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Author: Richard Copeland Publisher: ISBN: Category : Hydrocarbons Languages : en Pages : 0
Book Description
Detection of chemically important transient species is crucial to understanding the mechanism of hydrocarbon combustion. Though they often occur in low concentrations, these species determine the pathways and rates of many reaction steps. In this report we describe our efforts to develop and quantify diagnostic methods to measure these species in flames. We will describe methods to detect CH, CH3, C2H2, CH2, and HO2; the first four species have successfully been observed in flames during this project. The detection techniques we use are laser-induced fluorescence (LIF) and absorption techniques including photoacoustic detection spectroscopy (PAD). The polyatomic molecules mentioned above are much more difficult to detect than the diatomic molecules CH and OH, and we have developed and used new variations on the basic techniques to achieve the desired sensitivity. In this research, we improved diagnostic techniques for the radicals mentioned above, detected species not previously observed in the flame environment, and increased our knowledge of the important species in hydrocarbon combustion.
Author: Richard Copeland Publisher: ISBN: Category : Hydrocarbons Languages : en Pages : 0
Book Description
Detection of chemically important transient species is crucial to understanding the mechanism of hydrocarbon combustion. Though they often occur in low concentrations, these species determine the pathways and rates of many reaction steps. In this report we describe our efforts to develop and quantify diagnostic methods to measure these species in flames. We will describe methods to detect CH, CH3, C2H2, CH2, and HO2; the first four species have successfully been observed in flames during this project. The detection techniques we use are laser-induced fluorescence (LIF) and absorption techniques including photoacoustic detection spectroscopy (PAD). The polyatomic molecules mentioned above are much more difficult to detect than the diatomic molecules CH and OH, and we have developed and used new variations on the basic techniques to achieve the desired sensitivity. In this research, we improved diagnostic techniques for the radicals mentioned above, detected species not previously observed in the flame environment, and increased our knowledge of the important species in hydrocarbon combustion.
Author: Richard Copeland Publisher: ISBN: Category : Hydrocarbons Languages : en Pages : 504
Book Description
Detection of chemically important transient species is crucial to understanding the mechanism of hydrocarbon combustion. Though they often occur in low concentrations, these species determine the pathways and rates of many reaction steps. In this report we describe our efforts to develop and quantify diagnostic methods to measure these species in flames. We will describe methods to detect CH, CH3, C2H2, CH2, and HO2; the first four species have successfully been observed in flames during this project. The detection techniques we use are laser-induced fluorescence (LIF) and absorption techniques including photoacoustic detection spectroscopy (PAD). The polyatomic molecules mentioned above are much more difficult to detect than the diatomic molecules CH and OH, and we have developed and used new variations on the basic techniques to achieve the desired sensitivity. In this research, we improved diagnostic techniques for the radicals mentioned above, detected species not previously observed in the flame environment, and increased our knowledge of the important species in hydrocarbon combustion.
Author: Alan C. Eckbreth Publisher: CRC Press ISBN: 9789056995324 Category : Technology & Engineering Languages : en Pages : 636
Book Description
Focusing on spectroscopically-based, spatially-precise, laser techniques for temperature and chemical composition measurements in reacting and non-reacting flows, this book makes these powerful and important new tools in combustion research
Author: Wendong Wu Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 175
Book Description
Increasing concerns about air pollution and global climate change are drawing attention to the need for efficiency improvements and emission reductions for combustion processes, which account for more than 85% of energy production in United States. Combustion efficiency and emissions are affected by the mixing and reacting of fuel and oxidizer. Understanding such behavior plays a critical role in flame structure studies and combustion optimization. However, experimentally obtaining mixture fraction, which is a widely used quantity to describe the mixing behavior, has proven to be a challenge, especially for heavier hydrocarbon fuels or fuel rich flames. Moreover, measuring flame temperature simultaneously with mixture fraction adds complexity into the experimental setup. In this dissertation, laser plasma diagnostics techniques were developed to provide a straightforward method to simultaneously obtain composition and temperature measurements. The capability of these novel techniques is applicable to more complex fuels and a broader range of equivalence ratios than has heretofore been possible, and facilitates a better understanding of flame structure.Laser-induced breakdown spectroscopy (LIBS) is proposed as an alternative method of measuring mixture fraction. A back-scattering setup is utilized to mitigate the beam steering effects in non-uniform and unsteady flames. The calibration for the LIBS system was completed in an ethylene-air premixed flame under a broad range of equivalence ratios. The elemental species distributions for H, C, N, O were measured in a counter-flow diffusion flame. The measured mixture fraction compared favorably with the numerical results from OPPDIF flame code. On the basis of LIBS measured elemental species profile, the preferential diffusion effect was analyzed.Utilizing the sound emission from laser-induced plasmas, acoustic-based laser induced breakdown thermometry (LIBT) was developed as a novel method for flame temperature measurement. The established correlation between the optical emission and acoustic emission in a premixed flame demonstrated that the acoustic signal can serve as an internal standard in the gas phase LIBS measurement. The influences of flame temperature and composition on the acoustic signal were investigated independently. The composition effect was found to be second order comparing to the temperature effect. The statistics of the LIBT measurement were also analyzed to better understand the distribution of samples. Furthermore, the temperature and gas density distributions in a counter-flow diffusion flame were measured using LIBT and were found to compare favorably with numerical results. To evaluate the possibility of simultaneous composition and temperature measurement using laser plasma diagnostics, the spatial and temporal resolutions of LIBS and LIBT were carefully examined. The accuracy of LIBT technique was analyzed as a function of sample size from a statistical perspective. The results demonstrated that LIBT has spatial and temporal resolutions comparable to that of LIBS. Finally, a preliminary study using a Burke- Schumann flame and a Hencken burner was performed to understand the influence of turbulent flow.Measuring composition and temperature simultaneously using laser plasma diagnostics provides substantial benefits over traditional measurement technique. However, in exchange for such benefits, information on major species concentrations can no longer be directly measured. To infer the molecular species profile from the elemental species profile, the underlying partial-equilibrium assumption was examined. Among partially-equilibrated reactions, the water-gas shift (WGS) reaction is most often assumed to be in equilibrium because of its important role in the high temperature zone. Thus, the equilibrium domain of WGS reaction was systematically studied in different hydrocarbon flames under varying strain rates to evaluate the validity of partial equilibrium assumption. The underlying mechanism for WGS-equilibrium was also examined. The results suggested that even though the WGS reaction has a broad partial-equilibrium domain in syngas, methane, ethylene and propane flames, the mechanisms responsible for partial equilibrium were very different. In hydrocarbon flames, the water-gas-shift reaction can achieve partial equilibrium even though the two elementary reactions behind it are not equilibrated.
Author: Galen B. King Publisher: ISBN: Category : Languages : en Pages : 31
Book Description
This report describes progress on the development of a new laser based combustion diagnostic method for the quantitative measurement of both major and minor species in high pressure flames. The technique, Asynchronous Optical Sampling (ASOPS), is a state of the art improvement in picosecond pump/probe laser spectroscopy. The ASOPS signal has been observed using a solution of rhodamine B in methanol as the sample. The response of the instrument was shown to be proportional to pump power, probe power, and sample absorptance. Different frequency synthesizers and different modes of triggering were used to study their effect on signal stability. Cavity dumpers and frequency doublers have been added to the instrument to prepare for the measurement of the hydroxyl radical in atmosphere laminar flames.
Author: L. P. Goss Publisher: ISBN: Category : Combustion Languages : en Pages : 287
Book Description
Coherent anti-Stokes Raman spectroscopy (CARS) instruments have been developed for simultaneous measurement of temperature and species concentrations in turbulent-diffusion, sooty hydrocarbon flames. Contour maps of average temperature, rms temperature, average concentration, and rms concentration have been obtained on a laboratory-scale burner. Simultaneous N2 and O2 measurements by the CARS technique were made with a dual-dye-laser setup. A combination of the laboratory CARS system and a laser-Doppler-velocimetry (LVD) system was completed and tested on a Busen-burner premixed flame. Measurements indicated that simultaneously obtained velocity and temperature data were Favre averaged due to density weighting of the seed particles. Temperature-velocity correlations were obtained and compared to literature values on similar burners obtained with a combined fine-wire thermocouple and LDV. Normal-gradient and counter-gradient transport were observed in the premixed flame. An environmentally hardened CARS system was developed and employed to measure temperatures in the near-wake recirculating-flow region of a bluff-body-stabilized diffusion flame. Time-averaged temperature profiles and probability distribution functions were obtained and interpreted in terms of flow-field characteristics. A comparison of temperature data obtained by means of the CARS technique and using three thermocouples of different design was made. This comparison indicated that the physical design of the thermocouple probe is important and may influence the flow and, thus, the temperature.
Author: Richard Copeland
Author: Richard Copeland
Author: Richard Copeland
Author: Alan C. Eckbreth
Author: Bo Tian
Author: James Henry Werner
Author: Wendong Wu
Author: Galen B. King
Author: Kazuo Iinuma
Author: David Matthew Mosbacher
Author: L. P. Goss