Estimation of fire cycle has been conducted by using the negative exponential function as an approximation of time-since-fire distribution of a landscape assumed to be homogeneous with respect to fire spread processes...Estimation of fire cycle has been conducted by using the negative exponential function as an approximation of time-since-fire distribution of a landscape assumed to be homogeneous with respect to fire spread processes. The authors imposed predefined fire cycles on a virtual landscape of 100 cell×100 cell, and obtained a mosaic composing of patches with different stand ages （i.e. time since fire）. Graphical and statistical methods （Van Wagner 1978; Reed et al. 1998） were employed to derive fire cycle from the virtual landscape. By comparing the predefined and the derived fire cycles, the two methods and tested the effects of sample size and hazard of burning （i.e., stand＇s susceptibility to fire in relation to its stand age） were evaluated on fire cycle deviation. The simulation results indicated a minimum sample size of l0 times of the annual burnt area would be required for.partitioning time-since-fire distribution into homogeneous epochs indicating temporal change in fire cycle. Statistically, there was significant difference among the imposed and the derived fire cycle, regardless of sample sizes with or without consideration of hazard of burning. Both methods underestimated the more recent fire cycle without significant difference between them. The results imply that deviation of fire cycle based on time-since-fire distribution warrants cautious interpretation, especially when a landscape is spatially partitioned into small units and temporal changes in fire cycle are involved.展开更多
Two different combustion models,the autoignition(AI)model and flamelet/progress variable(FPV)model,have been applied to study the auto-ignition process of methane/air jet flame in vitiated co-flow.A priori study was c...Two different combustion models,the autoignition(AI)model and flamelet/progress variable(FPV)model,have been applied to study the auto-ignition process of methane/air jet flame in vitiated co-flow.A priori study was conducted to test the validity of the two models.Results show that the different range of predicted reaction rates is mainly responsible for their different performances in large eddy simulation(LES)studies.In this paper,beta PDF was used to model the mixture fraction distribution,while two different shapes of PDF,delta function and beta function,were applied for the reaction progress.Compared to the FPV model,the AI model combined with beta function for reaction progress could capture the auto-ignition process and predict the exact lifted height.Also the results indicate that the variance of reaction progress plays an important role in predicting the flame lifted height.展开更多
文摘Estimation of fire cycle has been conducted by using the negative exponential function as an approximation of time-since-fire distribution of a landscape assumed to be homogeneous with respect to fire spread processes. The authors imposed predefined fire cycles on a virtual landscape of 100 cell×100 cell, and obtained a mosaic composing of patches with different stand ages （i.e. time since fire）. Graphical and statistical methods （Van Wagner 1978; Reed et al. 1998） were employed to derive fire cycle from the virtual landscape. By comparing the predefined and the derived fire cycles, the two methods and tested the effects of sample size and hazard of burning （i.e., stand＇s susceptibility to fire in relation to its stand age） were evaluated on fire cycle deviation. The simulation results indicated a minimum sample size of l0 times of the annual burnt area would be required for.partitioning time-since-fire distribution into homogeneous epochs indicating temporal change in fire cycle. Statistically, there was significant difference among the imposed and the derived fire cycle, regardless of sample sizes with or without consideration of hazard of burning. Both methods underestimated the more recent fire cycle without significant difference between them. The results imply that deviation of fire cycle based on time-since-fire distribution warrants cautious interpretation, especially when a landscape is spatially partitioned into small units and temporal changes in fire cycle are involved.
基金supported by the National Natural Science Foundation of China(Grant Nos.51176178 and 50936005)
文摘Two different combustion models,the autoignition(AI)model and flamelet/progress variable(FPV)model,have been applied to study the auto-ignition process of methane/air jet flame in vitiated co-flow.A priori study was conducted to test the validity of the two models.Results show that the different range of predicted reaction rates is mainly responsible for their different performances in large eddy simulation(LES)studies.In this paper,beta PDF was used to model the mixture fraction distribution,while two different shapes of PDF,delta function and beta function,were applied for the reaction progress.Compared to the FPV model,the AI model combined with beta function for reaction progress could capture the auto-ignition process and predict the exact lifted height.Also the results indicate that the variance of reaction progress plays an important role in predicting the flame lifted height.
