Combustion experiments to produce smoke particles were
conducted in the configuration shown in Fig. 4 and described
in more detail in Ref. [17], where smoke particles from either
flaming or smoldering combustion are generated in a cubical
enclosure measuring 0.30 m along each edge and then flowed into
a standard UL 217 smoke box [18] through a variable-orifice iris
that controlled the rate of aerosol accumulation within the smoke
box. Inside the smoke box, three of the commercial smoke
detectors were placed on a platform and two small internal fans
were used to mix the incoming smoke particles to produce a
uniform distribution throughout the chamber. The optical density
of the aerosol was measured over a 1.483 m optical path using an
incandescent lamp and a standard photocell with a peak response
at a wavelength of 546 nm and a spectral response matching the
spectral response of the human eye. During the experiments,
smoke particle samples were continuously extracted through a
metal tube inserted into the top of the smoke box very close to the
location of the three commercial sensors and then flowed to three
of the prototype smoke detectors. In this configuration, data were
obtained for flaming No. 2 diesel fuel (a small pool flame), flaming
coal, flaming wood, flaming styrene butadiene rubber (SBR),
smoldering coal, smoldering wood, and smoldering SBR.
For diesel exhaust particles, the experimental system in which
the tests were conducted, known generically as a dust box, is
shown in Fig. 5 and described in greater detail in Ref. [19]. Briefly,
dusts or diesel exhaust particles are dispersed near the top of the
dust box, allowed to mix thoroughly and then fall via gravity
coupled with a small, imposed flow. Samples of diesel exhaust
particles are extracted through 10 mm cyclones near the bottom
of the dust box at nominal flow-rates of 2 lpm and flowed to three
prototype smoke detectors. In this configuration, data were
acquired for particles produced from the exhaust of a diesel
generator under different load conditions.
During the diesel exhaust experiments, a Tapered Element
Oscillating Microbalance (TEOM) [20] was used to continuously
measure the mass concentrations of aerosol. In the TEOM, a small
filter is mounted onto what amounts to a hollow tuning fork
vibrating at a fixed frequency. Particles in the flow through this
filter are deposited on the filter increasing the filter mass. As the
filter mass increases, the frequency of vibration decreases
proportionally so that the change in mass due to accumulation
of particles on the filter is measured as a function of time. The rate
of change of the filter mass (due to smoke particles) divided by the
volumetric flow rate through the filter yields the average mass
concentration.