Hydrogen-enriched methane Mild Combustion in a well stirred reactor

Abstract

The reduction of pollutants emission, such as NO x and soot, can be achieved by lowering and controlling the adiabatic temperature of the system. Mild Combustion processes employ great amounts of diluents and high inlet temperatures of reactants. The first aspect guarantees a high heat capacity of the system, hence lower working temperatures with respect to a traditional oxidation process; the latter feature comes out from the necessity to sustain the oxidation process with no-flammable mixtures working with so high dilution degree. This new kind of combustion presents several features that deserve a systematic study. Previous experimental works carried out in a jet stirred flow reactor showed a complex dynamic behavior of methane Mild Combustion. In practical applications, such instabilities do not allow to control the working temperature; thus they lower the efficiency of the combustion processes. In this paper, the effect of hydrogen addition to the methane combustion in Mild conditions was studied, with particular focus on the dynamic behavior detected in the past. The experimental results showed that the higher the inlet hydrogen content, the higher the increase of the system reactivity and a more significant reduction of the area in the T in–C/O plane where thermo-kinetics oscillations were observed. However, hydrogen addition did not affect significantly the typology of oscillations. Furthermore, it was observed that in the T in–C/O plane the dynamic region shifts towards lower temperatures as well as the irregular oscillation region extends as the hydrogen concentration increases. The experimental T in–C/O maps were then compared with the numerical ones, obtained with different kinetic mechanisms available in the literature. An overall good agreement was found between experimental and numerical data. The evolution of the oscillations region and the increase of reactivity due to the hydrogen addition were predicted quite well.