New operating regimes for engines and combustors and the advocated use of non-conventional transportation fuels demand investigation of the combustion chemistry of different classes of chemicals, especially under premixed conditions. Detailed species compositions during combustion are needed to estimate hazardous emissions, and models for their prediction must be validated for the intended combustion conditions.Molecular-beam mass spectrometry (MBMS) is a common technique to measure quantitative species concentrations in flames. It is widely employed to characterize the flame chemistry of laminar premixed combustion, and it has been complemented with optical measurements for the detection of a number of molecular species and radicals. Significant progress has been made in recent studies through the introduction of synchrotron-based MBMS instruments. They have improved the identification process by using tunable vacuum-ultraviolet radiation for photoionization of the species to be detected, and isomer-specific measurements are now almost routinely possible. Along with quantitative species measurements, the temperature profile is needed as input parameter for chemical kinetic modeling. It is usually determined either using thermocouples or laser spectroscopic techniques.It is an ongoing discussion how sampling probes affect these measurements, and how MBMS results can be compared to combustion modeling. The present article is intended to contribute to this discussion by providing optical and MBMS results obtained with several sampling configurations.

In recent years, there has been renewed interest in chemiluminescence, since it has been shown that these emissions can be used to determine flame parameters such as stoichiometry and heat release under some conditions. Even though the origin of these emissions has been known for a long time, little attention has been paid to the detailed analysis of the spectral structure.In this contribution, we present rotationally-resolved spectra of all important chemiluminescent emissions OH A-X, CH B-X, CH A-X, and C 2 d-a in CH 4 /air flames. A numerical model based on the LASKINν 2 code has been developed that allows, for the first time, to accurately predict the shape of the measured spectra for all of these transitions. Reabsorption of chemiluminescence within the emitting flame is shown to be a major factor, affecting both intensity and structure of OH * spectra. Even in lab-scale flames, it might change the intensity of individual lines by a factor of 5. The shape of chemiluminescence spectra depends on several processes including initial state distribution and rotational and vibrational energy transfer (which, in turn, depend on the collisional environment and the temperature). It is shown that chemical reactions form OH * in highly excited states and that the number of collisions is not sufficient to equilibrate the initial distribution. Therefore, high apparent temperatures are necessary to describe the shape of the measured spectra. In contrast, CH * is formed with less excess energy and the spectral shape is very close to thermal. The rotational structure of C * 2 is close to thermal equilibrium as well. Vibrational temperatures are, however, signif-A. Brockhinke ( ) · J. Krüger · M. Heusing · M. Letzgus icantly higher than the flame temperature. Implications and perspectives for flame measurements are discussed.