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Combustion in direct injection spark ignition (DISI) engines is strongly influenced by the in-cylinder charge motion. The charge motion depends both on the injection strategy as well as the geometry of the combustion chamber/air intake system and the physical location of the injectors (side mounted vs. centrally mounted). For boosted and downsized DISI engines, many manufacturers are favouring a single late injection or a split injection strategy. This has the advantage of creating high levels of turbulence which leads to faster combustion and improved thermodynamic efficiency. Furthermore the charge cooling offers enhanced knock resistance, thereby allowing more spark advance. The calibration of such engines is critical: the prize of greater thermodynamic efficiency must be balanced against the risks of charge inhomogeneity, namely excessive particulate emissions and poor drivability.

Injector fouling is an important contributory factor to particulate matter (PM) emissions in Gasoline Direct Injection (GDI) engines. Several publications have emerged in recent years which acknowledge the benefits of injector cleanliness, but others claim that high levels of Deposit Control Additive (DCA) could have detrimental effects that outweigh the benefits of the augmented cleaning potential. The paper is divided into two parts: The first part contains a critical review of the literature linking injector cleanliness and particulate matter emissions, and studies assessing the impact of higher treat rates of additives. The second part of the paper describes new evidence of the beneficial effects of DCAs, in the form of several separate (previously unpublished) studies, using both engines and vehicles. In this newly reported work, various DCA treat rates were employed, and some of the fuels had measured UWG levels well in excess of 50 mg/100 mL.

Injector nozzle deposits can have a profound effect on particulate emissions from vehicles fitted with Gasoline Direct Injection (GDI) engines. Several recent publications acknowledge the benefits of using Deposit Control Additives (DCA) to maintain or restore injector cleanliness and in turn minimise particulates, but others claim that high levels of DCA could have detrimental effects due to the direct contribution of DCA to particulates, that outweigh the benefits of injector cleanliness. Much of the aforementioned work was conducted in laboratory scenarios with model fuels. In this investigation a fleet of 7 used GDI vehicles were taken from the field to determine the net impact of DCAs on particulates in real-world scenarios. The vehicles tested comprised a range of vehicles from different manufacturers that were certified to Euro 5 and Euro 6 emissions standards.