How engine design improvement impacts on particle emissions from an HD SI natural gas engine

The dangerousness of ultrafine particles will require to regulate the emissions of sub-23 nm particles, from all engines. Natural Gas engines play a relevant role toward de-carbonization from transport sector. Considered as particulate matter-free, they have to become compliant with upcoming regulations. Several solutions are under development, but engine-side improvements represent a viable way to keep their competitiveness. The present work investigates on the relationship among piston-liner oil leakage, engine operations and particle emission over the World Harmonized Transient Cycle. The performance of an Euro VI spark ignition natural gas engine is compared with the one of a prototype version of the same engine. The results evidenced a correlation of particle emissions with some phases of the cycle, in correspondence to the passage from long idle periods to speed/load increments, where particle emissions proved to be more than 90% of the total. Literature analysis revealed that the reverse blow-by during high vacuum conditions appears the main driver of instantaneous oil consumption, corroborating the hypothesis of a correlation between instantaneous oil leakage and particle emission spikes during specific driving maneuvers. The piston ring pack design improvement greatly affects such phenomena, providing, as demonstrated in this work, relevant reduction of particle emissions.