In order to meet the EU6c, 6×1011 # / km particulate number emission target that will be introduced in 2017, some gasoline direct injection (GDI) engines might require the use of particulate filters (GPF). The lifetime of wall-flow filters is influenced by the composition of the engine lubricant due to the potential of the lubricant to contribute to ash accumulation in the GPF. In order to anticipate the potential need for new, lower ash lubricants, an endurance test was performed using a commercially available GPF. A radio-labelling method was used to identify the amount of lubricant derived ash trapped in the GPF in addition to conventional weighing measurements.
After the endurance test, during which 9 kg of 1.17% sulphated ash oil was consumed, approximately 50 g of ash had accumulated in the GPF. This amount is only 48% of the expected amount based on fresh oil sulphated ash concentration and oil consumption. Part of this difference can be explained by the same phenomena that also lead to the observed increase in concentration of lubricant additives in the engine sump (such as but not limited to volatile losses for example). Tracer monitoring of zinc (Zn) and calcium (Ca) via Zn and strontium (Sr) isotopes indicated that the lubricant derived ash contribution was limited to less than 50% of total collected ash, suggesting that other sources such as wear metals and fuel derived ash could also contribute to GPF deposits.
Three short tests were also conducted with high, mid and low SAPS (Sulphated Ash, Phosphorus and Sulphur) lubricants in order to evaluate the impact of lubricant formulation on Ca and Zn derived ash accumulation.
GPF and engine performance remained satisfactory after 9 kg of a 1.17% sulphated ash lubricant had been consumed suggesting that a mid SAPS lubricant, typically 0.8% sulphated ash, could satisfy the durability requirements of a GPF equipped engine.