Boosted HCCI Combustion Using Low-Octane Gasoline with Fully Premixed and Partially Stratified Charges 2012-01-1120

First, the key parameters for high-load HCCI operation were investigated, including 1) intermediate temperature heat release (ITHR), which determines the potential of using combustion retard to control the HRR, and 2) φ-sensitivity, which determines the effectiveness of mixture stratification for controlling the HRR. It is found that consistent with the low octane number, Hydrobate shows strong ITHR and φ-sensitivity even at P_in = 100 kPa. However, the ITHR of Hydrobate is not enhanced by increasing intake pressure, which is different from gasoline at P_in = 100 - 180 kPa, but similar to gasoline at P_in ≥ 180 kPa. For high-load operation, it is found that with a fully premixed charge, Hydrobate allowed higher loads than conventional gasoline for P_in ≺ 160 kPa, mainly due to the lower intake temperature allowing a higher fueling rate. However, for P_in ≥ 160 kPa, the maximum load reached by Hydrobate was lower than gasoline due to the higher level of EGR required, which limited the oxygen available for combustion. On the other hand, higher thermal efficiency was consistently observed with Hydrobate at all P_in tested, mainly due to the lower intake temperature and more advanced combustion phasing. Applying partial fuel stratification to Hydrobate combustion further improved thermal efficiency compared to the fully premixed case, since it allowed even more advanced combustion phasing; however, it only slightly extended the high-load limit, again due to the limited oxygen availability. This work indicates that low-octane gasoline is a superior HCCI fuel for naturally aspirated and modestly boosted operations.