Study On The Breakup And Autoignition Characteristics Of Cylinder Oil Droplets Of Low-speed Two-stroke Dual-fuel Engines

Otto cycle low-speed two-stroke dual-fuel engine has become one of the key technologies to meet IMO Tier III emission regulation.However,the frequent occurrence of abnormal combustion phenomena has become a major obstacle for the further performance improvement.Among the many causes of abnormal combustion,the cylinder oil autoignition is most complex and most threatening,which is also the core of this paper.For low-speed two-stroke dual-fuel engines,the cylinder oil stripping phenomenon near the scavenging ports is one of the main sources of the free cylinder oil droplets in the cylinder.The combustion of these oil droplets is also the main cause of pre-ignition and Particulate Matters(PM)emission.Therefore,it is necessary to investigate the cylinder oil stripping phenomenon,and study cylinder oil droplet breakup and autoignition characteristics.The research is helpful in preventing cylinder oil autoignition and pre-ignition in low-speed two-stroke dual fuel engines.In this paper,based on the geometric characteristics and operating parameters near the scavenging port of the engine,the cylinder oil stripping verification experiment was carried out under the actual scavenging pressure.Subsequently,the influence of scavenging velocity and cylinder pressure on cylinder oil stripping phenomenon was quantified by a single droplet generator,which was designed by the author.On this basis,not only was the distribution of oil in the cylinder at the TDC obtained by the simulation method of oil droplet path tracking,but also a control scheme of stripping phenomenon based on source control was proposed.In addition,considering that this part of cylinder oil may cause pre-ignition,this paper built a test bench to simulate the real cylinder environment.Meanwhile,after carrying out a quantitative simulation study on the cylinder oil stripping phenomenon based on the VOF method,the author obtained that the volume of small droplets after stripping near the scavenging port accounted for about 0.04% ~ 3.4% of the initial oil amount.