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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...
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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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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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As the human exploration of space expands, there is a need for better, more reliable monitoring of the constituents of the fixed mass atmosphere. Waste and toxic gas accumulation, namely CO and CO2 can cause harm to personnel, car...
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As the human exploration of space expands, there is a need for better, more reliable monitoring of the constituents of the fixed mass atmosphere. Waste and toxic gas accumulation, namely CO and CO2 can cause harm to personnel, cargo, or equipment. By modulating the frequency of the LEDs, the concentrations of these gases can be resolved on a parts-per-million (ppm) scale with a single photodiode detector, helping to maintain a low size, weight, and power (SWaP) requirement. This is an improvement on current laser-based detectors, where there are frequent false positives. The sensor is currently undergoing preparation for a suborbital flight, and designs are underway for further miniaturization to optimize the low SWaP compliance.
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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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The objective of this research is to validate properties of mixtures relevant to supercritical carbon dioxide (sCO_2) power cycles. Direct fired sCO_2 cycles are promising technology for the future power generation systems. The wo...
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The objective of this research is to validate properties of mixtures relevant to supercritical carbon dioxide (sCO_2) power cycles. Direct fired sCO_2 cycles are promising technology for the future power generation systems. The working fluid of sCO_2 cycles will be near and above critical point of CO_2. One of the challenges is that the simulation of mixtures should consider real gas behavior. Expected operating conditions of Allam cycles reach up to 300 bar and 1000 ℃. Characterizing the mixtures at the extreme conditions is an important issue in current researches and industrial applications. Thermophysical properties of mixtures may be beyond the valid range of the widely used database such as NIST REFPROP. Experimental data of mixtures properties in the literature is limited which is necessary to develop high-fidelity design tools for sCO_2 power cycles. We measured density and sound speed of several multi-component mixtures. A temperature-controlled high-pressure test cell was used for the density measurements. Sound speed was measured bv resonant frequency detection using an external speaker and a piezoelectric pressure sensor. Mixtures studied in this work includes carbon dioxide, methane, oxygen and water vapor. Properties of pure CO_2 were measured to show the validity of our technique. Compositions were selected to be close to frozen mixtures at the inlet, mid-progress and exhaust conditions of a model sCO_2 combustor in the previous numerical simulation work. Corresponding reaction progress variables (RPV) were RPV=0, 0.5, and 1. Temperature and pressure conditions of experiments are 310-450 K, and 0-150 bar. In our study, density and sound speed from NIST REFPROP database agree with experimental measurements within the range of our measurement uncertainties.
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The objective of this research is to validate properties of mixtures relevant to supercritical carbon dioxide (sCO_2) power cycles. Direct fired sCO_2 cycles are promising technology for the future power generation systems. The wo...
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The objective of this research is to validate properties of mixtures relevant to supercritical carbon dioxide (sCO_2) power cycles. Direct fired sCO_2 cycles are promising technology for the future power generation systems. The working fluid of sCO_2 cycles will be near and above critical point of CO_2. One of the challenges is that the simulation of mixtures should consider real gas behavior. Expected operating conditions of Allam cycles reach up to 300 bar and 1000 ℃. Characterizing the mixtures at the extreme conditions is an important issue in current researches and industrial applications. Thermophysical properties of mixtures may be beyond the valid range of the widely used database such as NIST REFPROP. Experimental data of mixtures properties in the literature is limited which is necessary to develop high-fidelity design tools for sCO_2 power cycles. We measured density and sound speed of several multi-component mixtures. A temperature-controlled high-pressure test cell was used for the density measurements. Sound speed was measured bv resonant frequency detection using an external speaker and a piezoelectric pressure sensor. Mixtures studied in this work includes carbon dioxide, methane, oxygen and water vapor. Properties of pure CO_2 were measured to show the validity of our technique. Compositions were selected to be close to frozen mixtures at the inlet, mid-progress and exhaust conditions of a model sCO_2 combustor in the previous numerical simulation work. Corresponding reaction progress variables (RPV) were RPV=0, 0.5, and 1. Temperature and pressure conditions of experiments are 310-450 K, and 0-150 bar. In our study, density and sound speed from NIST REFPROP database agree with experimental measurements within the range of our measurement uncertainties.
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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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Airborne meteorological instruments are key to climate science, of which understanding cloud formation is an important component. Cloud formation involves the entrainment of air with dissimilar convective, thermal, and humidity pr...
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Airborne meteorological instruments are key to climate science, of which understanding cloud formation is an important component. Cloud formation involves the entrainment of air with dissimilar convective, thermal, and humidity properties. Improved understanding of these meteorological parameters can improve forecasting. The National Oceanic and Atmospheric Administration (NOAA) currently relies on outboard sensors with 25 Hz sampling, giving 10 m spatial resolution during nominal fixed wing aircraft flights. Higher-resolution humidity and temperature data are needed. We describe a novel laser absorption-based instrument that can make high sensitivity airborne measurements with 25 cm spatial resolution. The use of mid-infrared (MIR) quantum cascade lasers (QCLs) enables high sensitivity humidity measurements based on strong fundamental vibrations of water vapor. Sampling at 1 MHz (averaged data output exceeding 1 kHz) enables the high spatial resolution from a jet platform that accesses near the ground to 45,000 ft. This technology could be extended using complementary lasers to identify any Chemical, Biological, Radiological, and Nuclear (CBRN) threats, or hazardous material incidents, based on their MIR absorption features. Additional applications could also include highly accurate information for combating wildfires and high-speed identification of anomalous gas-phase species in semiconductor processing.
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A pneumatic diaphragm bursting mechanism was implemented in the University of Central Florida shock tube to improve control over reflected shock conditions. The mechanism was tested with Lexan and Mylar diaphragm materials. The My...
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A pneumatic diaphragm bursting mechanism was implemented in the University of Central Florida shock tube to improve control over reflected shock conditions. The mechanism was tested with Lexan and Mylar diaphragm materials. The Mylar diaphragms had a thickness of 0.05 mm. The Lexan diaphragms had a thickness of 0.13 mm. The pressure-time history plot for an experiment with a reflected shock pressure was 0.29 bar is included. Reflected shock temperatures of 1767 K and 1808 K were achieved. The mechanism expanded the range of achievable conditions to include those relevant to sub-orbital flight. This work extends to the investigation of low-pressure, high-temperature gas dynamics, such as those found in hypersonic flight and re-entry conditions to validate models for rocket plumes.
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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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