Search for: All records

The diffraction behavior of gaseous detonations through an abrupt area change is investigated using hydrogen-oxygen-nitrogen mixtures at initial pressures of 0.5 and 1.0 bar. Critical conditions are noted and detailed discussion of the differing diffraction behaviors is undertaken, supported by simultaneous Schlieren and direct photography imaging as well as pressure-based velocity measurements. The experiments reveal four distinct diffraction regimes. The subcritical outcome is characterized by transmission failure with the leading shock front decoupling from the reaction zone, seen predominantly at lower oxygen concentrations. At intermediate oxygen levels, reinitiation from reflected shock waves is consistently observed. The critical regime exhibits both subcritical and supercritical outcomes, with detonation reinitiation at the diffraction dome's head leading to localized implosions for the supercritical case. Supercritical outcomes demonstrate successful detonation transmission, maintaining the shock front and reaction zone coupling. The effects of initial conditions on the probability of successful detonation transition and diffraction are highlighted. With the use of simultaneous direct photography and Schlieren imaging techniques, previously unseen details of the detonation and diffraction processes are recorded and explained. 

Elevated temperature and pressure laminar flame speed measurements of propane and n-heptane fuel blends were conducted using a Rapid Compression Machine-Flame (RCM-Flame) apparatus. Herein, the lack of experimental flame speed data at simultaneously high temperatures and pressures akin to practical combustion conditions is addressed. The RCM-Flame apparatus is validated against a larger constant volume combustion chamber (CVCC) and simulations using a propane-nitrogen-oxygen mixture at ambient temperature and different pressures, demonstrating high fidelity. Further experiments with an n-heptane-nitrogen-helium-oxygen mixture reveal agreement between experimental and simulated flame speeds at semi-elevated, post-compression conditions. Trials with a propane-helium-oxygen mixture over varied temperatures and pressures demonstrate measured flame speeds falling between two kinetic mechanism simulations, maintaining the general trend. A power-law model correlating laminar flame speeds with elevated temperatures and pressures is developed for propane-helium-oxygen flames at a unity equivalence ratio. Overall, the kinetic mechanisms are shown to be able to predict flame speeds at elevated temperatures and pressures providing validation at conditions not yet explored in literature, optimistically advancing combustion research for practical applications.