Identification of turbulent H2/air jet flame stabilization modes using chemical explosive mode analysis (CEMA)

Abstract

The flame propagation mechanisms of turbulent lifted hydrogen jet flames with different coflow temperatures (i.e. Tc = 750, 850, and 950 K) are investigated using 3-D direct numerical simulations (DNSs) with a detailed hydrogen/air chemical mechanism. The DNSs are performed at a jet Reynolds number of 8,000 with over 1.28 billion grid points. A chemical explosive mode analysis (CEMA) identifies important variables and reactions upstream of the flamebase. CEMA is used as diagnostic tool of detecting local combustion modes, such as auto-ignition, ignition assisted by diffusion and extinction. The local reaction and diffusion source terms are projected to the eigenvector of Jacobian matrix of reaction source term. Comparison of projected chemical and diffusion source terms shows local combustion propagation modes. A local combustion mode indicator α defined as ratio of projected diffusion term to chemical reaction term informs criterion of local combustion modes. This CEMA based analysis of combustion modes suggest more concreate criterion than empirically selected scalars, such as flmaebase definition. In this research, CEMA based criterion applies to three different cases of turbulent hydrogen jet flame, effect of coflow temperature and transition from diffusion assisted ignition to auto ignition propagation are discussed with comparison between previous analysis.