Experimental investigation of end-gas autoignition-to-detonation transition for an n-decane/O2/Ar mixture

The transition between different combustion regimes is investigated experimentally for a stoichiometric argon-diluted n-decane/O2 mixture. The focus is put on the influence of initial temperature (T = 420–470 K) and pressure (P = 1.5–3 bar) on the regime transitions. Fast schlieren visualization (≥ 120 kHz) and high-speed pressure and temperature measurements are used to monitor the evolution of the reactive processes inside a combustion chamber of square cross-section (40 mm × 40 mm × 172 mm). Results for P ≥ 2.5 bar and the entire temperature range and for P = 2 bar and T ≥ 440 K show three distinct stages following the adiabatic compression of fresh gases induced by the propagation of a flame into the chamber/test section, namely a cool flame, a main heat release stage, and detonation onset. For P = 1.5 bar, however, only the first two stages of the process are observed in the temperature range studied. A two-stage autoignition phenomenon, typical of large hydrocarbons, occurs systematically in the end gas and generates consecutive reactive fronts. The transition to detonation appears to result from the acceleration of the aforementioned fronts toward the speed of sound in fresh gases. Notably, the compression history plays a key role in setting conditions for detonation onset. Our results are in agreement with classical transition maps available in the literature.