Response of Non-premixed Jet Flames to Blast Waves

TL;DR

This study examines how non-premixed jet flames respond to blast waves, revealing flame lift-off, flickering, and re-attachment behaviors influenced by flow dynamics and validated through a theoretical model.

Contribution

It introduces a detailed experimental analysis of flame response to blast waves and develops a theoretical model to predict flickering and lift-off phenomena.

Findings

Flame lift-off occurs after blast interaction and depends on Re and Mach number.

Induced flow causes increased flickering and potential flame extinction.

Theoretical model aligns well with experimental observations.

Abstract

The work investigates the response dynamics of non-premixed jet flame to blast waves that are incident along the jet axis. In the present study, blast waves, generated using the wire-explosion technique, are forced to sweep across a non-premixed jet flame that is stabilised over a nozzle rim positioned at a distance of 264 mm from the source of blast generation. The work spans a wide range of fuel jet Reynolds numbers ($Re$) and incident blast wave Mach numbers ($M_{s,r}$). The interaction imposes a characteristic flow field over the jet flame, marked by a sharp discontinuity followed by a decaying profile and a delayed second spike. The second spike in the flow field profile corresponds to the induced flow that follows the blast front. While the response of the flame to the blast front was minimal, it was found to detach from the nozzle rim and lift off following the interaction with the induced flow. Subsequently, the lifted flame was found to re-attach back at the nozzle or extinguish, contingent on the operating $Re$ and $M_{s,r}$. Alongside flame lift-off, flame tip flickering was aggravated under the influence of the induced flow. A simplified theoretical model extending the vorticity transport equation was developed to estimate the change in flickering timescales and length scales owing to the interaction with the induced flow. The observed experimental trends were further compared against theoretical predictions from the model.