Burning droplets of heavy oil residual blended with diesel light oil: Characterization of burning steps

Abstract

Highlighting the burning process of heavy oil droplets resulted in the resolution of the whole process into four burning steps that in turn defined four component times (in succession): the ignition delay, flame lifetime, coke glowing delay, and coke ember time. The present work was devoted to measuring the component times in an atmospheric hot-air chamber, and to further analyzing their constitutional characteristics with respect to oil compositions and burning conditions by using hybrid oils blending a heavy oil residual (HOR) and a diesel light oil (LO) at different fractions to simulate the diversified heavy oils. The four burning steps generally prevailed during burning, but their time durations relative to the total burning time varied with oils, temperatures, and droplet sizes. The increase in the LO fraction considerably reduced the ignition delay and coke ember time but little affected the flame lifetime and coke glowing delay. Notwithstanding, the ratios of component times to total burning times appeared independent of the LO fraction when the fraction was definitely higher, such as greater than 30 wt.%. Increasing the chamber temperature much decreased the ignition delay and coke glowing delay but little changed the flame lifetime. This led the coke ember time and flame lifetime to become dominant in the total burning time at higher temperatures. The initial droplet diameter influenced the component times and their relative values, but the influence appeared secondary to the effects of oil composition and chamber temperature. With these results, the article suggested that the burner designs for different heavy oils should focus on the oil-induced differences in fuel ignition and coke burnout rather than in volatile burn-up.