Search Results

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.

Laminar and turbulent burning velocity are important parameters of a combustible mixture. Each is used in mathematical models of spark ignition engine combustion. However, reported data are inconsistent and sparse at elevated pressure and temperature. The present paper presents precise definitions and results of fundamental experiments at Leeds on both laminar and turbulent burning velocities. Reasons for the considerable differences in reported values are put forward and the often neglected effects of flame stretch rate and instabilities on burning velocities are discussed. Relevance is discussed in relation to observations of turbulent flame propagation in a research engine.