Experimental Investigation of the Autoignition Behavior of Surrogate Gasoline Fuels in a Constant-Volume Combustion Bomb Apparatus and Its Relevance to HCCI Combustion

The autoignition behavior of 21 surrogate gasoline fuels formulated with n -heptane, isooctane, methylcyclohexane, toluene, and 1-hexene using an augmented simplex-lattice mixture design was studied in an Ignition Quality Tester (IQT) and in a single-cylinder engine operating under homogeneous charge compression ignition (HCCI) conditions. The measured ignition delays were highly correlated to fuel composition, while the observed correlation between ignition delay and research (RON) and motor (MON) octane numbers was poor. The statistical modeling using canonical Scheffé polynomials indicated strong effects from n -heptane (autoignition enhancer), toluene, and isooctane (autoignition inhibitors), while methylcyclohexane and 1-hexene showed minor effects, acting essentially as inactive components in this system. The analysis of global burning rates showed that there was a limited correlation between burning rate and ignition delay, which suggests the possibility to control ignition delay and burning rate independently by manipulating the fuel chemistry. The measured ignition delays were also well correlated with the combustion phasing observed in the HCCI—measured as crank angle for 50% heat release (CA50).