Influence of LOX injector wall thickness on atomization and combustion of LOX/CH₄ sprays

This paper summarizes the results of a test campaign at the micro-combustor M3 in DLR Lampoldshausen performed with liquid oxygen (LOX)/methane (CH ₄); the micro-combustor has complete optical access and is provided with a single coaxial injector. These experiments are a first attempt to show experimentally the influence of the LOX injector wall thickness on the atomization and combustion behaviors. Two LOX injector wall thicknesses (0.4 and 0.6 mm) have been investigated. At injection, the Weber number ranged between 2.0·10³ and 1.2·10⁴, the fuel to oxygen momentum flux ratio J between 0.1 and 0.7. Combustion chamber pressures between 0.15 and 0.3 MPa were achieved. High speed flow visualization techniques have been applied; a high speed CCD camera with 4 kHz frame rate is used for shadowgraph, whereas an ICCD camera with 9 kHz frame rate is adopted for OH imaging in the UV range. In the thicker wall injection configuration, atomization is found to be more effective and combustion efficiency is enhanced, because of a more stable combustion, occurring nearer to the injector.