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

CPSC-MG95-1145
a good cmdidate for such measurements. The burner or pan temperature on the electric range
could be used in conjunction with other signatures if threshold temperate or integrated time and
temperature behavior were utilized to detect pre-i~ition wnditions.
3.2.2 Plume
Figures 10 through 16 show the plume thermocouple grid temperatures as a function of
tin-w for a test of oil heated on an electric range with the range hood off. The grid diagram of
Figure 3 helps in interpreting these figures. Figure 10 shows the vertical profile of the pancenterline
~mpera@es above the bwmer. Before ignition, none of the temperawes exceeded
100 ‘C. The plumes were relatively cool compared to the pans and food below. At the highest
point above the burner, the tempera~re only reached about 40 “C. Figures 11 and 12 show the
vertical temperature profiles 7.6 cm to the left and right (when facing the range) of the pan
centerline. The temperawres left of center were much less than those right of center. This
implies a high degree of asymmehy in the plume. At 16.8 cm above the burner, the temperature
right of the pan centerline was even 10 ‘C greater than the centerline temperature. Figure 13
shows the vertical temperature profile 15.2 cm to the left of the centerline. Of all of the vertical
tempera~res, these were the coolest.
Figures 14, 15, and 16 show the changes in horizontal temperatures with time along lines
16.8 ~m, 37.1 cm, and 67.6 cm above the burner, respectively. These figures also demonstrate
that the plume temperatures were shifted to the right of center. The plumes in the tests conducted
on the hi~-ou~ut gas range tended to shift to the left slightly. In every case, while the degree
was different for each test, the plumes tended to lean away from the center of the range.
Figure 17 shows a comparison of the centerline temperamre 37.1 cm above the burner for
all of the food and rmge-hood ~mbinations heated on the electric range. The behaviors of the
same foods were similar. Figure 18 shows a comparison of the centerline temperature 37.1 cm
above the burner for all of the food and range combinations heated on the high-output gas range.
The bacon temperature curves are similar, but the oil curves differ by about 20 ‘C and show
difierent trends. Sugar ignited very quickly, even relative to the parallel electric-range test.
These figures show that the range hood affects the ignition process and the plume to a minor
degree at most.
The plume may be a di~~cult location to position a tempera~re measuring device as a
range pre-ignition detector. The temperatures are not very high in the plume and do not change
significantly with time during heating.
3.2.3 Range and Range Hood
Figure 19 shows the tempera~res of the range and range-hood themomuples as a
function of time for a test of oil heated on an electric range with the range hood off. The outside
surface of the hood actually cooled prior to ignition. The range surface thermocouples equidistant
from the burner have similar tempera~re curves. The temperature of the range beneath the
burner w-passed 200 ‘C which means that the space beneath the burner is a relatively hot
environment.
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