Fuel Effects on Advanced Compression Ignition Load Limits

Several Advanced Compression Ignition (ACI) combustion modes can be implemented as part of a multi-mode combustion strategy to increase the part-load efficiency of spark-ignition engines. While ACI modes can offer a reduction in pumping losses and provide other thermodynamic benefits, their total operability is somewhat limited. Being able to extend the speed-load range of these ACI modes would enable greater part-load efficiency improvements for multi-mode combustion strategies. In this manuscript, we investigate fuel effects for six different fuels, including four 98 RON fuels with differing fuel chemistries, Iso-Octane, and a market representative E10 fuel, on the load limits for two different ACI strategies: Spark-Assisted Compression Ignition (SACI) and Partial Fuel Stratification (PFS) operation. Experimental results show that limits to intake boosting limit high load operation for most fuels, but high smoke emissions for high particulate matter index (PMI) fuels under SACI conditions could also be a limitation. Contrastingly, low load is limited by combustion efficiency, but these effects have more pronounced variation with fuel chemistry for PFS than with SACI. Additional, distinct effects affecting autoignition timing and peak heat release at higher speeds were identified for fuels having different low temperature heat release (LTHR) propensities for both ACI modes.