Numerical Analysis of Piloted Ignition Over a Combustible Solid
Tzung-Hsien Lin, Chia-Hung Wu
Department of Mechanical Engineering
Southern Taiwan University of Technology, Yung Kang, Tainan 710, Taiwan
This study develops a two-dimensional piloted ignition model of a
PMMA solid fuel heated by external radiation in a quiescent, normal
gravity environment. The gas phase model consist of two-dimensional,
time-dependent continuity, complete elliptic Navier-Stokes, energy and
species equations. The combustion is described by a one-step overall
chemical reaction with finite rate global kinetics. The solid phase is
modeled by an unsteady energy and mass conservation equations, which
coupled with the gas phase through the energy feed back term from the
gas phase. The solid pyrolysis is described by first-order Arrhenius
expression. The model investigated the piloted ignition phenomena and
subsequent transition to flame spread behaviors under various igniter,
fuel surface temperature and external heat flux. Besides the external
radiation source, the piloted ignition needs a high temperature piloted
igniter to trigger the thermal runaway in the gas phase. If the piloted
igniter located at or near the region which the fuel/air mixture are within
the flammable limitation, the flash or piloted ignition will occurs. In this
study, the piloted igniter used in the laboratory such as high temperature
particle, hot platinum wire and piloted small flame are modeled by the
multi-points, linear type and plane type hot region within the raising
plume in the gas-phase. Whereas the external radiant heat source used in
laboratory is modeled by a Gaussian distribution heat flux in the
computation model. This allows the pilot ignition as well as the flash
phenomena can be simulated readily. The study parameters used in this
work are the piloted igniter type, the location of the piloted igniter, the
fuel surface temperature and the intensity of external radiant heat flux. It
was found that the fuel surface temperature at the ignition increases with
the distance of the igniter to the surface. The trend was compared with
the previous experimental correlation. The ignition delay time under
various intensity of external radiant heat flux also predicted and
compared with experiments data for different igniter distance. Therefore,
the piloted ignition is more hazards than the auto-ignition.
Corresponding Author: Tzung-Hsien Lin
Department of Mechanical Engineering
Southern Taiwan University of Technology,
1 Nan Tai Street, Yung Kang, Tainan 710, Taiwan
Telephone : 886-6-2533131 Ext 3542
FAX
: 886-6-2425092
E-mail
: thlin@mail.stut.edu.tw