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.
A bench mounted four cylinder turbo DISI was operated with a fuel designed to promote injector fouling. After making the injectors dirty under normal driving conditions, a progressive increase in injection duration was observed, combined with deterioration in combustion efficiency. Normal operation using a fuel with detergent additive was found to be able to restore the performance of the engine.