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In this paper, innovative investigation of the flame dynamics of an industrial gas turbine combustor using high-speed imaging and flame luminosity measurement has been reported. Both digital and optical integration methods have been applied to study the flame dynamics of an unstable combustion mode, which has a fixed peak frequency around 105 Hz. It is found that the light emission of the seeded combustion possesses the same dominant peak frequency as the acoustic emission. On the other hand the natural flame light emission failed to match the spectrum of the acoustic emission due to signal drop-out, which is a common problem for direct imaging of unseeded flame. The paper has demonstrated that the transition from stable to unstable combustion could be captured successfully by high-speed imaging using a pre-trigger mode. Three stages of transition from stable combustion mode to unstable mode have been identified. In stage one, the flame luminosity and fluctuation increased gradually, which could be assumed as the incipiency of the instability. In stage two, there was a sudden and sharp burst in flame luminosity, which indicates that the combustion process was becoming very intense in the middle of transition. In the third stage, the drastic flame luminosity dissipated slightly and oscillated with constant amplitude and the combustion locked to unstable combustion mode. The two applied techniques have been cross-checked with reference to the unique peak frequency observed.

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This paper reports the latest results of a comprehensive project investigating the performance of a Ricardo Hydra direct injection diesel engine. Early work covered a number of aspects of research into the gross behaviour of this engine: this paper concentrates on techniques for obtaining quantitative data from photographs of the combustion process. Iligh-speed photographs, at framing rates up to 20000 framesls, were taken using a piston with a quartz bowl, at engine speeds up to 3000 rjmin. The pre-combustion period was illuminated using a synchronized copper vapour laser. After the initiation of combustion, the process is self-illuminating and information on the combustion process was obtained by analysing the radiation emitted by the carbon particles. The two-colour method was used to evaluate the temperature ofthe combustion gases over the full$eld of view. The images have also been analysed by a cross-correlation technique to obtain velocity information. Tests have been performed on the engine over a wide range of operating conditions, but this paper concentrates on the effect of swirl ratio on combustion. It will be shown that too much swirl increases the ignition delay period and results in an increase in the NO, emissions but a decrease in the soot. I t will also be shown that the velocity pattern after combustion is in good agreement with that evaluated by Arcoumanis et al. at the end of compression, which implies that swirl persists through the combustion period despite significant decay. NOTATION