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This study investigates the effects of octane quality on the performance, i.e., acceleration and power, and fuel economy (FE) of one late model US vehicle, which is powered by a small displacement, turbocharged, gasoline direct injection (GDI) engine. The relative importance of the gasoline parameters Research and Motor Octane Number (RON and MON) in meeting the octane requirement of this engine to run at an optimum spark timing for the given demand was considered by evaluating the octane index (OI), where OI = (1-K) RON + K MON and K is a constant depending on engine design and operating conditions. Over wide open throttle (WOT) accelerations, the average K of this Pontiac Solstice was determined as −0.75, whereby a lower MON would give a higher OI, a higher knock resistance and better performance.

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.

The growing availability of different biofuels and synthetic fuels is leading to increased diversity of automotive fuels. Understanding how fuel properties affect combustion and how engine calibration strategies can compensate for variations in fuel composition is crucial for ensuring proper engine operation in this world of increased fuel diversity. This study looks at the ability to compensate for wide changes in cetane quality. Four different fuels with variations in cetane number, volatility and composition have been tested in a single cylinder engine and compared to diesel fuel. The selected operating conditions represent the entire engine map of a passenger car diesel engine. In part load the effects were investigated for conventional and premixed Diesel combustion. The results show that part load operation is especially relevant for the detection and compensation of varying fuel properties and that, depending on engine load, different control strategies have to be applied.