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Ground-Based Gas Turbine Combustion: Metrics, Constraints, and System Interactions
... Axially staged combustion technology is widely used in advanced gas turbines to achieve load flexibility and low NOx emissions [1,2]. In axial-fuel-staged (AFS) combustion, the combustion chamber is divided into two parts in the axial direction: the traditional primary combustion stage and the secondary combustion stage, in which the secondary fuel is injected perpendicularly to the high-temperature main-flow through a nozzle and thermally ignited in a high-temperature, low-oxidant environment. ...
Advanced gas turbine adopts axially staged combustion to achieve the goal of increasing turbine inlet temperature while limiting NOx emissions. The premixing effect of secondary fuel injection has a significant influence on secondary combustion organization and flame-dynamic characteristics. In this paper, we proposed and experimental studied a novel twin-nozzle configuration for secondary fuel injection. Secondary fuel is injected from the front nozzle and air is injected from the rear nozzle. Operation codition studied includes the diameter (d) of front and rear nozzle from 1 mm to 3 mm, jet Reynolds number from 1900 to 5700, the jet spacing ranges from 2d to 4d, and the equivalence ratio of primary stage from 0.72 and 0.59. This flexible configuration controls the injection of fuel and air separately and allows fully lifted flame front organization, which is crucial for fuel/air mixing and NOx control. Using high-speed CH* imaging, the effects of primary stage equivalence ratio, nozzle diameter, and rear air injection ratio on the dynamical characteristics are investigated. We discussed the flame propagation mechanism, flame base pulsation frequency, ignition delay distance, and heat release distribution. We found that when the jet Reynolds number is reduced from 5700 to 1900, the flame pulsation frequency rises from 176 Hz to 586 Hz. When the rear air injection ratio increases from 0 to 3, the pulsation frequency decreases from 586 Hz to 88 Hz, the flame lift-off height increases, and the ignition delay distance decrease.
... One of the most widely adopted combustion systems is the gas turbine, which plays a preeminent role in aviation and energy production [2,3]. The gas turbines provide continuous combustion and follow the Brayton cycle [4]. ...
Gas turbine performance is closely linked to the turbine inlet temperature, which is limited by the turbine guide vanes ability to withstand the massive thermal loads. Thus, steam cooling has been introduced as an advanced cooling technology to improve the efficiency of modern high-temperature gas turbines. This study compares the cooling performance of compressed air and steam in the renowned radially cooled NASA C3X turbine guide vane, using a numerical model. The conjugate heat transfer (CHT) model is based on the RANS-method, where the shear stress transport (SST) k−ω model is selected to predict the effects of turbulence. The numerical model is validated against experimental pressure and temperature distributions at the external surface of the vane. The results are in good agreement with the experimental data, with an average error of 1.39% and 3.78%, respectively. By comparing the two coolants, steam is confirmed as the superior cooling medium. The disparity between the coolants increases along the axial direction of the vane, and the total volume average temperature difference is 30 K. Further investigations are recommended to deal with the local hot-spots located near the leading- and trailing edge of the vane.
... The emissions from gas turbines are relatively low as compared to other power plants. A complete comparison for emissions of CO 2 , SO 2 , NO x , and Particulate Matter (PM) between various power plants is presented in Fig. 2 [2]. For instance, a Gas Turbine Combined Cycle (GTCC) reduces CO 2 emissions by more than 50%, NO x emissions by approximately 80%, and eliminates sulfur dioxide (SO 2 ) compared to the power plants burning coal. ...
The society is going through transformations at a rate that is unprecedented in human history. One such transformation is the energy transition, which will affect almost every facet of our society. Gas turbine engines are state of the art machines, a backbone of modern society, and used in various applications, right from power generation to propelling aircraft and ships. This paper reviews the possibilities offered by the Inter-stage Turbine Burner (ITB) configuration for both aviation and power generation with a view on sustainability and fuel flexibility.
First, the thermodynamic characteristics of a Brayton-Joule cycle with ITB is elaborated, followed by discussions on the design and the off-design performance characteristics of such a gas turbine architectural variation. Finally, the viability of ITB architecture in reducing emissions and enabling "Energy Mix" in aviation is elaborated. The paper concludes with an outlook on the technological readiness ladder that the engineering community will have to address in the future.
... Typical low emission gas turbines operate near lean blow-off conditions (i.e., low equivalence ratios) to reduce combustion temperatures and therefore reduce temperature dependent formation of unwanted pollutants such as NOx. To attain the lowest NOx emissions, uniformly low reaction temperatures must be assured and thus the reactants must be well mixed prior to combustion [2]. With the addition of hydrogen into the fuel, issues arise such as higher flame speeds compared to carbon based fuels at a given equivalence ratio and flame temperature. ...
Hydrogen derived from non-fossil sources is an attractive candidate to replace carbon based fuels in gas turbines, as it is inherently carbon free. Yet the unusual combustion properties of hydrogen requires some care to successfully use it in gas turbines. To attain the lowest NO x emissions, uniformly low reaction temperatures must be assured thus the reactants must be well mixed. This is accomplished in low emission gas turbines by mixing the reactants within a pre-mixer section prior to entry into the combustor. With the addition of hydrogen into the fuel, certain issues arise such as higher flame speeds compared to carbon based fuels. Flashback is a phenomena that occurs when the flame no longer propagates beyond the exit of the premixer/injector but instead retracts and propagates upstream towards, and ultimately into the pre-mixer, causing significant damage due to such high temperatures. Flashback occurs when the flame speed exceeds either the local or bulk flow velocity. In practice, the question arises regarding the impact of turbulence levels. While an increase in turbulence intensity may help improve mixing, it also known to increase turbulent burning velocity. In the present work, the influence of bulk turbulence intensity of the flow on boundary layer flashback is investigated. Data are acquired for a different turbulence intensities at pressures from 3 to 8 bar with preheated reactants up to 750 deg. K. Various mixtures of hydrogen and methane are evaluated. The results show that even with significantly different bulk flow turbulence intensities (based on the ratio of flow centerline turbulence to centerline axial velocity) boundary layer flashback is not strongly affected. This is attributed to the role of the quenching distance in connection with damping within the boundary layer. It is noted that core flow flashback or other flashback mechanisms may be affected differently.
... To attain the lowest NOx emissions, uniformly low reaction temperatures must be assured and thus the reactants must be well mixed. This is accomplished in low emission gas turbines by mixing the reactants within a premixer section prior to entry into the combustor [2]. With the addition of Hydrogen into the fuel, certain issues arise such as higher flame speeds compared to carbon based fuels at a given equivalence ratio and flame temperature. ...
Hydrogen derived from non-fossil sources is an attractive candidate to replace carbon based fuels in gas turbines, as it is inherently carbon free. Yet the unusual combustion properties of hydrogen requires some care to successfully use it in gas turbines. To attain the lowest NO x emissions, uniformly low reaction temperatures must be assured thus the reactants must be well mixed. This is accomplished in low emission gas turbines by mixing the reactants within a premixer section prior to entry into the combustor. With the addition of hydrogen into the fuel, certain issues arise such as higher flame speeds compared to carbon based fuels. Flashback is a phenomena that occurs when the flame no longer propagates downstream of the injector but instead retracts and propagates upstream towards the premixer and injector causing significant damage in equipment due to such high temperatures. Flashback occurs when the flame speed exceeds either the local or bulk flow velocity. To date, systematic study of the role of turbulence levels has not been investigated at gas turbine conditions. While increasing turbulence intensity can potentially improve the mixing of the fuel with the oxidizer, it will also increase the local turbulent flame speed, potentially making flashback more prominent. However, due to the interaction of the fluid with the wall, the turbulence levels from the bulk flow may be buffered. As a result, the manner in which bulk flow turbulence intensity affects boundary layer flashback is complex. The current work suggests that bulk flow turbulence levels may not have a strong effect on boundary layer flashback and that the velocity gradient near the wall remains the critical parameter.
... The latter has less restrictions in terms of combustor volume and weight, 1770 and no requirement for re-light capabilities. Additional restrictions could be imposed due to 1771 cycle differences (recuperation or intercooling, for example) [153]. Other differences are the 1772 possibility of having external recirculation (EGR) in land-based gas turbines, which may have 1773 a major impact on design constraints and strategies, and their usual longer residence times 1774 [154]. ...
Since its discovery, the Flameless Combustion (FC) regime has been seen as a promising alternative combustion technique to reduce pollutant emissions of gas turbine engines. This combustion mode is often characterized by well-distributed reaction zones, which can potentially decrease temperature gradients, acoustic oscillations and, consequently NOx emission. However, the application of FC to gas turbines is still not a reality due to the inherent difficulties faced in attaining the regime while meeting all the engine requirements. Over the past years, investigations related to FC have been focused on understanding the fundamentals of this combustion regime, the regime boundaries, its computational modelling, and combustor design attempts. This article reviews the progress achieved so far, discusses the various definitions of the FC regime, and attempts to point the directions for future research. The review suggests that modelling of the FC regime is still not capable of predicting intermediate species and pollutant emissions. Comprehensive experimental databases with conditions relevant to gas turbine combustors are not available, and moreover, many of the current experiments do not necessarily represent the FC regime. By analysing the latest developments in computational modelling, the review points to the most promising approaches for the prediction of reaction zones and pollutant emissions in FC. The lessons learned from previous design attempts provide valuable insights into the design of a successful gas turbine engine operating under the FC regime. The review concludes with some examples where the gas turbine architecture has been exploited to advance the possibilities of FC in gas turbines.
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