Experimentelle und numerische Untersuchung magerer Methan-Hochdruckverbrennung unter Mikrogravitation

摘要

The experimental and numerical examination of laminar lean premixed combustion of methane air mixtures at high pressures under normal and microgravity is the aim of this thesis. The elimination of buoyancy under microgravity is essential for the exact determination of the flammability limit and the burning velocity and furthermore allows the analysis of flame instabilities. First the lean flammability limit for upward combustion of methane was determined by the pressure increase inside the combustion chamber for pressures up to 70 bar under normal gravity. The chamber was equipped with an optical access which was used for filming the combustion in the microgravity experiments. These experiments were conducted at the Bremen drop tower which allows 4,7 sec microgravity. In the experiments the combustion chamber was first filled with a predefined methane air mixture which was then ignited by a spark. The combustion was then filmed by a high speed camera with schlieren optics. These films were used to determine the flame speeds and the burning velocity. The burning velocity for mixtures close to the flammability limit were ca. 1 mm/s. The flammability limit under microgravity is leaner than under normal conditions. Furthermore flame front instabilities were observed. The development of the amplitudes of the cellular instabilities were different to each other and a small change in the initial conditions had a large influence on the behavior of the flame front. The numerical simulations of one-dimensional plane flames in an idealized combustion chamber were conducted with the program FlameMaster. Both the flammability limit and the burning velocities from the simulations showed a good correlation to the experimental results.