Numerical and experimental investigation of methane/air HFM flames at elevated pressure

  • K. Coumans

Student thesis: Master

Abstract

The development of reliable, low-emissions and cost-competitive gas turbine technologies for hydrogen-rich syngas combustion is the primary goal of the H2-IGCC project. Partners from 10 European countries are working together in a 4-year project to accomplish this goal. The combustion group at the TU/e will generate a gas turbine relevant combustion properties database of syngas fuels. For this database, the adiabatic burning velocities of H2 : CO mixtures need to be measured at elevated preheating temperature and elevated pressures over a range of lean equivalence ratios. This parameter set will be measured with the heat ux method (HFM), which was developed at the TU/e. The heat ux burner uses a burner plate with a large amount of small holes in a hexagonal pattern to create a stabilized at ame. The principle of the HFM is based on the heat balance in the burner plate which is indicated by the radial temperature prole of the plate. The temperature prole is measured with thermocouples that are implemented in the burner plate and the adiabatic burning velocity is determined from these results. In this thesis, measurements are performed with a methane/air mixture to validate the setup at elevated pressure. When the heat ux method provides reliable results, measurements in the future can be performed with the H2 : CO mixtures. The adiabatic burning velocities are determined for methane/air mixtures up to 5 bar, for equivalence ratios ranging from 0.8 to 1.4. The results show a good correspondence with data from literature. Therefore, it is concluded that the heat ux method provides reliable results at elevated pressure. Power law correlations are derived from the results to describe the dependency of the burning velocity on the pressure. Numerical simulations have been performed in the one dimensional ame code CHEM1D to calculate the burning velocities that can be expected at pressures up to 30 bar. These simulations were performed for the stoichiometric methane/air ame and the results are used as an input parameter for the axisymmetric simulations of the burner plate in Fluent. In addition, the burning velocities of two H2 : CO compositions in the mixture ratios of 50:50 and 85:15 (by volume) are determined, as these mixtures are of interest for future measurements. Simulations from previous studies have shown that the at ame on the heat ux burner starts to show a small curvature for high burning velocities and elevated pressures [5, 30, 33]. An axisymmetric model of one hole in the burner plate was created in ANSYS Fluent to investigate the curvature of the at ame. Three burner plates were modeled to determine the in uence of the burner plate parameters on this curvature. It was found that the ame curvature can be decreased by choosing a smaller hole diameter and a larger porosity i.e. a smaller distance between the holes. From these results, the optimal parameters are deter mined for a burner plate that can be used at high pressures. An analysis of the experimental and numerical results shows that the ame curvature causes a negligible error in the measured burning velocities for methane/air mixtures up to 5 bar. The calculated surface area increase of the curved ame at 5 bar compared to an ideal at ame is around 2 %, when it is determined according to the 900 K isotherm of the ame. The simulations show that for higher pressures, the ame curvature will increase non-linearly. The surface area increase of the methane/air ame is around 16 % at 15 bar with the burner plate that is used in the current setup. This can be reduced by manufacturing a new burner plate with a smaller hole diameter and a larger porosity.
Date of Award30 Nov 2011
Original languageEnglish
SupervisorM. Goswami (Supervisor 1) & Rob J.M. Bastiaans (Supervisor 2)

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