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A novel dual seeding method has been developed to obtain full bore cyclically resolved simultaneous flame images and associated velocity fields in an optically accessed single cylinder research spark ignition engine. The technique has been used to study interaction between the propagating flame and in-cylinder gas motion. Light generated by a fast repetition rate copper vapour laser was formed into a thin light sheet, which passed horizontally through the disc shaped combustion space of a spark ignition engine having complete overhead optical access. Mie scattered light from relatively sparse and large particles (∼65μm) at successive intervals allowed flow definition by particle tracking velocimetry. Simultaneous scattering from dense small seed (∼0.22μm) was used to generate flame front images, which were digitised and analysed to quantify turbulent flame structure and development. The flame was shown to have significant effect on local unburned gas motion as well as vice versa.

A range of multiple and sequential Mie scattering imaging techniques have been employed to investigate turbulent flame propagation in a relatively quiescent optically accessed two-stroke spark ignition engine. Flame structure and turbulence scales have been characterised by a number of methods. These include fractal analysis, simple flame perimeter to area ratios and techniques based on Fourier analysis of an independent stationary coordinate. From this was derived an integral scale of flame wrinkling and a parameter related to turbulent flame thickness. Fully developed values of these turbulence parameters proved independent of cyclic variation, mixture strength and (apart from increasing flame thickness) apparent flame extinction. Islands of unburned gas behind the flame front were associated with encirclement by large scale structures rather than partial quench or total quenching due to flame stretch.

A 2-D simulation of fluid dynamic and chemistry interaction following end gas autoignition has demonstrated three distinct modes of reaction, dependent upon the temperature gradient about an exothermic centre. All three modes (deflagration, developing detonation and thermal explosion) can contribute to knock; the developing detonation case, associated with intermediate temperature gradient, has been identified as the more damaging. The simulation code (LUMAD) has been used in a systematic parametric study designed to separate the complex interacting events which can lead to mixed modes in real engines. A most significant finding related to the sequential autoignition of multiple exothermic centres.

A 3-zone thermodynamic cycle model has been developed which incorporates the Leeds correlations of turbulent burning velocity. The correlations encompass both the beneficial effects of turbulence in flame wrinkling and the detrimental effects of flame strain, which can lead to partial or total flame quench. Allowance has been made for the effects of “developing turbulence”, as the initially laminar flame kernel grows and is progressively influenced by larger scales of turbulence. Available experimental cylinder pressure and flame propagation data were used to check the plausibility of the simulation code and to establish values for the various constants employed to characterize the turbulence. The program was then used to explore the effects of engine speed, mixture strength, induction pressure and turbulence levels on the development of the combustion event.