Gasoline Oxidation Stability: Deposit Formation Tendencies Evaluated by PetroOxy and Autoclave Methods and GDI/PFI Engine Tests

Abstract

Deposit formation from the gasoline autoxidation process has attracted more and more attention since the emergence of new systems operating at a higher pressure range and higher temperatures, imposing new fuel constraints and so favoring the appearance of deposits on different engine parts in contact with the fuel (e.g., injection systems, valves, pumps, and pistons). This study aims to evaluate the oxidation stability of a non-additized standard European gasoline SP95 Euro 6 containing 10% v/v ethanol (SP95E6E10) complying with the EN228 standard and the impact of additives such as methylcyclopentadienyl manganese tricarbonyle (MMT) and dimethyl disulfide (DMDS) on deposit formation to mimic other world market fuels such as Africa or China. The stability of these fuels was compared to that of a commercial Nigerian gasoline which has a higher sulfur content (800 mg/kg) to evaluate the sulfur effect on deposit formation. The fuel degradation tendencies [induction period (IP)] obtained from a PetroOxy apparatus and an Autoclave reactor were compared to the real engine tendencies to form deposits. The deposits targeted are those created on the injector nozzle of a VW EA111 engine (direct injection) and on the valve using an M102E engine (indirect injection). PetroOxy results show the negative impact of DMDS and MMT on the IP of the gasoline, SP95 E10 ULG Euro 6: an IP decrease of up to 30%. Comparison of the IP results in PetroOxy and Autoclave with the results of the direct injection (VW EA111) and indirect injection (M102E) engine tests suggests that the PetroOxy results follow the trend of the mass of deposits formed on the valves of the indirect injection, M102E, engine tests, with the IP decreasing as the valve deposit mass increases. On the contrary, the Autoclave results appear to follow the trend of the results of the direct injection, VW EA111 engine tests: IP decreases when the injection time increases. These features could allow us to identify fuel tendencies to form deposits on specific spare parts based only on laboratory-scale methods, helping to optimize and to target the maintenance operation and preventing failures or damages on real engine systems.