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.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.