Kc. Smyth et Np. Bryner, SHORT-DURATION AUTOIGNITION TEMPERATURE-MEASUREMENTS FOR HYDROCARBON FUELS NEAR HEATED METAL-SURFACES, Combustion science and technology, 126(1-6), 1997, pp. 225-253
An apparatus has been designed, built, and extensively tested For maki
ng short-duration autoignition temperature measurements of hydrocarbon
fuels under atmospheric pressure conditions where the fuel/air stoich
iometry, the nature of the hot metal surface, and the contact time bet
ween the fuel/air mixture and the heated surface are well controlled.
This approach provides a much more reliable database to establish the
importance of fuel structure and surface effects on measured autoignit
ion temperatures than the current ASTM E659 procedure, which involves
variable ignition delay times and unspecified stoichiometries for igni
tion in a heated glass flask. Two series of tests have been conducted:
(1) over 1100 individual autoignition temperature determinations for
the ignition of 15 hydrocarbon fuels containing 1 to 8 carbon atoms on
heated nickel, stainless steel, and titanium surfaces for three diffe
rent stoichiometries (phi = 0.7, 1.0 and 1.3); and (2) similar to 190
determinations for 10 linear and branched alkanes on heated nickel for
stoichiometric conditions. Excellent repeatability has been achieved
within a given series of measurements, and good replicate values have
been obtained for data collected on Separate days. Autoignition temper
atures measured under short-contact time conditions are much higher (b
y typically 500 K or more) than found in most prior investigations, wh
ere exposure times were longer and test conditions less well controlle
d. The autoignition temperatures generally decrease for the larger hyd
rocarbons and for richer mixtures, although the C-2 hydrocarbons (etha
ne, ethylene and acetylene) have particularly low values. The highest
autoignition temperatures are observed for nickel surfaces and the low
est for stainless steel, with titanium being an intermediate case. Ove
rall, the different metal sufaces exhibit a moderate influence on the
observed autoignition temperatures. Prior experimental and modeling in
vestigations indicate that the branched alkanes should be more resista
nt to autoignition than the linear isomers, and thus present a reduced
hazard. Data obtained in the present study are consistent with this p
rediction, although the differences in measured autoignition temperatu
res are typically less than 100 K for isomers containing the same numb
er of carbon atoms.