Experimental investigation of evaporation and auto-ignition characteristics of lubrication oil droplets

Abstract

Auto-ignition of lubrication oil droplets is considered as a possible mechanism of pre-ignition in low-speed two-stroke gas engines. Extending the ignition delay time of lubrication oil can fundamentally postpone the occurrence of pre-ignition. Therefore, investigating the evaporation and auto-ignition characteristics of lubricating oil droplets is essential for pre-ignition inhibition. The droplet suspension technology is employed to examine the impact of ambient temperatures and oil physical parameters (viscosity and alkalinity) on the evaporation and ignition characteristics of lubrication oil. The experimental results indicate that the evaporation process comprises three stages: heating, rapid evaporation, and stable evaporation. Combustion also encompasses three main stages: heating and evaporation, premixed combustion, and diffusion combustion. Lubrication oil droplets with high alkalinity and low viscosity demonstrate shorter evaporation life, faster evaporation rates, and a reduced ignition delay time, which tend to increase the occurrence of pre-ignition. This phenomenon is primarily associated with the rupture and micro-explosion of the droplet during the evaporation process. High alkalinity, low viscosity, and high temperatures promote micro-explosion, leading to a significant reduction in evaporation life and ignition delay time.