<p>A hot surface is one of the
ignition sources which may lead to fires in the presence of aviation fluid
leakage. Bleeding ducts and exhaust pipes that are at elevated temperatures are
potential sources of ignition. A database
of Minimum Hot Surface Ignition Temperatures (MHSIT) resulting from experiments
conducted three decades ago at the Air Force Research Laboratory (AFRL), Dayton,
OH has served as a valuable source of estimating safe operating temperatures. However,
MHSIT for some of the aviation fluids such as Jet-A and MIL-PRF-23699
(lubrication oil) are not readily available. Further, the ranges of the hot
surface and flammable liquids’ temperatures and the range of the air stream
velocities need to be extended for use in higher pressure ratio and higher
performance aircraft engines developed since the generation and interpretation
of the original data. The air velocities (V<sub>A</sub>) in the modern engines
have increased by a factor of two and documenting their effects on the MHSIT
for a range of test fluid temperatures and air temperatures (T<sub>F</sub>, T<sub>A</sub>)
is important.</p>
<p>The
objectives of this study are to develop a generic test apparatus to study MHSIT
and to model an air-fuel mixture space to find the range of temperatures and
velocities that lead to ignition. Among various leakage scenarios, the test
apparatus simulates spray (atomized particles injected through a nozzle) and
stream (dripping from a 3 mm tube) injection. A semiempirical ignition model was
developed using an ignition temperature and delay time expression based on an
energy balance between the heat lost to the cross-stream flow, the heat added
from the hot surface and the heat released by the nascent chemical reactions to
estimate the MHSIT.</p>
<p> </p>
<p>MHSIT is measured including the
effects of V<sub>A</sub>, T<sub>F</sub>, T<sub>A </sub>and the effects of
obstacles. Ignition probability is evaluated as a function of the hot surface
temperature. The probabilistic nature of the hot surface ignition process was established.
New flammable fluids (Jet-A & MIL-PRF-23699) have been tested and MHSIT
database was expanded. A large number of ignition experiments were completed to
evaluate ignition probability at various flow conditions of aviation fluids:
(1) Jet-A, (2) Hydraulic oil (MIL-PRF-5606) and (3) Lubrication oil
(MIL-PRF-23699). Uncertainty of the experimental measurements for these tests
have been documented. Air velocities were extended up to 7 m/s. Effects of
flammable liquid and air temperature on MHSIT were studied. The empirical constants
for the semi-empirical model were determined using these experimental data.</p><p>The ignition probability is strongly correlated
with hot surface temperature and progressively weakly correlated with air
velocity, fluid parcel size, air temperature, and test fluid temperature. Parameters
investigated in this study are useful design choices considering MHSIT for a
given flow condition.</p><p></p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12252905 |
| Date | 07 May 2020 |
| Creators | Mehmed S Ulcay (8802791) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/EXPERIMENTAL_INVESTIGATION_AND_MODELING_OF_MINIMUM_HOT_SURFACE_IGNITION_TEMPERATURE_FOR_AVIATION_FLUIDS/12252905 |
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