Premixed flame propagation and interaction with turbulent flow structures in a semi-confined combustion chamber.
Applications of premixed turbulent combustion are common in the modern environment. The diversity of the applications spans turbulent flame propagation in explosions to combustion in an internal combustion engine. The research effort in the former is directed towards the improvement of plant safety and the latter to the reduction of harmful emissions. In this thesis key examples of the use of turbulent combustion in practical situations highlight the need for increased understanding within this field of combustion. Thus, this thesis presents a detailed laser diagnostic investigation into three fundamental areas within the study of premixed turbulent combustion. These are firstly ignition, flame kemal formation and laminar flame propagation; secondly the interaction of a propagating flame with a vortex; and finally flame interaction with solid obstacles. The first investigation involved the accurate recording of unrestricted flame propagation. Development of a high speed laser sheet flow visualisation technique provided the basis for recording ignition kemal development and flame propagation. The effects of mixture stoichiometry and chamber exit blockage were studied. Results provided an estimate of the unstretched laminar burning velocity. Initiating a flame within a premixed charge and allowing it to interact with solid blockages placed along the centre line of the combustion chamber replicates practical examples of turbulent combustion. The second area of the study provided quantification of flow field and flame front development during flame/vortex interactions. An application of particle image velocimetry, PIV, was employed to quantify the mixture flow field. A new development of the PIV technique, incorporating two individual systems analysing the exact same region allowed the temporal quantification of flame and flow. The results provided the basis for extraction of flame properties such as flame displacement speed and stretch. Correlations between flame displacement speed and stretch with the local radius of curvature were highlighted. In the final study, the newly developed laser diagnostic techniques were applied to characterise the interaction between flame and multiple solid obstacles located along the chamber centreline. Increasing the number of blockages ahead of the flame caused an increase in the apparent turbulent nature of the flame. Results highlighted the increase in translational flame speed, with number of obstacles. Quantification of flow fields in the wake of the blockages demonstrated the formation of turbulent structures by vortex shedding from the obstacle sides. Application of the twin camera PIV diagnostic provided results for flame displacement speed in the wake of each obstacle. An increase in the calculated value of displacement speed was seen with increased obstacle number. Examples of flame stretch were shown that matched findings presented in the literature.