Studies on Characteristics of Nanoparticles Generated in a Gasoline Direct-Injection Engine 2019-01-2328
Particles generated from lubricant in a gasoline direct injection (*GDI) engine were investigated in detail with the aim to understand the influence of components in lubricant on the amount of particles generated as well as their size. Analytical approach employed in this study was real-time engine tests combined with X-ray spectroscopic and electron-microscopic analyses. Real-time engine tests where particle number (PN) and particle size distribution were consecutively measured with oil consumption for lubricants with different formulas enabled us to extract information regarding lubricant-derived particles. This can be achieved only when sulfur species in lubricant are used as a “tracer” and thus, sulfur-free fuel possessing low PM Index (i.e., isooctane) needs to be used for the measurements.
It was revealed that the size of particles increased with an increase in oil consumption in the vicinity of 10 nm, and such particles were assumed to be mainly generated as a result of combustion of metal-based additives used in lubricant. Moreover, STEM-EDX images strongly indicated that the particles with a ~10 nm diameter are composed of metal oxides, sulfates and/or phosphates with Ca, Mo and/or Zn as a cation.
This study clearly suggested that novel molecular design of metal-free lubricant additives for wear-protection, detergent, and dispersant will be a key area to dramatically decrease nanoparticles smaller than ~50 nm which particularly threaten human health.