The nature of early flame development in a lean-burn stratified-charge spark-ignition engine

Characterisation of flame development with ethanol, butanol, iso-octane, gasoline and methane in a direct-injection spark-ignition engine

“…Quantitative analysis of the degree of wrinkling and large-scale distortion of the flames (e.g. based on methods in [78]) will allow study of turbulence and Lewis number effects in greater detail and with a view of improving current combustion diagrams to reduce the order of magnitude limitations in the transitions between burning regimes, especially validated over many fuels in practical combustion systems;…”

Flame front analysis of ethanol, butanol, iso-octane and gasoline in a spark-ignition engine using laser tomography and integral length scale measurements

“…However, one can derive various types of 'roundness' or 'wrinkling' parameters for a flame, with many different definitions used historically (ratio of instantaneous contour and filtered contour perimeter, ratio of instantaneous contour perimeter and circumference of circle of same area, etc. [64]); future work could focus on assessing several of those and discussing resultant trends with different fuels.…”

“…Furthermore, to enable continuous tracing, pixelation was removed by filtering, followed by binary conversion using Otsu's method (e.g. see [53,64,66]). Any residual noise caused by the spark plug ground electrode and the edges of the exhaust valves was finally manually removed.…”

Assessment of elliptic flame front propagation characteristics of iso-octane, gasoline, M85 and E85 in an optical engine

“…Generally, previous studies have assumed that the propagation of the spark-initiated oxidation is isotropic, i.e. spherical flame propagation [15,16,18,21,25,28,29,39,38,[30][31][32][33][34][35][36]. Only a few studies mentioned different flame-front geometries [14,15,30,39] and looked into implications arising from the assumption that the flame front surface had a spherical geometry.…”

“…Applying the isotropic propagation assumption, the two-dimensional projected contours of spherical flames can be digitized and their various geometrical properties determined. Actual flame speeds and flame shapes were measured in a small number of studies, where the flame radii were calculated using the ''equivalent radius'' (EQR) method [39,25,15,38,16,32,33,40,41], which determines the radius from the measured area:…”