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

CI%C-IAG-95-1145
tirou@out this section. The results and discussion focus pfimatily on comparing the same
memurement from each different fire on the same plot and judging the potential use of that
memurement as a universal pre-ignition signature. Not all of the measurements are compared,
but certain measurements within each family of similar measurements were selected as both
typical of the type of memurement and most practical for future implemen~tion based on
location. The comparison plot curves all begin at the time the burner was energized and end
about two seconds before the i~ition time. The oil and bacon in the electric-range tests ignited
significantly faster than the same foods in the hi~-output gas-range tests. For this reason, the
me~urement comparisons are separated by range type. “On” and “OW in the comparison plots
legends refer to the status of the range hood for each test.
3.2 ~e~~erat~res
3.2.1 Pan arid Food
Figure 5 shows the temperatures from the pan and food thermocouples as a function of
time for a test of oil heated on an electric range with the range hood off. There was apparently
no temperature gradient within the oil since the two food curves coincide. The pan inside-wall
temperature was also identical to the food tempera~rm until ignition when the thermocouples in
the oil were displaced from the pan by the lid as it was used to extinguish the fire. After
ignition, the food tempera~es no longer indicated the temperature of the food since the
themocmples lost contact with the food and were on top of the lid. After ignition, the panbottom
temperature gradually approached the pan-side temperature.
Figure 6 shows a comparison of the pan-bottom temperatures for all of the food and
rmge-hood mmbinatiom heated on the electric range. The sugar results exhibit a much faster
temperature rise because heat is tiasfemed to sugar less efficiently than to oil which allows the
metal pan to retain more of its heat in the sugar case. The oil and bacon curves are all similar
to each other. Figure 7 shows a comparison of the pan-bottom temperatures for all of the food
and range ~mbinations heated on the hi@-output gas range. The tests of bacon and oil with the
range hood off experienced much higher temperatures than the same foods with the range hood
on. It is utiom whether this was due to the lack of heat extraction by the hood or some other
reason. It could also have been a conf@uration effect because a minor change in the proximity
of the themowuple to the burner flame could greatly influence the measured temperatures.
Figure 8 shows a comparison of the pan-side temperatures for all of the food and rangehood
mmbinations heated on the electric range. Except for the test of oil with the range hood
on, all of the temperature curves are similar. Figure 9 shows a comparison of the pan-side
temperawes for all of the food and range ecnnbinations heated on the high-output gas range. The
oil tests’ trends are similar, but the test with an inactive range hood does show faster heating.
The sugar test results show a much faster temperature rise due to the initially dry state of the
sugar, and the bacon test has a much slower temperature rise than either the sugar or oil.
The temperatures of the food and pan may show reproducible and predictable pre-ignition
behavior, but the locations are quite inconvenient for measurements during cooking. CM the
electric range, the burner and pan bottom should experience similar conditions so the burner is
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