Study of Technology for Detecting Pre-Ignition Conditions of ... - NIST

CPSC-IAG95-1145
Figure 30 shows the total hyh-oca.rlxm ad water areas as a function of time fen-a test of
~~]~ea~e~ on ~ elec~ic range with the range hood off. Hydrocarbon area is the area under the
hydrocarbon spectral peak integrated from 2782 cm-l to 3029 cm-l. Thk frequency range
corresponds to the spectral band produced by the stretching of carbon-hydrogen bonds in alkanes,
alkenes, and aromatic hydrocarbons. 9 The limited spectral resolution of the instrument and the
likely overlap and interference of the spectra of many hydrocarbons prevented fi.uther
identification of specific organic compounds within the broad peak. The hydrocarbon curve rises
sharply in a manner similar to the laser attenuation curves. The water area is the area under the
water spectral peak integrated from 1644 cm-l to 1755 cm-l. Water increases more gradually
than the hydrocarbons and peaks at one fourth of the hydrocarbon amount.
Figure 31 shows a wmparison of the hydrocarbon-area measurements for all of the food
and range-hood combinations heated cm the electric range- Sugar produces similar levels of
hydrocarbons to those produced by the other foods, but in a shorter period of time. The CWVeS
closely resemble those for laser attenuation except sugar generates the most hydrocarbons,
followed by bacon and oil.
Figure 32 shows a comparison of the hydrocarbon-area measurements for all of the food
and range combinations heated on the high-output gas range. The gas range seems to produce
similar levels of hydrocarbons from heating food to those produced by the electric range. The
coarse time resolution of these measurements makes it difficult to accurately compare the
maximum levels since the last spectral scans before ignition are averaged with scans tier
ignition, The data points shown are those averages that were not tainted by post-ignition scans,
Figure 33 shows a comparison of the water-area measurements for all of the food and
range-hood combinations heated on the electric range. The heating of sugar produces much more
water than either bacon or oil due to the breakdown of the chemical structure of sucrose. For
bacon, water initially boils off due to the water content of the meat, and then more water vapor
forms later as a pyrolysis product. Heating of the oil produces no water initially, but increasing
amounts form as some components of the oil begin to break down.
Figure 34 shows a comparison of the water-area measurements for all of the food and
range combinations heated on the high-output gas range. Water was measured immediately upon
the start of each test using the gas range. This is due to the addition of a constant level of water
vapor from combustion of the burner flame to the water contributed from the foods.
~ effort was made to generate Coz mea cu~es by integrating the C02 SPeCtral band
from 2320 cm-l to 2383 cm-]. The results initially seemed nonphysical because of negative areas
which implied a decrease in C02 from ambient levels. One possible explanation is that little or
no air, which contains C02 on the order of several hundred ppm, WaS en~ained by the PIume ~d
passed by the FTIR beam in the section of the path length over the pan. Thk would cause less
C02 to be measured during the experiments than was measured as background levels. Since the
background data were subtracted from the experimental da@ negative areas resulted. Another
explanation is that the increased temperature of the plume relative to the cool background caused
the C02 molecules to spread apart, and the decreased number density of COZ molecules was
interpreted as an absolute decrease in C02 by the FTIR. A third possibility is that the increase
in plume temperature during the test over the ambient background temperature produced enough
additional infrared radiation from the plume to cause the relative absorbance by C02 in the hot
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