Experimental research on the spray and particle characteristics of cylinder lubricating oil in low-speed two-stroke gas fuel engines

Abstract

For low-speed two-stroke engines, cylinder lubricating oil is directly injected into the cylinder by the injectors located on the cylinder liner. This method of lubrication inevitably leads to the release of free oil droplets from the oil spray or their impact against the cylinder wall, creating potential auto-ignition sites that can induce pre-ignition within the cylinder. The high-viscosity of the cylinder oil can significantly influence the spray characteristics, necessitating an examination of the properties of the oil spray. This research delves into the macroscopic and microscopic attributes of the cylinder oil spray (with nozzle diameter of 0.7 mm) using both visualization experiments and laser Phase Doppler Particle Analysis (PDPA). Initially, we analyze the impact of oil temperature (ranging from 50 to 200 °C) and injection pressure (ranging from 4 to 8 MPa) on the spray cone angle and projection area. Subsequently, we explore the behavior of oil droplets upon striking the cylinder wall under varying conditions. Finally, the effects of oil temperature and injection pressure on the diameter and velocity of the spray particles are scrutinized. It is observed that the oil temperature is the primary factor. At 6 MPa injection pressure, the average values of the stable spray cone angle for 80 °C, 110 °C, 160 °C, and 200 °C are 4.23°, 6.09°, 8.61°, and 10.35°, respectively. As the temperature goes from 80 °C to 200 °C, the cone angle increases 145 %. Conversely, the Sauter Mean Diameter (SMD) decreases with rising oil temperature and injection pressure. The distribution pattern of particle diameters exhibits a bimodal pattern (35–40 μm and 70 μm), which is not affected by oil temperature and injection pressure.