Investigation of the MILD combustion regime via Principal Component Analysis

Moderate or Intense Low oxygen Dilution (MILD) combustion is particularly appealing for coupling very high combustion efficiencies with very low pollutant emissions. Experimental and numerical studies have been devoted to MILD combustion. However, fundamental aspects of such combustion regime are still not completely understood and this generates uncertainties, especially from the modeling perspective. A novel methodology based on Principal Component Analysis (PCA) is proposed for the investigation of the main features characterizing the MILD combustion regime. High fidelity experimental datasets of CH4/H-2 flames propagating into a hot and diluted co-flow are employed to this purpose. Results indicate that the proposed methodology can provide progress variables which coherently follow the modification of the flame structure experimentally observed at different levels of oxygen dilution in the co-flow. A local PCA approach is also proposed, based on the partition of the data sets into cluster, followed by the local application of PCA. Such approach ensures that the low-dimensional projection is characterized by the minimum parameterization error. Results indicate that local PCA leads to the identification of regions of the flow characterized by different physical processes, thus allowing the determination of optimal progress variables in each of them. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.