Abstract
To clarify the effects of oxygen on cool‐flame, hotflame,
and two‐stage ignition, n‐decane droplet ignition
experiments were conducted at various ambient oxygen
volume fractions. The ambient oxygen volume fraction was set
to 15%, 21%, or 35%, with nitrogen added as the balance gas.
Ambient pressure and temperature were varied from 0.1 to 0.5
MPa and 530 to 890 K, respectively. The results showed that the
lower ambient temperature limit for hot‐flame ignition
decreased as the oxygen volume fraction increased. In contrast,
the effects on the upper ambient temperature limit for coolflame
ignition were minimal, likely due to the limited impact on the equilibrium constant of lowtemperature
oxidation reactions. Consequently, the no‐ignition region narrowed with the increase of
ambient oxygen volume fraction. One of the most significant findings was the observation of two‐stage
ignition at 0.2 MPa when the oxygen volume fraction was 35%. This suggests that the two‐stage ignition
behavior of hydrocarbon fuel droplets can be evaluated at 0.2 MPa, a condition under which combustion
experiments can be conducted on the Kibo module in accordance with safety regulations.
