EXPERIMENTAL INVESTIGATIONS ON THE ROLE OF GROUP COMBUSTION MODE IN LIFTED SPRAY FLAMES WITH KEROSENE FUEL

In the present work, detailed experimental investigations on lifted spray flames have been carried out to identify the various combustion modes using group combustion number analysis with kerosene fuel. The solid cone pressure swirl nozzle N1 (<(m) over dot)>(f) = 1.7 kg/h at delta P-inj = 9 bar) is considered, and fuel injection pressure varied from 3 to 48 bar. Detailed droplet size and droplet velocity measurements using shadowgraphy and particle image velocimetry (PIV) helped obtain the group combustion number and dimensionless droplet separation distance. A Chiu et al. (1977, 1982) criterion of group combustion number is used with experimental observations to understand the spray combustion mode in lifted spray flames. Internal group combustion mode is observed at lower injection pressures (3 bar) in which individual droplet combustion is significant. The combustion mode is de-fined by internal group combustion with a double reaction zone at intermediate pressures. The inner reaction zone burns with local extinction, and the outer reaction zone burns like a diffusion flame. A group combustion number range of 1-10(3) is investigated for various combustion modes in lifted spray flames without coflow air. For air coflow conditions (V-coflow = 0.4 m/s), both the individual droplet burning mode and double reaction zone flame structure disappear from the flame. Small fuel vapor clouds burning with the external group combustion mode at higher injection pressures are observed in the G range of 10(3)-10(6).