Critical Issues of Chemical Kinetics in MILD Combustion

Abstract

Mild combustion processes occur with mixtures highly diluted and preheated by a strong recirculation of hot exhausted gases (thus mass and sensible enthalpy) within the combustion chamber. This strategy configures a process based on autoignition kernels outside or close to flammability limits transported by convection in the combustion chamber, thus defining a process with unique physical and chemical features drastically different from traditional deflagrative-diffusive flames. The article aims at analyzing the recent issues relative to kinetic aspects involved in moderate or intense low-oxygen dilution (MILD) combustion processes. First, the article comes through the identification of peculiar experimental features of simple hydrocarbons oxidation process induced by highly preheated and diluted conditions in model reactors typical of chemical engineering. Second, the effects of steam and carbon dioxides on fuel oxidation process, whose presence within the combustion chamber is imposed by high levels of hot gas recirculation, are addressed. Third, the article comes through a thorough analysis of recent scientific contributions on kinetic aspects of MILD combustion processes to identify the critical points in modeling activities.

Alcohols as Energy Carriers in MILD Combustion

“…The features of the MILD reactive structure based on a complex interplay between chemical kinetic and fluid dynamic issues should be addressed through proper computational fluid dynamics (CFD) simulations, but turbulence− chemistry interaction models 66−68 and kinetic oxidation mechanisms 69−71 still represent significant issues to be addressed under MILD operative conditions. 72,73 This would be even more evident for the complex kinetics of alcohols.…”

“…In general, this approach aims at interpreting the experimental results through a simplified but very effective methodology, reducing the nature of the problem to a zero-dimensional (0D) and/or one-dimensional (1D) elementary process. The features of the MILD reactive structure based on a complex interplay between chemical kinetic and fluid dynamic issues should be addressed through proper computational fluid dynamics (CFD) simulations, but turbulence–chemistry interaction models − and kinetic oxidation mechanisms − still represent significant issues to be addressed under MILD operative conditions. , This would be even more evident for the complex kinetics of alcohols.…”