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

Abstract

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. Solid cone pressure swirl nozzle N1 ((m_f ) ̇ =1.7 kg/hr at ΔPinj = 9 bar) is considered and fuel injection pressure varied from 3 - 48 bar. Detailed droplet size and droplet velocity measurements using shadowgraphy and PIV helped obtain the group combustion number and dimensionless droplet separation distance. A Chiu (1977, 1982) criterion of group combustion number is used along 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. At intermediate pressures, the combustion mode is defined by internal group combustion with a double reaction zone. 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 - 103 is investigated for various combustion modes in lifted spray flames without coflow air. For air coflow conditions (Vcoflow = 0.4 m/s), both individual droplet burning mode and double reaction zone flame structure disappear from the flame. At higher injection pressures, small fuel vapor cloud burning with external group combustion mode is observed in the G range of 103 - 106.