Effects of Gravity and Flow Velocity on Ignition Characteristics of MMA/Air and DME/Air Mixtures

Date

2016-07-10

Journal Title

Journal ISSN

Volume Title

Publisher

46th International Conference on Environmental Systems

Abstract

Fire safety in spacecraft such as the International Space Station is one of the most important requirements for any manned space activities. It is necessary to understand the fire outbreak mechanism in great detail to prevent fire in space. We have focused on ignition phenomena and conducted various ignition experiments. The ignitability of materials used in space has been evaluated on the ground by NASA-STD-6001. However, combustion behaviors in microgravity are very different from those on the ground due to absence of natural convective flow. Ignition phenomena could be also affected by gravity. Then, in this study, effects of gravity on the ignition limit of flammable mixtures were investigated experimentally by parabolic flight. Furthermore, since flow field could exist in spacecraft due to the movement of crews or air circulation unit, effects of flow velocity on the ignition limit were also investigated. MMA/air mixtures and DME/air mixtures were used as the experimental objects. Laser-induced spark ignition in which minimum ignition energy can be measured constantly regardless of focal length of convex lens was adopted for an ignition method. The ignition energy was calculated by measuring the difference between the incident energy and the transmitted energy. The development of ignited kernels and propagating flames were recorded with a high-speed camera. The ignition energy for the mixtures with various equivalence ratios was measured to identify the ignition limit. The ignition energy in microgravity was lower than that in normal gravity. This tendency was remarkable for mixtures close to the lean ignition limit. This result indicated that the lean ignition limit could expand in microgravity. In shadowgraph images of flame kernel development, local quenching behaviors were observed in normal gravity. On the other hand, they were suppressed in microgravity. Flow velocity of flammable mixtures also affected the ignition energy and flame kernel formation.

Description

Japan
University of Tokyo
509
ICES509: Fire Safety in Spacecraft and Enclosed Habitats
Vienna, Austria
Yoshinari Kobayashi, University of Tokyo, Japan
Shinji Nakaya, University of Tokyo, Japan
Mitsuhiro Tsue, University of Tokyo, Japan
The 46th International Conference on Environmental Systems was held in Vienna, Austria, USA on 10 July 2016 through 14 July 2016.

Keywords

Fire safety in space, Gravity, Flow velocity, Laser-induced spark ignition, Ignition energy, Flame kernel development

Citation