Experimental investigation of particle emissions from a Dieseline fuelled compression ignition engine

Achieving low-smoke and low-NOx premixed compression ignition (PCI) combustion at a wide engine operating load range has been a challenge; especially in multi-cylinder engines running at higher loads for which less data is available in the literature. More specifically, it is of interest to characterise particle emissions under these conditions and identify their possible reduction benefit in different size classes compared to conventional diesel combustion. Mixing diesel with gasoline (Dieseline) as an incentive to reduce fuel reactivity (cetane-number) and consequently improve premixing is believed to be useful for PCI. In this study, the feasibility and benefits of using low cetane-number (< 30) and wide boiling range G75-Dieseline (75% gasoline in diesel based on volume) in a production light-duty 4-cylinder CI engine are investigated at medium-high loads of 6, 12 and 17.3 bar BMEP. It was found that G75 combustion resulted in lower particle emissions (both number and mass), by up to 99.5%, while maintaining the same range of efficiency and NOx compared to diesel combustion. Bimodal particle size distributions were observed for both G75 and diesel while concentrations of G75 particles were much lower across the entire diameter range. For G75, increasing the fuel injection pressure decreased particle number concentration (especially in nucleation mode) while particle mass was less affected. At medium loads, because of longer ignition-dwell of G75 compared to diesel, variations of combustion and emission characteristics were more sensitive to injection timing. At high loads, mixing-controlled combustion phase was observed for G75 and highlighted the importance of investigating advanced intake pressure boosting systems and interactions between fuel spray and piston.