Experimental investigation on the puffing and micro-explosion characteristics of droplet combustion in i-paraffin blends and cycloparaffin blends fuel

This study used high-speed backlight imaging technology and the two-color pyrometry method to investigate the droplet combustion characteristics and puffing/micro-explosion characteristics of iso -paraffins and cycloparaffins with carbon numbers of 8, 12, and 16, as well as binary fuels. For single-component fuels, the maximum flame temperature T max was highest for iso -paraffins with carbon numbers 16, 8, and 12, in that order, while for cycloparaffins, it increased with increasing carbon numbers. Furthermore, when comparing fuels with the same carbon number (C8, 12, 16), T max of cycloparaffins were 50.6, 92.9, and 210.3 K higher than that of iso -paraffins, respectively. The soot tendency increased with increasing carbon in iso -paraffins, whereas it tended to decrease in cycloparaffins. In binary fuels, the ignition delay time and burning time decrease as the proportion of the low-boiling-point component increases. For binary cycloparaffin fuels with carbon numbers of 8 and 16, the droplet lifetime at a mixing ratio of 75:25 was 14.7% shorter than at a mixing ratio of 25:75. Furthermore, based on an index of droplet diameter instability, droplet breakup behavior was classified into three classes. The probability of large-scale droplet breakup increased in binary fuels with a large boiling point difference between components and a high proportion of low-boiling-point components. Furthermore, among combinations of components with the same carbon number, cycloparaffins tend to produce larger-scale breakup than iso -paraffins. When micro-explosions occurred, T max temporarily rose by up to 200–300 K and then dropped by up to 100–200 K when KL -factor subsequently increased. This was attributed to the alternating occurrence of localized high temperatures caused by rapid fuel evaporation and soot formation and temperature drops associated with temporary fuel enrichment, resulting in intermittent fluctuations in T max and KL -factor.