Combustion of liquid fuels in a Rijke type pulse combustor

The research presented in this thesis focused on the investigation of the performance of a liquid fuel burning Rijke type pulse combustor, which utilized a novel tangential air/fuel injection system, and the mechanisms that controlled its operation.; The combustor that was developed under this program consisted of a vertical steel tube with two decouplers at both ends. Most of the combustion air and all the fuel entered the combustor through an air and fuel injection system, which was attached to the combustor tangentially and generated a swirling flow inside the combustor tube.; The performance and controlling mechanisms were investigated by measuring acoustic pressures, space and time resolved radiation emissions, steady temperatures, and exhaust flow compositions. In addition, high speed video and intensified images were used to visualize the reacting flow field.; The performance investigations showed that this combustor could operate in a pulsating mode over a wide range of nondimensional air/fuel ratios. The interaction between the acoustic oscillations and the combustion process resulted in high combustion efficiencies of various fuel oils ranging from No. 2 to No. 6 with relatively little excess air and low NO{dollar}sb{lcub}rm x{rcub}{dollar} concentrations in the exhaust flow.; To study the mechanisms that control the operation of this combustor, an experimental setup was developed with access for detailed optical measurements. Propane was employed as fuel because the absence of liquid drops and combustion generated particulates in the combustion region significantly simplified the optical diagnostics.; Flow visualization by the imaging system and the results from radiation intensity distribution measurements revealed that the periodic combustion processes was accompanied by the periodic vortex shedding process. High radiation intensity occurred during a relatively short period of time and was in phase with the pressure oscillations, indicating that Rayleigh's criterion was satisfied. In addition, acoustic pressure measurements in the air and fuel feed lines uncovered the presence of travelling pressure waves inside the feed lines. These travelling waves produced periodic fuel and air feed rates which, in turn, resulted in periodic combustion and heat release processes within the combustor. Pulse combustion became impossible when the air and fuel feed lines were choked by installing sonic orifices in the lines. This result indicated that air and fuel flow rate modulations were a critical element in the driving of the pulse combustion operation of the developed pulse combustor.