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

Abstract

a b s t r a c tPremixed fuel-air flame propagation is investigated in a single-cylinder, spark-ignited, four-stroke optical test engine using high-speed imaging. Circles and ellipses are fitted onto image projections of visible light emitted by the flames. The images are subsequently analysed to statistically evaluate: flame area; flame speed; centroid; perimeter; and various flame-shape descriptors. Results are presented for gasoline, isooctane, E85 and M85. The experiments were conducted at stoichiometric conditions for each fuel, at two engine speeds of 1200 rpm (rpm) and 1500 rpm, which are at 40% and 50% of rated engine speed. Furthermore, different fuel and speed sets were investigated under two compression ratios (CR: 5.00 and 8.14). Statistical tools were used to analyse the large number of data obtained, and it was found that flame speed distribution showed agreement with the normal distribution. Comparison of results assuming spherical and non-isotropic propagation of flames indicate non-isotropic flame propagation should be considered for the description of in-cylinder processes with higher accuracy. The high temporal resolution of the sequence of images allowed observation of the spark-ignition delay process. The results indicate that gasoline and isooctane have somewhat similar flame propagation behaviour. Additional differences between these fuels and E85 and M85 were also recorded and identified.

A review of the combustion and emissions properties of advanced transportation biofuels and their impact on existing and future engines

“…While the faster turbulent premixed flame speed could result in higher compressed end-gas temperatures, the reduced low-temperature chemistry from methanol will prevent auto-ignition and engine knock; therefore, the faster flame speed would have a positive impact on engine performance because it leads to faster, more-complete combustion. Indeed, a recent flame-visualization study within an optically-accessible engine has confirmed that the methanol blend (M85) produced the highest in-cylinder flame speed, with the ethanol blend (E85) slightly faster than either gasoline or isooctane, which were similar to each other [191]. Another recent study observing flames in optically-accessible engines showed that ethanol flames propagate faster than butanol, followed by gasoline and iso-octane [192], consistent with the laminar flame experiments discussed above [180][181][182][183][184][185].…”

Effect of Ethanol Ratio on Ignition and Combustion of Ethanol-Gasoline Blend Spray in DISI Engine-Like Condition

“…Although some literatures reported a higher flame speed of ethanol in real DISI engine [39], recent studies reveal that gasoline can potentially achieve a faster flame propagation than ethanol in DISI engines under a part load [35,40]. A similar result was also obtained by using the elliptic flame front analysis [41]. For the ethanol-gasoline combustion, the latent heat of ethanol should be considered as the significant factor that influences the flame speed during the fast combustion period.…”

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

“…Even though simple, this method is believed to return very similar results to more complex elliptical fittings, except for the very early flame kernels, e.g. see [63]. In an attempt to quantify the flame front general distortion, the flame roundness was calculated as the degree by which the ratio of area to perimeter converged towards the circular shape following the relation 4A/P 2 , where A the area and P the perimeter of the flame.…”