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Rapid compression machine (RCM) and shock-tube facilities have been employed to study the oxidation of natural gas blends at high pressure and intermediate to high temperatures. The use of both types of facilities allows a broad temperature envelope to be investigated and therefore encompasses the complete range applicable to gas turbines. A detailed chemical kinetic mechanism has been developed to simulate these results and will be used to approximate similar fuels. Mixtures of CH 4 /C 2 H 6 /C 3 H 8 /n-C 4 H 10 /n-C 5 H 12 have been studied in the temperature range 630-1550 K, in the pressure range 8-30 bar, and at equivalence ratios of 0.5, 1.0, and 2.0 in "air". For shock-tube experiments, the diluent gas was nitrogen, whereas in the RCM experiments the diluent gas composition ranged from pure nitrogen (at lower temperatures) to pure argon (at the highest temperatures). In addition, the combustion chamber in the RCM was fitted with a thermostat and heating tape to control and vary the initial temperature thereby varying the compressed gas temperature. Because the time-scale of a rapid compression machine experiment is so long, heat losses are significant. Thus, a series of nonreactive experiments were performed in order to account for the heat loss associated with each mixture composition and pressure.

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Imaging of OH* or CH* chemiluminescence with intensified cameras is often employed for the determination of heat release in premixed flames. Proportionalitx is commonly assumed, hut in the turbulent case this assumption is not justified. Substantial deviations from proportionality are observed, which are due to turbulence-chemistry interactions.In this study a model based correction method is presented to obtain a better approximation of the spatially resolved heat release rate of lean turbulent flames from OH* measurements. The correction method uses a statistical strain rate model to account for the turbulence influence. The strain rate model is evaluated with time-resolved velocity measurements of the turbulent flow. Additionally, one-dimensional simulations of strained counterflow flames are peiformed to consider the nonlinear effect of turbulence on chemiluminescence intensities. A detailed reaction mechanism, which includes all relevant chemiluminescence reactions and deactivation processes, is used. The result of the simulations is a lookup table of the ratio between heat release rate and OH* intensity with strain rate as parameter. This lookup table is linked with the statistical strain rate model to obtain a correction factor which accounts for the nonlinear relationships between OH* intensity, heat release rate, and strain rate. The factor is then used to correct measured OH* intensities to obtain the local heat release rate. The corrected intensities are compared to heat release distributions which are measured with an alternative method. For all investigated flames in the lean, partially premixed regime the corrected OH* intensities are in very good agreement with the heat release rate distributions of the flames.1.2 Purpose of the Study. The nonlinear influence of turbulence on chemiluminescence intensities has to be considered to Journal of Engineering for Gas Turbines and Power