Experimental Investigation of Pressure Development and Flame Characteristics in a Pre-Combustion Chamber
Creators: name: Miller, Jared C
Publisher: name: Purdue University Graduate School
Year: 2024
Subjects: classificationCode: 401799
subject: Mechanical engineering not elsewhere classified

description: This study contributes to research involving wave rotor combustors by studying thedevelopment of a hot jet issuing from a cylindrical pre-combustion chamber. The pre-chamber wasdeveloped to provide a hot fuel-air mixture as an ignition source to a rectangular combustionchamber, which models the properties of a wave rotor channel. The pre-combustion chamber inthis study was rebuilt for study and placed in a new housing so that buoyancy effects could bestudied in tandem with other characteristics. The effectiveness of this hot jet is estimated by usingdevices and instrumentation to measure properties inside the pre-chamber under many differentconditions. The properties tracked in this study include maximum pressure, the pressure and timeat which an aluminum diaphragm ruptures, and the moment a developed flame reaches a preciselocation within the chamber. The pressure is tracked through use of a high-frequency pressuretransducer, the diaphragm rupture moment is captured with a high-speed video camera, and theflame within the pre-chamber is detected by a custom-built ionization probe. The experimentalapparatus was used in three configurations to study any potential buoyancy effects and utilizedthree different gaseous fuels, including a 50%-50% methane-hydrogen blend, pure methane, andpure hydrogen. Additionally, the equivalence ratio within the pre-chamber was varied from valuesof 0.9 to 1.2, and the initial pressure was set to either 1.0, 1.5, or 1.75 atm. In all cases, combustionwas initiated from a spark plug, causing a flame to develop until the diaphragm breaks, releasinga hot jet of fuel and air from the nozzle inserted into the pre-chamber. In the pressure transducertests, it was found that hydrogen produced the highest pressures and fastest rupture times, andmethane produced the lowest pressures and slowest rupture times. The methane-hydrogen blendprovided a middle ground between the two pure fuels. An equivalence ratio of 1.1 consistentlyprovided the highest pressure values and fastest rupture out of all tested values. It was also foundthat the orientation has a noticeable impact on both the pressure development and rupture momentas higher maximum pressures were achieved when the chamber was laid flat in the “vertical jet”orientation as compared to when it was stood upright in the “horizontal jet” orientation.Additionally, increasing the initial pressure strongly increased the maximum developed pressurebut had minimal impact on the rupture moment. The tests done with the ion probe demonstratedthat an equivalence ratio of 1.1 produces a flame that reaches the ion probe faster than anequivalence ratio of 1.0 for the methane-hydrogen blend. In its current form, the ion probe setup18has significant limitations and should continue to be developed for future studies. The propertiesanalyzed in this study deepen the understanding of the processes that occur within the pre-chamberand aid in understanding the conditions that may exist in the hot jet produced by it as the nozzleruptures. The knowledge gained in the study can also be applied to develop models that can predictother parameters that are difficult to physically measure.