Contribution of Lubricant Additives to Ash Generation on a Close-Coupled GPF
In order to meet the particulate emission targets (6 x 1011 #/km), 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 its potential to contribute to the ash accumulation in the GPF.
Due to space constraints and to facilitate trapping and soot regeneration, a large number of GPFs will be in closed-coupled configuration. A study was carried out on an endurance test with a radio labelling method and conventional mass gain measurement to evaluate this GPF configuration, and verify the impact of metallic additives contained in the lubricant such as magnesium (Mg) and calcium (Ca) based detergent, a zinc (Zn) based anti-wear, and a molybdenum (Mo) based friction modifier.
Two oils were evaluated, with two levels (0.85%-1.1%) of SAPS (Sulphated Ash, Phosphorus and Sulphur). In total, 4.5kg of oil were consumed for a global mass gain of the TWC and the GPF of 30g. The test methodology allowed to determine the laws of evolution of the GPF ash loading for each element monitored (Ca, Mg, Zn, Mo), based on the content of the element in the oil and oil consumption. This, in order to facilitate oil formulation and GPF sizing. This study also demonstrate that the main contributor is the detergent, far beyond Mo and Zn. The post-mortem ashes analysis showed that the lubricant is not the only contributor to the ashes, wear elements and fuel impurities are also involved.