rate of reaction. Although there has been increasing amount of literature on other factors which could modulate these instabilities, little attention has been paid to the inlet mixture – flame temperature effects on the combustion system. Thus, this study investigates these effects, using the open source acoustic simulator, (OSCILOS). Results demonstrate the temperature ratio variation as a potential method for controlling combustion instability in continuous combustion systems.
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 toward industrial implementation. Thus, the aim of this study is to identify reaction mechanisms that accurately represent 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 the 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 order 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.
