  In this work, oblique detonation of n-heptane/air mixture in high-speed wedge
flows is simulated by solving the reactive Euler equations with a
two-dimensional (2D) configuration. This is a first attempt to model
complicated hydrocarbon fuel ODWs with a detailed chemistry (44 species and 112
reactions). Effects of freestream equivalence ratios and velocities are
considered, and the abrupt and smooth transition from oblique shock to
detonation are predicted. Ignition limit, ODW characteristics, and
predictability of the transition mode are discussed. Firstly, homogeneous
constant-volume ignition calculations are performed for both fuel-lean and
stoichiometric mixtures. The results show that the ignition delay generally
increases with the wedge angle. However, a negative wedge angle dependence is
observed, due to the negative temperature coefficient effects. The wedge angle
range for successful ignition of n-heptane/air mixtures decreases when the
wedge length is reduced. From 2D simulations of stationary ODWs, the initiation
length generally decreases with the freestream equivalence ratio, but the
transition length exhibits weakly non-monotonic dependence. Smooth ODW
typically occurs for lean conditions (equivalence ratio < 0.4). The
interactions between shock / compression waves and chemical reaction inside the
induction zone are also studied with the chemical explosive mode analysis.
Moreover, the predictability of the shock-to-detonation transition mode is
explored through quantifying the relation between ignition delay and chemical
excitation time. It is demonstrated that the ignition delay (excitation time)
increases (decreases) with the freestream equivalence ratio for the three
studied oncoming flow velocities. Smaller excitation time corresponds to
stronger pressure waves from the ignition location behind OSW.
