The Experts below are selected from a list of 190218 Experts worldwide ranked by ideXlab platform
Zuohua Huang - One of the best experts on this subject based on the ideXlab platform.
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effects of fuel composition and Initial Pressure on laminar flame speed of h2 co ch4 bio syngas
Fuel, 2019Co-Authors: Quan Zhou, Chun Shun Cheung, C W Leung, Zuohua HuangAbstract:Abstract Biomass-derived syngas composition varies considerably depending on different feedstocks and processing techniques and thereby complicates the combustion control. A study on the effects of variations in the fuel composition and Initial Pressure on the characteristics of premixed H2/CO/CH4 flames was conducted using the spherical expanding flame method and CHEMIKIN package. Experimental measurements and numerical simulations were performed at an Initial temperature of 303 K, equivalence ratios of 0.6–1.5 and Pressures of 0.1–0.5 MPa with a wide range of H2/CO/CH4 compositions. The thermal and chemical kinetic analyses are also presented. The measured laminar flame speed was compared with simulations using the Li mechanism. The experimental data show a reasonable agreement with the calculated values, especially at fuel-lean and low Pressure conditions. With the increase of H2 fraction in the fuel, the laminar flame speed increases significantly, but for the CH4 enrichment flame, the behavior is quite the contrary that it has the lowest laminar flame speed. With the increase of CO fraction in the fuel, the laminar flame speed does not change much. The thermal and chemical kinetic analyses indicate that the CO addition has more effect on the adiabatic flame temperature but only plays a small role in the chemical effect compared to that of the H2 addition. On the other hand, at elevated Pressures, the Li mechanism gives slight overestimations for lean mixtures but underestimations for rich mixtures. The laminar flame speed decreases with the increase of Initial Pressure under tested equivalence ratio which is mainly due to the increasing unburned mixture density and decreasing H, OH radicals concentrations.
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comparative study on the explosion characteristics of pentanol isomer air mixtures
Fuel, 2015Co-Authors: Yu Cheng, Wu Jin, Zuohua HuangAbstract:Abstract A comparative study was experimentally performed on the explosion characteristics of four pentanol isomer–air mixtures (n-pentanol, 3-methyl-1-butanol, 2-methyl-1-butanol, 2-methyl-2-butanol), at various Initial temperatures and Initial Pressures. The explosion parameters of explosion Pressure, maximum rate of Pressure rise, combustion duration and combustion development period were measured. The influence of Initial conditions on the explosion characteristics were discussed. Results show that the peak explosion Pressure is linear function of the reciprocal of Initial temperature, but the maximum rate of Pressure rise is insensitive to the temperature variation. With the Initial Pressure elevated from 0.1 to 0.25 MPa, the peak explosion Pressure increases significantly, but the increase rate is decelerated when the Pressure is further increased. Among the four pentanol isomer–air mixtures, in the order of n-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol and 2-methyl-2-butanol, the peak explosion Pressure and maximum rate of Pressure rise decrease while the combustion duration and flame development period increase, reflecting the decreasing flame speed. Difference among the isomers tends to be decreased for the peak explosion Pressure while increased for the maximum rate of Pressure rise with the increase of Initial Pressure. Pressure oscillation occurs at the rich mixture and high Pressure, resulting in short combustion duration, but influencing the flame development period little.
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experimental and numerical study on laminar burning velocities and flame instabilities of hydrogen air mixtures at elevated Pressures and temperatures
International Journal of Hydrogen Energy, 2009Co-Authors: Zuohua Huang, Haiyan MiaoAbstract:Experimental and numerical study on hydrogen–air flames at elevated Pressures and temperatures was conducted. Meanwhile, the calculation is extended to Initial Pressure and temperature up to 8.0 MPa and 950 K, respectively. Laminar burning velocities and Markstein lengths were obtained at the elevated Pressures and temperatures. Sensitivity analysis and flame structure were also analyzed. The results show good agreement between the computed results and experimental data. The study shows that laminar burning velocities are increased with the increase of Initial temperature, and they decrease with the increase of Initial Pressure. With the increase of Initial Pressure, advancement of the onset of cellular instability is presented and Markstein length is decreased, indicating an increase of flame instability with the increase of Initial Pressure. The study shows insensitivity of flame instability to Initial temperature. Laminar burning velocity is depended on the competition between the main chain branching reactions and chain termination reaction. The chain branching reactions are the temperature-sensitive reaction, while the termination reaction is the temperature-insensitive reaction. Through the extraction of the overall reaction orders, it is demonstrated that with increasing Pressure, the overall reaction orders give a decreasing trend and then increasing trend. This behavior suggests an analogy to three explosion limits of hydrogen/oxygen mixtures. Numerical study also shows that the suppression (or enhancement) of overall chemical reaction with the increase of Initial Pressure (or temperature) is closely linking to the decrease (or increase) of H, O and OH mole fractions in the flames. Strong correlation is existed between burning velocity and maximum radical concentrations of H and OH radicals in the reaction zone of premixed flames. On the basis of the numerical data, an empirical formula for laminar burning velocity is correlated for the hydrogen–air premixed mixture at elevated Pressures and temperatures. The correlated laminar burning velocities are in good agreement with the known experimental results and simulated results with CHEMKIN. The correlation can be used in the calculation of laminar burning velocities at evaluated Pressures and temperatures.
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measurements of laminar burning velocities and onset of cellular instabilities of methane hydrogen air flames at elevated Pressures and temperatures
International Journal of Hydrogen Energy, 2009Co-Authors: Zuohua Huang, Jianjun Zheng, Haiyan MiaoAbstract:An experimental study on laminar burning velocities and onset of cellular instabilities of the premixed methane–hydrogen–air flames was conducted in a constant volume combustion vessel at elevated Pressures and temperatures. The unstretched laminar burning velocity and Markstein length were obtained over a wide range of hydrogen fractions. Besides, the effects of hydrogen addition, Initial Pressure and Initial temperature on flame instabilities were analyzed. The results show that the unstretched flame propagation speed and the unstretched laminar burning velocity are increased with the increase of Initial temperature and hydrogen fraction, and they are decreased with the increase of Initial Pressure. Early onset of cellular instability is presented and the critical radius and Markstein length are decreased with the increase of Initial Pressure, indicating the increase of hydrodynamic instability with the increase of Initial Pressure. Flame instability is insensitive to Initial temperature compared to Initial Pressure. With the increase of hydrogen fraction, significant decrease in critical radius and Markstein length is presented, indicating the increase in both diffusional-thermal and hydrodynamic instabilities as hydrogen fraction is increased.
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laminar burning velocity and markstein length of nitrogen diluted natural gas hydrogen air mixtures at normal reduced and elevated Pressures
International Journal of Hydrogen Energy, 2009Co-Authors: Qi Jiao, Haiyan Miao, Qian Huang, Zuohua HuangAbstract:Abstract Flame propagation of premixed nitrogen diluted natural gas/hydrogen/air mixtures was studied in a constant volume combustion bomb under various Initial Pressures. Laminar burning velocities and Markstein lengths were obtained for the diluted stoichiometric fuel/air mixtures with different hydrogen fractions and diluent ratios under various Initial Pressures. The results showed that both unstretched flame speed and unstretched burning velocity are reduced with the increase in Initial Pressure (except when the hydrogen fraction is 80%) as well as diluent ratio. The velocity reduction rate due to diluent addition is determined mainly by hydrogen fraction and diluent ratio, and the effect of Initial Pressure is negligible. Flame stability was studied by analyzing Markstein length. It was found that the increase of Initial Pressure and hydrogen fraction decreases flame stability and the flame tends to be more stable with the addition of diluent gas. Generally speaking, Markstein length of a fuel with low hydrogen fraction is more sensitive to the change of Initial Pressure than that of a one with high hydrogen fraction.
Haiyan Miao - One of the best experts on this subject based on the ideXlab platform.
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experimental and numerical study on laminar burning velocities and flame instabilities of hydrogen air mixtures at elevated Pressures and temperatures
International Journal of Hydrogen Energy, 2009Co-Authors: Zuohua Huang, Haiyan MiaoAbstract:Experimental and numerical study on hydrogen–air flames at elevated Pressures and temperatures was conducted. Meanwhile, the calculation is extended to Initial Pressure and temperature up to 8.0 MPa and 950 K, respectively. Laminar burning velocities and Markstein lengths were obtained at the elevated Pressures and temperatures. Sensitivity analysis and flame structure were also analyzed. The results show good agreement between the computed results and experimental data. The study shows that laminar burning velocities are increased with the increase of Initial temperature, and they decrease with the increase of Initial Pressure. With the increase of Initial Pressure, advancement of the onset of cellular instability is presented and Markstein length is decreased, indicating an increase of flame instability with the increase of Initial Pressure. The study shows insensitivity of flame instability to Initial temperature. Laminar burning velocity is depended on the competition between the main chain branching reactions and chain termination reaction. The chain branching reactions are the temperature-sensitive reaction, while the termination reaction is the temperature-insensitive reaction. Through the extraction of the overall reaction orders, it is demonstrated that with increasing Pressure, the overall reaction orders give a decreasing trend and then increasing trend. This behavior suggests an analogy to three explosion limits of hydrogen/oxygen mixtures. Numerical study also shows that the suppression (or enhancement) of overall chemical reaction with the increase of Initial Pressure (or temperature) is closely linking to the decrease (or increase) of H, O and OH mole fractions in the flames. Strong correlation is existed between burning velocity and maximum radical concentrations of H and OH radicals in the reaction zone of premixed flames. On the basis of the numerical data, an empirical formula for laminar burning velocity is correlated for the hydrogen–air premixed mixture at elevated Pressures and temperatures. The correlated laminar burning velocities are in good agreement with the known experimental results and simulated results with CHEMKIN. The correlation can be used in the calculation of laminar burning velocities at evaluated Pressures and temperatures.
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measurements of laminar burning velocities and onset of cellular instabilities of methane hydrogen air flames at elevated Pressures and temperatures
International Journal of Hydrogen Energy, 2009Co-Authors: Zuohua Huang, Jianjun Zheng, Haiyan MiaoAbstract:An experimental study on laminar burning velocities and onset of cellular instabilities of the premixed methane–hydrogen–air flames was conducted in a constant volume combustion vessel at elevated Pressures and temperatures. The unstretched laminar burning velocity and Markstein length were obtained over a wide range of hydrogen fractions. Besides, the effects of hydrogen addition, Initial Pressure and Initial temperature on flame instabilities were analyzed. The results show that the unstretched flame propagation speed and the unstretched laminar burning velocity are increased with the increase of Initial temperature and hydrogen fraction, and they are decreased with the increase of Initial Pressure. Early onset of cellular instability is presented and the critical radius and Markstein length are decreased with the increase of Initial Pressure, indicating the increase of hydrodynamic instability with the increase of Initial Pressure. Flame instability is insensitive to Initial temperature compared to Initial Pressure. With the increase of hydrogen fraction, significant decrease in critical radius and Markstein length is presented, indicating the increase in both diffusional-thermal and hydrodynamic instabilities as hydrogen fraction is increased.
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laminar burning velocity and markstein length of nitrogen diluted natural gas hydrogen air mixtures at normal reduced and elevated Pressures
International Journal of Hydrogen Energy, 2009Co-Authors: Qi Jiao, Haiyan Miao, Qian Huang, Zuohua HuangAbstract:Abstract Flame propagation of premixed nitrogen diluted natural gas/hydrogen/air mixtures was studied in a constant volume combustion bomb under various Initial Pressures. Laminar burning velocities and Markstein lengths were obtained for the diluted stoichiometric fuel/air mixtures with different hydrogen fractions and diluent ratios under various Initial Pressures. The results showed that both unstretched flame speed and unstretched burning velocity are reduced with the increase in Initial Pressure (except when the hydrogen fraction is 80%) as well as diluent ratio. The velocity reduction rate due to diluent addition is determined mainly by hydrogen fraction and diluent ratio, and the effect of Initial Pressure is negligible. Flame stability was studied by analyzing Markstein length. It was found that the increase of Initial Pressure and hydrogen fraction decreases flame stability and the flame tends to be more stable with the addition of diluent gas. Generally speaking, Markstein length of a fuel with low hydrogen fraction is more sensitive to the change of Initial Pressure than that of a one with high hydrogen fraction.
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measurements of laminar burning velocities and markstein lengths of propane hydrogen air mixtures at elevated Pressures and temperatures
International Journal of Hydrogen Energy, 2008Co-Authors: Chenglong Tang, Zuohua Huang, Chun Jin, Jinhua Wang, Xibin Wang, Haiyan MiaoAbstract:Abstract Experimental study on the laminar burning velocities and the onset of cellular instabilities of propane–hydrogen–air mixtures with spherically expanding flames was conducted at elevated Pressures and temperatures and different hydrogen fractions at the equivalence ratio of 0.8 and 1.2. The results show that the unstretched flame propagation speed and the unstretched laminar burning velocity increase with the increase of hydrogen fraction and Initial temperature, and they decrease with the increase of Initial Pressure. An earlier onset of cellular instability and the decrease in the critical radius and the Markstein length are presented with the increase of Initial Pressure, indicating that the hydrodynamic instability is enhanced with the increase of Initial Pressure. At the equivalence ratio of 0.8, where the propane–air mixture is thermal-diffusionally stable and the hydrogen–air mixture is thermal-diffusionally unstable, the critical radius and the Markstein length decrease significantly with the increase of hydrogen fraction, indicating that hydrogen addition will increase the diffusional-thermal and the hydrodynamic instability. At equivalence ratio of 1.2, where the propane–air mixture and hydrogen–air mixture are both thermal-diffusionally neutral, a moderate decrease in the critical radius and the Markstein length is presented. This indicates the increase of hydrodynamic instability as hydrogen is added.
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effect of Initial Pressure on laminar combustion characteristics of hydrogen enriched natural gas
International Journal of Hydrogen Energy, 2008Co-Authors: Haiyan Miao, Zuohua Huang, Qi Jiao, Deming JiangAbstract:Abstract Flame propagation of premixed natural gas–hydrogen–air mixtures was studied in a constant volume combustion bomb. Laminar burning velocities and mass burning fluxes were obtained under various hydrogen fractions and equivalence ratios with various Initial Pressures, while flame stability and their influencing factors (Markstein length, density ratio and flame thickness) were obtained by analyzing the flame images at various hydrogen fractions, Initial Pressures and equivalence ratios. The results show that hydrogen fraction, Initial Pressure as well as equivalence ratio have combined influence on both unstretched laminar burning velocity and flame instability. Meanwhile, according to flame propagation pictures taken by the high speed camera, flame stability decreases with the increase of Initial Pressures; for given equivalence ratio and hydrogen fraction, flame thickness is more sensitive to the variation of the Initial Pressure than to that of the density ratio.
Mark A Anastasio - One of the best experts on this subject based on the ideXlab platform.
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parameterized joint reconstruction of the Initial Pressure and sound speed distributions for photoacoustic computed tomography
Siam Journal on Imaging Sciences, 2018Co-Authors: Thomas P Matthews, Joemini Poudel, Lihong V Wang, Mark A AnastasioAbstract:Accurate estimation of the Initial Pressure distribution in photoacoustic computed tomography (PACT) depends on knowledge of the sound speed distribution. However, the sound speed distribution is t...
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parameterized joint reconstruction of the Initial Pressure and sound speed distributions in photoacoustic computed tomography conference presentation
Photons Plus Ultrasound: Imaging and Sensing 2018, 2018Co-Authors: Thomas P Matthews, Joemini Poudel, Lihong V Wang, Mark A AnastasioAbstract:Accurate estimation of the Initial Pressure distribution in photoacoustic computed tomography (PACT) requires some knowledge of the sound speed distribution. However, the sound speed distribution is typically unknown. Further, the Initial Pressure and sound speed distributions cannot both, in general, be stably recovered from PACT measurements alone. In this work, a joint reconstruction method for the Initial Pressure distribution and a low-dimensional parameterized model of the sound speed distribution is proposed. By employing a priori information about the structure of the sound speed distribution, both the Initial Pressure and sound speed can be accurately recovered. The joint reconstruction problem is solved by use of a proximal optimization method that allows constraints and non-smooth regularization functions for Initial Pressure distribution. The gradients of the cost function with respect to the Initial Pressure and sound speed distributions are calculated by use of an adjoint state method that has the same per-iteration computational cost as calculating the gradient with respect to the Initial Pressure distribution alone. This approach is quantitatively evaluated through 2D computer-simulation studies for a small animal imaging model. The impact of the choice of the parameterized sound speed model is investigated. Even when the assumed parameterized sound speed model is inconsistent with the true sound speed distribution, the estimated Initial Pressure distribution is more accurate than that obtained by assuming a constant sound speed. The utility of the proposed approach is also demonstrated through application to experimental in vivo measurements of a mouse.
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joint reconstruction of Initial Pressure distribution and acoustic skull parameters in transcranial photoacoustic computed tomography conference presentation
Photons Plus Ultrasound: Imaging and Sensing 2018, 2018Co-Authors: Joemini Poudel, Thomas P Matthews, Mark A Anastasio, Lihong V WangAbstract:The development of photoacoustic computed tomography (PACT) for neuroimaging in humans will fill an important void left by available imaging techniques. However, due to the presence of the skull, accurate image reconstruction in transcranial PACT remains challenging. Variations in the shear and longitudinal wave speed distributions due to the skull can induce strong aberrations in the measured photoacoustic wavefields. To mitigate these artifacts, image reconstruction methods in transcranial PACT require knowledge of these acoustic properties. However, such information may be difficult to obtain in practice. To circumvent this, we developed a joint reconstruction (JR) method for transcranial PACT where the longitudinal and shear speed distributions are reconstructed concurrently with the sought-after Initial Pressure distribution. The joint estimation of the Initial Pressure, longitudinal speed, and shear speed distributions from PACT data alone is unstable. To overcome this instability, we propose to incorporate prior information about the acoustic properties of the skull. Specifically, a low-dimensional parameterized acoustic representation of the skull is established with the aid of adjunct CT data. The use of a low-dimensional representation of the acoustic skull parameters effectively overcomes the instability of the JR problem and allows stable reconstruction of the acoustic skull parameters and the Initial Pressure distribution concurrently. To validate the proposed method, we conducted 3D numerical studies based on realistic human skull models derived from adjunct CT data. The efficacy of the proposed JR method was demonstrated through accurate reconstruction of the Initial Pressure, longitudinal speed, and shear speed distributions from PACT measurement data alone.
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joint image reconstruction of Initial Pressure distribution and acoustic parameters in elastic media with application to transcranial photoacoustic tomography conference presentation
Medical Imaging 2018: Ultrasonic Imaging and Tomography, 2018Co-Authors: Joemini Poudel, Thomas P Matthews, Mark A AnastasioAbstract:The development and investigation of PACT as an effective neuroimaging modality is highly warranted. Amajor challenge in transcranial PACT brain imaging is to compensate for aberrations in the measured datadue to the propagation of the photoacoustic wavefields through the skull. To properly account for these effects,image reconstruction methods in transcranial PACT require knowledge of the spatial distribution of the acousticparameters of the skull. However, estimating the spatial distribution of the acoustic parameters of the skullremains challenging. Inspired by our observation that information about the distribution of skull acousticparameters is encoded in PACT measurements, we propose to jointly reconstruct the Initial Pressure distributionand the spatial distributions of the acoustic parameters of the skull from PACT data alone. In this study, weimplement a joint image reconstruction algorithm to estimate both the Initial Pressure distribution as well asthe spatial distribution of the acoustic parameters of the skull for 3D transcranial PACT. The joint estimationof the Initial Pressure and spatial distributions of the acoustic parameters of the skull from PACT data alone isunstable. To overcome this instability, we propose to incorporate prior information about the acoustic propertiesof the skull from adjunct image data. The developed joint reconstruction algorithm is validated and investigatedthrough computer-simulation studies.
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a forward adjoint operator pair based on the elastic wave equation for use in transcranial photoacoustic computed tomography
Siam Journal on Imaging Sciences, 2017Co-Authors: Kenji Mitsuhashi, Thomas P Matthews, Joemini Poudel, Lihong V Wang, Alejandro Garciauribe, Mark A AnastasioAbstract:Photoacoustic computed tomography (PACT) is an emerging imaging modality that exploits optical contrast and ultrasonic detection principles to form images of the photoacoustically induced Initial Pressure distribution within tissue. The PACT reconstruction problem corresponds to an inverse source problem in which the Initial Pressure distribution is recovered from measurements of the radiated wavefield. A major challenge in transcranial PACT brain imaging is compensation for aberrations in the measured data due to the presence of the skull. Ultrasonic waves undergo absorption, scattering and longitudinal-to-shear wave mode conversion as they propagate through the skull. To properly account for these effects, a wave-equation-based inversion method should be employed that can model the heterogeneous elastic properties of the skull. In this work, a forward model based on a finite-difference time-domain discretization of the three-dimensional elastic wave equation is established and a procedure for computing the corresponding adjoint of the forward operator is presented. Massively parallel implementations of these operators employing multiple graphics processing units (GPUs) are also developed. The developed numerical framework is validated and investigated in computer19 simulation and experimental phantom studies whose designs are motivated by transcranial PACT applications.
Bo Zhang - One of the best experts on this subject based on the ideXlab platform.
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experimental study of detonation limits in methane oxygen mixtures determining tube scale and Initial Pressure effects
Fuel, 2020Co-Authors: Bo Zhang, Hong Liu, Bingjian YanAbstract:Abstract In this paper, detonation limits in stoichiometric methane-oxygen mixtures with varying tube inner diameter and Initial mixture Pressure were investigated. Detonations in tubes with different inner diameter (D = 36 mm, 25 mm, 20 mm and 13 mm) and low Initial Pressure from 3.5 to 18 kPa were studied. Smoked foils were applied to observe the evolution of the detonation cellular structure for various Initial conditions. An alternate length scale at the limits is examined, Ldcs, which is the maximum length from the beginning of the test section after which cellular patterns can no longer be observed. Simultaneous local velocity measurements were obtained by photodiodes to complement the Ldcs results. The study also aims to reveal relation between the near-limit detonation dynamics, the tube geometry, and the thermodynamic properties of the mixture. Past the failure limit, Ldcs decreases with decreasing Initial mixture Pressure for a given tube diameter, and Ldcs decreases faster in a smaller diameter tube. In the D = 13 mm tube, galloping detonation mode is observed, and the length of the galloping cycle is reduced with an increase in Initial Pressure. To further characterize the onset of detonation limits, a scaling analysis of Ldcs with tube inner diameter (D) and detonation cell size (λ) was performed. The experimental results show that the decrease of Ldcs/D and Ldcs/λ are more abrupt in smaller diameter tubes with decreasing Initial Pressure. At low Initial Pressure, the boundary layer displacement thickness growth is significant in the flow structure. Since the distribution of global curvature over the whole detonation front is faster in smaller tube, it thus leads to a more abrupt decrease sensitive to Initial Pressure. For increasing Pressure closer to the critical failure limit, the boundary layer displacement thickness is becoming less comparable to the tube diameter. The failure mechanism appears to be more dominant by the rate of transverse waves attenuation or cell disappearance. Lastly, by comparing the detonation cell size and the tube scale at the critical limits condition in different tubes, λ = π⋅D is shown to be an appropriate limit criterion of detonation propagation in agreement previous studies.
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explosion characteristics of argon nitrogen diluted natural gas air mixtures
Fuel, 2014Co-Authors: Bo ZhangAbstract:Abstract This work was initiated to address safety concerns related to natural gas (NG)–air mixtures. NG, being an alternative fuel for vehicles and a chemical feedstock in the manufacture of organic chemicals, has been widely used in the industrial process in the past decade. NG is a flammable, gaseous fuel and thus presents a fire and explosion hazard. In this study, an investigation of the explosion characteristics including flammability limits, maximum explosion Pressure ( p max ), maximum rate of Pressure rise (d p /d t ) max , and laminar burning velocity ( S L ) is carried out by systematically measuring the Pressure histories in a standard 20-L spherical vessel. The dilution effects on the explosion characteristics are also explored through the addition of two diluents, i.e., argon (Ar) and nitrogen (N 2 ), into the NG–air mixture. The experimental results indicate that the flammability region ranges from 5.5% to 15% NG by volume at ambient conditions. It is found that reducing the Initial Pressure decreases the interval width of flammability limits. This is due to the distance between the molecules of the gas being shorter as the Initial Pressure increases and therefore, resulting in a higher probability of effective collision between molecules. Consequently, this effect in turn promotes the Initial and subsequent chemical reactions. The results also show that increasing diluent ratio results in a narrower flammability region and that the effect of N 2 addition is more pronounced than Ar. The present results also confirm that the variation of p max with the equivalence ratio of NG exhibits an inversely “ U -shaped” behavior and p max decreases with decreasing Initial Pressure. In general, the addition of Ar and N 2 would decrease the value of p max . However, it is observed in this study that the value of p max fluctuates when argon is added, especially for those mixtures with φ p max remain relatively constant within an interval of dilution percentage for fuel lean mixtures (e.g., with fuel concentration C NG equal to 5% and 6%). Finally, results also indicate that S L decreases with an increase of Initial Pressure and the rate of decrease of S L is faster when the mixture is diluted with N 2 compared to the effect of Ar. This can be explained by the fact that the density dominates over the retarding effect for S L .
Thomas P Matthews - One of the best experts on this subject based on the ideXlab platform.
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parameterized joint reconstruction of the Initial Pressure and sound speed distributions for photoacoustic computed tomography
Siam Journal on Imaging Sciences, 2018Co-Authors: Thomas P Matthews, Joemini Poudel, Lihong V Wang, Mark A AnastasioAbstract:Accurate estimation of the Initial Pressure distribution in photoacoustic computed tomography (PACT) depends on knowledge of the sound speed distribution. However, the sound speed distribution is t...
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parameterized joint reconstruction of the Initial Pressure and sound speed distributions in photoacoustic computed tomography conference presentation
Photons Plus Ultrasound: Imaging and Sensing 2018, 2018Co-Authors: Thomas P Matthews, Joemini Poudel, Lihong V Wang, Mark A AnastasioAbstract:Accurate estimation of the Initial Pressure distribution in photoacoustic computed tomography (PACT) requires some knowledge of the sound speed distribution. However, the sound speed distribution is typically unknown. Further, the Initial Pressure and sound speed distributions cannot both, in general, be stably recovered from PACT measurements alone. In this work, a joint reconstruction method for the Initial Pressure distribution and a low-dimensional parameterized model of the sound speed distribution is proposed. By employing a priori information about the structure of the sound speed distribution, both the Initial Pressure and sound speed can be accurately recovered. The joint reconstruction problem is solved by use of a proximal optimization method that allows constraints and non-smooth regularization functions for Initial Pressure distribution. The gradients of the cost function with respect to the Initial Pressure and sound speed distributions are calculated by use of an adjoint state method that has the same per-iteration computational cost as calculating the gradient with respect to the Initial Pressure distribution alone. This approach is quantitatively evaluated through 2D computer-simulation studies for a small animal imaging model. The impact of the choice of the parameterized sound speed model is investigated. Even when the assumed parameterized sound speed model is inconsistent with the true sound speed distribution, the estimated Initial Pressure distribution is more accurate than that obtained by assuming a constant sound speed. The utility of the proposed approach is also demonstrated through application to experimental in vivo measurements of a mouse.
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joint reconstruction of Initial Pressure distribution and acoustic skull parameters in transcranial photoacoustic computed tomography conference presentation
Photons Plus Ultrasound: Imaging and Sensing 2018, 2018Co-Authors: Joemini Poudel, Thomas P Matthews, Mark A Anastasio, Lihong V WangAbstract:The development of photoacoustic computed tomography (PACT) for neuroimaging in humans will fill an important void left by available imaging techniques. However, due to the presence of the skull, accurate image reconstruction in transcranial PACT remains challenging. Variations in the shear and longitudinal wave speed distributions due to the skull can induce strong aberrations in the measured photoacoustic wavefields. To mitigate these artifacts, image reconstruction methods in transcranial PACT require knowledge of these acoustic properties. However, such information may be difficult to obtain in practice. To circumvent this, we developed a joint reconstruction (JR) method for transcranial PACT where the longitudinal and shear speed distributions are reconstructed concurrently with the sought-after Initial Pressure distribution. The joint estimation of the Initial Pressure, longitudinal speed, and shear speed distributions from PACT data alone is unstable. To overcome this instability, we propose to incorporate prior information about the acoustic properties of the skull. Specifically, a low-dimensional parameterized acoustic representation of the skull is established with the aid of adjunct CT data. The use of a low-dimensional representation of the acoustic skull parameters effectively overcomes the instability of the JR problem and allows stable reconstruction of the acoustic skull parameters and the Initial Pressure distribution concurrently. To validate the proposed method, we conducted 3D numerical studies based on realistic human skull models derived from adjunct CT data. The efficacy of the proposed JR method was demonstrated through accurate reconstruction of the Initial Pressure, longitudinal speed, and shear speed distributions from PACT measurement data alone.
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joint image reconstruction of Initial Pressure distribution and acoustic parameters in elastic media with application to transcranial photoacoustic tomography conference presentation
Medical Imaging 2018: Ultrasonic Imaging and Tomography, 2018Co-Authors: Joemini Poudel, Thomas P Matthews, Mark A AnastasioAbstract:The development and investigation of PACT as an effective neuroimaging modality is highly warranted. Amajor challenge in transcranial PACT brain imaging is to compensate for aberrations in the measured datadue to the propagation of the photoacoustic wavefields through the skull. To properly account for these effects,image reconstruction methods in transcranial PACT require knowledge of the spatial distribution of the acousticparameters of the skull. However, estimating the spatial distribution of the acoustic parameters of the skullremains challenging. Inspired by our observation that information about the distribution of skull acousticparameters is encoded in PACT measurements, we propose to jointly reconstruct the Initial Pressure distributionand the spatial distributions of the acoustic parameters of the skull from PACT data alone. In this study, weimplement a joint image reconstruction algorithm to estimate both the Initial Pressure distribution as well asthe spatial distribution of the acoustic parameters of the skull for 3D transcranial PACT. The joint estimationof the Initial Pressure and spatial distributions of the acoustic parameters of the skull from PACT data alone isunstable. To overcome this instability, we propose to incorporate prior information about the acoustic propertiesof the skull from adjunct image data. The developed joint reconstruction algorithm is validated and investigatedthrough computer-simulation studies.
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a forward adjoint operator pair based on the elastic wave equation for use in transcranial photoacoustic computed tomography
Siam Journal on Imaging Sciences, 2017Co-Authors: Kenji Mitsuhashi, Thomas P Matthews, Joemini Poudel, Lihong V Wang, Alejandro Garciauribe, Mark A AnastasioAbstract:Photoacoustic computed tomography (PACT) is an emerging imaging modality that exploits optical contrast and ultrasonic detection principles to form images of the photoacoustically induced Initial Pressure distribution within tissue. The PACT reconstruction problem corresponds to an inverse source problem in which the Initial Pressure distribution is recovered from measurements of the radiated wavefield. A major challenge in transcranial PACT brain imaging is compensation for aberrations in the measured data due to the presence of the skull. Ultrasonic waves undergo absorption, scattering and longitudinal-to-shear wave mode conversion as they propagate through the skull. To properly account for these effects, a wave-equation-based inversion method should be employed that can model the heterogeneous elastic properties of the skull. In this work, a forward model based on a finite-difference time-domain discretization of the three-dimensional elastic wave equation is established and a procedure for computing the corresponding adjoint of the forward operator is presented. Massively parallel implementations of these operators employing multiple graphics processing units (GPUs) are also developed. The developed numerical framework is validated and investigated in computer19 simulation and experimental phantom studies whose designs are motivated by transcranial PACT applications.
