Countercurrent Flame Propagation and Quenching Behaviour in a Packed Bed of Spherical PMMA Beads in an Upward Flow of Pure Oxygen

ABSTRACT

Countercurrent flame propagation and quenching behavior in a packed bed of spherical polymethyl methacrylate (PMMA) beads in an upward flow of pure oxygen was experimentally studied. Monosized PMMA beads of 2, 5, 8 or 10 mm in diameter (d) were packed in a vertical quartz tube of 35 mm ID to form a bed of 180 mm in height. In a typical experimental run, upon ignition from the top, a blue flame formed and propagated downwards. For d = 10, 8, or 5 mm, there existed a minimum oxygen flow rate (q) to sustain a quasi-steady state flame propagation, and the minimum q increased as d decreased from 10 to 5 mm. However, for d = 2 mm, it was not possible for the flame to propagate downwards irrespective of the q value. The apparent pyrolysis rate (m_py) of PMMA was estimated by monitoring the bed mass loss rate, from which the nominal equivalence ratio upon flame quenching was also estimated. The equivalence ratio was found to be less than unity upon flame quenching, suggesting insufficient pyrolysis gases to sustain the combustion. The heat transfer between flame and PMMA bead was analyzed theoretically, and it was revealed that the minimum m_py to sustain the quasi-steady state flame propagation inversely correlates with the PMMA particle size, and therefore a higher oxygen flow rate is required to sustain the flame propagation in a packed bed of smaller PMMA particles.

KEYWORDS:

• Countercurrent flame propagation
• flame quenching
• packed bed
• PMMA
• pyrolysis

Acknowledgement

This work has received funding support from the National Natural Science Foundation of China (No. 51806230 and 51906251), Australian Research Council (ARC DP210103766 and DP220100116) and the Future Energy Export Cooperative Research Centre (FEnEx CRC Project# 21.RP2.0059). The start-up financial support from QIBEBT, CAS provided to the Thermal Energy Engineering Team is also acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [51806230,51906251]; Australian Research Council [DP210103766, DP220100116]; Future Energy Export Cooperative Research Centre [FEnEx CRC Project# 21.RP2.0059].