Low Temperature Combustion (LTC) is currently being researched as a way to reduce problematic emissions (i.e., NOx and PM) from compression-ignition engines while maintaining high fuel efficiency. One of the primary types of LTC is Premixed Compression Ignition (PCI), with some examples of PCI being homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI), reactivity controlled compression ignition (RCCI) and partially premixed combustion (PPC). These LTC strategies use early fuel injections to allow sufficient time for air/fuel mixing before combustion. By increasing the amount of air/fuel premixing, NOx and PM emissions can be lowered due to the reduced local and global equivalence ratios. The lean nature of PCI also maintains high thermal efficiency due to the reduced heat transfer losses from the reduced peak combustion temperatures. However, too much air/fuel premixing can lead to rapid energy release rates, limiting the operation space for PCI. To combat this problem, the combustion strategy of interest for the study, RCCI, uses fuel reactivity gradients to increase combustion duration (i.e., reduce the energy release rate) and phasing control, thereby increasing the engine operating space for PCI operation.
Previous tests [1-7] have shown promising results for petroleum-based fuels with RCCI. Recent work at Oak Ridge National Laboratory (ORNL) has shown how blends of biofuels with petroleum fuels can improve RCCI combustion performance [8,9] The work sets out to examine biofuel performance over a wide engine operating space both at steady-state and transient operating conditions with RCCI combustion. It is hoped to demonstrate the capability and effects of using bio-derived fuels in place of conventional petroleum-derived fuels for advanced combustion strategies under real-world operating conditions. In RCCI operation, blends of biodiesel and ethanol fuels will be investigated to examine the fuel effects on the combustion event.