Browsing by Author "Igie, Uyioghosa"
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Item Open Access Aero engine compressor cooling by water injection - Part 1: Evaporative compressor model(Elsevier, 2018-06-10) Block Novelo, David Alejandro; Igie, UyioghosaThe need for more fuel-efficient jet engines has led to a rise in compressor pressure ratio and turbine inlet temperature respectively. The latter has been possible with advancements in turbine blade technology. Nevertheless, this higher temperature during combustion increases the production of thermal Nitrogen Oxides. Contrary to this high-pressure, high-temperature aero-engine design trend, regulations are pushing towards capping or reducing emissions. Injecting atomised water into a jet engine is an alternative to mitigate Nitrogen Oxides that is applied extensively to stationary gas turbines. The application for jet engines is very limited and dates back to the early Boeing 707 and 747 for thrust augmentation. The focus of this study is to investigate the performance benefits of water injection when applied to 2 and 3-spool compressors, under a wide range of different environmental conditions, and for different injection properties. In this first paper, a thermo-analytical compressor model with water droplet investigations in the Lagrangian frame of reference is explored. The methodology is applied to two different engine architectures, representative of modern turbofan engines. This injection study focuses on cooling the core and shows that the percent reduction in compressor discharge temperature is promising over a wider range of ambient conditions than expected. The effect of droplet sizes or quantity utilised were seen to be more influential. The 3-spool compressor also appears to benefit more from water injection in this investigation, mainly due to the higher operating pressures and temperatures found on the Intermediate Pressure Compressor which enables more efficient evaporation, as compared to a booster compressor. Given the design of this compressor, two locations of injections were considered. Reductions in Compressor Discharge Temperature of 60 and 80K were seen for the 2 and 3-spool engines, for a 2% injection ratio, accompanied by reductions in specific compressor work of 16 and 17%. Part 2 of this study has considered boundary conditions obtained here, to investigate the performance and emissions of complete jet engines.Item Open Access Aero engine compressor cooling by water injection - Part 2: Performance and emission reductions(Elsevier, 2018-05-28) Block Novelo, David Alejandro; Igie, UyioghosaTake-off and climb up to 3000 ft are the flight segments in which the aero-engine experiences the highest operating temperatures, which are known to be accompanied by a high production rate of Nitrogen Oxides (NOx). This contaminant has negative health implications on the human population, vegetation and wildlife that is in frequent proximity or exposure. Water injection into the compressor offers the possibility of reducing NOx. Nevertheless, limited studies have focused on the emissions reduction potentials and the wider questions of the influence of engine type and of wide-ranging ambient conditions. This study continues from Part 1 and explores the implications of the studied ambient conditions on the overall respective engine systems and their consequent emission reduction. An in-house gas turbine performance simulation software has been implemented to model and simulate the engine performance. For the emissions estimation, correlations were made from the information provided by the Engine Emissions Data Bank to quantify the reductions in Nitrogen Oxides. The 2 and 3-spool engine models investigated demonstrated significant reductions in compressor discharge and turbine inlet temperatures due to water injection. In this condition, the rotational speeds of the compressors are seen to be reduced to counter the mass flow augmenting effect of water injection and to satisfy the fixed thrust constraint. This along with lower compressor specific work brings about an improvement in the specific fuel consumption (5.3% and 7.8%, respectively) and general performance at low and high ambient temperatures. A higher advantage was seen for the 3-spool engine over the 2-spool as shown. Significant reductions in Nitrogen Oxide emissions of over to 50% are also demonstrated.Item Open Access Aeroderivative gas turbine back-up capability with compressed air injection(Elsevier, 2020-08-08) Abudu, Kamal; Igie, Uyioghosa; Roumeliotis, Ioannis; Szymanski, Artur; Di Lorenzo, GiuseppinaThe transition to more renewable energy sources of power generation is associated with grid instability and the need for backup power, due to their intermittency. This provides an opportunity for gas turbine engines, especially the aeroderivative (AD) types that generally have higher ramp rates than heavy-duty engines. Nonetheless, higher ramp rates are still necessary to meet more stringent grid requirements, with increased renewables subscription. The study examines ramp rate improvements and performance enhancement through compressed air injection at the back of the high-pressure compressor (HPC). Two configurations of AD engines are considered in the investigation. In-house gas turbine performance simulation software has been used to simulate the steady-state and transient operations for design and off-design performance. Compressed air injection in the study is facilitated by an assumed compressed air storage or an external compressor. The steady-state analysis for power augmentation shows that for the two-spool engine with fixed speed low-pressure compressor (LPC), a 16% increase in power is obtained with 8% of flow injection. The other engine that is intercooled and consists of a variable speed LPC with power turbine shows a 21% increase in power for the same injection amount. Above 8% injection, the HPC of both engines tends towards an adverse rise in pressure ratio. However, up to 15% of flow injection is allowed before the surge point. It is seen generally that the operating point of the LPC moves away from surge, while the opposite is the case for the HPC. For transient simulations focused on ramp rates, the better improvements are shown for the intercooled engine that runs at variable speed. This is a ramp rate improvement of 100% with air injection, while that of the other engine increases by 85%Item Open Access Aerodynamic limits air injection for heavy-duty gas turbine: compressor aerodynamic limits for power augmentation and ramp-up capabilities(SAGE, 2022-04-24) Szymanski, Artur; Igie, Uyioghosa; Hamilton, RichardImproved operational flexibility of gas turbines can play a major role in stabilising the electric power grid, by backing up intermittent renewable power. Gas turbines offer on-demand power and fast dispatch of power that is vital when renewable power reduces. This has brought about increasing demand to improve the ramp-up rate of gas turbines. One approach is through the injection of compressed air from energy storage or an auxiliary compressor. This method is the focus of the present work, which shows for the first time, the implications and limits of compressor air injection in a high-fidelity Computational Fluid Dynamics model (CFD). The 3D multi-stage model of the compressor was developed in ANSYS CFX v19.2, while the boundary conditions related to the injection cases have been obtained from a corresponding 0D engine model. The upper limits to air injection determine how much air can be injected into the engine, providing indicative values of power augmentation and ramp-up rate capabilities. These have been previously addressed by the authors using 0D models that do not consider the compressor aerodynamics in great detail. The CFD study has shown that for power augmentation, 16% of compressed air (based on compressor exit) is allowed based on the onset of stall. It also shows that increasing air injection amplifies losses, blockage factor and absolute velocity angle. Also, about 30% of the blade span from the hub is dominated by a rise in the total pressure loss coefficient, except the outlet guide vane for which separation occurs at the tip. For the ramp-up rate analysis, up to 10% air injection is shown to be sustainable. The work shows that the improvements in the 0D analytical engine model are plausible, in addition to demonstrating similar limits at different ambient temperatures.Item Open Access Aerodynamic limits of gas turbine compressor during high air offtakes for minimum load extension(Elsevier, 2021-02-18) Szymanski, Artur; Igie, Uyioghosa; Abudu, Kamal; Hamilton, RichardRenewable energy sources (RES) have become a favoured alternative to fossil fuel energy generation that has been driven by environmental concerns. Their intermittent nature has meant that gas turbines have remained relevant to support them as a backup. Current grid operation requires gas turbines to operate at as low power as possible when their demand drops, and also ramp-up quickly when power generation from renewables declines. Air extraction from a gas turbine compressor can address the first requirement, as this mechanism reduces the load or power of the engine while storing the air for further pressurised reinjection, related to ramp-up rate improvements. This study demonstrates the aerodynamic implications and the limits to air extraction behind the last stage of the compressor, to achieve further minimum load reduction. To achieve this, a zero-dimensional (0D) analytical model of an engine at design and off-design conditions (air extraction) has been used to determine the boundary conditions for a 3D compressor Computational Fluid Dynamics (CFD) model. The multi-stage CFD model shows the aerodynamic implications of low to high air extractions that are limited by choke, high flow separation, and loss in the pressure at the hub region of OGV and last stage stator. As such, the back of the compressor was more affected than the earlier stages. Based on these, the limit of flow extraction is 18% (of the compressor discharge). The compressor of the analytical engine model showed similarity in trends for comparable conditions with the stand-alone 3D compressor, however, more optimistic than the latter. The work has shown that the compressor is capable of high airflow extractions to reduce the minimum load further.Item Open Access Application of compressor water injection for the reduction of civil aircraft NOᵪ emissions.(2018-12) Block Novelo, David Alejandro; Igie, Uyioghosa; Nalianda, DevaiahGas turbine Nitrogen Oxide (NOx) emissions are directly proportional to combustion temperature. These contaminants are associated with respiratory diseases and damage to the local water quality and wildlife. Higher demand on civil aviation, coupled to high-pressure ratio (and thus, temperature-ratio) engines, have caused aviation-borne NOᵪ Gas turbine Nitrogen Oxide (NOx) emissions are directly proportional to combustion temperature. These contaminants are associated with respiratory diseases and damage to the local water quality and wildlife. Higher demand on civil aviation, coupled to high-pressure ratio (and thus, temperature-ratio) engines, have caused aviation-borne NOᵪ emissions to double since 1990. This is of concern around airports, at operations below 3,000 ft. where the concentration of air traffic is high and the population faces direct exposure to engine contaminants. This thesis explores the use of atomized water droplets into an engine compressor as a way of intercooling the cycle and in doing so reducing NOᵪ emissions. The use of water injection is proposed to be applied only during take-off and climb up to 3,000 ft. The analysis of water injection is firstly applied to common turbofan architectures (2 and 3-spool), under varied ambient conditions. The gas turbines are simulated by means of an in-house performance simulating tool, Turbomatch. The changes in cycle temperature when water injection is applied, are accounted for by means of a stand-alone analytical compressor model. The platform calculates the thermodynamic exchange between the gas path of the engine and the water droplets in the Lagrangian frame of reference. The engine models are then integrated into an in-house aircraft performance simulating tool, Hermes. Two types of aircraft, narrow and wide-body, are considered for operations with the water injection system. The performance benefits noted in the stand-alone engine section, are evaluated considering the extra system weight for different missions ranging from 500 to 11,000 km. The observed theoretical trends are then confirmed by means of an experiment performed on a stationary gas turbine. The test includes performance monitoring (pressures, temperatures, mass flows), water droplet measurements, and exhaust emissions analysis. The most optimistic case of water injection shows a reduction of NOx emissions greater than 50%, for the period when water is used. This technology, when applied after the fan compressor, is effective at ambient temperatures as low as 5°C and is more promising in 3-spool engines. For the shortest mission considered, equivalent to a journey from London to Paris, the aircraft benefits from a small fuel saving, despite of the extra weight. For longer missions, there is a negligible fuel penalty (0.05%) derived from the extra payload. In all the cases Landing and Take-Off (LTO) emissions are estimated to be reduced by 42-43%. A reduction of NOx emissions of 25% is achieved experimentally when injecting 2% water-to-air ratio. The study concludes that compressor water injection is a feasible solution that can significantly reduce the environmental footprint of aviation emissions to double since 1990. This is of concern around airports, at operations below 3,000 ft. where the concentration of air traffic is high and the population faces direct exposure to engine contaminants. This thesis explores the use of atomized water droplets into an engine compressor as a way of intercooling the cycle and in doing so reducing NOᵪ emissions. The use of water injection is proposed to be applied only during take-off and climb up to 3,000 ft. The analysis of water injection is firstly applied to common turbofan architectures (2 and 3-spool), under varied ambient conditions. The gas turbines are simulated by means of an in-house performance simulating tool, Turbomatch. The changes in cycle temperature when water injection is applied, are accounted for by means of a stand-alone analytical compressor model. The platform calculates the thermodynamic exchange between the gas path of the engine and the water droplets in the Lagrangian frame of reference. The engine models are then integrated into an in-house aircraft performance simulating tool, Hermes. Two types of aircraft, narrow and wide-body, are considered for operations with the water injection system. The performance benefits noted in the stand-alone engine section, are evaluated considering the extra system weight for different missions ranging from 500 to 11,000 km. The observed theoretical trends are then confirmed by means of an experiment performed on a stationary gas turbine. The test includes performance monitoring (pressures, temperatures, mass flows), water droplet measurements, and exhaust emissions analysis. The most optimistic case of water injection shows a reduction of NOᵪ emissions greater than 50%, for the period when water is used. This technology, when applied after the fan compressor, is effective at ambient temperatures as low as 5°C and is more promising in 3-spool engines. For the shortest mission considered, equivalent to a journey from London to Paris, the aircraft benefits from a small fuel saving, despite of the extra weight. For longer missions, there is a negligible fuel penalty (0.05%) derived from the extra payload. In all the cases Landing and Take-Off (LTO) emissions are estimated to be reduced by 42-43%. A reduction of NOx emissions of 25% is achieved experimentally when injecting 2% water-to-air ratio. The study concludes that compressor water injection is a feasible solution that can significantly reduce the environmental footprint of aviation.Item Open Access Case for exploring compressor water injection for airport emission reduction(ASME, 2017-06-30) Block Novelo, David Alejandro; Igie, UyioghosaThe increasing world population, higher accessibility to air transportation, coupled with new low-cost airline models has resulted in an unprecedented increase in demand for civil aviation. The industry is currently experiencing a global increase of operational civil aircraft at a rate of 5–6% annually. This growth suggests a vibrant future for the industry, however, the environmental implications and the footprint is worth considerable attention given the expected scale of growth in the industry and the possible side effects to human health. The stakeholders involved, some of which include: airports and airline operators, jet engine and airframe manufacturers and various government bodies, are introducing measures in order to mitigate the increase in certain emissions and hence their impact. This study focuses on one of the many existing approaches targeting the reduction in gaseous emissions, predominantly nitrogen oxides (NOx). This is through compressor water injection that is estimated to reduce NOx emissions by almost half under certain ambient conditions and water-to-air ratio. Apart from reviewing this technology, the study, more importantly, presents the ideas in relation to other major existing approaches/concepts. It would be observed that compressor water injection can be more readily applied to the existing infrastructure when compared to other approaches. This technique is one of the most promising methods for reducing NOx emissions, an area of particular importance given that modern engines, though more thermally efficient, operate at higher pressure ratios and flame temperature, both of which enhance nitrogen oxides formation. One of the main contributions of this paper is the categorisation of existing approaches focused on reducing aircraft-borne airport emissions. Different technologies and operational changes are classified according to the key pollutants that they target with respect to the landing and takeoff cycle based on 11 different engine types. These gaseous-emissions mitigating approaches are analyzed based on their individual merits, limitations and feasibilities. Compressor water injection is re-introduced here as a more readily applicable solution despite its technological challenges, many of which can be better resolved with today’s knowledgeItem Open Access Co-firing of hydrogen and natural gas in a practical DLN combustor model(American Society of Mechanical Engineers, 2023-09-28) Zhao, Rang; Igie, Uyioghosa; Abbott, David; Wiranegara, Raditya YudhaTo reduce carbon dioxide emissions, the combustion of natural gas-hydrogen blends in a lean premix gas turbine combustor has been investigated. Previous studies have mostly investigated the fuel blends at relatively low pressure (up to 5 bar) with relatively low hydrogen concentrations (up to 50vol%) on lab-scale or generic burner configurations. However, the influence of higher pressure and higher hydrogen content (over 50vol%) has not been widely studied, particularly on a practical industry-scale lean premixed burner as presented in this study. Such an operation is more challenging as it increases the turbulent flame speed gradient, which is an important factor in determining the likelihood of boundary layer flashback. A preliminary RANS-based Computational Fluid Dynamics (CFD) study has been conducted using ANSYS Fluent 2021R1, employing the Realizable K-Epsilon turbulence model and the Flamelet-Generated Manifold (FGM) combustion model. The combustor consists of a diffusion pilot and premixed main fuel nozzles. Methane-hydrogen blends of up to 90vol% hydrogen were investigated at a fixed fuel energy input. 100vol% methane at 15 bar pressure was taken as the baseline reference case. To investigate the flame characteristics, contour plots of OH mass fraction, equivalence ratios and temperatures (at different planes) are presented. This study shows that the expected reduction in the flame length with increasing hydrogen concentration occurs up to 40vol%. Significantly different flame shapes (as indicated by OH contours) were seen at higher hydrogen content. For this model, the flashback occurred at 90vol% H2 as indicated by a premature development of the flame within the nozzle of the main fuel burner. NOx emissions are shown to progressively rise with increasing hydrogen content up to 60vol% but reduce as the hydrogen content increases to 70vol%. The decrease appears to be related to an improvement in the quality of fuel-air mixing. It is important to note that the apparent rate of increase in NOx with increasing hydrogen is dependent on the reporting approach used. When reporting conventionally (parts per million by volume corrected to 15% O2 on a dry basis) the increase is significantly greater than when reporting on a mass per fuel energy input basis (gram per Joule). Reporting in the conventional manner disadvantages hydrogen because of the impact of oxygen consumption and water production on the corrections.Item Open Access Entropy generation and efficiency of a transonic rotor with water injection - a numerical study(American Society of Mechanical Engineers, 2021-01-11) Zawadzki, Natan; Szymanski, Artur; Block Novelo, David Alejandro; Igie, UyioghosaThe application of compressor water injection in aeroengines is of renewed interest in the civil aviation industry. Water due to its unprecedented heat capacity has the potential to cool the engine air through evaporation and thus reduce the NOx emissions formed in a combustion process. It is well known that the evaporative cooling increases thermodynamic cycle efficiency and thus improves the fuel economy. A relatively unexplored area, however, is the entropy generation due to water phase change as well as the balance between the corresponding entropy yield and the savings from the cooling of the core compressor flow. Hence, little consensus in the literature exists on the ultimate effect of water injection on compressor efficiency. In this study, a numerical analysis of water injection on an axial transonic rotor was carried out. The compressor model was tested at near-peak efficiency conditions with and without water injection. The flow was analysed using the Eulerian-Lagrangian approach with two-way coupling and the k-ω Shear Stress Transport turbulence model with Reattachment Modification. A universal, second thermodynamic law approach to quantify the entropy generation is proposed and used to evaluate the compressor flow. Results show that evaporation can facilitate the compression process and does not impair the compressor efficiency if applied at favourable conditions. The entropy generation in droplet-laden flow scales according to the gains from cooling effect and losses due to the evaporation and increased friction in the fluid. Some of the discrepancies in the public domain could be addressed, showing that the observed improvement in compressor efficiency is highly sensitive to the entropy flux measurement location. Most benefits from water injection were observed at the rotor tip proving the case for part-span injection from an entropy balance perspective.Item Open Access Evaluating gas turbine fouling degradation and impact of washing on engine performance.(2017-11) Lewis, Andy; Igie, UyioghosaFouling of the compressor of a gas turbine is one of the major contributors to its performance degradation, not only in terms of a reduction in the potential power output revenue and increased fuel costs but also raising the operating temperatures to levels that will have an impact on the servicing intervals and costs. In view of the current economic climate and with the ever-increasing pressure on governments to reduce emissions that contribute to global warming, the need to operate power generating gas turbines in the most efficient way possible is becoming more important. The aim of this study is to demonstrate that using a single compressor dual high-pressure washing system, on multiple gas turbines and a combination of a strict on-line compressor washing regime it is possible not only reduce the rate of compressor degradation, that will enable the period between off-line washes to be extended but also maintain a higher rate of power output throughout this period. Additional benefits will include better fuel efficiency which will lead to a lowering of emissions and the added flexibility of the overall plant operation by reducing the service interventions and shutdowns for off-line washes to the minimum. This study utilises the readily available data from the gas turbine control system to understand how the performance is affected by compressor fouling over time. Once corrected to remove the variations caused by changes in the ambient conditions, the performance trend of the data can be examined in 2 ways. The comparison of the recorded degradation against the gas turbine’s own historic figures and secondly against the relative performances of adjacent machines over similar time periods. The data gathered, from 4 gas turbines, over the 3 years 8 months recording period, provided the opportunity to select 'like for like' starting points in the various life cycles. This enabled direct comparisons of the results, between the various gas turbines that had operated with different compressor washing regimes. These comparisons demonstrated that maintaining an effective on-line compressor washing regime allows for greater potential revenue from exported power; whilst at the same time being more fuel efficient and lowering operating temperatures.Item Open Access Experimental investigation of gas turbine compressor water injection for NOx emission reductions(Elsevier, 2019-04-03) Block novelo, David alejandro; Igie, Uyioghosa; Szymański, ArturThe global rising demand for civil air travel shows good prospects for the industry, however, this growth is inevitably matched with higher levels of emissions and fuel consumption. In this study, demineralised water injection is presented as an alternative to reduce NOx emissions and enhance engine performance. The experimental study firstly presents the droplet size characterisation of a spray nozzle. This is done for varied injection pressure, water temperature and at varied axial and radial locations using an impaction pin nozzle. The single-shaft Artouste engine is used in conducting the compressor water injection test with water-to-air ratios of 0.5, 1 and 2%. The water droplet diameter, engine gas path and exhaust emissions are all monitored in real time. For the engine tests, droplets are measured at the spraying point and correlations are used to account for the droplet size at the inlet of the compressor due to measurement difficulties in this region. The test showed a reduction in compressor discharge temperature by up to 34 K and a NOx decrease by 25%. Nevertheless, the higher reductions in NOx at higher water-to-air ratios are attributed to a predominant cooling in the combustor because of unevaporated water in the compressor. At 0.5% water-to-air ratio, the drop in NOx is mainly due to compressor cooling and signified by the only case in which the fuel-to-air ratio reduces. The study presents evidence of the combined effects of compressor and combustor water ingestion. The CO is seen to increase significantly and associated with reduced combustor efficiency.Item Open Access Gas turbine compressor fouling and washing in power and aerospace propulsion(ASME, 2017-09-06) Igie, UyioghosaThis paper presents a well-researched subject area within academia, with a high degree of application in the industry. Compressor fouling effect is one of the commonest degradations associated with gas turbine operations. The aim of this review is to broadly communicate some of the current knowledge while identifying some gaps in understanding, in an effort to present some industry/operational interest for academic research. Likewise, highlight some studies from academia that present the current state of research, with their corresponding methods (experimental, numerical, actual operations, and analytical methods). The merits and limitations of the individual method and their approaches are discussed, thereby providing industry practitioners with a view to appreciating academic research outputs. The review shows opportunities for improving compressor washing effectiveness through computational fluid dynamics (CFD). This is presented in the form of addressing the factors influencing compressor washing efficiency. Pertinent questions from academic research and operational experiences are posed, on the basis of this review.Item Open Access Gas turbine compressor washing economics and optimisation using genetic algorithm(American Society of Mechanical Engineers (ASME), 2022-08-09) Musa, Gali; Igie, Uyioghosa; Di Lorenzo, Giuseppina; Alrashed, Mosab; Navaratne, RukshanStudies have shown that online compressor washing of gas turbine engines slows down the rate of fouling deterioration during operation. However, for most operators, there is a balancing between the performance improvements obtained and the investment (capital and recurring cost). Washing the engine more frequently to keep the capacity high is a consideration. However, this needs to be addressed with expenditure over the life of the washing equipment rather than a simple cost-benefit analysis. The work presented here is a viability study of online compressor washing for 17 gas turbine engines ranging from 5.3 to 307MW. It considers the nonlinear cost of the washing equipment related to size categories, as well as nonlinear washing liquid consumption related to the variations in engine mass flows. Importantly, the respective electricity break-even selling price of the respective engines was considered. The results show that for the largest engine, the return of investment is 520% and the dynamic payback time of 0.19 years when washing every 72 hours. When this is less frequent at a 480-hour interval, the investment return and payback are 462% and 0.22 years. The optimisation study using a multi-objective genetic algorithm shows that the optimal washing is rather a 95-hour interval. For the smallest engine, the investment was the least viable for this type of application.Item Open Access Gas turbine efficiency and ramp rate improvement through compressed air injection(SAGE, 2020-06-15) Abudu, Kamal; Igie, Uyioghosa; Minervino, OrlandoWith the transition to more use of renewable forms of energy in Europe, grid instability that is linked to the intermittency in power generation is a concern, and thus, the fast response of on-demand power systems like gas turbines has become more important. This study focuses on the injection of compressed air to facilitate the improvement in the ramp-up rate of a heavy-duty gas turbine. The steady-state analysis of compressed airflow injection at part-load and full load indicates power augmentation of up to 25%, without infringing on the surge margin. The surge margin is also seen to be more limiting at part-load with maximum closing of the variable inlet guide vane than at high load with a maximum opening. Nevertheless, the percentage increase in the thermal efficiency of the former is slightly greater for the same amount of airflow injection. Part-load operations above 75% of power show higher thermal efficiencies with airflow injection when compared with other load variation approaches. The quasi-dynamic simulations performed using constant mass flow method show that the heavy-duty gas turbine ramp-up rate can be improved by 10% on average, for every 2% of compressor outlet airflow injected during ramp-up irrespective of the starting load. It also shows that the limitation of the ramp-up rate improvement is dominated by the rear stages and at lower variable inlet guide vane openings. The turbine entry temperature is found to be another restrictive factor at a high injection rate of up to 10%. However, the 2% injection rate is shown to be the safest, also offering considerable performance enhancements. It was also found that the ramp-up rate with air injection from the minimum environmental load to full load amounted to lower total fuel consumption than the design case.Item Open Access Gas turbine minimum environmental load extension with compressed air extraction for storage(Elsevier, 2020-08-14) Abudu, Kamal; Igie, Uyioghosa; Minervino, Orlando; Hamilton, RichardThe fact that most renewable forms of energy are not available on-demand and are typically characterised by intermittent generation currently makes gas turbine engines an important source of back-up power. This study focuses on one of the capabilities that ensure that gas turbines are more flexible on the electric power grid. The capability here is the minimum environmental load that makes it possible to keep a gas turbine engine on the grid without a shut-down, to offer grid stability, adding inertia to the grid in periods when there is no demand for peak power from the engine. It is then desirable to operate the engine at the lowest possible load, without infringing on carbon monoxide emissions that becomes dominant. This paper demonstrates this potential through the extraction of the pressurised air from the back end of the compressor into an assumed energy storage system. The simulation of the engine performance using an in-house tool shows the additional reduction of the power output when the maximum closing of variable inlet guide vane is complemented with air extractions. However, the identified key strategy for achieving a lower environmental load (with same carbon monoxide emission limit) is to always maintain the design flame temperature. This is contrary to the conventional approach that involves a decrease in such temperatures. Here, a 34% reduction in load was achieved with 24% of flow extraction. This is shown to vary with ambient temperatures, in favour of lower temperatures when the combustor inlet pressures are higher. The emission models applied were based on empirical correlations and shows that higher combustor inlet pressures, high but constant flame temperatures with core flow reduction is crucial to obtaining a low environmentally compliant load. The compressor analysis shows that choking is a noticeable effect at a higher rate of extractions; this is found to occur at the stages closest to the extraction locationItem Open Access Hydrogen-enriched natural gas co-firing: a comparison of FGM and EDC models(American Society of Mechanical Engineers, 2023-09-28) Zhao, Rang; Igie, Uyioghosa; Abbott, DavidTo facilitate the transition from natural gas to a future hydrogen economy, the combustion of natural gas/hydrogen blends in gas turbines will play an important role in power generation. The influence of hydrogen content on technically premixed swirl-stabilized flame using large eddy simulation has proven to be powerful but with high computational costs. Hence, RANS-based models are useful for preliminary investigations and sensitivity studies. Flamelet Generated Manifold (FGM) and Eddy-Dissipation Concept (EDC) are two widely used RANS-based combustion models. EDC, in particular, accounts for the interaction between chemistry and turbulence using detailed chemical mechanisms, but at the cost of higher computational resources. FGM preprocesses the flamelet as a function of mixture fraction and progress variable and pre-integrates the chemistry-turbulence interaction into a Probability Density Functions (PDF) table, which makes FGM computationally inexpensive. This study aims to compare the predictions of these models with experimental data of a methane-fueled technically premixed swirl-stabilized low-pressure burner. The better-performing model is used to evaluate the influence of methane and hydrogen blends (up 40% by volume) in a higher-pressure burner also validated with experiments. The study has shown that EDC produces better agreement with the experimental data than FGM in estimating the flame temperature, flow velocity, and carbon dioxide profiles. FGM did not correctly capture the flame pattern and overestimated the reaction rate. This is possibly due to its simplified preprocessed chemistry mechanism, which could not evaluate the local thermal properties of the gas mixture properly. For the higher pressure evaluation at 5 bar, the EDC model captured the influence of hydrogen content addition on flame behaviour. As the hydrogen content increased, the chemical reaction rate increased, and the flame length indicated by OH decreased. This reduction in flame length is consistent with the experimental results. The CFD showed that at 20% H2, the change in NOx emission compared to 100% methane is negligible using the mass of NOx per unit of heat release calculation. A slight increase in NOx is shown for the same case using the concentration by volume corrected to 15% O2 approach. Nevertheless, both approaches showed NOx reductions at 40% H2. This study has shown that the behaviour of a technically premixed swirl-stabilized flame-firing methane/hydrogen blend is well represented by a non-adiabatic RANS-EDC model with low computation cost. This confirms its applicability in evaluating acceptable lean premixed burners characteristics for gas turbines.Item Open Access Impact of compressed air energy storage demands on gas turbine performance(Sage, 2020-02-16) Igie, Uyioghosa; Abbondanza, Marco; Szymański, ArturIndustrial gas turbines are now required to operate more flexibly as a result of incentives and priorities given to renewable forms of energy. This study considers the extraction of compressed air from the gas turbine; it is implemented to store heat energy at periods of a surplus power supply and the reinjection at peak demand. Using an in-house engine performance simulation code, extractions and injections are investigated for a range of flows and for varied rear stage bleeding locations. Inter-stage bleeding is seen to unload the stage of extraction towards choke, while loading the subsequent stages, pushing them towards stall. Extracting after the last stage is shown to be appropriate for a wider range of flows: up to 15% of the compressor inlet flow. Injecting in this location at high flows pushes the closest stage towards stall. The same effect is observed in all the stages but to a lesser magnitude. Up to 17.5% injection seems allowable before compressor stalls; however, a more conservative estimate is expected with higher fidelity models. The study also shows an increase in performance with a rise in flow injection. Varying the design stage pressure ratio distribution, brought about an improvement in the stall margin utilized, only for high extraction.Item Open Access Impact of gas turbine flexibility improvements on combined cycle gas turbine performance(Elsevier, 2021-02-20) Abudu, Kamal; Igie, Uyioghosa; Roumeliotis, Ioannis; Hamilton, RichardThe improvement of gas turbines flexibility has been driven by more use of renewable sources of power due to environmental concerns. There are different approaches to improving gas turbine flexibility, and they have performance implications for the bottoming cycle in the combined cycle gas turbine (CCGT) operation. The CCGT configuration is favourable in generating more power output, due to the higher thermal efficiency that is key to the economic viability of electric utility companies. However, the flexibility benefits obtained in the gas turbine is often not translated to the overall CCGT operation. In this study, the flexibility improvements are the minimum environmental load (MEL) and ramp-up rates, that are facilitated by gas turbine compressor air extraction and injection, respectively. The bottoming cycle has been modelled in this study, based on the detailed cascade approach, also using the exhaust gas conditions of the topping cycle model from recent studies of gas turbine flexibility by the authors. At the design full load, the CCGT performance is verified and subsequent off-design cases from the gas turbine air extraction and injection simulations are replicated for the bottoming cycle. The MEL extension on the gas turbine that brings about a reduction in the engine power output results in a higher steam turbine power output due to higher exhaust gas temperature of the former. This curtails the extended MEL of the CCGT to 19% improvement, as opposed to 34% for the stand-alone gas turbine. For the CCGT ramp-up rate improvement with air injection, a 51% increase was attained. This is 3% point lower than the stand-alone gas turbine, arising from the lower steam turbine ramp-up rate. The study has shown that the flexibility improvements in the topping cycle also apply to the overall CCGT, despite constraints from the bottoming cycle.Item Open Access Impact of inlet filter pressure loss on single and two-spool gas turbine engines for different control modes(ASME, 2014-05-05) Igie, Uyioghosa; Minervino, OrlandoInlet filtration systems are designed to protect industrial gas turbines from air borne particles and foreign objects, thereby improving the quality of air for combustion and reducing component fouling. Filtration systems are of varying grades and capture efficiencies, with the higher efficiency systems filters providing better protection but higher pressure losses. For the first time, two gas turbine engine models of different configurations and capacities have been investigated for two modes of operation (constant turbine entry temperature (TET) and load/power) for a two- and three-stage filter system. The main purpose of this is to present an account on factors that could decide the selection of filtration systems by gas turbine operators, solely based on performance. The result demonstrates that the two-spool engine is only slightly more sensitive to intake pressure loss relative to the single-spool. This is attributed to higher pressure ratio of the two-spool as well as the deceleration of the high pressure compressor (HPC)/high pressure turbine (HPT) shaft rotational speed in a constant TET operation. The compressor of the single-spool engine and the low pressure compressor (LPC) of the two-spool shows similar behavior: slight increase in pressure ratio and reduced surge margin at their constant rotational speed operation. Loss in shaft power is observed for both engines, about 2.5% at 1000 Pa loss. For constant power operation there is an increase in fuel flow and TET, and as a result the creep life was estimated. The result obtained indicates earlier operating hours to failure for the three-stage system over the two-stage by only a few thousand hours. However, this excludes any degradation due to fouling that is expected to be more significant in the two-stage system.Item Open Access Minimum environmental load extension through compressed air extraction: numerical analysis of a dry low NOx combustor(Elsevier, 2023-02-17) Wiranegara, Raditya Yudha; Igie, Uyioghosa; Ghali, Pierre; Abudu, Kamal; Abbott, David; Hamilton, RichardThe operational flexibility of gas turbine (GT) engines is a key requirement to coexist alongside increasing renewable energy that is often intermittent. One of the GT flexibility criteria is the Minimum Environmental Load (MEL). This is the lowest load the engine can be operated, without infringing on emissions limits (particularly CO) and is relevant to periods when there is a priority to renewable generation or low power demand. This study along with a series of related works of the authors proposes compressor air extraction for MEL extension. Here, a stand-alone three-dimensional numerical dry low NOx combustor demonstrates the technical viability concerning combustor performance and emissions. In addition, supplemented with low-order models for durability and stability evaluations. For the first time, there is evidence to show that the combustor can handle the 18% compressed air extraction to sustain a new MEL. This operation is characterised by a 12.3% reduction in CO through an increase of the fuel split ratio by 2% after design exploration cases. However, at the expense of a smaller overall rise in NO emissions by 5%. The durability analysis focused on the wall liner temperature assessments, which show no unusually high temperature rise for the new MEL. Similarly, the thermoacoustic instability frequencies and gains are around the normal operation mode. When benchmarked against previous related engine-level analysis, the evidence shows that the new MEL is a 7% points reduction of load.