Experimental determination of the laminar burning velocity of methane-oxygen-flames stabilized with cylindrical burners at various preheating temperatures

The laminar burning velocity of pure methane-oxygen flames stabilized with a cylindrical tube burner was determined experimentally via optical methods (Schlieren-technique and CH* chemiluminescence). Both flow exit profiles were examined: a fully developed and a plug flow profile. The experiments were conducted for an equivalence ratio range of 0.5 < Φ < 2.2, while the inlet temperature of the educts was set to 293 K. The results of the CH4-O2 flames show a maximum laminar burning velocity of approx. 360 cm/s near stoichiometric conditions

Development of a porous burner for low calorific gaseous fuels offering a wide operating range [in press]

This work presents the development of a burner for the utilization of low calorific value waste gas, as it arises in the production of high purity hydrogen from biogas using an oxidative steam reforming process. Stable combustion of different fuel gases with fluctuating gas composition over a wide operating range is assured by the application of combustion in an inert porous medium (PIM) utilizing a kinematic flame stabilization mechanism. The development of the PIM-burner bases on calculated effective flame speeds within PIM derived from a 1-D numerical model including harsh operating conditions with preheating temperatures above 800 K and carbon dioxide concentration of 70 %-vol in the fuel gas. Experiments are conducted on a tailored test rig in order to validate numerical predictions by comparison of calculated effective flame speeds to eff ective flame speeds derived from temperature measurements in PIM

Implementation and Validation of a Computationally Efficient DNS Solver for Reacting Flows in OpenFOAM

To meet future climate goals, the efficiency of combustion devices has to be increased. This requires a better understanding of the underlying physics. The simulation of turbulent flames is a challenge because of the multi-scale nature of combustion processes: relevant length scales span over five orders of magnitude and time scales over more than ten. Because of this, the direct numerical simulation (DNS) of turbulent flames is only possible on large supercomputers. A DNS solver for chemically reacting flows implemented in the open-source framework OpenFOAM is presented. The thermo-chemical library Cantera is used to compute detailed transport coefficients based on kinetic gas theory. The multi-scale nature of time scales, which are much lower for the combustion chemistry than for the flow, are bridged by an operator splitting approach, which employs the open-source solver Sundials to integrate chemical reaction rates. Because the direct simulation of turbulent flames has to be performed on supercomputers, special care has been taken to improve the computational performance. A tool was developed which generates highly optimized C++ source code for the computation of chemical reaction rates. Additionally, a load balancing approach specifically made for the computation of chemical reaction rates is employed. In total, these optimizations can reduce total simulation times by up to 70 %. The accuracy of the new solver is assessed from different canonical testcases: 2D and 3D Taylor-Green vortex simulations show that the solver can reach up to fourth order convergence rates and that results differ by less than 1 % when compared to spectral DNS codes. Molecular diffusion and chemical reaction rates are compared to solutions of 1D flames from Cantera, showing perfect agreement. The solver is used to simulate the Sydney/Sandia burner. The simulation is performed on one of Germany\u27s largest supercomputer on 28 800 CPU cores, employing 150 million cells and a chemical reaction mechanism with 19 species and about 200 reactions. Comparison with experimental data shows excellent agreement for time averaged and RMS values