Analysis of Laminar Acetylene-Air Diffusion Flames Using Reduced Reaction Mechanisms and State Relationships

Abstract

In the development of state relationships much of the research has been experimental and limited to steady and lightly sooting flame configurations. This study computationally investigates soot and radiation effects on the state relationships in an unsteady, spherical, moderately sooting, acetylene/air diffusion-flame by coupling the gas phase and soot reaction mechanisms. The gas phase species concentrations are computed either by using a reduced reaction mechanism or by invoking the laminar flamelet concept. Comparisons are made between these two formulations. For moderately sooting, acetylene/air, unsteady diffusion-flames, calculations show that universality for most of the major gas species concentrations does not exist when the species are plotted in either gas phase or total mixture fraction space. In line with experimental results, defining a modified gas species mass fraction and utilizing the apparent gas phase mixture fraction extends the state relationships for most major gas species concentrations to these sooting diffusion flames. The effects of using detailed transport properties on the burning process are evaluated. The mixture C/H ratio is computed and shown to deviate from the fuel value.

Key words:

• Laminar flamelet (state relationships)
• soot
• reduced mechanisms