Browse Publications Technical Papers 2014-01-1216

The Effects of Octane, Sensitivity and K on the Performance and Fuel Economy of a Direct Injection Spark Ignition Vehicle 2014-01-1216

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. Over a part load cycle, a positive average K value was identified, whereby higher MON would give a (generally desirable) higher octane index, however, because lower load operation tends to be less constrained by knock, the impact of MON (high or low) on FE and efficiency under such conditions is smaller.
Results from the one car tested for this report support the observation that the K value of an engine depends on speed and load - a clear negative correlation between charge pressure and K value was recorded.


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