Wolfgang Mayer

Injection and Mixing Processes in High-Pressure Liquid Oxygen/Gaseous Hydrogen Rocket Combustors

The injection, mixing combustion processes in a liquid oxygen (LOX)/gaseous hydrogen (GH2) rocket engine combustor at high chamber pressures (10 MPa) are studied and modeled. An experimental LOX/GH2 rocket motor consisting of a single coaxial shear injector element and a cylindrical chamber with optical access has been used for flow visualizations and measurements. Cold-flow injection test utilizing liquid nitrogen and gaseous helium at elevated pressures have been done for flowfield characterization by different diagnostic methods such as flash-ligth photography and high-speed cinematography using a shadowgraph setup. The injection visualizations and studies under cold-flow and combusting conditions revealed a remarkable difference between subcritical spray formation and evaporation and the supercritical injection and mixing process. The study shows that aproaching supercritical chamber pressures injection can no longer be regarded as a spray formation but rather as a fluid/fluid mixing process. As the flow visualizations indicate, the effect of the coaxial atomizer gas is less effective as previously expected. The flame is attached to the LOX post and develops in the LOX post wake. The observed flame holding mechanism is discussed. An evaluation of the radiation spectrum of the flame inside the combustion chamber revealed that radiation in the visible range is mainly due to water vapor.

Characterization of Cryogenic Injection at Supercritical Pressure

Understanding the Complex environment of the rocket chamber involves good knowledge of the injection phenomena. Understanding the injection phenomena allows the rocket designer to employ time and cost saving modeling tools to design a higher performance rocket engine. The rocket engine performance is highly dependent on the injection processes within the chamber. This project looked at injection processes in the supercritical regime of the injected fluid, cryogenic nitrogen, in order to better understand realistic conditions in the rocket engines of today. The investigation considered test conditions from 4.0 to 6.0 MPa at two different injection velocities and temperatures. Experimental data taken by Raman imaging and Shadowgraphy were compared to computational models for these various test conditions. The test data allows comparisons of density, length scales and jet spreading angles. The results validate the computational models fairly well and agree with classical theory.This agreement allows further use of the models to predict injection behavior under these operating conditions. Also, further comparisons were made between the various test cases using the computational models to consider the effects of pressure, velocity and temperature variations on the cryogenic jet.

Propellant Atomization and Ignition Phenomena in Liquid Oxygen/Gaseous Hydrogen Rocket Combustors

The mixing and combustion processes in a liquid oxygen/gaseous hydrogen rocket combustor were studied. The research focused on observations of atomization phenomena during steady-state combustion and ignition transients of a rocket engine. Cold-e ow atomization as encountered before ignition has been studied using liquid oxygen/gaseous hydrogen and simulation e uids liquid nitrogen/helium. The theoretical assessments show that for binary- and multicomponentsystems atranscriticalregion existswheresurfacetension ispresenteven atpressures above the critical pressure of one component as long as the critical mixing temperature is not exceeded. Also, hote retestsutilizing liquid oxygen/gaseoushydrogen demonstratethestrong ine uenceofthee ameon theatomization process.Thee amepropagation duringignitioncouldbeidentie edbythechangeoftheatomizationphenomenology before and during the ignition process. Nomenclature da = outer diameter di = inner diameter Pr = reduced pressure p = pressure T = temperature u, v = velocity π = chemical potential Ω = density ae = surface tension Subscripts c = chamber crit = critical gas = gas i = specie liq = liquid s = saturation

Rocket Engine Coaxial Injector Liquid/ Gas Interface Flow Phenomena

Coaxial injectors are used for the injection and mixing of propellants H2/O2 in cryogenic rocket engines. The aim of the theoretical and experimental investigations presented here is to elucidate some of the physical processes in coaxial injector flow with respect to their significance for atomization and mixing. Experiments with the simulation fluids H2O and air were performed under ambient conditions and at elevated counter pressures up to 20 bar. This article reports on phenomenological studies of spray generation under a broad variation of parameters using nanolight photography and high-speed cinematography (up to 3 x 10(exp 4) frames/s). Detailed theoretical and experimental studies of the surface evolution of turbulent jets were performed. Proof was obtained of the impact of internal fluid jet motions on surface deformation. The m = 1 nonaxisymmetric instability of the liquid jet seems to be superimposed onto the small-scale atomization process. A model is presented that calculates droplet atomization quantities as frequency, droplet diameter, and liquid core shape. The overall procedure for implementing this model as a global spray model is also described and an example calculation is presented. 15 refs.

Cryogenic rocket engine research within the National Technology Program TEKAN at the German Aerospace Center

The paper presents the highlights and a summary report of the research activities on cryogenic propulsion at the German Aerospace Center in Lampoldshausen within the National Technology Program. The research is conducted in cooperation with European industries and research establishments. The German National Technology Programme on Cryogenic Rocket Engines TEKAN, which is presented here, is a joint DLR/Astrium GmbH project with the aim to provide key technologies for future cryogenic rocket engines. The research work at the German Aerospace Center is focused on the injector, combustor, and nozzle technology and related topics.

Observation of LOX/Hydrogen Combustion Flame in a Rocket Chamber During Chugging Instability

To obtain concrete information on the mechanism of unstable combustion of liquid oxygen-hydrogen rocket engines, a rectangular rocket chamber with four glass windows was developed. The chamber was designed to simulate a 100-kN-sized cylindrical rocket chamber. Combustion tests were conducted at a chamber pressure of 1.7MPa. Combustion flames and oxygen jets were visualized with a high-speed video at a rate of 4,000 frame/s during low frequency unstable combustion. Oxygen jet images with a backlight, combustion flame and intensity of combustion flame were obtained. Stability analysis based on the double time lag model by Szuch was conducted to assist the understanding of the mechanism of unstable combustion.