Ignition of Cellulosic Fuels by Heated and Radiative Surfaces.
Ignition of Cellulosic Fuels by Heated and Radiative
Surfaces.
(8944 K)
Pitts, W. M.
NIST Technical Note 1481; NIST TN 1481; 105 p. March
2007.
Keywords:
cellulosic fuels; ignition; mufflers; catalytic
converters; scenarios; surface temperature; wind
effects; air flow; fuel beds; combustion; flaming
combustion; ignition time; thermal conduction; thermal
radiation; cone calorimeters; polyurethane foams;
surface ignition; newsprint; grasslands
Abstract:
Experiments designed to characterize the ignition
behavior of typical outdoor fuels by heated mufflers and
catalytic converters found on outdoor power equipment
are described. Ignition by direct contact with a heated
surface and by radiation from a heated surface were
considered. For the first scenario the fuel was placed
in contact with an electrically heated surface, and the
times required for ignition measured as a function of
surface temperature. The effects of a wind on heated
plate ignition were studied by passing air flows of 1.1
m/s and 2.5 m/s over the fuel bed. Fuels tested included
shredded newsprint, four types of grass, pine needles, a
grass/pine needle mixture and three types of dry leaves.
Both glowing combustion and flaming were observed. The
transition to flaming required glowing combustion to be
present. Ignition times generally increased with
decreasing surface temperature until a temperature was
reached where ignition was no longer observed. Ignition
times for given applied wind and surface temperature
conditions and transition to flaming behavior were fuel
dependent. An applied wind generally reduced the time
required for ignition, with the reduction being greater
for the higher velocity. A commercially available cone
calorimeter operated in the non piloted ignition mode
was used to impose known radiative heat fluxes on the
fuel surface, and ignition times were measured as a
function of applied heat flux. Shredded newsprint, two
types of grass, pine needles, and non fire-retarded
flexible polyurethane foam were studied. Ignition times
for radiative heating increased with decreasing applied
heat flux until levels were reached where ignition did
not occur. The polyurethane foam had a distinctly
different behavior than the cellulosic fuels. Comparison
of the heated plate and radiative heating experiments
suggests that they can be related using the black body
temperature corresponding to the applied radiative heat
flux.
