Influence of piston ring component structural parameters on diesel engine blow-by and oil consumption

Abstract: Volume rate of blow-by and oil consumption are both critical indexes of assessing piston ring assembly development activities. Gas blow-by along with oil consumption exerts a bad influence on engine performance, worsening emissions and polluting the environment. It is indicated in the literature that the in-cylinder oil consumption through piston-ring-cylinder liner friction pair is an important source of particulate matter（PM）emissions of diesel engines. Controlling in-cylinder oil consumption proves to be an effective way of meeting stricter emission control limits. Blow-by could contribute to oil aging, thus deteriorating engine components lubrication, which can also lead to fuel corrosion and PM emissions. Factors affecting in-cylinder oil consumption and blow-by primarily includes piston ring radial thickness, piston ring end gap, tangential elastic force, cylinder bore match clearance, cylinder clearance and other structure parameters, as well as oil quality/pressure and working condition. The piston assembly of a four-cylinder common rail diesel engine was chosen as the research object in this study. Piston temperature distribution was measured by using a hardness plug method. The hardness plug was mounted in piston top surface, combustion chamber bottom and throat along with the top, second, and third ring groove. Temperature of key points on cylinder liner outer surface was obtained using thermocouples mounted axially every 90° around the circumference. The test data showed that there was an apparent temperature distribution difference on piston top where a max temperature of 356 ℃ was obtained on combustion chamber throat near the exhaust. The average temperature of ω-shaped combustion bottom was 307 ℃, whereas the temperature of combustion chamber center hump reached up to 328 ℃. The average temperature decreased from top to the third ring groove. The lowest temperature on cylinder liner outer surface was 96.8 ℃ obtained by the thermocouples. Top temperature gradients changed dramatically in the range of 30 mm down from the top of the cylinder liner and the highest temp in this region was 178.3 ℃. The cylinder pressure data, and the temperature field of the piston and cylinder obtained by the experiment were used for setting the boundary conditions for the dynamic simulation model. The weighed oil consumption verified the accuracy of the model. The influence rules of different clearance of piston ring land, piston ring groove and piston ring gap along with radial elastic force of top piston ring on in-cylinder oil consumption as well as blow-by was investigated. Results obtained using response surface methodology of Box-Behnken design showed that blow-by and oil consumption went up with the increase of piston ring land clearance and piston ring gap. The blow-by and oil consumption can be reduced if piston ring land gap and ring gap decreased when the performance of piston ring component was guaranteed. Variation of ring groove depth and top piston ring upper clearance had a slight influence on blow-by. Radial elastic force of the top ring is found obviously linear with blow-by, the sealing ability to the air of the top ring was better than that of the second ring.