284 publications from this institution
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.
Increasing interest in alternative fuels for gas turbines has motivated research in gaseous fuels other than natural gas. Methane enriched with hydrogen or diluted with carbon dioxide are of considerable interest. The latter seems quite relevant for development of technologies such as oxyfuel combustion for carbon capture and storage in order to control temperatures in the combustion chamber. Thus, this paper presents an experimental study on the combustion of methane-carbon dioxide mixtures at atmospheric conditions. Gas mixtures have been examined by using different levels of premixing with different injection strategies with and without swirl and with and without central injection. A 20 kW burner has been used to investigate the flame stability and emissions performance by using these blends to examine the effect of CO2 addition. The burner configuration consisted of a centre body with an annular, premixed gas/air jet introduced through five, 60° swirl vanes. A TESTO 350XL gas analyzer was used to obtain NOx and CO emission trends to characterize all the injection regimes whilst using different fuel blends. CH chemiluminescence diagnostics was also used and correlated to the levels of emissions produced during the trials. The resulting images were analysed using Photron FASTCAM PFV ver 2.4.1.1 software and MATLAB R2015a. CO2 dilution decreased flame stability and operability range. The introduction of CO2 reduces temperatures in the combustion zone thus causing a reduction in emissions of nitrous oxides across all equivalence ratios. CO emissions also decreased with a limited (15%) CO2 addition. In terms of injection regimes, the outer purely premixed injection regime has lower NOx and CO, as expected. CH chemiluminescence distribution indicated that pure methane with central injection produced high fluctuation in CH production. The use of central premixed injection produces the most chaotic CH production case, possibly as a consequence of production of radicals in the central recirculation zone.
Ammonia, a molecule that is gaining more interest as a fueling vector, has been considered as a candidate to power transport, produce energy, and support heating applications for decades. However, the particular characteristics of the molecule always made it a chemical with low, if any, benefit once compared to conventional fossil fuels. Still, the current need to decarbonize our economy makes the search of new methods crucial to use chemicals, such as ammonia, that can be produced and employed without incurring in the emission of carbon oxides. Therefore, current efforts in this field are leading scientists, industries, and governments to seriously invest efforts in the development of holistic solutions capable of making ammonia a viable fuel for the transition toward a clean future. On that basis, this review has approached the subject gathering inputs from scientists actively working on the topic. The review starts from the importance of ammonia as an energy vector, moving through all of the steps in the production, distribution, utilization, safety, legal considerations, and economic aspects of the use of such a molecule to support the future energy mix. Fundamentals of combustion and practical cases for the recovery of energy of ammonia are also addressed, thus providing a complete view of what potentially could become a vector of crucial importance to the mitigation of carbon emissions. Different from other works, this review seeks to provide a holistic perspective of ammonia as a chemical that presents benefits and constraints for storing energy from sustainable sources. State-of-the-art knowledge provided by academics actively engaged with the topic at various fronts also enables a clear vision of the progress in each of the branches of ammonia as an energy carrier. Further, the fundamental boundaries of the use of the molecule are expanded to real technical issues for all potential technologies capable of using it for energy purposes, legal barriers that will be faced to achieve its deployment, safety and environmental considerations that impose a critical aspect for acceptance and wellbeing, and economic implications for the use of ammonia across all aspects approached for the production and implementation of this chemical as a fueling source. Herein, this work sets the principles, research, practicalities, and future views of a transition toward a future where ammonia will be a major energy player.
This paper presents a series of experiments and numerical simulations using commercial software (ANSYS) to determine the behaviour and impact on the blowoff process with various geometries and simulated syngas compositions at fixed power outputs. Experiments were performed using a generic premixed swirl burner. The Central Recirculation Zone and the associated turbulent structure contained within it were obtained through CFD analyses providing details of the structures and the Damkolher Number (Da) close to blowoff limits. The results show how the strength and size of the recirculation zone are highly influenced by the blend, with a shift of Da and turbulence based on carbon-hydrogen ratio, shearing flows and Reynolds number. Instabilities such as thermoacoustics, flashback, autoignition and blowoff are highly affected by the flow structures and chemical reactions/diffusivity. Moreover, it has been observed that turbulence close to the boundaries of the central recirculation zone, a region of high stability for swirling flows, is highly altered by the chemical characteristics of the fuel blends. In terms of blowoff, the phenomenon is still not entirely understood. As the process occurs, its theoretical limits do not match its real behaviour. Therefore, one possibility could be the difference in turbulence and Da numbers across the flame, being critical at the base of the flame where the system is stabilized.
The research investigates the changes in the surface properties and surface chemistry following laser microtexturing of stainless steel parts, in relation to their applications in the energy sector. In particular, the material compositions of the laser surface textured (LST) parts, together with the oxide compound formation on them are evaluated with respect to their wettability property. Wettability is crucial for heat exchange processes as it affects the efficiency of heat transfer by influencing surface contact and the formation of droplets on the heat exchanger surface. Here, two simple LST geometries, viz. channel and cross-hatch, were produced using a nanosecond fibre laser micromachining system. The wettability of the textured surfaces was then examined over a period of 45 days with an interval of 15 days. It was observed that the former geometry rendered a hydrophilic surface initially, which transformed to a hydrophobic surface after 45 days, whereas the latter LST design exhibited hydrophobic characteristic over the entire duration of the assessment. The material compositions and the oxide compound formation on the LST parts were analysed via energy dispersive spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction techniques and the results were correlated with the measured wettability data.
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.
Ammonia has been produced over the last centuries in several ways, with the Haber–Bosch process leading current production due to its efficiency and feasible deployment. However, previous to the leading positioning of the Haber–Bosch process, ammonia used...
