The results of toluene and heptane show an immediate
transition to a flaming fire after ignition. This is indicated
in Figs. 5 and 6 where concentrations of CO, CO2, and
smoke begin to rise at the same time. On the other hand,
the results of HDPE in Fig. 7 show a period of smoldering
fire (indicated by a sharp rise in CO and smoke
concentrations) immediately after ignition, then transitioning
to a flaming fire 180 s later (indicated by a sharp rise in
CO2 concentrations).
Noise in the CO and CO2 measurements were 3 and
600 ppm, respectively. As a result, the background
concentrations of CO and CO2 in the atmosphere before
the burning tests cannot be measured. Noise and baseline
drift can be minimized by selecting absorption lines of CO
and CO2 that do not overlap with each other. The limited
tuning range of the DFB laser prevented the full resolution
of these absorption line shapes. The use of a vertical cavity
surface emitting laser, which can scan several absorption
lines over a single laser current scan, could potentially
resolve these issues. Additional calibration of the gas
measurement system could reduce the baseline drift as well.