MILD combustion of ethanol-air with diluted hot oxidant by recirculation in opposite jet

Abstract

Moderate Intensity Low Oxygen Diluted (MILD) combustion has been investigated for a long time in order to minimize NOX emission still enhancing thermal efficiencies in the combustion equipment. Many researches about MILD combustion have been recently performed, but studies on MILD combustion of renewable fuel such as ethanol has been very scarce and particularly, specific information on the NOX production in ethanol-air MILD combustion has not been reported yet. In order to satisfy the condition for MILD combustion, internal recirculation is known to be essential in order to entrain the combustion products gas into air and fuel jets of combustion system. In this work, a series of numerical analysis with simplified opposed jet geometry have been done using the OPPDIF in Ansys program. Numerical analysis on how the recirculation ratio (KV) affects NOX emission in the ethanol-air combustion for MILD formation were carried out under the condition of various burnt gas dilution in reactant flow. The results show that the temperature was decreased by the increase of the recirculation ratio and the maximum heat release value became also low by the increase of the recirculation ratio. It was also found that the pyrolysis zone of the heat release was disappeared and the two heat release peaks are merged into one as combustion pattern is changed to MILD combustion mode.

Keywords

• mild combustion
• recirculation ratio
• bio-ethanol
• opposite-jet
• nox formation