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Recent findings from the US Energy Information Administration (EIA) project an increase in domestic fossil fuel consumption (e.g., petroleum, natural gas) and global greenhouse gas (GHG) emissions through 2050 [1]. Consequently, a...
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Recent findings from the US Energy Information Administration (EIA) project an increase in domestic fossil fuel consumption (e.g., petroleum, natural gas) and global greenhouse gas (GHG) emissions through 2050 [1]. Consequently, advanced combustion research aims to identify fuels to mitigate fossil fuel consumption while minimizing exhaust emissions. Ammonia (NH_3) is one of these candidates, as it has historically been shown to provide high energy potential and zero carbon emission (CO and CO_2) [2]. As a hydrogen (H_2) carrier, NH_3 serves as a possible solution to the U.S. Department of Energy's (DOE) Hydrogen Program Plan by providing efficient H_2 storage and conservation capabilities [3]. As a result, applied turbine-combustion research of NH_3 and H_2 fuel has been conducted to identify combustion performance parameters that aid in the design of sustainable turbomachinery [4]. One of these key combustion parameters is the laminar burning speed (LBS). While abundant literature exists on the combustion of NH_3 and H_2 fuels, there is not sufficient evidence in high-pressure environments to provide a comprehensive understanding of NH_3 and H_2 combustion phenomena in turbine-combustor settings. To advance the state of the knowledge, NH_3, and H_2 mixtures were ignited in a spherical chamber across a range of equivalence ratios at 296 K and 5.07 Bar (5 atm) to understand their flame characteristics and LBS which was determined using a multizone constant-volume method. The experimental conditions were selected according to primary turbine-combustor conditions, as much research is needed to support NH_3-H_2 applicability in turbomachinery for power generation. The effect of H_2 addition to NH_3 fuel was observed by comparing the LBS for various NH_3-H_2 mixture compositions. Experimental results revealed increased LBS values for H_2 enriched NH_3 with the maximum LBS occurring at stoichiometry. The experimental data were accurately predicted by the UCF NH_3-H_2 mechanism developed for this investigation, while NUI 1.1 simulations overestimated recorded LBS data by a significant margin. This study demonstrates and quantifies the enhancing effect of H_2 addition to NH_3 fuels via LBS and strengthens the literature surrounding NH_3-H_2 combustion reactions for future work.
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The premixed conditional moment closure (CMC) method has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in a RANS environment. Here the premixed CMC...
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The premixed conditional moment closure (CMC) method has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in a RANS environment. Here the premixed CMC method is extended to Unsteady RANS. The new model is validated with the PIV and Raman turbulent, enclosed reacting methane jet data from DLR. The experimental data has a rectangular test section at atmospheric pressure and 573 K with a single inlet jet. A jet velocity of 90 m/s is used with an adiabatic flame temperature of 2,064 K. Contours of major species, temperature and equivalence ratio along with their rms values are provided. The CMC model falls into the class of table lookup turbulent combustion models where the combustion model is solved offline over a range of conditions and stored in a table that is accessed by the CFD code. The scalar dissipation is used to account for the effects of the small scale mixing on the reaction rates. A presumed shape beta function PDF is used to account for the effects of large scale turbulence on the reactions. The unsteady RANS version of the open source CFD code Open FOAM is used with the PISO algorithm solved with the finite volume method. Velocity, temperature and major species are compared to the experimental data. Once validated, this tool will be useful for designing lean premixed combustors for gas turbines. The results match the experimental data better than the steady RANS of and are able to pick up the unsteadiness of the flame.
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The premixed conditional moment closure (CMC) method has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in a RANS environment. Here the premixed CMC...
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The premixed conditional moment closure (CMC) method has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in a RANS environment. Here the premixed CMC method is extended to Unsteady RANS. The new model is validated with the PIV and Raman turbulent, enclosed reacting methane jet data from DLR. The experimental data has a rectangular test section at atmospheric pressure and 573 K with a single inlet jet. A jet velocity of 90 m/s is used with an adiabatic flame temperature of 2,064 K. Contours of major species, temperature and equivalence ratio along with their rms values are provided. The CMC model falls into the class of table lookup turbulent combustion models where the combustion model is solved offline over a range of conditions and stored in a table that is accessed by the CFD code. The scalar dissipation is used to account for the effects of the small scale mixing on the reaction rates. A presumed shape beta function PDF is used to account for the effects of large scale turbulence on the reactions. The unsteady RANS version of the open source CFD code Open FOAM is used with the PISO algorithm solved with the finite volume method. Velocity, temperature and major species are compared to the experimental data. Once validated, this tool will be useful for designing lean premixed combustors for gas turbines. The results match the experimental data better than the steady RANS of and are able to pick up the unsteadiness of the flame.
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The success of the global Energy Transition hinges on meeting the world's growing demand for power, while at the same time reducing greenhouse gas (GHG) emissions. Achieving this will require significant growth in electricity gene...
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The success of the global Energy Transition hinges on meeting the world's growing demand for power, while at the same time reducing greenhouse gas (GHG) emissions. Achieving this will require significant growth in electricity generation from clean and carbon-free energy sources. Several energy providers [1,2] have already begun the transition from traditional carbon-based fuels to cleaner alternatives, such as hydrogen (H2) and hydrogen enriched natural gas (HENG). However, there are still many technical questions/challenges that must be addressed when applying these fuels in gas turbines. The application of H_2 or H_2/natural gas (NG) blends to advanced class gas turbines, which have higher operating pressures and temperatures, has raised concerns about the potential for leakages or fuel sequencing operations where flammable mixtures of fuel and air could auto-ignite. Public information on the auto-ignition of H_2 in air at atmospheric pressure is well documented. Such data shows auto-ignition temperature (AIT) of H_2 is ～100℃ lower than that of methane (CH4). Studies also show that as pressure increases, methane's AIT decreases. However, there was insufficient information in the published literature to characterize the influence of pressure on auto-ignition for hydrogen fuel applications. This study describes the test methodology used to evaluate conditions where auto-ignition occurs for various fuel-air mixtures operating at different pressures (1-30 atm) and temperatures. Testing was completed with 100% H_2 and multiple H_2/NG blends at various equivalence ratios (φ). Testing was similarly performed for 100% NG to validate the test and data collection methods cited in prior published literature. Results indicate that, at atmospheric pressures, an increase in H_2 concentration results in a reduced AIT. However, at 30 atm, the AIT of H_2 increased. Variations of auto-ignition delay times (AIDT) were also observed during the testing and are compared to modeling predictions, providing insight into auto-ignition characteristics.
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The current study investigated the effects of a sustained detonation wave on a RP-2 droplet in a detonation tube environment. The detonation waves were initiated using a methane-oxygen mixture. Two sets of high-speed images were r...
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The current study investigated the effects of a sustained detonation wave on a RP-2 droplet in a detonation tube environment. The detonation waves were initiated using a methane-oxygen mixture. Two sets of high-speed images were recorded for detonation waves traveling through mixtures with equivalence ratios of 1.0 and 0.9 at a frame rate of 340,000 fps and 900,000 fps, respectively. The initial temperature and pressure in the detonation tube were 293 K and 760 torr, respectively. The results show that the displacement, deformation, and disintegration of the RP-2 droplets are comparable to previous studies investigating the interaction of shock waves on nonreacting water droplets and on liquid fuel droplets. This may imply that the droplet disintegration process may be largely independent of the presence of combustion.
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We have measured OH concentration time-histories during methylcyclohexane (MCH) oxidation behind reflected shocks waves in a heated, high-pressure shock tube. Measurements were made over temperatures of 1205 to 1332 K, at pressure...
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We have measured OH concentration time-histories during methylcyclohexane (MCH) oxidation behind reflected shocks waves in a heated, high-pressure shock tube. Measurements were made over temperatures of 1205 to 1332 K, at pressures near 15 atm, in dilute MCH/O_2/Ar mixtures with an equivalence ratio (φ) of 0.5. Initial fuel concentrations of 1000 ppm and 750 ppm were used. Measurements were conducted using narrow-linewidth ring-dye laser absorption near the R-branchhead of the OH A-X (0,0) system at 306.47 nm. These measurements provide experimental data needed for validation and refinement of combustion reaction mechanisms for MCH. Comparisons of the present data with predictions of candidate detailed kinetic mechanisms are presented as well as sensitivity analyses and suggestions for mechanism improvements.
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Ignition delay times from undiluted mixtures of natural gas (NG)/H_2/Air and NG/NH_3/Air were measured using a high-pressure shock tube at the University of Central Florida. The combustion temperatures were experimentally tested b...
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Ignition delay times from undiluted mixtures of natural gas (NG)/H_2/Air and NG/NH_3/Air were measured using a high-pressure shock tube at the University of Central Florida. The combustion temperatures were experimentally tested between 1000-1500 K near a constant pressure of 25 bar. As mentioned, mixtures were kept undiluted to replicate the same chemistry pathways seen in gas turbine combustion chambers. Recorded combustion pressures exceeded 200 bar due to the large energy release, hence why these were performed at the high-pressure shock tube facility. The data is compared to the predictions of the NUIGMech 1.1 mechanism for chemical kinetic model validation and refinement. An exceptional agreement was shown for stoichiometric conditions in all cases but strayed at lean and rich equivalence ratios, especially in the lower temperature regime of H_2 addition and all temperature ranges of the baseline NG mixture. Hydrogen addition also decreased ignition delay times by nearly 90%, while NH_3 fuel addition made no noticeable difference in ignition time. NG/NH_3 exhibited similar chemistry to pure NG under the same conditions, which is shown in a sensitivity analysis. The reaction CH_3 + O_2 = CH_3O + O is identified and suggested as a possible modification target to improve model performance. Increasing the robustness of chemical kinetic models via experimental validation will directly aid in designing next-generation combustion chambers for use in gas turbines, which in turn will greatly lower global emissions and reduce greenhouse effects.
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Ignition and flame propagation in methane/O_2 mixtures diluted with CO_2 are studied. A laser ignition system and dynamic pressure data are utilized to ignite the mixture and to record the combustion pressure, respectively. The la...
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Ignition and flame propagation in methane/O_2 mixtures diluted with CO_2 are studied. A laser ignition system and dynamic pressure data are utilized to ignite the mixture and to record the combustion pressure, respectively. The laminar burning velocities (LBV) are obtained at room temperature and atmospheric pressure in a spherical combustion chamber. Flame initiation and propagation is recorded by using a high-speed camera in select experiments to visualize the effect of CO_2 proportionality on the combustion behavior. The laminar burning velocity is studied for a range of equivalence ratios (φ =0.8-1.3, in steps of 0.1), and oxygen ratios, D=O_2/(O_2+CO_2) (26-38% by volume). It was found that the LBV decreases by increasing the CO_2 proportionality. It was observed that the flame propagates toward the laser at a faster rate as the CO_2 proportionality increases. Current experiments are in very good agreement with existing literature data. The premixed flame model from CHEMKIN PRO software and two mechanisms (GRI-Mech 3.0 and ARAMCO Mech 1.3 ) are used to simulate the current data. In general, simulations are in reasonable agreement with current data though the mechanisms predict slower flame speeds. The LBV values obtained by the ARAMCO 1.3 mechanism are closer to the experimental values. Additionally, sensitivity analysis is carried out to understand the important reactions that influence the predicted flame speeds. Improvements to the GRI predictions are suggested after incorporating latest reaction rates from literature for key reactions.
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摘要 :
Ignition and flame propagation in methane/O_2 mixtures diluted with CO_2 are studied. A laser ignition system and dynamic pressure data are utilized to ignite the mixture and to record the combustion pressure, respectively. The la...
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Ignition and flame propagation in methane/O_2 mixtures diluted with CO_2 are studied. A laser ignition system and dynamic pressure data are utilized to ignite the mixture and to record the combustion pressure, respectively. The laminar burning velocities (LBV) are obtained at room temperature and atmospheric pressure in a spherical combustion chamber. Flame initiation and propagation is recorded by using a high-speed camera in select experiments to visualize the effect of CO_2 proportionality on the combustion behavior. The laminar burning velocity is studied for a range of equivalence ratios (φ =0.8-1.3, in steps of 0.1), and oxygen ratios, D=O_2/(O_2+CO_2) (26-38% by volume). It was found that the LBV decreases by increasing the CO_2 proportionality. It was observed that the flame propagates toward the laser at a faster rate as the CO_2 proportionality increases. Current experiments are in very good agreement with existing literature data. The premixed flame model from CHEMKIN PRO software and two mechanisms (GRI-Mech 3.0 and ARAMCO Mech 1.3 ) are used to simulate the current data. In general, simulations are in reasonable agreement with current data though the mechanisms predict slower flame speeds. The LBV values obtained by the ARAMCO 1.3 mechanism are closer to the experimental values. Additionally, sensitivity analysis is carried out to understand the important reactions that influence the predicted flame speeds. Improvements to the GRI predictions are suggested after incorporating latest reaction rates from literature for key reactions.
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摘要 :
Ignition and flame propagation in methane/O_2 mixtures diluted with CO_2 are studied. A laser ignition system and dynamic pressure data are utilized to ignite the mixture and to record the combustion pressure, respectively. The la...
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Ignition and flame propagation in methane/O_2 mixtures diluted with CO_2 are studied. A laser ignition system and dynamic pressure data are utilized to ignite the mixture and to record the combustion pressure, respectively. The laminar burning velocities (LBV) are obtained at room temperature and atmospheric pressure in a spherical combustion chamber. Flame initiation and propagation is recorded by using a high-speed camera in select experiments to visualize the effect of CO_2 proportionality on the combustion behavior. The laminar burning velocity is studied for a range of equivalence ratios (φ=0.8-1.3, in steps of 0.1), and oxygen ratios, D=O_2/(O_2+CO_2) (26-38% by volume). It was found that the LBV decreases by increasing the CO_2 proportionality. It was observed that the flame propagates toward the laser at a faster rate as the CO_2 proportionality increases. Current experiments are in very good agreement with existing literature data. The premixed flame model from CHEMKIN PRO [1] software and two mechanisms (GRI-Mech 3.0 [2] and ARAMCO Mech 1.3 [3]) are used to simulate the current data. In general, simulations are in reasonable agreement with current data though the mechanisms predict slower flame speeds. The LBV values obtained by the ARAMCO 1.3 mechanism are closer to the experimental values. Additionally, sensitivity analysis is carried out to understand the important reactions that influence the predicted flame speeds. Improvements to the GRI predictions are suggested after incorporating latest reaction rates from literature for key reactions.
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