We performed a quantitative analysis of time-resolved laser-induced breakdown air plasma spectra to obtain the evolution of temperatures and species relative fractions.The air plasma was generated by focusing a 100 mJ...We performed a quantitative analysis of time-resolved laser-induced breakdown air plasma spectra to obtain the evolution of temperatures and species relative fractions.The air plasma was generated by focusing a 100 mJ Nd:YAG laser pulse,and the time-resolved spectra were recorded by an intensified charge-coupled device camera with incremental delay.The attention was mainly focused on the emission spectra of the first negative system of nitrogen(N_(2)^(+),B^(2)Σ-(u)^(-)-X^(2)Σ^(+)g)and the violet system of carbon nitride(CN,B^(2)Σ^(+)-X^(2)Σ^(+))located at 383-396 nm.A custom-built model was developed to perform the simulation and fitting of the N_(2)^(+)and the CN spectra from the air plasma.The model was verified by comparing to a published model with a 0.9860 Spearman correlation coefficient.With this model,the time-resolved non-equilibrium temperatures and relative fractions of N_(2)^(+)and CN were obtained with a fitting correlation coefficient higher than 0.9108.展开更多
Flame features and dynamics are important to the explanation and prediction of a lean blowout(LBO)phenomenon.In this paper,recognition of near-LBO flame features and oscillation characterization methods were proposed ...Flame features and dynamics are important to the explanation and prediction of a lean blowout(LBO)phenomenon.In this paper,recognition of near-LBO flame features and oscillation characterization methods were proposed based on flame spectroscopic images.High-speed planar laser-induced fluorescence measurements of OH were used to capture unique dynamic features such as the local extinction and reignition feature and entrained reactant pockets.The Zernike moment demonstrated a good performance in recognition of stability and near-LBO conditions,though the geometric moment had more advantages to characterize frequency characteristics.Low-frequency oscillations,especially at the obvious self-excited oscillation frequency around 200 Hz,were found when approaching an LBO condition,which can be expected to be used as a novel prediction characteristic parameter of the flameout limit.Proper orthogonal decomposition(POD)and dynamic mode decomposition(DMD)were used to conduct dynamic analysis of near-LBO flames.POD modes spectra showed the unique frequency characteristics of stable and near-LBO flames,which were basically in line with those at the heat-release frequency.The primary POD modes demonstrated that the radial vibration mode dominated in a stable flame,while the rotation mode was found to exist in a near-LBO flame.Analysis of modal decomposition showed that flame shedding and agminated entrained reactant pockets were responsible for generating self-excited flame oscillations.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.62305087)。
文摘We performed a quantitative analysis of time-resolved laser-induced breakdown air plasma spectra to obtain the evolution of temperatures and species relative fractions.The air plasma was generated by focusing a 100 mJ Nd:YAG laser pulse,and the time-resolved spectra were recorded by an intensified charge-coupled device camera with incremental delay.The attention was mainly focused on the emission spectra of the first negative system of nitrogen(N_(2)^(+),B^(2)Σ-(u)^(-)-X^(2)Σ^(+)g)and the violet system of carbon nitride(CN,B^(2)Σ^(+)-X^(2)Σ^(+))located at 383-396 nm.A custom-built model was developed to perform the simulation and fitting of the N_(2)^(+)and the CN spectra from the air plasma.The model was verified by comparing to a published model with a 0.9860 Spearman correlation coefficient.With this model,the time-resolved non-equilibrium temperatures and relative fractions of N_(2)^(+)and CN were obtained with a fitting correlation coefficient higher than 0.9108.
基金supported by the Heilongjiang Provincial Natural Science Foundation of China(No.LH2021F028)。
文摘Flame features and dynamics are important to the explanation and prediction of a lean blowout(LBO)phenomenon.In this paper,recognition of near-LBO flame features and oscillation characterization methods were proposed based on flame spectroscopic images.High-speed planar laser-induced fluorescence measurements of OH were used to capture unique dynamic features such as the local extinction and reignition feature and entrained reactant pockets.The Zernike moment demonstrated a good performance in recognition of stability and near-LBO conditions,though the geometric moment had more advantages to characterize frequency characteristics.Low-frequency oscillations,especially at the obvious self-excited oscillation frequency around 200 Hz,were found when approaching an LBO condition,which can be expected to be used as a novel prediction characteristic parameter of the flameout limit.Proper orthogonal decomposition(POD)and dynamic mode decomposition(DMD)were used to conduct dynamic analysis of near-LBO flames.POD modes spectra showed the unique frequency characteristics of stable and near-LBO flames,which were basically in line with those at the heat-release frequency.The primary POD modes demonstrated that the radial vibration mode dominated in a stable flame,while the rotation mode was found to exist in a near-LBO flame.Analysis of modal decomposition showed that flame shedding and agminated entrained reactant pockets were responsible for generating self-excited flame oscillations.
