Effect of nozzle diameter on macroscopic spray behavior of heavy-duty diesel engine under cold-start conditions

Nozzle diameters play a key role in the atomization and evaporation processes of diesel fuel. However, the influence of nozzle diameter on the spray characteristics of heavy-duty diesel engines rarely involves cold-start conditions, especially considering the coupling of the nozzle with the ambient temperature and fuel properties. The macroscopic liquid- and vapor-phase spray behaviors of −50#, −35#, and −10# diesel fuels were measured at temperatures of 550 K–850 K by Mie-scattering and shadowgraph methods, respectively, in a constant volume combustion chamber. The results showed that regardless of fuel properties the liquid spray from a 0.32-mm-diameter nozzle penetratds excessively due to the incapability in achieving a balance between injection and evaporation at low temperatures, leading to a much longer penetration length compared with that of small nozzles with diameters of 0.12 and 0.22 mm. The up to 70 mm penetration at 750 K led to inevitable fuel wall/piston impingement under common cold-start conditions. Also, compared with small nozzles, temperature reduction inhibited the spray evaporation of larger nozzles more significantly, indicating a greater possibility of fuel/wall impingement in heavy-duty diesel engines. The penetration and spray area of the three fuels tested decreased in the order of −10#, −35#, and −50# diesel fuels due to their physical differences. Based on the obtained experimental data, a new empirical correlation is established to provide a preliminary estimation of the liquid penetration length of heavy-duty diesel engines in low-temperature environments.