Flow Field and Combustion Characteristics in Localized Stratified Swirling Tubular Flame Burner: Numerical Investigation

A three-dimensional numerical simulation of a localized stratified tubular flame burner is carried out by using propane as fuel. The characteristics of the flow field, species distribution, flame structure, and stability limit are investigated. Results show that in the cold flow field, a specific distribution of species is formed due to the unique inlet structure and the effects of vortex breakdown, in which propane is mainly distributed near the wall, while oxygen is uniformly distributed in the burner. At the burning state, propane and oxygen are mixed at the inlet section of the burner and produce a stratified mixture from fuel lean to fuel rich, thus forming a flame that is similar to a triple flame, which plays an important role in promoting the combustion stability. Based on the localized stratification property and the effect of precessing vortex core, the main reaction takes place in the fuel-rich region (Lewis number <1 for C3H8 as fuel). Hence, the tubular flame easily forms and is hardly extinguished. In addition, the flow field promotes the chemical enthalpy supply to the reaction zone, thereby enhancing combustion. Essentially, this type of burner does not require a uniform premixed gas to establish the tubular flame which differs from the typical tubular flame burner. The stability limit of the localized stratified tubular flame is greatly improved compared with that of the rapidly mixed tubular flame, especially under lean conditions.