LUBRICANT FILM THICKNESS MEASUREMENTS IN A DIESEL-ENGINE PISTON RING ZONE

Oil film behavior at the piston ring-cylinder wall interface was studied in a modified version of the four stroke cycle diesel engine. The technique used to measure film thickness was one of laser fluorescence through a quartz window inserted flush into the cylinder liner. Previously, such experiments have been conducted in motored rigs that did not permit fired engine operation. This study extended the technique to a fired engine and discusses a survey of the results. Film thickness data is compared for each stroke to discern lubrication trends for different parts of the engine operating cycle. The data is used as a means to infer local oil transport results in the oil control region of the piston. One of the primary difficulties with measuring oil film thickness with a laser fluorescent technique is the calibration of the system. The authors used tool marks on the skirt of a production piston to calibrate the signal for these experiments. These results were compared to the results of a bench calibration. Although the difference between the two techniques is appreciable, the calibration from the tool marks is within the total calibration range defined in the bench calibration. The dominant quantity of oil resides in the oil control region of the piston. The oil control rails are fully flooded for all conditions. Within the oil control region, the beveled area on the piston beneath the oil control ring has the majority of oil. Film thickness in the region of the piston bevel were on the order of 200-mu-m. Upstrokes were typically found to have thicker films that downstrokes, and gas exchange strokes typically had thicker films than either compression or expansion strokes. Oil transport results indicated that local oil flows are much larger than oil consumption. The local flow reverses directions on power revolutions at 2000 RPM. No effects of load on local flows were apparent.