The present thesis investigates the interaction of a shock wave with a cellular flame and the ensuing mechanisms on the dynamics of the subsequent flame deformation. The inter- action is known to disrupt the flame surface through the Richtmyer-Meshkov instability, hence potentially enhancing the local combustion rates. This study aims to clarify the evolution of a flame when perturbed head-on by a shock wave. Two novel series of experiments were conducted in a vertically-oriented Hele-Shaw cell, which could successfully isolate a quasi-bidimensional cellular flame structure at ambient conditions. In the first configuration, the passage of the shock wave arising in the burned products of a deflagration wave was investigated, while both waves propagated in the same outward direction. In the other configuration, the shock wave centrally emerged in the unburned gases and collided with a cellular flame front traveling in the opposite direction. The event was captured using a Z-type Schlieren imaging system to visualize the growth of the flame cells. Shock characterization was determined in the Hele-Shaw apparatus to estimate the strength of the blast wave generated by energy deposition using a high-voltage igniter or by decoupled detonation from a detonation tube. A combustion study was also performed to determine the laminar flame speed in a mixture of hydrogen-air according to different equivalence ratios in the apparatus. The experiments revealed that inherent cellular flame instabilities are well developed in the observation scale of the Hele-Shaw geometry. The shock-flame complex was therefore analyzed experimentally for selected mixtures. As the shock wave traversed the interface separating the burned and unburned gases, the flame became more corrugated. Following the interaction, the flame cusps were stretched and/or flattened. At later times, the wrinkled interface was reversed and developed finer scales. A time scale analysis was performed to identify the contribution of the competing effects of Richtmyer-Meshkov and Rayleigh-Taylor instabilities on the flame interface deformation. For the case of a shock wave traversing the flame interface from the unburned to the burned side, the early perturbations were mainly governed by the Richtmyer-Meshkov instability. Finally, Rayleigh-Taylor instability resulted from the decaying pressure profile of the blast wave and tended to stabilize the perturbed interface to eventually reverse the cellular structure. Experimental and inert numerical results on the flame cell’s amplitude growth were found to be in good agreement.

Indiana University-Purdue University Indianapolis (IUPUI) / Investigations of a constant-volume combustor ignited by a penetrating transient jet (a puff) of hot reactive gas have been conducted in order to provide vital data for designing wave rotor combustors. In a wave rotor combustor, a cylindrical drum with an array of channels arranged around the axis spins at a high rpm to generate high-temperature and high-pressure product gas. The hot-gas jet ignition method has been employed to initiate combustion in the channels. This study aims at experimentally investigating the ignition delay time of a premixed combustible mixture in a rectangular, constant-volume chamber, representing one channel of the wave rotor drum. The ignition process may be influenced by the multiple factors: the equivalence ratio, temperature, and the composition of the fuel mixture, the temperature and composition of the jet gas, and the peak mass flow rate of the jet (which depends on diaphragm rupture pressure). In this study, the main mixture is at room temperature. The jet composition and temperature are determined by its source in a pre-chamber with a hydrogen-methane mixture with an equivalent ratio of 1.1, and a fuel mixture ratio of 50:50 (CH4:H2 by volume). The rupture pressure of a diaphragm in the pre-chamber, which is related to the mass flow rate and temperature of the hot jet, can be controlled by varying the number of indentations in the diaphragm. The main chamber composition is varied, with the use of four equivalence ratios (1.0, 0.8, 0.6, and 0.4) and two fuel mixture ratios (50:50, and 30:70 of CH4:H2 by volume). The sudden start of the jet upon rupture of the diaphragm causes a shock wave that precedes the jet and travels along the channel and back after reflection. The shock strength has an important role in fast ignition since the pressure and the temperature are increased after the shock. The reflected shock pressure was examined in order to check the variation of the shock strength. However, it is revealed that the shock strength becomes attenuated compared with the theoretical pressure of the reflected shock. The gap between theoretical and measured pressures increases with the increase of the Mach number of the initial shock. Ignition delay times are obtained using pressure records from two dynamic pressure transducers installed on the main chamber, as well as high-speed videography using flame incandescence and Schileren imaging. The ignition delay time is defined in this research as the time interval from the diaphragm rupture moment to the ignition moment of the air/fuel mixture in the main chamber. Previous researchers used the averaged ignition delay time because the diaphragm rupture moment is elusive considering the structure of the chamber. In this research, the diaphragm rupture moment is estimated based on the initial shock speed and the longitudinal length of the main chamber, and validated with the high-speed video images such that the error between the estimation time and the measured time is within 0.5%. Ignition delay times decrease with an increase in the amount of hydrogen in the fuel mixture, the amount of mass of the hot-jet gases from the pre-chamber, and with a decrease in the equivalence ratio. A Schlieren system has been established to visualize the characteristics of the shock wave, and the flame front. Schlieren photography shows the density gradient of a subject with sharp contrast, including steep density gradients, such as the flame edge and the shock wave. The flame propagation, gas oscillation, and the shock wave speed are measured using the Schlieren system. An image processing code using MATLAB has been developed for measuring the flame front movement from Schlieren images. The trend of the maximum pressure in the main chamber with respect to the equivalence ratio and the fuel mixture ratio describes that the equivalence ratio 0.8 shows the highest maximum pressure, and the fuel ratio 50:50 condition reveals lower maximum pressure in the main chamber than the 30:70 condition. After the combustion occurs, the frequency of the pressure oscillation by the traversing pressure wave increases compared to the frequency before ignition, showing a similar trend with the maximum pressure in the chamber. The frequency is the fastest at the equivalence ratio of 0.8, and the slowest at a ratio of 0.4. The fuel ratio 30:70 cases show slightly faster frequencies than 50:50 cases. Two different combustion behaviors, fast and slow combustion, are observed, and respective characteristics are discussed. The frequency of the flame front oscillation well matches with that of the pressure oscillation, and it seems that the pressure waves drive the flame fronts considering the pressure oscillation frequency is somewhat faster. Lastly, a feedback mechanism between the shock and the flame is suggested to explain the fast combustion in a constant volume chamber with the shock-flame interactions.