Octane Index Applicability over the Pressure-Temperature Domain

Tommy R. Powell, James P. Szybist, Flavio Dal Forno Chuahy, Scott J. Curran, John Mengwasser, Allen Aradi and Roger Cracknell
Additional contact information
Tommy R. Powell: Oak Ridge National Laboratory, Knoxville, TN 37932, USA
James P. Szybist: Oak Ridge National Laboratory, Knoxville, TN 37932, USA
Flavio Dal Forno Chuahy: Oak Ridge National Laboratory, Knoxville, TN 37932, USA
Scott J. Curran: Oak Ridge National Laboratory, Knoxville, TN 37932, USA
John Mengwasser: Shell Global Solutions (US) Inc., Houston, TX 77082, USA
Allen Aradi: Shell Global Solutions (US) Inc., Houston, TX 77082, USA
Roger Cracknell: Shell Global Solutions Ltd., London SE1 7NA, UK

Energies, 2021, vol. 14, issue 3, 1-23

Abstract: Modern boosted spark-ignition (SI) engines and emerging advanced compression ignition (ACI) engines operate under conditions that deviate substantially from the conditions of conventional autoignition metrics, namely the research and motor octane numbers (RON and MON). The octane index (OI) is an emerging autoignition metric based on RON and MON which was developed to better describe fuel knock resistance over a broader range of engine conditions. Prior research at Oak Ridge National Laboratory (ORNL) identified that OI performs reasonably well under stoichiometric boosted conditions, but inconsistencies exist in the ability of OI to predict autoignition behavior under ACI strategies. Instead, the autoignition behavior under ACI operation was found to correlate more closely to fuel composition, suggesting fuel chemistry differences that are insensitive to the conditions of the RON and MON tests may become the dominant factor under these high efficiency operating conditions. This investigation builds on earlier work to study autoignition behavior over six pressure-temperature (PT) trajectories that correspond to a wide range of operating conditions, including boosted SI operation, partial fuel stratification (PFS), and spark-assisted compression ignition (SACI). A total of 12 different fuels were investigated, including the Co-Optima core fuels and five fuels that represent refinery-relevant blending streams. It was found that, for the ACI operating modes investigated here, the low temperature reactions dominate reactivity, similar to boosted SI operating conditions because their PT trajectories lay close to the RON trajectory. Additionally, the OI metric was found to adequately predict autoignition resistance over the PT domain, for the ACI conditions investigated here, and for fuels from different chemical families. This finding is in contrast with the prior study using a different type of ACI operation with different thermodynamic conditions, specifically a significantly higher temperature at the start of compression, illustrating that fuel response depends highly on the ACI strategy being used.

Keywords: octane sensitivity; octane index (OI); low temperature heat release (LTHR); knock; multimode; advanced compression ignition (ACI); partial fuel stratification (PFS); spark assisted compression ignition (SACI) (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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