Comparison study the particulate matter characteristics in a diesel/natural gas dual-fuel engine under different natural gas-air mixing operation conditions

The particulate matter emissions have seriously negative effect on the human health, especially the ultrafine particulates and an experiment study has been conducted to evaluate the particulate emissions characteristics in a diesel/natural gas dual-fuel engine. In this paper, the particulate mass (PM) and particulate number (PN) concentration as well as particulate size distributions (PSD) characteristics under different natural gas-air mixture state operation conditions are investigated. The earlier (−500°CA ATDC, −480°CA ATDC) and later (−260°CA ATDC, −240°CA ATDC) natural gas injection timings are applied to form a homogenous and stratification natural gas-air mixture and the air fuel ratio (AFR) are maintained at a constant value during experiments. The results indicated that the natural gas-air mixture state have significant influence on the combustion process. The PN, especially ultrafine particulate emissions, is sensitive to the natural gas-air mixture state and the stratified-like mixture is benefit to reduce the PN of smaller size under low load. Moreover, in the diesel/natural gas dual-fuel engine, over 60% of the PN emissions are the ultrafine particulate while it just contributes to no more than 10% in the PM emissions.