Monitoring of atomic metastable state lifetimes by the laser-enhanced ionization technique—A new method for probing local stoichiometric combustive conditions

Abstract

The lifetimes of atomic metastable states in an acetylene/air flame have been investigated using the laser‐enhanced ionization technique. The lifetimes were found to be several orders of magnitude less than the natural ones, which clearly shows that they are fully determined by the surrounding environment. The lifetime of a specific state has been investigated as a function of flame conditions. It was found that the lifetime is strongly dependent on the local flame composition, with a distinct maximum for stoichiometric conditions. For fuel‐lean local conditions, the excess of O2 acts as an effective quencher of the metastable state, while for fuel‐rich conditions the quenching is dominated by unburned fuel components. An acetylene/air flame has been probed both as a function of height in the flame, as well as a function of fuel/air composition fed to the burner. The experiments show clearly for which heights and fuel/air compositions that lean, stoichiometric or rich conditions prevail. This makes a monitoring of metastable state lifetimes a useful technique for combustion analysis.