Particle Formation and Emissions from Dual Fueled CNG DI and Gasoline PFI SI Research Engine

Compressed natural gas (CNG) is considered as cleaner fuel compared to gasoline and has emerged as an alternative transport fuel in view of its abundant availability. CNG has been implemented in transport sector globally. PM and NOx emissions were reduced, nevertheless, recent studies highlighted the presence of ultrafine particle emissions at the exhaust. The present study deals of the effect of CNG on particle formation and emissions when it was direct injected and when it was dual fueled with gasoline. In this latter case, the CNG was direct injected and the gasoline port fuel injected. Measurements were performed in cylinder and at the exhaust of a single cylinder SI research engine similar to modern commercial engine for passenger cars. The in-cylinder formation process of particles was evaluated by high spatial and temporal resolution optical measurements based on 2D chemiluminescence measurements from UV to visible. Two "ad hoc" filters, at 310 and 431 nm, were used to detect two representative radical species that influence the in-cylinder pollutants formation and oxidation. In particular, OH* and CH* spatial distribution were measurement to evaluate the local air fuel ratio in the cylinder too. Simultaneously, the exhaust emissions were characterized and the particle size distribution function was measured by an Engine Exhaust Particle Sizer in the range from 5.6 to 560 nm. The local air fuel ratio spatial distribution was strongly correlated to oxidation and particle emissions.