Flame speed enhancement in narrow channels of low effusivity aerogel

Abstract

Flame dynamics in narrow channels are governed by thermal and momentum interactions at the walls, which become increasingly dominant as the surface-area-to-volume ratio increases. Understanding these near-quenching phenomena is critical for the development of small-scale combustion devices, such as microcombustors and flame arresters. This study investigates the influence of low-thermal-conductivity polyimide aerogel walls (Airloy H116) on freely propagating, constant-pressure ethylene–air flames, benchmarking the results against aluminum, PMMA, and soda-lime glass. Experiments were conducted in rectangular channels (25.4 mm depth, 305 mm length) with widths varying from 1.5 to 12.7 mm. High-speed imaging and synchronized pressure measurements revealed that while flame speeds were relatively insensitive to channel width for conventional materials above 4.7 mm, aerogel-confined flames exhibited a dramatic velocity enhancement in excess of 300%, just prior to the critical quenching width. This pronounced acceleration is attributed to the aerogel’s exceptionally low thermal effusivity, which elevates gas-wall interface temperatures and preheats the near-wall reactants. These findings demonstrate that strategic selection of wall materials can transform boundary layers from traditional loss mechanisms into combustion enhancers. Such extreme variation in flame speed has significant implications for the thermal management, efficiency, and safety parameters of microscale propulsion and power systems.

Novelty and significance statement: This study reports an unprecedented enhancement in flame propagation speeds near quenching limits, identifying a phenomenon unique to low-effusivity aerogel walls. We demonstrate that near-adiabatic boundary layers can fundamentally transform from a loss mechanism into a combustion enhancer. These findings provide a novel framework for “tuning” microscale devices, where millimeter-scale adjustments to channel geometry toggle between total flame extinction and peak thermal performance.