Potential of kerosene-diesel blends as alternative fuels for diesel engines: Perspectives from spray combustion characteristics

To explore the application potential of kerosene (RP-3)/diesel blends as alternative fuels for diesel engines, the spray combustion characteristics of neat diesel, neat RP-3 and RP-3/diesel blends (varied from 25 % to 75 % of RP-3) were systematically compared in an optical constant volume combustion chamber under non-evaporating (0 % O2, 293 K), evaporating (0 % O2, 900 K) and combustion (21 % O2, 900 K) conditions. Their spray, evaporation, combustion and soot emission characteristics were visualized using various high-speed imaging techniques. The results show that RP-3/diesel blending ratio has significant effects on the spray and combustion processes. Under non-evaporating condition, higher RP-3 contents slightly decrease the spray penetration but increase the corresponding spray angle and volume. Under evaporating condition, the spray angle and volume follow the similar trend as those under non-evaporating condition except for slight fluctuations, but the liquid length decreases with the increase of blending ratio. Unexpectedly, the vapor penetrations of neat diesel and RP-3 are similar and longer than those of their blends. Under combustion condition, both the ignition delay and flame lift-off length increase with the RP-3 blending ratio. In addition, RP-3 component reduced the peak soot mass by 9.78 %, 14.7 % and 17.56 % for R25, R50 and R75, respectively. In summary, this study suggests that RP-3/diesel blends are suitable alternative fuels for diesel engines, in terms of faster evaporation and lower soot emissions. We recommend a blending ratio of 25 % as the most promising fuel for further investigations in real engines.