The Experimental Research On The Evaporation And Auto-ignition Characteristics Of Lubricating Oil Of Low-speed 2-stroke Marine Engine

Low-speed 2-stroke dual-fuel engine that adopts low gas injection pressure and Otto-cycle can meet IMO Tier III harmful emission standard without using aftertreatment. In the five years, this kind of engine have attracted great interest from shipbuilding and shipping industry. But due to the limitation of abnormal combustion, Otto-cycle dual-fuel engine' power performance and fuel economy are inferior than Diesel-cycle dual-fuel engine. The knock caused by lubricating oil auto-ignition is one of the major abnormal combustions of Otto-cycle dual-fuel engines. Thanks to the complexities of lubricating oil droplets' evaporation and auto-ignition, the lubricating oil auto-ignition leading knock is the toughest key problem for the development of Otto-cycle dual-fuel engines. In order to solve this problem, this dissertation investigated the evaporation and auto-ignition characteristics of low-speed 2-stroke engine's cylinder lubricating oil. The suspended droplet technique was used to study the single droplet evaporation and ignition characteristics of lubricating oil, 150BS base oil,400SN refined oil and mixed oil droplets under atmospheric pressure and different ambient temperatures.As for the droplet evaporation process, different oils show significantly different behaviors. The results of lubricating oil droplet evaporation may undergo the following periods:heating up, evaporation, pyrolysis and polymerization. The 150BS base oil droplet evaporation may contain following periods:heating up, evaporation and pyrolysis. The 400SN refined oil droplet evaporation may undergo two periods:heating up and evaporation. The evaporation of the lubricating oil and 150BS base oil droplet at high temperature is accompanied with bubble formation, droplet distortion and droplet fragmentation and leads to incomplete micro-explosion. With the ambient temperature increased or droplet initial diameter decreased, the droplet lifetime will be shorten for all oils.As for the droplet auto-ignition characteristics, for all the four oils, there exists a minimum diameter for ignition and it decreases as the ambient temperature is increased. The results also indicate a decrease in ignition delay as the ambient temperature is increased. The results of 150BS base oil droplet show that there exists an optimum droplet size corresponding to a minimum ignition delay time.