Global sensitivity analysis and uncertainty quantification of soot formation in an n-dodecane spray flame

Abstract

Quantifying the uncertainty of soot formation in a turbulent combustion simulation remains a challenging task. In this work, global sensitivity analysis and uncertainty quantification of soot formation in the widely known Spray-A flame have been carried out. The numerical simulation reasonably predicts the measured penetration length, ignition delay, flame lift-off length, and soot volume fraction at quasi-steady state, providing a good baseline for the subsequent analysis. The active subspace method has been applied to perform global sensitivity analysis, with the peak soot volume fraction on centerline (PSVF-c) and the axial location of the peak soot volume fraction on centerline (LPSVF-c) at 4 ms being chosen as the quantities of interest (QoIs), and the parameters in soot and turbulence model being considered as the uncertainty inputs. It is found that at the early stage of the spray flame, e.g., 1 ms after the start of injection, more than one dimensional active subspace is needed to characterize the input space, while the active subspace tends to one dimension as the spray flame approaches the quasi-steady state. At the quasi-steady state of the spray flame, surface growth rate parameter is the controlling parameter for PSVF-c. Meanwhile, LPSVF-c is controlled by turbulence model parameters. Uncertainty quantification for soot formation is performed by constructing the response surfaces in the active subspace to map the input parameters to the QoIs. The 95% confidence interval due to the uncertainty of turbulence model, soot model and the overall uncertainty of these two models are [6.64,6.91], [6.59,8.05] and [6.52,8.02] ppm for PSVF-c, and [78.17,81.02], [79.39,80.21] and [78.26,81.22] mm for LPSVF-c. This work demonstrates the potential of using the active subspace method for global sensitivity analysis and uncertainty quantification of the soot formation in turbulent spray flames.