摘要 :
Laminar burning speeds and flame structures of spherically expanding flames of mixtures of H_2/CO with air have been studied over a wide range of temperatures, pressures, equivalence ratios and mixing ratios of H_2/CO. Experiments...
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Laminar burning speeds and flame structures of spherically expanding flames of mixtures of H_2/CO with air have been studied over a wide range of temperatures, pressures, equivalence ratios and mixing ratios of H_2/CO. Experiments have been conducted in a constant volume cylindrical vessel. Laminar burning speed was measured using a thermodynamic model employing the dynamic pressure rise during the flame propagation in the vessels. The cylindrical vessel was installed in a shadowgraph system equipped with a high speed CMOS camera, capable of taking pictures up to 40,000 frames per second, to study the structure of propagating flame. Experiments were performed on the mixtures with initial pressure of 1 and 2 atm and initial temperatures of 298 to 500 K for a wide range of mixing ratios. Ratio of Hydrogen in the H_2/CO mixture was varied from 5% to 30% and the range of fuel air equivalence ratios covered from 1 to 5. Burning speeds were measured for up to 670 K and 4.2 atm. Burning speed measurements have only been reported for laminar and smooth flames.
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Laminar burning speed calculation at high pressures is challenging because of unstable surface conditions at large flame kernel diameters. It is therefore desired to take these measurements at small dimensions (i.e., during and im...
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Laminar burning speed calculation at high pressures is challenging because of unstable surface conditions at large flame kernel diameters. It is therefore desired to take these measurements at small dimensions (i.e., during and immediately after the ignition discharge process) when the flame kernel is smooth and stable. Taking accurate measurements at these sizes is challenging because the kernel growth rate does not only depend on the chemical reaction but also on other phenomena such as energy discharge, as well as radiative and conductive energy losses. The effect of these events has not been adequately assessed, due to the generation of ionized gas (i.e., plasma). In order to better understand the effect of the ignition plasma in this work, spark ignition in air for 1-5 atm of pressure is studied. Understanding the ignition event and modeling its behavior is important to capture accurate combustion measurements at pressures pertinent to the advanced high-pressure engines and technologies. The relationship between the electrical energy supplied to the spark and the thermal energy dissipated within a gas mixture has been studied. This work relates the electrical discharge power to the volume of the ignition kernel measured via schlieren imagery. Voltage and current data are also captured as the input to a thermodynamic model which is used to predict the volume versus time data of the spark event. The model, which utilizes measured electrical power, thermodynamic properties of ionized air, and radiation losses in air show agreement with the experimental kernel measurements in terms of overall shape of the volume data within the measured kernel uncertainty. With these results and further experimental validation the present model is considered to represent the relationship between the electrical spark power and the measured ignition kernel volume. Future work will be done to determine inaccuracies present in the arc discharge regime as well as the effectiveness of the model in combustible media.
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摘要 :
Laminar burning speed calculation at high pressures is challenging because of unstable surface conditions at large flame kernel diameters. It is therefore desired to take these measurements at small dimensions (i.e., during and im...
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Laminar burning speed calculation at high pressures is challenging because of unstable surface conditions at large flame kernel diameters. It is therefore desired to take these measurements at small dimensions (i.e., during and immediately after the ignition discharge process) when the flame kernel is smooth and stable. Taking accurate measurements at these sizes is challenging because the kernel growth rate does not only depend on the chemical reaction but also on other phenomena such as energy discharge, as well as radiative and conductive energy losses. The effect of these events has not been adequately assessed, due to the generation of ionized gas (i.e., plasma). In order to better understand the effect of the ignition plasma in this work, spark ignition in air for 1-5 atm of pressure is studied. Understanding the ignition event and modeling its behavior is important to capture accurate combustion measurements at pressures pertinent to the advanced high-pressure engines and technologies. The relationship between the electrical energy supplied to the spark and the thermal energy dissipated within a gas mixture has been studied. This work relates the electrical discharge power to the volume of the ignition kernel measured via schlieren imagery. Voltage and current data are also captured as the input to a thermodynamic model which is used to predict the volume versus time data of the spark event. The model, which utilizes measured electrical power, thermodynamic properties of ionized air, and radiation losses in air show agreement with the experimental kernel measurements in terms of overall shape of the volume data within the measured kernel uncertainty. With these results and further experimental validation the present model is considered to represent the relationship between the electrical spark power and the measured ignition kernel volume. Future work will be done to determine inaccuracies present in the arc discharge regime as well as the effectiveness of the model in combustible media.
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The change in laminar burning speed and ignition delay time of iso-octane with the addition of oxygenated fuels are investigated. As oxygenated fuels, ethanol and 2,5 dimethyle furan (DMF) are used. To confirm the process and mech...
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The change in laminar burning speed and ignition delay time of iso-octane with the addition of oxygenated fuels are investigated. As oxygenated fuels, ethanol and 2,5 dimethyle furan (DMF) are used. To confirm the process and mechanism a detailed validation is done on laminar burning speed and ignition delay time. Further, three different blending ratios of 5%, 25% and 50% for both ethanol/iso-octane and DMF/isooctane are investigated separately. Wide range of equivalence ratio from 0.6-1.4 is considered in calculating laminar burning speed. Ignition delay time is measured under various temperatures from 650 K to 1100 K. Results of each blending are compared with the pure fuels. A comparison is also done between the effects of these two oxygenates. It has found that for each blending case presence of DMF brings larger change in the behavior of iso-octane than ethanol. This observation refers to further study on comparison of these two oxygenates.
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摘要 :
The change in laminar burning speed and ignition delay time of iso-octane with the addition of oxygenated fuels are investigated. As oxygenated fuels, ethanol and 2,5 dimethyle furan (DMF) are used. To confirm the process and mech...
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The change in laminar burning speed and ignition delay time of iso-octane with the addition of oxygenated fuels are investigated. As oxygenated fuels, ethanol and 2,5 dimethyle furan (DMF) are used. To confirm the process and mechanism a detailed validation is done on laminar burning speed and ignition delay time. Further, three different blending ratios of 5%, 25% and 50% for both ethanol/iso-octane and DMF/iso-octane are investigated separately. Wide range of equivalence ratio from 0.6-1.4 is considered in calculating laminar burning speed. Ignition delay time is measured under various temperatures from 650 K to 1100 K. Results of each blending are compared with the pure fuels. A comparison is also done between the effects of these two oxygenates. It has found that for each blending case presence of DMF brings larger change in the behavior of iso-octane than ethanol. This observation refers to further study on comparison of these two oxygenates.
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This study presents fundamentals of spray and partially premixed combustion characteristics of directly injected methane inside a constant volume combustion chamber (CVCC). The constant volume vessel is a cylinder with inside diam...
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This study presents fundamentals of spray and partially premixed combustion characteristics of directly injected methane inside a constant volume combustion chamber (CVCC). The constant volume vessel is a cylinder with inside diameter of 135 mm and inside height of 135 mm. Two end of the vessel are equipped with optical windows. A high speed complementary metal oxide semiconductor (CMOS) camera capable of capturing pictures up to 40,000 frames per second is used to observe flow conditions inside the chamber. The injected fuel jet generates turbulence in the vessel and forms a turbulent heterogeneous fuel-air mixture in the vessel, similar to that in a compressed natural gas (CNG) direct injection engine. The fuel-air mixture is ignited by centrally located electrodes at a given spark delay timing of 1, 40, 75 and 110 milliseconds after fuel injection has been completed to reflect different turbulence intensities. For comparative study, by increasing the spark delay timing to five minutes, a homogeneous premixed mixture is also prepared in the vessel which provides information on laminar homogeneous mixture combustion. Spray development and characterization including spray tip penetration, spray cone angle and overall equivalence ratio were investigated under 30-90 bar fuel pressures and 1-5 bar chamber pressure. Flame propagation images and combustion characteristics were determined via pressure-derived parameters and analyzed at a fuel pressure of 90 bar and a chamber pressure of 1 bar at different stratification ratios (from 0% to 100%) at overall equivalence ratios of 0.6, 0.8 and 1.0. Shorter combustion duration and higher combustion pressure were observed in direct injection-type combustion at all fuel air equivalence ratios compared to those of homogenous combustion.
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摘要 :
This study presents fundamentals of spray and partially premixed combustion characteristics of directly injected methane inside a constant volume combustion chamber (CVCC). The constant volume vessel is a cylinder with inside diam...
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This study presents fundamentals of spray and partially premixed combustion characteristics of directly injected methane inside a constant volume combustion chamber (CVCC). The constant volume vessel is a cylinder with inside diameter of 135 mm and inside height of 135 mm. Two end of the vessel are equipped with optical windows. A high speed complementary metal oxide semiconductor (CMOS) camera capable of capturing pictures up to 40,000 frames per second is used to observe flow conditions inside the chamber. The injected fuel jet generates turbulence in the vessel and forms a turbulent heterogeneous fuel-air mixture in the vessel, similar to that in a compressed natural gas (CNG) direct injection engine. The fuel-air mixture is ignited by centrally located electrodes at a given spark delay timing of 1, 40, 75 and 110 milliseconds after fuel injection has been completed to reflect different turbulence intensities. For comparative study, by increasing the spark delay timing to five minutes, a homogeneous premixed mixture is also prepared in the vessel which provides information on laminar homogeneous mixture combustion. Spray development and characterization including spray tip penetration, spray cone angle and overall equivalence ratio were investigated under 30-90 bar fuel pressures and 1-5 bar chamber pressure. Flame propagation images and combustion characteristics were determined via pressure-derived parameters and analyzed at a fuel pressure of 90 bar and a chamber pressure of 1 bar at different stratification ratios (from 0% to 100%) at overall equivalence ratios of 0.6, 0.8 and 1.0. Shorter combustion duration and higher combustion pressure were observed in direct injection-type combustion at all fuel air equivalence ratios compared to those of homogenous combustion.
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Measurements of a propagating flame are crucial to the understanding and verification of important flame phenomena. Specifically, laminar, unstretched flame speed is employed to describe complex flame behavior such as turbulence o...
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Measurements of a propagating flame are crucial to the understanding and verification of important flame phenomena. Specifically, laminar, unstretched flame speed is employed to describe complex flame behavior such as turbulence or stability. This data is necessary because advanced and more efficient combustion devices operate at these high pressures where this data is less reliable from the onset of flame instabilities. This research aims to develop a new flame speed measurement technique as an improvement over the traditional method. The analysis utilizes a constant pressure technique where the velocity of a spherical flame is visually measured. Flame propagation of stoichiometric flame from 1-6 atm are examined at radius up to 20mm at 300K. The novel analysis method incorporates flame data which is ignition affected to improve the traditional constant pressure methods. This allows for with the inclusion of ultra-small, highly stretched flame radii (0-10 mm). Electrical measurements of the ignition are utilized with a thermodynamic model to predict the velocity and temperature which result from plasma formation. This predicted temperature is used describe the influence ignition has on the flame velocity and is compared to the traditional adiabatic flame propagation over the radius observed. The extrapolated laminar burning speed measurement is found for both traditional and novel methods where the novel method has the benefit of additional, previously unused, flame propagation at the high stretch regime. Additionally, practical information about the plasma morphology, crucial to the experimental application of this method is also discussed.
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Reducing the size of a detail chemical kinetic is necessary in the prospect of numerical computation. In this work a skeleton reduction is done on a detail mechanism of ethanol. The detailed ethanol mechanism used here is develope...
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Reducing the size of a detail chemical kinetic is necessary in the prospect of numerical computation. In this work a skeleton reduction is done on a detail mechanism of ethanol. The detailed ethanol mechanism used here is developed through reaction mechanism generator (RMG). The generated mechanism is validated at wide range of engine relevant operating conditions using laminar burning speed (LBS), ignition delay time (IDT) and species mole fraction calculation at different reactor conditions. This detail mechanism consists of 67 species and 1031 reactions. Though the mechanism is in a very good agreement at various operating ranges with experimental data, it is costly to use a detail mechanism for 3D computational fluid dynamics (CFD) analysis. To make the mechanism applicable for CFD simulation further reduction of species and reactions is essential. In this work a skeleton mechanism is generated using directed relation graph technique with error propagation and sensitivity analysis (DRGEPSA). The DRGEPSA method, works based on error calculation at user defined condition. This technique is a combination of two methods, directed relation graph with error propagation (DRGEP) and directed relation graph with sensitivity analysis (DRGASA). To ensure the wide range of applicability of the skeleton mechanism, IDT is calculated at temperature, pressure, and equivalence ratio ranges from 700-2000 K, 1-40 atm and 0.6-1.4 respectively. A 10% error estimation is considered during the process. Initially DRGEP is applied on the detail mechanism to eliminate unimportant species. Further, sensitivity analysis helps to identify and reduce more unimportant species from the mechanism. Reactions related to the deleted species are automatically removed from the mechanism in each step. The final skeleton mechanism has 42 species and 464 reactions. This skeleton mechanism is validated and compared with different IDT data for the conditions not used in reduction technique. Results of LBS and different species concentration from reactor conditions is considered for validation. The skeleton mechanism can reduce computational time by 35% for LBS and 25% for IDT calculation. For future work, this skeleton mechanism will be considered in optimum reduction process.
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The effects of hydrogen addition, diluent addition, injection pressure, chamber pressure, chamber temperature and turbulence intensity on methane-air partially premixed turbulent combustion have been studied experimentally using a...
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The effects of hydrogen addition, diluent addition, injection pressure, chamber pressure, chamber temperature and turbulence intensity on methane-air partially premixed turbulent combustion have been studied experimentally using a constant volume combustion chamber (CVCC). The fuel-air mixture was ignited by centrally located electrodes at given spark delay times of 1, 5, 40, 75 and 110 milliseconds. Experiments were performed for a wide range of hydrogen volumetric fractions (0% to 40%), exhaust gas recirculation (EGR) volumetric fractions (0% to 25% as a diluent), injection pressures (30-90 bar), chamber pressures (1-3 bar), chamber temperatures (298-432 K) and overall equivalence ratios of 0.6, 0.8, and 1.0. Flame propagation images via the Sclieren/Shadowgraph technique, combustions characteristics via pressure derived parameters and pollutant concentrations were analyzed for each set of conditions. The results showed that peak pressure and maximum rate of pressure rise increased with the increase in chamber pressure and temperature while changing injection pressure had no considerable effect on pressure and maximum rate of pressure rise. The peak pressure and maximum rate of pressure rise increased while combustion duration decreased with simultaneous increase of hydrogen content. The lean burn limit of methane-air turbulent combustion was improved with hydrogen addition. Addition of EGR increased combustion instability and misfiring while decreasing the emission of nitrogen oxides (NO_x).
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