摘要 :
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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摘要 :
In recent years, hydrogen-carrying compounds have accrued interest as an alternative to traditional fossil fuels due to their function as zero-emission fuels. As such, there is interest in investigating hydrogen-carrying compounds...
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In recent years, hydrogen-carrying compounds have accrued interest as an alternative to traditional fossil fuels due to their function as zero-emission fuels. As such, there is interest in investigating hydrogen-carrying compounds to improve understanding of the fuels' characteristics for use in high-pressure systems. In the current study, the oxidation of ammonia/natural gas/hydrogen mixtures was carried out to study CO formation profiles as well as the ignition delay times behind reflected shock waves in order to refine chemical kinetic models. Experiments were carried out in the University of Central Florida's shock tube facility by utilizing chemiluminescence to obtain OH* emission and laser absorption spectroscopy to obtain CO profiles. Experimental results were then compared with the GRI 3.0 mechanism, as well as the proprietary UCF 2022 mechanism utilizing CHEMKIN-Pro software. In general, both models were able to capture the trend in autoignition delay times and CO time histories for natural gas and ammonia mixtures. However, for ammonia-hydrogen mixtures, GRI 3.0 failed to predict ignition delay times whereas the UCF 2022 mechanism was able to capture the IDTs within the uncertainty limits of the experiments. A sensitivity analysis was conducted for different mixtures to understand the important reactions at the experimental conditions. Finally, a reaction pathway analysis was carried out to understand important ammonia decomposition pathways in the presence of hydrogen and natural gas.
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摘要 :
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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This study explores the combustion characterization of high-fuel percentage, air-diluted mixtures of H_2 mixed with natural gas (NG) as well as mixtures of H_2 and NH_3 at temperatures and pressures relevant to turbine operating c...
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This study explores the combustion characterization of high-fuel percentage, air-diluted mixtures of H_2 mixed with natural gas (NG) as well as mixtures of H_2 and NH_3 at temperatures and pressures relevant to turbine operating conditions (20-30 bar, 1000-1500 K). Lower temperatures (below 1070 K) exhibit preignition characteristics due to non-homogeneity. An attempt to mitigate these occurrences at high pressures is investigated using the constrained reaction volume (CRV) stage-filling technique. Due to the need to further refine the facility CRV stage-filling uncertainty, only higher temperature data will be interpreted at this time. The test conditions in this study closely replicate the temperatures, pressures, and mixtures that would be seen in hydrogen-powered gas turbines, making it the first to explore such conditions. The experimental IDTs were compared against the current state-of-the-art chemical kinetic models for mechanism validation. The current work will advance H_2-powered turbines and aims to determine the optimum molecular ratio of H_2 when mixed with natural gas.
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Catalytic metal foils were adhered to the end wall of a shock tube with stoichiometric methane mixtures, achieving pressures from 18.9 to 24 atm and temperatures between 1178 - 1642 K. Preliminary results show little effect on vol...
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Catalytic metal foils were adhered to the end wall of a shock tube with stoichiometric methane mixtures, achieving pressures from 18.9 to 24 atm and temperatures between 1178 - 1642 K. Preliminary results show little effect on volumetric ignition delay time. Emission spectroscopy, laser Schlieren, and pressure histories record before the main ignition event. Activation energies have been found, and the feasibility of this technique to study catalytic surface effects have been established.
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Methane oxidation experiments have been performed at 100 and 200 bar in argon and CO_2 bath gases. The insight gained from qualitative laser absorption spectroscopy measurements using a helium-neon IR laser at 3391 nm clarifies th...
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Methane oxidation experiments have been performed at 100 and 200 bar in argon and CO_2 bath gases. The insight gained from qualitative laser absorption spectroscopy measurements using a helium-neon IR laser at 3391 nm clarifies the interpretation of ignition due to the dual-peaks seen in emissions traces during combustion in mixtures heavily diluted in CO_2. Further, it calls into question interpretation of other work in the pressure regime. Models were used and compared to qualitative laser absorption data to elucidate ignition delay time in experiments with multiple interpretations.
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This paper investigates the ignition delay times of natural gas at pressures and temperatures equivalent to rocket thrust chamber conditions (100-300 bar and 1000-1400 K). Higher-order hydrocarbons (C_2H_6, C_3H_8, C_4H_(10), and ...
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This paper investigates the ignition delay times of natural gas at pressures and temperatures equivalent to rocket thrust chamber conditions (100-300 bar and 1000-1400 K). Higher-order hydrocarbons (C_2H_6, C_3H_8, C_4H_(10), and iC_4H_(10)) were varied in the mixtures to represent reactive impurities naturally found in raw natural gas. The experiments were performed in a high-pressure shock tube and compared to an oxy-methane mixture to show the impurity effects on ignition characteristics. The AramcoMech 3.0 mechanism was used for model validation and showed deviation from the initial 100 bar experimental ignition delay times on the upper bound of the temperature scale for the mixtures containing larger amounts of the higher-order alkanes. The current work provides a better understanding of natural gas combustion at elevated pressures and further improves chemical kinetic models.
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Shock tube experiments were performed for stoichiometric oxygen-methane and oxygen-natural gas mixtures with varying levels of CO_2 dilution at conditions relevant to the startup of supercritical carbon dioxide (sCO_2) power gener...
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Shock tube experiments were performed for stoichiometric oxygen-methane and oxygen-natural gas mixtures with varying levels of CO_2 dilution at conditions relevant to the startup of supercritical carbon dioxide (sCO_2) power generation cycles. Ignition delay times were measured using sidewall pressure and emission data and compared to model predictions. Reasonable agreement is observed between the model predictions and experimental measurements for methane regardless of CO_2 dilution. Natural gas combustion with varying levels of CO_2 dilution is identified as a potential area for refinement in the model.
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This study reports the autoignition delay times of hydrogen/ammonia mixtures at conditions similar to turbine engine operating conditions (23 bar, 1100-1250 K). H_2 was mixed with NH3 and shock-heated using synthetic air as the ox...
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This study reports the autoignition delay times of hydrogen/ammonia mixtures at conditions similar to turbine engine operating conditions (23 bar, 1100-1250 K). H_2 was mixed with NH3 and shock-heated using synthetic air as the oxidizer. The data is compared against the current state-of-the-art NH3 chemical kinetic mechanisms found in the literature for undiluted fuel validation and refinement. Experiments were performed in a high-pressure shock tube and have shown detonation pressures reaching 200 bar. Lower temperature points have also exhibited non-ideal behavior, which calls for extensive chemical analysis to accurately report the IDTs. This work will aid in the design of air-breathing turbine engines using hydrogen and ammonia as fuel and develop a well-built NH_3-based chemical kinetic mechanism.
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Stoichiometric oxy-methane mixtures at pressures of 18.9 to 24 bar and temperatures between 1178 -1642 K were studied in a shock tube. Emission spectroscopy, laser Schlieren, pressure histories, and fixed wavelength laser absorpti...
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Stoichiometric oxy-methane mixtures at pressures of 18.9 to 24 bar and temperatures between 1178 -1642 K were studied in a shock tube. Emission spectroscopy, laser Schlieren, pressure histories, and fixed wavelength laser absorption spectroscopy at 3.39 μm has been used to measure methane decomposition rates and find the absorption cross-section of methane at 3.39 μm at these conditions. Various catalytic end walls were employed to determine any surface effects caused by the catalytic material observable at a location remote from the end wall.
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