Two Sides Ignition Over a Thin PMMA Sheet in Microgravity
Y N. Nakamura, Takashi Kashiwagi, S L. Olson, K K. Nishizawa, O -. Fujita
A series of the experiments was conducted in microgravity to study the ignition characteristics of a thin PMMA sheet (thicknesses of 0.2 mm and 0. 4 mm) using a CO2 laser as an external radiant source. Two separate ignition events were observed, the first was ignition over the irradiated surface (frontside ignition) and the second was ignition over the backside surface (backside ignition) after some delay following the first ignition. The backside ignition was achieved in two different ways. One way occurred after the termination of the laser irradiation subsequent shrinkage of the flame that was initiated by the frontside ignition; as the flame shrank close to the frontside surface it traveled through a small, open hole generated by the consumption of PMMA from the frontside to the backside. The other way occurred with the presence of the traveling flame from the fronside ignition during the laser irradiation. The former process was observed in 21 % oxygen and the latter process was observed in 35 % oxygen. The duration of the laser irradiation appears to have important effects on the onset of backside ignition. The backside ignition was attained with a 3 s laser duration in 21 % oxygen but backside ignition was not observed for a 6 s laser duration within the available test time10 s. In 35 % oxygen, the numerical calculation predicts fresh oxygen supply flow from the backside gas phase to the frontside gas phase through an open hole, which mixes with accumulated hot MMA and initiates second ignition in the frontside gas phase above the hole. Then, the flame initiated from the second ignition travels through the hole to ignite the accumulated flammable mixture in the backside gas phase near the hole and to attain backside ignition.
, Kashiwagi, T.
, Olson, S.
, Nishizawa, K.
and Fujita, O.
Two Sides Ignition Over a Thin PMMA Sheet in Microgravity, Thirtyth International Symposium on Combustion
(Accessed December 9, 2023)