Publications

Environmental Life Cycle Analysis of an Ammonia-Ethanol Fueled Internal Combustion Engine (ICE) for Power Generation

Climate change and other environmental impacts have been an enormous worldwide concern in recent decades. Decarbonizing strategic and economic industries is mandatory. Using carbon-free fuels such as ammonia (NH3) has been promoted as a promising solution for decarbonizing both energy and industrial sectors. The use of biofuels has also been encouraged as an attractive alternative to replace conventional petroleum-based fuels in transportation. Therefore, the present study evaluates the environmental profile of using ammonia-ethanol blends in internal combustion engines (ICE) for power generation systems through a life cycle assessment (LCA) framework using the OpenLCA v1.10.3 software. The experiments were conducted in a single-cylinder spark-ignition engine that employs direct injection using three different fuel compositions (in mole fraction) of ethanol/ammonia (75/25, 50/50, and 25/75), with two different intake pressures (0.5 and 1 bar) at 1000 rpm. The functional unit (FU) was set at 1 kWh. The GWP results for 0.5 bar of intake pressure are between 0.07 and 0.95 kg CO2/kWh. The scenario running on Brazilian ethanol and green ammonia is the most environmentally friendly case. The carbon footprint for ethanol/ammonia-based ICE at 1 bar fluctuates between 0.052 and 0.68 kg CO2/kWh. Similarly, regarding GWP, there is a slight difference in Fossil Depletion Potential (FDP) when using ethanol from Brazil and ethanol from Ecuador due to the lack of circular economy strategies in Ecuador's agriculture, compared to Brazil. Regarding the contribution analysis, for a 50% green ammonia – 50% ethanol scenario for power generation, ethanol production has the highest contribution for global warming, fossil depletion, and freshwater eutrophication potential impacts. Compared to the analysed environmental impacts, some of our proposed scenarios depict better performance than the average electricity production in the United Kingdom, France and Europe. Therefore, ethanol-ammonia fuel-based for power generating systems could be an important option to contribute to the decarbonization of the electric sector.

Advancements of combustion technologies in the ammonia-fuelled engines

The worldwide decarbonisation movement has turned ammonia into one of the attractive alternative fuel for power generation. This paper reviews the progress of ammonia combustion technologies in spark ignition engine, compression ignition engine, and gas turbine. Relevant publications from prominent academic journals were acquired from credible scholarly databases and analysed. Ammonia dissociation and separate hydrogen supply were typically employed to deliver hydrogen to enhance ammonia reaction in the spark ignition engine. To achieve satisfactory engine performances with thermal efficiency of around 30%, a hydrogen mass fraction of roughly 10% is required for the ammonia/hydrogen engine. Engine parameters optimisation may be needed to increase hydrogen mass fraction further. Aqueous ammonia elevates heat release rate of full load compression ignition engine by almost 10%. However, prolonged ignition delay could potentially lead to higher engine noise levels. Multiple fuel injection optimisation is seemingly a more promising solution for improving ammonia compression ignition engine performances. In recent years, partial premixed combustion has gained considerable interest in hydrogen/ammonia gas turbine combustion research. This is mainly due to its ability to operate at equivalence ratio as low as 0.4, and in the slight fuel-rich regime. For operation at equivalence ratio 1.05, the nitric oxide concentration was decreased by a factor of approximately 5.9 when compared with that of stoichiometric condition. In all, ammonia offers a practical opportunity for sustainable power generation via internal combustion engines and gas turbine. Ground-breaking combustion technologies are crucial to boost the adoption of ammonia in these engines.

Oxygenated sunflower biodiesel: Spectroscopic and emissions quantification under reacting swirl spray conditions

The spray combustion characteristics of sunflower (Helianthus annuus) biodiesel/methyl esters (SFME) and 50% SFME/diesel blend and diesel were investigated via a liquid swirl flame burner. The swirl flame was established at atmospheric condition by using a combined twin-fluid atomiser-swirler configuration at varied atomising air-to-liquid ratios (ALR) of 2.0–2.5. Diesel flame showed a sooty flame brush downstream of the main reaction zone, as opposed to the biodiesel flame which showed a non-sooty, bluish flame core. Biodiesel flame exhibited a more intense flame spectra with higher OH* radicals as compared to diesel. Higher preheating main swirl air temperature led to higher NO emission, while CO correspondingly decreased. Sunflower-derived biodiesel generally exhibited slightly higher NO and CO levels than diesel when compared at the same power output, mostly due to higher flame temperature and fuel chemistry effect. By increasing ALR, a significant reduction of NO and CO for both fuel types were concurrently achieved, presenting a strategy to control emissions and atomise biodiesel with higher viscosity under swirl combustion mode.

A proposed method for enhancing the thermal characteristics of bio-inspired microtextured surfaces for energy sector applications

The research involves generation of textured surfaces using micro-wire electro discharge machining (µ-WEDM) for controlling boundary layers, drag forc

Recognition of large coherent structures in a tangential swirl burner

Experimental and modeling study on ignition delay of ammonia/methane fuels

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.

Identification and Dynamics of Coherent Structures in a Coanda Swirling Jet Flow

Swirl stabilised flows are the most common technology for gas turbine combustion stabilisation. Although success on the characterization of these flows is tangible, there are several structures that appear in such flows that are still a concern for fundamental and applied research. One of these structures is the Precessing Vortex Core (PVC), whose ambiguous characteristics make it an adequate mechanism for chemical mixing whilst being a detrimental component for thermoacoustic stabilisation. The PVC has been extensively characterised in swirling jet flows exhibiting vortex breakdown (in this study named Open Jet Flow or OJF). However this has not been the case for swirling Coanda (i.e. wall attached) jet flows (CoJF). Therefore, this research presents experimental work detailing the identification and visualisation of coherent structures in both types of jet flows. A generic swirl burner was fitted with a base plate in a position so that any of these two flows, OJF and CoJF, could be obtained within the same burner geometry. High speed stereo particle image velocimetry (S-PIV) was used to obtain a time-resolved flow field of each flow state at different flow rates. Two PVCs were clearly identified in both flows, one in the inner shear layer between the vortex breakdown bubble and the jet and one between the jet and the ambient. Precessing frequencies for the CoJF where ~8.5% higher (St~0.9-1.0) than those of the OJF (St~0.8-0.9). Spectral proper orthogonal decomposition was used to identify the coherent structures in the flow. Swirl strength (λci) analysis was conducted on the coherent modes to establish quantitative and qualitative results and to produce a 3D reconstruction of the flow field. The results indicate that precessing coherent flow structures are present in wall attached Coanda swirling flows and these are similar to the structures found in swirling jet flows undergoing vortex breakdown.

Effects of different nozzle configurations on swirl flow topology in tangential swirl burners

Flame flashback is one of the central combustion instabilities, especially when it appears in the form of boundary layer flashback (BLF) or combustion induced vortex breakdown (CIVB) flashback, some of the most common instabilities in swirl combustors. This paper focuses on mitigating the phenomenon of CIVB and BLF flashback mechanisms using different nozzle configurations while using central air injection. Studies were conducted on a 150-kW tangential swirl burner manufactured and previously characterised at Cardiff University. The effects of different nozzle heights (hn) with and without microstructure on the swirl flow characteristics were investigated experimentally by utilising an LDA system. Different strip heights (hm) of a wire woven mesh have been employed as a liner on the smooth nozzle to change its surface roughness. It was found that longer smooth nozzles (hn/Ro=2.3) led to promotion of stability in the swirl burner by minimising the axial velocity defect while decreasing turbulence downstream the dump plane. Moreover, the average measurements show that the burner nozzles with microstructured surfaces enable improvements in controlling the BLF flashback and hence reduces outflow drag. It was found that the microstructured mesh alters the flow structure near the wall by increasing the velocity adjacent to this region delivering further resistance to BLF. On the other hand, using both central air injection and the nozzle with and without the microstructured surface can affect the operability of the gas turbine combustors.

Effect of Swirler Configurations on Combustion of Humidified Lean Premixed Methane-Hydrogen Mixtures

In the present work, we investigate effects of variation in swirler configuration (co- and counter-rotating swirl flows in a dual swirl burner) on isothermal and reacting flow fields and flame structure when the burner is operating on steam-diluted premixed methane-hydrogen-air mixture at ��=0.9. Reynolds Averaged Navier Stokes (RANS) simulation with the SST ��−�� model and Flamelet Generated Manifold combustion (FGM) model are employed to predict the flow field and combustion. We present the results based on the characterization of the turbulent flow field in the nozzles and the combustor, temperature distribution, flame structure, NOx and CO emissions. The counter-rotating swirler flow fields show the presence of high turbulence in the shear layers which enhance the mixing of incoming reactants and hot gases in the recirculation zones thereby stabilizing the flame inside the combustor. We observe the existence of a shorter and compact M-shaped flame attached to the center body of the burner in case of counter-rotating configuration with a small NOx emissions reduction of 5%

Data-Driven Prediction of Laminar Burning Velocity for Ternary Ammonia/Hydrogen/Methane/Air Premixed Flames

Zero-carbon fuels such as hydrogen and ammonia play a pivotal role in the energy transition by offering cleaner alternatives to natural gas (methane), especially in industrial combustion systems. Binary and ternary blends of these fuels offer a transitionary, low-carbon solution in the near future. Laminar burning velocity (LBV), as a fundamental combustion property, is significantly different for ammonia, hydrogen, and methane. Although the LBV of binary blends of these fuels is well-studied, ternary blends have not been extensively studied. In this study, the primary objective is to employ a simple ensemble learning method to predict the LBV of ternary ammonia/hydrogen/methane/air mixtures. The training dataset consists of experimental data sourced from a large number of publications (3846 data points), as well as synthetic data generated by 1D freely propagating premixed flame simulations in Cantera using a detailed chemical kinetic model. Three machine learning algorithms, namely artificial neural networks, gaussian process regression, and extreme gradient boosting trees are trained and optimised. Then, a simple ensemble averaging method is used to reduce overfitting and improve robustness. The ensemble model achieves a coefficient of R2 = 0.991 with an inference time that is approximately 8,000 times faster than the 1D simulation run time. The ensemble model is capable of predict ing LBVs of ammonia/hydrogen/methane/air mixtures for T = [295−756K], P = [1 − 10bar], ϕ = [0.5 − 1.8] across all possible blending ratios.

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 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.

A High-temperature and corrosion-resistant Co-Al2O3 composite superhydrophobic coating for marine exhaust emission systems

To address the challenges of high-temperature corrosion in marine exhaust systems this study utilizes a one-step electrodeposition technique to fabricate a superhydrophobic Co-Al 2 O 3 composite coating on low-carbon steel. A comprehensive analysis was conducted to examine the coating’s surface morphology, hydrophobic characteristics, self-cleaning capability, corrosion resistance, and thermal stability. The results demonstrated that the composite coating exhibited remarkable hydrophobicity, with a contact angle (CA) of approximately 163.7°. Furthermore, after heating to 500 °C, the coating maintained superior corrosion resistance, achieving a corrosion protection efficiency ( η ) of 89.8 % in a 3.5 wt % sodium chloride solution. Electrochemical impedance spectroscopy (EIS) revealed that the coating effectively suppressed electrochemical reactions, thus prolonging the protection of the metal surface. These findings suggest that the Co-Al 2 O 3 composite coating provides potential protective capabilities for metals in marine environments, making it suitable for high-temperature corrosion resistance in gas turbines. This approach has the potential to extend equipment lifespan and reduce maintenance costs.

Studies of the Precessing Vortex Core in Swirling Flows

Large scale coherent structures play an important role in the behavior of the combustion regime inside any type ofcombustor stabilized by swirl, with special impact on factors such as flame stability, blow off, emissions and theoccurrence of thermo-acoustic oscillations. Lean premixed combustion is widely used and is known to impact many ofthese factors, causing complex interrelationships with any coherent structure formed. Despite the extensiveexperimentation in this matter, the above phenomena are poorly understood. Numerical simulations have been usedto try to explain the development of different regimes, but their extremely complex nature and lack of time dependentvalidation show varied and debatable results. The precessing vortex core (PVC) is a well-known coherent structurewhose development, intensity and occurrence has not been well documented. This paper thus adopts an experimentalapproach to characterize the PVC in a simple swirl burner under combustion conditions so as to reveal the effects ofswirl and other variables on the latter. Aided by a high speed photography (HSP) system, the recognition and extentof several different types of PVCs were observed and discussed.

Targeting Global Environmental Challenges by the Means of Novel Multimodal Transport: Concept of Operations

Novel modes of transport form the basis of environmentally friendly and economically efficient transport system of the future. This paper introduces the feasibility study of a Dock to Dock (D2D) use case, combining aspects of route development and infrastructure definition, for the transport of goods in South West England and South Wales. The proposed system makes use of new, more flexible and environmentally friendly means of transport, such as electric Vertical Take-Off and Landing (eVTOL) aircraft and electric Autonomous ZeroEmission (eAZE) vessels. To meet the environmental targets set out for the transport sector, the use of alternative hydrogen- based fuels is investigated for air, surface and marine vehicles. Logistics, regulations and infrastructure required for the safe and efficient production and distribution of such low-emission energy vectors is also considered. Digital twin of the system is proposed to study its safety and viability, while the analysis of energy requirements is proposed to inform policy makers and define the necessary infrastructure to meet future emission-free transport energy needs.

Experimental study to enhance swirl burner against boundary layer flashback

In gas turbine systems, operation stability represents the major challenge to any successful device deployment. Climate change combined with fossil fuel pollution has led to the need of considering high hydrogen content fuels, thus putting more pressure to stabilise gas turbines at operation conditions. Flashback is one of the main operation stability problems that represent a real challenge for gas turbine designers when using fast reacting fuels with high hydrogen content. One mechanism that has shown to contribute to flashback considerably is the propagation of the flame through its boundary layer. Although the latter has been studied, there are still several unknowns in its evolution through the system. Thus, boundary layer flashback of a swirling turbulent flame was investigated in a 150 kW tangential swirl burner previously characterised. To produce controlled changes to the boundary layer, the internal side of the burner was covered by woven wire steel mesh to mimic biological skin techniques in flow drag improvement. Two different wire meshes were used to study the effect of the regular roughness size on the boundary flashback. Moreover, the effects of using the wire mesh in such swirling flow with and without central air injection for reduction of other flashback phenomena were studied. The results show good enhancement of the system to boundary layer flashback, and a new map of the combustion stability of the rig has been produced.

Experimental Investigation of the Effects of Central Fuel Injectors on Premixed Swirling Flames

The demand for alternative fuels has increased significantly during the previous decades in order to reduce pollutants and increase the amount of energy that can be generated from nonfossil fuels.However, the use of new fuels faces many issues especially the problem of stability of operation which sometimes can cause severe damages to the system hardware.Thus the development of flexible combustion systems for gas turbines becomes urgent in order to achieve high reliability with these new sources of energy.Swirl stabilized combustion is the most widely spread deployed technology used to stabilize and control combustion in gas turbines and numerous other systems.However, the interaction of the swirling flows with the burner geometries is very complex and it has been proved that any change in the burner geometry can affect the flow field inside the combustion chamber, close to the burner mouth and downstream the combustion zone.Most burners are generally provided with a diffusive injector that centrally delivers well-known fuels allowing the stabilization of the system previous to entirely premixed conditions.Moreover, the injector anchors the central recirculation zone formed downstream of the nozzle.However, the use of injectors can also affect the stability limits of the system, especially the propagation of flashback through changes of shape of the shear layer since other structures such as the Combustion Induced Vortex Breakdown are suppressed due to the presence of this central body.However, the characterization of the flow and its impacts on the propagation of these and other flashback structures using different injectors has been briefly documented.Thus, this paper presents a series of experiments using a well-characterized tangential swirl burner to determine the impact of different central injector geometries on the flow field characteristics which directly affect the flow stagnation point downstream of the burner mouth and consequently the propagation of the Combustion Induced Vortex Breakdown.Results show how the use of various injectors and swirl numbers can impact on the flashback limits with a minimum outside diameter before which the Combustion Induced Vortex Breakdown is altered.

CARSOXY (CO2-Argon-Steam-OxyFuel) Combustion in Gas Turbines for CCS Systems

No abstract is provided for this article.

Use of Ammonia for Heat, Power and Propulsion

To date, a number of mechanical, electric, thermal and chemical approaches have been developed for storing electric energy for small devices and utility-scale services. However, the only sufficiently flexible mechanism allowing large quantities of energy to be stored over long periods is chemical energy storage in the form of carbon (as with existing hydrocarbon resources) or hydrogen. Fossil fuel consumption rate is on decline as a consequence of environmental issues, whilst current implementation of pure hydrogen technologies presents several technical barriers. Therefore another chemical with high hydrogen content considered for potential storage and as a fuel source is ammonia. For this reason, this chapter approaches the most common methods for conversion of ammonia to power. This collaborative work includes details of the fundamentals behind each technology, their use into ammonia-fuelled systems and their application in demonstrative cases that have been conceived around the world. This chapter aims to establish the background around the subject for readers interested in the development of ammonia-fuelled devices, thus contributing to the progression of the concept for the reduction of fossil fuels via the increase in technologies capable of producing zero-carbon energy at various scales.

Gas Turbine Co-Firing of Steelworks Ammonia With Coke Oven Gas or Methane: A Fundamental and Cycle Analysis

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.