An experimental setup for the generation and investigation of periodic equivalence ratio oscillations in laminar premixed flames is presented. A special low pressure burner was developed which generates stable flames in a wide pressure range down to 20 mbar and provides the possibility of rapid mixture fraction variations. The technical realization of the mixture fraction variations and the characteristics of the burner are described. 1D laser Raman scattering was applied to determine the temperature and concentration profiles of the major species through the flame front in correlation to the phase-angle of the periodic oscillation. OH* chemiluminescence was detected to qualitatively analyze the response of the flame to mixture fraction variations by changing shape and position. Exemplary results from a flame at p = 69 mbar, forced at a frequency of 10 Hz, are shown and discussed. The experiments are part of a cooperative research project including the development of kinetic models and numerical simulation tools with the aim of a better understanding and prediction of periodic combustion instabilities in gas turbines. The focus of the current paper lies on the presentation of the experimental realization and the measuring techniques.

This work presents an analysis of the response of laminar, stretched, premixed CH 4 -air counterflow flames subject to periodical perturbations of the inflow mixture composition and the flow field in the context of ILDM and REDIM. Investigations of the perturbation propagation show, that the perturbation reaches the flame under certain conditions only; changes of the perturbation due to dissipative processes are investigated. Different methods are applied to gain an in-depth view of the influence of the perturbation on the chemical kinetics, namely correlation analyses of species in state space and timescale and element composition analyses. For the timescale analyses, two methods are applied, the ILDM method and a new concept for timescale analysis within the REDIM method. It is shown, that the perturbation does not change the global behaviour of the chemical kinetics and it is suggested to apply REDIMs for a low-dimensional description of perturbed flames.

In this paper, a mathematical model is introduced for the calculation of sensitivities of Intrinsic LowDimensional Manifolds (ILDMs) with respect to kinetic data. This model allows treatment of questions that have not yet been discussed in sufficient detail in the context of ILDM: Which reactions are governing the ILDM, are they the same reactions that govern the detailed mechanism, and how does the ILDM change due to changes in the kinetic data in the underlying detailed mechanism? Based on the governing equation for the ILDMs, sensitivity equations are derived by partial differentiation with respect to kinetic parameters. Special numeric techniques are applied to allow a scaling-invariant calculation of the underlying Jacobian matrices. Some sample calculations are introduced for the stoichiometric CO/H 2 /O 2 /N 2 -system to validate the approach. The examples shown in the paper also give some first impressions of the values of the sensitivities for some important reactions and they show the sensitive reactions within the sample system. In this context of results, the sensitivity of an ILDM is compared to the sensitivity of a Perfectly Stirred Reactor (PSR).

A new implementation scheme for reduced mechanisms based on hierarchically generated and extended intrinsic low-dimensional manifolds (ILDMs) created ''on-demand" is presented. The algorithm includes the use of ILDMs in generalized coordinates and a new hierarchical concept for the extension of the ILDMs into the domain of slow chemistry. Problems of pre-calculated ILDM tables are overcome by generating ILDM cells on-demand during the flame calculation, yielding an increased efficiency of the table generation and implementation. In view of a future generation of ILDMs with adaptive dimension based on a local online error control, the presented algorithm includes the possibility to increase the ILDM dimension hierarchically after the stationary solution (solution after 10 4 s) of the first flame calculation with an n c -dimensional ILDM is reached and to re-calculate the result of this first flame calculation using higher-dimensional manifolds with a subsequent error test. The paper presents the generation of hierarchically extended ILDMs in generalized coordinates as well as the on-demand implementation scheme. A sample free flame calculation for the syngas-air system validates the algorithms.